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Servo-Hydraulic Test Controller Review

Please note that this review is now archived, and will not be updated. The information was current in the fall of 2004. For latest product information, please see our new Buyers Guide.

Introduction

This is an unbiased review of servo controllers offered by a group of vendors in the market of automotive structural testing. I have been able to review all these controllers “in-the-flesh” either at the manufacturer’s facility, at installed locations, or at my facility. My intent is to leave personal opinions out as much as possible. All these products have both strengths and weaknesses, and it is up to you to read the facts and make a decision based on your own situation. Every lab has unique requirements, and while one controller might be a perfect fit in one situation, it might not be in another.

 

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Price and reliability are important, but they are left out of this review. It is difficult for me, without using these controllers day in and day out, to assess how many bugs there are. However, since this is an important issue, there is a link at the left for you to add your own comments. Your comments will be added to the end of the report so that folks can get a better overall picture. I also invite the manufacturers of these controllers to add their own comments.

 

Secondly, I didn’t want to get into the middle of the often-controversial pricing issue. If you are interested in purchasing a controller in this category, I suggest you get a quote from all these folks, and assess their local service and support. Also, just because a feature is mentioned in this review, it doesn't mean it is a part of the standard package. Carefully review the quotation to ensure you are getting everything you need. Take a look at the options and compare apples with apples.

 

The controllers reviewed are all PC and/or instrument based, and have applications designed for automotive structural fatigue testing. They all provide the ability to develop complex test procedures. 

 

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Supplier Backgrounds

This review covers controllers supplied by the following companies (in alphabetical order):

·        FCS

·        FCS-COM (formerly COM, Inc.)

·        Instron/IST

·        MTS

·        Servotest

·        Tiab

While there are other players in this business, they do not have turn-key PC or instrument based controllers that provide extensive capabilities for automotive fatigue testing. If you are aware of a controller that should be reviewed, please let me know. This review is intended to be a floating document, and will be updated, as new products are made available. Other players in this market who, in my opinion, do not have controllers in this category are: DTE www.dynamic-testing.com, Zwick www.zwick.com, and Team  www.teamcorporation.com. Please note that this review does not cover products that fit in the general category of random vibration controllers, or programmable controllers that allow you to build your own, such as the Moog M3000, or the Delta Tau P/MAC UMAC. To be included, controllers must have the capability of constructing block-profile tests or playback time histories.

FCS-COM

This company is probably best known to you as COM Inc. COM, was a division of Enprotech, but it was purchased in the fall of 2003 by FCS Control Systems, a Netherlands company (FCS). COM, based in Ann Arbor Michigan, was incorporated in 1972, and spent its first 20 years working on custom automation for test labs and production lines. Their market is split between automotive and aerospace. In 1992 they began developing a test site controller in partnership with GM. The SIMCON 2100 controller was launched in 1995. Initially a Test Site Controller, it did not include servo-control. It was partnered with analog controllers provided by other vendors. In 2002 they released embedded digital servo-control capabilities.

 

FCS started as Fokker Control Systems. They originally developed test systems to test aircraft, and have since broadened their base to include all applications of servo-hydraulics for structural testing. They have developed a controller that meets the needs of all their markets. This has resulted in a product that brings many of the unique aerospace testing techniques into the automotive world. FCS also purchased the British company Kelsey Instruments, now called FCS-Kelsey.

 

Since FCS purchased COM, they have integrated their products. Joe Morrill, a leading light in the testing community, manages FCS COM. He has many of years experience at GM Proving Grounds, and presents white papers on testing techniques around the country.

 

Their websites can be found at www.fcs-com.com and www.fcs-cs.com

IST

This is a division of Instron, and was formed from the structural test division they had in England, the Schenck HydroPulse group in Darmstadt, and the Schenck Pegasus group in Detroit. Very little remains of the later group (Schenck Pegasus), and the operations of this division have all now been consolidated in the former Schenck facility in Darmstadt (as of January 2003). From the standpoint of their controllers, they have done a good job of focusing on one platform: the 8x00, which will be reviewed here. This must have involved some difficult decisions because the Schenck Pegasus group had some powerful controller products at one time. However, I think the decision was a good one. It is better to focus on a single unified platform rather than spread resources over several competing products. This is the controller platform used across the Instron Corporation. Instron has representation worldwide, and is well established in the material testing market. Schenck and Instron independently fought hard to become major players in the structural testing market, and as a single company, they continue to aggressively pursue a strong position. Unfortunately, through the turmoil of acquisitions and mergers, they are only just finding their feet as a single company with one voice, and are now positioned become a formidable competitor.

 

Their website can be found at www.instron.com/ist

MTS

I don’t think anyone would argue with the statement that MTS is the largest player in this market. Formed in 1968 from a spin off of Research Incorporated, they have become a juggernaut that has taken a strong position. They have many controller platforms that are used in this market, some share the same hardware platform, and some share the same software platform. This has lead to a lot of confusion around which product fits where. I will attempt to clear this up. While I am going to focus on the FlexTest® GT and SE controllers, I will mention the FlexTest IIs, FlexTest IIm, TestStar® II, and TestStar IIs to help you navigate through the maze. MTS is well represented worldwide, and while they have acquired several companies, their core vehicle testing business is largely unaffected. MTS is based in Eden Prairie Minnesota, and has representation worldwide.

 

Their website can be found at www.mts.com

Servotest

This UK based company has been in the business of building servohydraulic test equipment for many years. They have established a strong niche in the area of testing Formula One cars, although they have products in all areas where servohydraulic test equipment is used.  Their current controller is the newly released Pulsar® Digital Control System (Summer 2003). It is a rewrite of the DSC 2000 system, and currently uses the same hardware. Servotest is planning to release new hardware in the summer of 2004. The Pulsar system is installed at several locations around Europe.

 

Their website can be found at www.servotest.com

Tiab

Tiab is a small UK company. It was founded in 2002 by Conway Young, a motorsport R&D expert. He felt that the control products that were available for servohydraulic testing were cumbersome and expensive. Using government funding, he has developed what he believes is a simple, versatile, inexpensive solution.

 

The Tiab website can be found at www.tiab.co.uk

 

Controllers Under Review

The products I will focus on are below. This review will be updated as information on the new products becomes available.

·        FCS—SmarTEST ONE®

·        FCS COM (formerly COM, Inc.)—SIMCON 2100

·        IST—Labtronic® 8800/8400

·        MTS—FlexTest GT/SE

·        Servotest—Pulsar Digital Control System

·        Tiab—A8D8/eSolution88

What Is Covered and What Is Not Covered

The main focus of this review is the controller hardware infrastructure, multi-station capabilities, servo-controller and tuning, events and limits, optimization algorithms, block programming, and time history playback. While I will mention a little about the real-time iterative simulation packages that are available as add-ons for each platform, I am not providing a review of them here. That might well come at a future date. I am also not going to talk about pricing, or support. These vary on geographic location. Make sure you get quotations from all these manufacturers, and research their local support, parts availability etc. before making your final decision. Also, make sure your quotations all include the options you need. Just because a capability is mentioned in this review does not mean it is included in the standard package.

 

As far as reliability is concerned, please  add your own comments. Since I do not use all these controllers daily, I have no idea about how many bugs and workarounds there are. I know some of them, but not all, so it is not fair for me to comment.

Hardware Architecture

By taking a step back, and looking at the architecture of all these controllers you will notice that they all implement a “client-server” model. What I mean by this is that the real time operations of the controllers occur in a processor  in the controller itself. The PC is not involved with the time-critical functions. The Windows® Graphical User Interface (GUI) takes commands issued by the user, and packages them into instructions that the test processor understands, the test processor then modifies its behavior according to the new set of instructions. Information piped-up to the PC from the test processor is interpreted, manipulated, and displayed to the operator in a user-friendly manner. The Instrument based controllers offered by FCS-COM, MTS, and IST are all stand-alone versions of their PC applications. A more simple, dedicated user interface has been developed, which runs on a small screen on the front of the device itself, obviating the need for a PC in most applications. If, however, the user wants the power, flexibility and screen real-estate offered by the PC, they can connect one to any of these three controllers, and operate it remotely.

Pulsar™ Digital Control System

Click here for a diagram

The new Pulsar software currently runs on the DSC 2000 hardware. It is based on Digital Signal Processor (DSP) architecture. All the real-time controller code is executed on the DSP. The dedicated PC acts as a front-end, and communicates operator interaction to the DSP. The single DSP resides on a board that is on the PC bus. This PCI card uses the TMS320C44-60 64 MHz chip. All software is downloaded to the DSP on boot-up. This means that software updates are possible without having to upgrade firmware.

 

The DSP board communicates with up to four conditioner boxes via a XBUS. Each box has 17 slots, which can be populated with the following (configuration limits depend on a complex combination):

·        2 channel conditioner

o       Both DC and AC conditioning

o       16bit/20 kHz

·        1 channel valve driver

o       Multiple two stage or

o       Single three-stage (in standard configuration)

o       Single channel high-level input

·        4 channel high level input

o       500 Hz 4 pole low pass anti-aliasing

o       +/- 10 volts

·        6 channel high level output

o       +/- 10 volts

·        16 channel digital I/O

o       All channels are fully bi-directional

 

One box typically handles a maximum of 6 servo-control channels. With four boxes, a single PC can handle up to 24 channels, which can be split among up to 16 test rigs. A/D and D/A conversion is 16 bit at a maximum aggregate loop closure rate of 8192 Hz (divide by the number of channels to get maximum rate per channel). Loop closure typically occurs at 1024 or 2048 Hz, although it is possible to run as fast as 4096 Hz and as slow as 102.4 Hz. Maximum rates are difficult to define because of the infinite number of configuration options.

 

Pump and manifold control is performed using the Digital I/O module. E-Stops are hardwired and do not go through the software. Up to 8 test stations can be supported.

 

Servotest is in the process of developing a servohydraulic controller based on a new hardware architecture. The newer Pulsar hardware solution, due to be released by the Summer of 2004,  is based upon an external DSP (Texas Instruments TMS320C6711-200) which links to any PC using FireWire (IEEE1394a). The synchronized Pulsar I/O is comprised of up to 24 nodes distributed using Optostar fiber optic technology. Each node, which may be configured for actuators or transducers  handles up to 6 channels of servo-control, which may be configured for AC/DC transducers, 2/3 stage valve drivers, high level analog I/O etc.  Alternatively, the node can be configured for up to 12 transducers. Another node is used for pump control. The new system will also feature intelligent transducers, with built in identification/calibration.  Click here for a diagram.

 

SIMCON 2100

Click here for a diagram

This is the controller that was previously offered by COM Inc. It is still available. The system is based on the VME architecture, although they have developed, and delivered a new PCI-based system. These boxes are connected to the Ethernet, and any PC on the network can communicate and send commands to them. Boxes can contain multiple chassis, and come in many sizes. They can also be subdivided to multiple rigs (as many as there are channels). Each box includes two processors, which run all the real-time code, and a networked disk. The network is therefore not used for any time-critical activity. Each group of 6 servo channels is controlled by a DSP board. A single chassis can handle a maximum of 12 servo channels, or 32 analog control channels (or any combination). Up to 15 additional chassis can be added to expand the system with up to 16 Channels per expansion chassis.  A DSP board is comprised of the following:

·        2 channel conditioner

o       A/C or D/C based on daughter board options

o       Maximum of 3 per DSP

·        1 channel valve driver

o       3 stage valves require one conditioner from above

o       Maximum of 6 per DSP

·        32 high level analog or digital I/O

The standard raw sample rate is 2048 samples per second (10240 samples per second for the PCI based system), and anti-aliasing filters are typically set at 80 Hz (switch selectable). Loop closure is between 2048 Hz. and 8K Hz. depending upon the number of channels. Data is decimated to the required sample rate (no digital filtering/down sampling).

SmarTEST ONE

Click here for a diagram

The SmarTEST ONE controller is a member of a family of SmartTEST controllers. The SmarTEST hardware architecture allows extension up to 256 simultaneous control channels in one test

 

The architecture is based on a controller board, called the SCU, which takes-up two slots in a chassis. The SCU standard configuration is as follows:

·        Two DC (loadcell) conditioned inputs

·        One AC (LDVT) conditioned input

·        One high level analog input

·        Two high level analog outputs

·        One servovalve output (current or voltage)

 

An optional daughter board provides LVDT conditioning for a 3-stage valve driver, position encoder and acceleration transducer (ICP). The SCU connection panel comes in many different configurations. FCS provides connector panels to match any custom requirement, including direct connection with existing cabling (MTS, Schenck, others). A fault management system switches in backup A/Ds in the event of a failure. Interlocks are daisy-chained between boards.

 

The multi-station SmarTEST ONE chassis includes the following:

·        Intel Processor

·        20GB hard drive

·        Ethernet or Fiber Optic networking

·        Ten slots available to support up to 4 servo channels and a additional I/O cards

·        Control of up to 12 channels

 

An expansion chassis can be added that adds a further 16 slots (8 channels). For multiple hydraulic stations a hydraulic switch unit can be added for up to 4 manifolds. This will interface with DC, AC or Proportional solenoids. Since the controller board takes up two slots, the SmartTEST ONE typically has four control channels, and two spare slots for other boards that include:

 

·        Digital I/O boards (24v opto-isolated)

o       8 in 8 out

o       16 out

o       16 in

·        Analog I/O boards (+/-10v 16bit differential)

o       8 in 8 out

The maximum channel count for a single test with the SmartTEST ONE architecture is 12. This is the maximum number of channels that can be driven from the single small screen on the front of the chassis. If more channels are required, FCS uses the larger SmartTEST architecture, which allows multiple boxes to be slaved together through the fiber optic or Ethernet networks.

A standard PS2 keyboard can be plugged into the front of the device, to simplify operation. A common configuration for the SmarTEST ONE is to mount it into a rack with a keyboard and monitor. The controller can also be operated from a networked PC, where a single window provides the same user interface at the front panel

 

In the standard configuration, the adjustable loop closure rate is typically 2500Hz for multiple channels, and 10kHz for a single channel.

Labtronic 8800/8400

Click here for a diagram

The fundamental building block of the architecture used in the Instron controller is the Integrated Axis Controller (IAC). This one board contains two DSPs (one for control, one for signal conditioning), and all the resources required for a single channel of control. It has four slots for combinations of the following:

·        1 channel Sensor Conditioning/Control Module (SCM)

o       Patented over-sampling system (see Sampling and Filtering below)

o       A/C D/C Encoder, or high level input

o       Valve driver

o       Maximum of 4 per IAC

o       RS232 for Remote Man-Machine-Interface (MMI)

·        1 channel Sensor Conditioning Module (SCM)

o       Patented over-sampling system (see Sampling and Filtering below)

o       A/C D/C Encoder, or high level input

o       Maximum of 4 per IAC

o       RS232 for Remote Man-Machine-Interface (MMI)

The IAC also includes the following:

·        4 digital inputs

·        4 digital outputs

·        1 high level input

·        4 high level outputs

·        Transducer linearization

 

IAC boards may be configured for control, or data acquisition only (using the different SCMs above). These IAC boards are installed into different chassis configurations depending on the application. The 8400 is an instrument-based single channel controller with one IAC, the 8800 comes in the form of a tower, or rack mount. In its tower configuration, it takes up to six boards. Multiple towers can be slaved together, and slaved with 8400s, or up to 30 IAC boards can be installed in a rack. The chassis also contains four digital inputs, four digital outputs, four analog outputs and one analog input (+/-10v). Channels can be assigned to up to eight Test Groups (independent test rigs). A tower can handle a maximum of four Test Groups. While it is theoretically possible to have more than one axis of control per IAC, it is important to note that the entire board runs at one sample rate.

 

Communication with the host PC is via the IEEE488 parallel interface (also known as a GPIB). It’s the same communication used for the standard printer port on a PC. A single PC is therefore dedicated to the control system.

 

An optional remote MMI can be used for each axis of control through an RS232 interface to the IAC. This provides remote access to common servo-loop functions at the test site. Also, a jog handset is available for the 8400.

 

Loop closure is at 5 kHz.

FlexTest SE/GT

Click here for a diagram

While this review focuses on FlexTest GT and SE, I think it fair to first talk about all the PC-based controllers in the MTS lineup. MTS controllers are split into two hardware platforms, and two software platforms. Unfortunately, the division between these platforms is not along the same lines. One hardware platform I will call FlexTest II, the other I will call Model 493. The software split is a little easier to explain, since there is only one controller that stands alone: FlexTest IIs. So, in a nutshell, here is the breakdown:

 

Product

Hardware Platform

Software Platform

Channels

FlexTest IIs

FlexTest II

Unique

Customizable

FlexTest IIm

FlexTest II

Common

32

FlexTest II CTM

FlexTest II

Common

Customizable

FlexTest II GT

Model 493

Common

8

FlexTest GT Supervisor

Model 493

Common

6

FlexTest SE

Model 493

Common

2

TestStar IIs

Model 493

Common

1

TestStar IIm

Model 493

Common

8

 

·        The FlexTest IIs controller is built for specific applications. For example, it controls MAST tables, crash sleds etc. It is not intended to be a user configurable system. It allows MTS engineers to design front-end interfaces that are application specific.

·        The FlexTest IIm, is a platform for large channel-count systems, its capabilities grow as processing horsepower increases. It is currently sold with a maximum of 16 control channels and four test stations, although MTS can configure it with 24+ channels for applications such as 6 degree of freedom road simulators.

·        The TestStar IIs is a single channel PC based system primarily aimed at the material testing market

·        The TestStar IIm is essentially the same as the FlexTest GT, but for the material testing market

·        MTS offers two products, the FlexTest II CTM and FlexTest GT Supervisor that provide control for existing analog systems, the later being upgradeable to full Digital Control. This is a path for labs that are currently fully analog, and want to gradually transition to digital control

·        This review will focus on the FlexTest GT and SE controllers, based on the TestStar II (model 493) hardware platform. The FlexTest SE is a single channel version of the FlexTest GT. It is instrument-based (no PC required) and can be combined with others for multi-channel tests

 

The TestStar II architecture is based on a VME chassis. In the case of the FlexTest GT, the chassis is mounted into a box that contains: the processor, interlock board, and 32 slots available for the following:

·        Digital Universal Conditioners (DUC)

o       A/C or D/C

o       24 bit 100 kHz sampling

·        Valve driver

o       2 stage standard (3 stage optional)

o       Maximum of 8

·        16 channel digital I/O

o       16 channels of input and 16 channels of output

o       Breakout box with simple connection interface

o       One only (as an option)

·        6 channel high level input

o       16 bit resolution

o       Maximum of 3 (as an option)

o       8 station GT only has room for one

·        6 channel high level output

o       One only (as an option)

·        Remote Station Control Interface board (see below)

o       Up to four stations (as an option)

 

In the case of the FlexTest SE, the  box that contains: the processor, interlock board, user interface, and the following:

·        Up to three DUCs (2 standard)

o       A/C or D/C

o       24 bit 100 kHz sampling

·        Up to two valve drivers

o       2 stage standard (3 stage optional)

·        1 channel high level input (more optional)

o       16 bit resolution

·        3 channel high level output

·        4in 4out digital I/O

o       One I/O pair for hydraulic interlock

o       One I/O pair for run/stop

o       Two I/O pairs for user definition

 

The boxes are connected to a PC via a dedicated Ethernet (SE's do not require the PC). If the PC also resides on a corporate network, it needs a second Network Interface Card (NIC). The maximum channel count for a single GT box is 8, assignable to up to eight test stations (test rigs). It is possible to have multiple PCs connected to a single GT box, allowing a “PC per Station.” The SE is a single station device. Multiple SEs can be connected together for a higher channel tests, and SE boxes can be combined with GT boxes in single or multiple stations.

 

A Remote Station Control (RSC) device allows an operator to operate common control commands through a MMI close to the test system. One RSC is used for each station, and connects to the GT chassis via a RS 422 connection. You cannot use the RSC with 6 or 8 station boxes, or with the SE.

 

Loop closure rate is up to 6 kHz.

Tiab

Click here for a diagram

 

The Tiab controller is a dedicated single station box that communicates with a dedicated PC though a USB. The box contains a  DSP board and currently provides 4 channels of control and 8 analog inputs. All signal conditioning is performed using off the shelf signal conditioners. The valve drivers are either current or voltage. 48 assignable discrete opto-isolated I/O channels are also provided.

 

The box includes a safety interlock that gracefully shuts the system down when the USB is unplugged. 

 

Loop closure rate is at 5 kHz.

 

Packaging

The DCS 2000 system includes a PC, and boxes that contain the X-Bus. These boxes (up to four) are 150mm H x440mm W x480mm D. The interface for the actuator is via a snake that has robust military connectors at both ends. The snake terminates in a breakout box for the individual connections to the actuator. The benefit of this approach is that there is only one cable to run for each actuator, and (presumably) more control over noise etc. A similar approach is used for the hydraulic control, where a remote box provides for pump and solenoid control, along with an emergency stop mushroom. The system comes packaged with an Uninterruptible Power Supply (UPS). 19-inch rack mountable options are available.

 

The SIMCON 2100 is built into a 19-inch rack, and integrated into a workstation, with the hydraulic control interface and connections. The connectors are MTS compatible, so that customers can effortlessly switch between controllers. There is also a smaller desktop version.

 

The SmarTEST ONE is built into a dedicated box with carry handle, which may stand alone, or rack mounted 177mm H x450mm W x280mm D x9.2Kg. It includes its own color screen and dedicated user interface on the front panel. The VGA (640x480) screen  is clear and bright, but small. However, as a standard feature, a VGA connection is available to connect a bigger screen. Field cable connections may be MTS, Schenck, IST compatible, or user defined.

 

The Labtronic 8800 comes in a tower configuration or rack mount. The tower dimensions are 650mm H x280mm W x570mm D. Each IAC has two SCM connectors on the front, via a pull-down hatch, and two at the rear. Hydraulic control is incorporated into the top of the tower through an angled panel, and the user has the ability to label each of the hydraulic buttons with a removable mask. Hydraulics can also be controlled from the PC. Connectors are a combination of Limo BNC, and “D” connections.

 

The 8400 is built into a dedicated box with carry handle, which may stand alone, or rack mounted. It includes its own monochrome screen and dedicated user interface on the front panel.  Connections are the same as the 8800.

 

The FlexTest GT looks futuristic. The box looks a little like a PC on steroids: 457mm H x127mm W x508mm D. Connections are all D type. Except for high-level I/O, which are BNC (as far as I could remember, this is true for all controllers). A rack mountable chassis is also available. 

 

The SE is built into a very light dedicated box with carry handle, which may stand alone, or rack mounted 130mm H x430mm W x430mm D x8.6Kg. It includes its own color screen and dedicated user interface on the front panel. Connections are the standard MTS D type.

 

The Tiab offers a range of enclosures. From a purpose designed bench top box that has optional ears for 19inch rack mounting to systems in off-the-shelf packaging. Tuchel connectors are offered as standard. Canon, BNC, Lemo or other customer requirements can readily be met.

Sampling and Filtering

The bandwidth and accuracy of a control system depends on the type of sampling and anti-aliasing used. Anti-aliasing is necessary whenever the acquired data is used for frequency domain analysis of any kind (all real-time simulation packages fall into this category). There are various techniques employed by the manufacturers.

Analog Filtering

The first method is the traditional method of analog filtering. High quality analog filters are used at the front end before the data is sampled. These filters must have excellent gain and phase relationships across channels in the pass-band to ensure the data is not time shifted unequally. The roll-off of the filters must be sharp enough to maximize the ratio between sample rate and bandwidth.

 

The SIMCON 2100 controller uses this technique. Filters are adjustable through hardware jumpers. They are 5-pole Bessel filters. Note that these are optional; be sure to specify them if you plan to do anything in the frequency domain. The filters are typically set at 80 Hz, which covers the bandwidth most folks are interested in. The data is sampled at 2048 samples per second, and decimated to the rate specified by the operator. Note that the decimation must not drop below twice the frequency at which the filter roll off drops below the noise floor.

 

The Tiab system can sample data to disk at 21Khz. The analog filtering is set to minimize phase delay. The analog filters can be readily adjusted. Filters are 2-pole Butterworth, with a nominal cutoff frequency (-3db) set at 2.5kHz.

 

The Pulsar system uses dynamic Butterworth low pass filters with software selectable poles.

Digital Filtering and Down-Sampling

Another technique is to sample at a very high rate, with less expensive “guard” filters. These filters have a gentle roll off, and hence do not have the strict gain/phase requirements of those in the Analog Filtering section. If the sample rate is high enough, these inexpensive filters will be flat in the bandwidth of interest, and the aliasing that occurs does not get reflected into the bandwidth of interest. The data is then digitally filtered and down-sampled, with ideal “brick-wall” filters. This is the technique, employed by most, maximizes the ratio between sample rate and bandwidth, making the most of your storage resources.

Other Proprietary Techniques

The folks at Instron have developed their own patented technique that maximizes transducer accuracy. By sampling at very high rates (40 kHz), they are able to quantize the noise of the transducer to the point where its noise floor exceeds the noise of the quantization process itself. This allows them to extract the most resolution that is physically possible from any given transducer. At the same time, they control the excitation of the transducer to get the most gain they can, while getting down to the thermionic noise level. The user can fix, or set limits on the excitation voltage. Through their patented algorithm, they are able to acquire anti-aliased data at a bandwidth of 1 kHz with 19 bits of resolution. This technique obviates the need for multiple transducer ranges.

 

MTS accomplishes this by building DUCs that sample at 100 kHz (49.15 kHz to be exact) at 24 bits. This also allows them to work without multiple transducer ranges, but this does not apply to the analog inputs, which are still 16bit. These might be required for simulation (if you are using external conditioners).

 

FCS samples the incoming data at 100 kHz and downsamples to the loop closure frequency.

Calibration

The Labtronic 8800/8400, SmarTEST ONE and FlexTest GT/SE products support the “lump in the wire” calibration system, with their own proprietary systems. This is a set of electronics in the wire that identify the transducer to the system, and includes the shunt calibration resistor. With the “lump in the wire” feature, the controller automatically detects a transducer and its calibration parameters as soon as it is plugged-in. Very simple from the operator standpoint, and it minimizes opportunity for error. The MTS and SmarTEST ONE systems work with or without these transducers. The 8x00 requires that transducer cables be modified with the appropriate electronics to be recognized by the controller (they call it being “Instronized”). The Pulsar, Tiab, SmarTEST ONE, Labtronic, and MTS controllers include dynamic linearization of non-linear transducers. The SIMCON 2100 uses a straight-line calibration for command generation windows, but the controller operation is all performed in volts (uncalibrated).

User Interface

This section covers the Graphical User Interface (GUI) presented to the user. All the systems covered in this review run on a Windows XP Platform, and make use of the standard windows interface, and three of them have their own instrument screens, which can be used without a PC. 

 

One of the more challenging GUI tasks is to handle the operation of multiple test rigs asynchronously. Complete asynchronous operation means that the test rigs all run at their own rate, and can be started and stopped independently. Handling the user interface for multiple stations presents a challenge. Every station requires its own instance of a complex set of windows, and keeping track of which windows relate to which station is very important. Make note of how each manufacturer implements their multi-station capabilities. Note that the FlexTest SE, 8400, and the Tiab controller are all single station devices. If you want more stations, you buy more boxes. The SmarTEST ONE is the only multi-station instrument-based controller with up to four stations (defined by grouping the channels on the function generation/test programming side). The MTS FlexTest GT and IST 8800 are the only 8 station devices (SE and 8400 controllers can also be combined into 8 stations using a PC).

 

By using the client-server model discussed in the architecture, all the manufacturers provide the ability to write applications that layer on top of the controller. In some cases users can write their own applications using Virtual Instruments (VIs), or Visual Basic®. But in most cases, the manufacturers write the specific application software themselves, and sell them as options. All controllers have a system configuration application, a controller operation application (tuning, set point, spans etc.), and a general purpose, or generic application, that is used for flexible testing of a variety of components, and is probably used 80-90% of the time. This generic application provides the ability to perform block programming, time history playback, etc. This review will focus on the generic applications.

 

Pulsar

A launch pad is used to start the application.

 

Advanced users can configure the system using an explorer-style tree view. This allows the user to define resources connected to the DSP, perform calibration functions and define units, identify all analog and digital signals used by the other objects.

 

Once the station is set-up, the user launches the main window, which provides access to all the functions loaded with the package. This main window, instanced for each station, contains windows for signal generators, actuator control (PID ramp/park position, FGs, spans etc.), park and ramp, meters, scopes and so on. Windows are launched by right-clicking the "desktop" and selecting from a menu, or by pulling down the Edit menu at the top of the screen. By focusing a window (clicking on it) a second window provides setup parameters. This window can remain on the screen so that the user can quickly click around the windows to see their parameters.

 

Pump/manifold controls program run/stop and enable/disable limits buttons are in a fixed window in the top left of the screen, and limits are permanently displayed in a reserved area at the bottom of the window.

 

The main window uses user-defined wallpaper as the backdrop. This wallpaper can be a schematic of the system, and the user can distribute the windows (meters etc.) around so that they correspond to the actuators shown in the background. This provides a quick visual view of the system.

 

A feature of this paradigm is that the user can define multiple views of a single system, by defining different windows. One station takes one single instance on the Windows Taskbar, so all the windows associated with a station can be minimized using the standard Windows function. If a limit trips, the window will pop-up automatically.

 

Pulsar is written in .net (Microsoft) and uses an XML database.  Both are current standard environments which will be supported well into the future.

SIMCON 2100

First, the user adds a box, called a QNX Host, to the user interface (QNX is the name of the operating system used in the hardware). This assigns a drive letter to the box, allowing the user Windows Explorer access to its disk, and presents the user with a list of resources that are available in the device. The user checks on the resources that are to be assigned to each station within the box.

 

The SIMCON 2100 was developed as a Test Site Controller first, then expanded to perform digital control. Its implementation is therefore unique. FCS-COM allows the user to differentiate between logical stations and physical stations. In other words, tests are designed and built first, then assigned to specific stations. All calibration is performed on the logical side of the fence, rather than the physical side. So all functions that occur on the physical side are performed in volts, so that when a test is loaded, it makes the connection between the volts at the physical layer, with the engineering unit assignment at the logical layer. One benefit of this implementation is that tests can easily be redirected to different stations, and stations can contain a mix of digital and analog control channels. The disadvantage is that whenever the user is operating the servocontroller, they are not working in engineering units.

 

All screens that are presented for a given station have a thick color-coded bar at the top, with a large number prominently displayed to give the station number the screen is referencing. This is a very clear indication of the station the user is working on.

 

Once the station has been defined, the user launches the Stations Main Screen, which provides access to all the applications that are available, from Servo Control to Test Monitoring. A window is instanced for each test station.

SmarTEST ONE

The user operates the system using the 150mm wide color screen on the box and the soft keys on the front, or via an external VGA monitor and/or keyboard. The screen is divided into four main sections. A set of indicators across the top provide a quick review of the test status, two panes tiled horizontally for various displays, and context-specific menu items across the bottom. The horizontal panes each have a set of optional windows that can be displayed, one graphic and one numeric in each half, and each can be split down the middle to allow a display of up to four windows simultaneously. The top pane displays a scope alone, or a scope and numeric table, the latter of which provides a real-time numeric display of system variables (aka DVM). The bottom half manages application specific displays.

 

The green number in the top left corner of the screen shows the current channel number being manipulated/viewed. The letter 'A' means all channels. The other indicators across the top of the screen are colored green, yellow, or red for alert severity. An additional removable message pane  appears automatically when a yellow or red alert is presented

 

The soft buttons on the front of the device are intuitive, and are used to vary displays and parameters. A big rotary knob selects and adjusts parameters, and is pushed to enter. To the right is an alpha numeric keypad and play/pause/stop/rewind buttons. Soft keys beneath the display are used to select the various menu items. The number of menu levels is limited to three to keep the user from getting “lost” in the menu structure.

 

The SmarTEST ONE controller handles stations differently than the other controllers. A station is an entity within the command generation layer rather than at the channel definition level. When a user defines a test, they select the channels to be included in the test. Up to four independent tests may be setup and run.

 

When the user needs to run more complex block programs, or real time simulation, an external PC is hooked to the box via Ethernet. Tests are created on the PC and downloaded to the hard drive on the box. PC utilities also allow file management and upgrading.

Labtronic 8400

The soft buttons on the front of the device are arranged into 4 areas. The display always shows which channel is in control, the status of channel limits, the status of events and the action of the function keys. The display also includes a screensaver, which dims the screen after ten minutes of inactivity. As soon as a button is pressed, the screen saver is cancelled.

 

Numeric keys are used to enter values for parameters at the various stages of setting up a test. The rotary knob is used for entering parameter values or to generate alphabetic symbols for labeling channels or user state names.

 

The four start, hold, stop and reset keys have an illuminated display to their right when they are activated. Below the keys is a writable area to enable you to add a specific label for the controller.

 

The four illuminating hydraulic keys, control the hydraulic pressure to the system and illuminate when activated. The small red stop key, below the Emergency Stop, can be programmed to stop the system in three different ways. In addition, if the system is being operated from a PC, it restores the control to the front panel.

 

All the operations of the 8400 can also be performed using software on a PC. This is identical to the software supplied with the 8800, and so I will not deal with it separately. For details on operating the 8400 from a PC, read the 8800 information.

Labtronic 8800

The servo-controller functions of the 8800 are performed via an application called RS Console. Available resources are attached to test groups or stations using the Configuration Manager. This window provides an Explorer-style tree view of the hardware, and allows the user to assign the hardware to groups. This application provides a toolbar that sits on the side of the screen and gives an iconic view of the various stations. Via a code of icons and colors, the toolbar provides a quick overview of the test status. While these icons seem somewhat cryptic, I understand that once operators get used to them, they are easy to understand. The toolbar provides the platform to launch the various windows.

 

Tests themselves are defined in RS BasLab. This is a database driven application that allows the user to define projects, users, specimens, event actions, signals, schedules, etc. From there applications are launched that define the requisite profiles, for example, RS Block is the block programming application.

 

The Project Manager provides an Explorer-style tree view of all the projects on the system, with easy access to the various files and test definitions. Password protection is used to deny certain users access to critical setup areas of the software. These areas are user-definable.

 

Instron also provides VIs that allow you to build your own custom applications

 

FlexTest SE

The SE has a vast array of controls that have specific functions rather than a few buttons that change context. The main menu items are hard coded into one set of buttons that provide immediate access to the functions of the controller. Once in a menu system, soft menus appear on the right side of the screen that are navigated using the adjacent keys. The display shows the test log, meters, and the current status. If the optional scope is purchased, it sits in front of the test log.  Store and recall buttons allow the user to save views as bookmarks, and return to them at any time. All the operations of the SE can also be performed using software on a PC. This is identical to the software supplied with FlexTest GT, and so I will not deal with it separately. For example, the Multi Purpose TestWare® (MPT) described below can also be used to setup block profiles for the SE box.  For details on operating the SE from a PC, read the FlexTest GT information.

FlexTest GT

The FlexTest software is divided into three layers. Station configuration is performed by the Station Builder application. This drag and drop interface has available resources listed on the right, and station resources listed on the left. The user chooses which resources should be applied to which stations.

 

Once a station is defined, the user then launches the Station Manager. This is instanced for each station. All servo control functions are performed at this level. Once the servo loop is setup, the user can launch specific programming applications from this window. Multi Purpose TestWare® (MPT) is the application used to define block programs and time history replay. Functions for all the applications that are launched from the Station Manager are available from within the same window. Password protection is used to deny certain users access to critical setup areas of the software. The main window includes control for the function generator, hydraulics, and interlocks.

 

The Desktop Organizer puts a taskbar at the bottom of the screen for each test station. By clicking on one of a pair of arrows, all windows relating to a station can be expanded up onto the screen, or collapsed out of sight. This provides the user with all the available screen real estate for a single station at a time. the Indicator “LEDs” on the taskbar provide the user with a quick look at the state of the test.

 

MTS provides VIs and a Visual Basic API for you to build your own custom applications.

Tiab

The Tiab software is written using National Instruments® LabVIEW®. All the VIs are therefore available to write custom applications. However, I will review the stardard controller software that is available "off the shelf" from Tiab.

 

Each Tiab system runs its own intranet site and can allow protected access to all its operation and data files from anywhere in the world with only standard web explorer software. Webcam and digital camera features link in with Report Publishing and automated Test Sheet Generation.

 

Once the software is launched, the user selects the relevant configuration file, which may be edited using a simple editor, and is then presented with a Main Control Panel This is the launch-pad for all the functions of the controller. The buttons invoke the following (from left to right, top to bottom):

·        Signal Generators

·        PID Controls

·        Limits

·        Oscilloscope

·        Multi-Axis Model (for simulating a real system)

·        Trigger Timer

·        Meters

·        User (custom) VI

 

In the middle of the Main Control Panel is a set of buttons and indicators that, in this example, are used to switch hydraulics and limits. The user has the ability to define these buttons and indicators to switch and read any controller two-state variable. This is defined in the System Configuration File

Servo-Control and Tuning

All the controllers in this review except the SmarTEST ONE use PID control, and include delta-P stabilization (usually an option). I will briefly describe the control system FCS uses in the SmarTEST ONE section.

 

The more tools in the controller toolbox you have available, the better chance you have of controlling that awkward axis, that is very non linear and/or has a bad resonance. While a lot of controllers have auto-tuning, I have not found an algorithm that works well. I usually tune loops manually. So ease of use is important here. Especially considering that during the tuning process, you need to be able to easily switch between channels, while looking at command/feedback signals on a scope, switch function generation, and have easy access to the sliders for each servo controller setting.

Pulsar

Access to the PID window is discussed in the User Interface section above. The properties of the actuator window includes a tab which allows the user to adjust the PID parameters. The servo controller has the standard Proportional, Integral, Differential, and Feed-Forward (PIDF) parameters with bump-less mode switching. The main window provides access to the function generator; the user launches a scope that has access to any internal signal (feedback, error, command, etc). A square-wave is selected and the process begins on the first channel. Once complete, if mode switching is required, the control mode of the channel is changed on the main screen, Setup>Tuning is selected again, and the scope channels are changed. Once the second mode is tuned, the user moves on to the next channel and the process is repeated. An unlimited number of meters for any system signal are available in a separate window with instantaneous, average, RMS, max/min readings.

 

Sevotest recommends that the user perform tuning using an "EZflow" process. EZflow will be discussed later, but suffice it to say that this allows the user to predefine processes, one of which is an auto-tuning function which they assure me works well. I was unable to test this under load control with a soft specimen, the condition which usually challenges auto-tuning algorithms. All the controllers reviewed do include auto-tuning, but I have deliberately avoided it because it has not proven to be a useful tool. However, the Servotest algorithm does seem different from the more ubiquitous approach of using swept sinusoids. Servotest uses a random signal, and tunes the system to achieve a user-defined desired frequency response curve that can be saved to disk. This could be useful where you need to reproduce the tuning on two different test systems, say a drive file was developed on one, and you need to replay it on another. It is also easy, using this technique, to perform test quality monitoring (detecting changes in servoloop response over time).

SIMCON 2100

Access to the PID window is via a toolbar shortcut in the Servo Control Application that is launched via the toolbar on the main station window. Feedback is selected via a setup window (no mode transfer). The servo controller has the standard Proportional, Integral, Differential, and Feed-Forward (PIDF) parameters. Access to the function generator is in this same window , along with a graphical display that shows the command. To see the feedback, the scope is used. The scope has access to system responses. Current values and following error are digitally displayed on the Main Servo screen. Servo controller tuning parameters can be saved to a configuration file, and may be recalled later when a given test is loaded.

SmarTEST ONE

 FCS uses a "Patented Force Loop Model Follower Controller." Don't let this mislead you, it can be used for either force, displacement, or acceleration control. They also have a more traditional PID displacement control loop in the controller. The "Force Loop Model Follower Controller" is not a PID(F) controller, it internally computes force, displacement, velocity and acceleration into the same domain. Force and displacement commands can be rapidly switched on the fly, or even applied together, providing an implicit seamless control mode transfer.

 

In each domain, they have the ability to perform certain actions to improve control stability. When in the Force Domain, a Breakout force can be defined (that limits the maximum force that can be applied in displacement control). When reached, the controller switches to force control. This is useful to protect the specimen, or personnel.

 

While in the velocity domain, the user has the ability to add damping. This is useful for controlling sharp resonances. It is similar to the "D" term in a standard PID loop.

 

Also, in the velocity domain, they provide the ability to control cross coupling. If you have one actuator that causes error in another due to fixture or specimen kinematics, you can feed its velocity directly in, providing the control channel the ability to react more quickly to the external disturbance.

 

When performing acceleration control, it is very easy to apply a displacement offset.

 

This control loop also has other features that are not available in the other products: feed forward gains are independently applied to force, acceleration, velocity and position; limits can be applied for maximum velocity, position and servovalve command, that clip the valve command; and the servovalve command can have an asymmetric positive and negative gain for non-linear systems.

 

To perform the tuning, the Setup item is selected from the main menu, followed by Controller (after selecting the relevant channel). The screen is automatically populated with a scope preset with the command and response, function generator, bar graphs and tuning parameters. The user selects the function generator in the top right of the screen, and enters the parameters for a square wave, and then varies values in the spreadsheet in the bottom right. The loop's performance can be monitored via the scope in the top left, and bar meters in the bottom right that show command, feedback and error (gain and phase). To switch channels, simply exit, select the next channel, and re-enter.

 

Of course, with this control scheme, there are a lot more parameters to tweak, which can be a blessing and a curse. Auto-tuning is available, but, as with all others, it does not do a good job.

Labtronic 8400

To perform the tuning, the user sets the waveform to a square wave in the respective channel, and with the hydraulic pressure on high, presses the start button. From the home screen, the user presses the Setup and Loop soft keys. Soft keys are then available to adjust the parameters, and a scope, preset with command and response is on the screen. To switch channels, the user returns to the function generator screen, stops the program, and begins again.

 

When tuning the 8400 from the PC, the procedure is identical to the 8800 (below).

Labtronic 8800

Access to the tuning tool is via a tab on the controller properties window, accessed from the tools menu on the taskbar. A single window provides access to all the items needed to tune a channel: tuning parameters, scope (preset to view command and response) and a function generator. Instron uses a PIDFL loop. The “L” stands for phase lag, which helps to control through difficult resonances. A graphical editor is used to configure the control loop, showing exactly how parameters will be applied, and allows the user to enter and graphically edit the parameters of a filter in the forward path. A system summary table shows all channels, their gains and parameters. This allows the user to compare gain settings etc. to ensure they are consistent between similar channels. Meters are available in a separate window with instantaneous, max/min, mean/amplitude and peak/valley readings. These meters can be sized from full screen all the way down to summary views on the taskbar.

FlexTest SE

To perform tuning on the device itself, the user selects the tuning button. This populates the screen with the scope, preloaded with command and feedback, and the softkeys provide access to the PIDF parameters for adjustment. Switching channels is easy. When tuning the FlexTest SE from the PC, the procedure is identical to the FlexTest GT (below).

FlexTest GT

Access to the tuning parameters is via the Station Setup window accessible from the main Station Manager window. Through an Explorer-style tree, the user can select the channel and control mode. An icon selects the tuning parameters. The servo controller has Proportional, Integral, Differential, Feed-Forward (PIDF) and Forward Loop Filter (bandwidth) parameters with bump-less mode switching. The function generator is on the main window, and the relevant channel must be selected there, along with the control mode. A scope is launched from the main window, and its parameters are selected to view command and feedbacks from the relevant channel. To use the mode switch, the user then switches the control parameters screen, switches the function generator control mode, and scope channels. Once the second mode is tuned, all the parameters are changed for the next channel. Up to 9 meters are available in a separate window with instantaneous, max/min, mean/amplitude and peak/valley readings. The meters can be sized up or down by dragging the corner of the window.

Tiab

The PID settings panel is invoked from the main window. The user then opens a scope and a function generator. The scope is set up along with the function generator, oil is applied to the actuator, the function generator is run and the PID settings are adjusted to give the requisite response. To switch to another channel, the function generator, scope and PID settings window must be switched. Meters (called aliases) are readily available from the main control panel.

 

Tiab offers "Remote Tuning". This allows mixed-mode control. For example, the controller can follow a sinusoidal program of load when in position control. A rate adjustment allows for soft or stiff test specimens. The algorithm used ensures the adaptive tuning is halted if a valve limit is reached or there is any interruption of the sinusoidal drive signal. The same technique can be used to ensure an actuator in position control does achieve the full amplitudes requested. 

 

One feature that sets this controller apart in this category, is the system modeler. It is possible to build a model of the system to be controlled, and use it to tune the system first. This is useful if the specimen is highly degradable or expensive, and cannot be used for tuning purposes.

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Handling Limits and Events

In general, limits are set at the controller level, the test programming level, and in the test monitoring system. The limits at the controller level are global, fail safe limits, and are typically implemented early in the signal path, at the highest possible sample rate. The limits set at the test programming level are typically tighter, and more germane to the activity that is occurring at that time. Limits set for monitoring are based on some kind of analysis of the system responses that happens in the background. The controller limits are the most immediate, and the monitoring limits take the longest to trip, because of the processing time required. This section gives a description of the controller limits, and an overview of the program and monitoring limits. The latter two types of limits will be covered more rigorously in the Block Programming, Time History, and Monitoring sections to follow.

Pulsar

Limits are set at the bottom of the main window. Limit status and values are permanently displayed in a reserved portion. Tabs are used to show limit status, overpeak and underpeak settings.  Defined limits are always active in high pressure, but may be disabled globally in low pressure.

 

Limits are given a unique name and can be defined to Shutdown, Trip or Indicate. They can have different actions for positive limits or negative limits.

 

Controller limits can be set on the following:

·        Max/Min

·        Underpeak

·        Cycle Counter

·        Timer

·        Digital Inputs with Counter (action after a user-defined number of transitions)

 

The user is able to control how each of these functions in the event of a trip or shutdown:

·        Controller

·        Signal Generators

·        Rampers

·        File Replay

·        Data Logging

 

The status window provides information on the status of the limits. When a limit trips, the status window changes color to show a shutdown (red),  trip (orange), or indicate (yellow). Limits can be reset by right-clicking.

 

The Pulsar software allows these limits to be changed during programming and provides flow control of the sequencing. Limits can cause a trap to a specific block that provides instructions given the event—more later (in the Block Programming section).

 

SIMCON 2100

The Digital Servo Control application allows the user to set warn and abort limits for displacement, load and error on each channel. This window is accessed directly from a tool on the servo-controller window. This window is also used to enable, disable and reset limits. All limits for all channels on one station can be viewed and edited at one time. As with the PID parameters, these limits are saved into a configuration file and may be recalled for a specific test.

 

Monitoring limits are also available for trend statistics and time histories. These are covered in the Monitoring section below.

SmarTEST ONE

The SmarTEST controller provides two sets of limits,  absolute and relative. Three limit values can be entered for each limit: alarm, script and failsafe. Alarm is used as a warning, failsafe is used as a shutdown, and when a script level is activated, the controller executes a user-defined script that can command the controller to go to rest condition, log event into log file, get and set values, and/or begin data acquisition.

 

A standard feature of the controller is the "dying seconds buffer," or flight recorder. This is a buffer of data that stores the events that lead up to, and just after an event has occurred. The buffer can be stored to disk, and restored later. This can be useful when debugging a specimen or system failure.

 

Limits can be saved to disk and recalled at any time. This allows one set of limits to be used for multiple tests.

 

Labtronic 8400/8800

Controller limits can be set on every transducer connected to the system. There are two sets of limits, Physical and Primary. Primary limits are used when the user is running modes that have different units than the primary transducer itself. For example in a 6 DOF vibration table there would be 6 actuators in position control (the physical transducer is a LVDT) and the system is configured to command pitch and roll, defined in degrees. The primary limits could be set in degrees rather than native units of the controlling transducer.

 

The limits can be set by hitting the limits soft button on the main screen of the 8400 or in the conditioner properties window of the 8800, accessible from the toolbar. An upper and lower limit is provided; the user enters a value, and an associated action from a list of the following:

·        Actuator off

·        System stop

·        Hold

·        Reset

·        Unload

·        System reset

·        System unload

Also a "Dynamic rampdown" is available. This option executes a script when a limit trips. For example:  switch to position control and go to (n) mm or drive a parabolic ramp to zero load.

 

Limits are armed for each transducer, or armed as a group (all transducers for a given channel).

 

The user can also enter servovalve current limits to protect 15mA valves for example. One set of limits are defined for low pressure and another set for high-pressure operation. 

 

Limits are also available for programming and monitoring. These will be described later, in the Block Programming and Monitoring section.

FlexTest GT/SE

The user can set upper and lower limits on any transducer and error for a given channel of control. Actions available are:

·        Indicate

·        Hydraulics off

·        System interlock

·        User defined:

o       Send message to log file

o       Ramp to level in a given time, and in a given control mode

o       Hold at level

o       Set/clear digital output

On the PC, limits are armed in the station setup window, and globally reset on the main Station Manager window. A reset/override switch temporarily disarms limits for up to 60 seconds, while the user applies hydraulics, moves a set point, etc. The Station setup window also provides an overview of all the limits, and their status. On the SE, limits can be set by selecting the limits menu from the front panel.

 

Limits are also available for programming and monitoring. These will be described later, in the Block Programming and Monitoring section.

Tiab

The limits panel is accessed from the main control panel. Max and Min values can be set for any system variable. These limits are defined as monitor (enters a message in the log file only), trip (ramps program to zero but maintains pressure) or shutdown (ramp to zero and shut off hydraulics).

 

Actions can also be applied if there is an error during auto tuning--the tuning is halted if a valve limit is reached or there is any interruption of the sinusoidal drive signal.

Optimization and Other Algorithms

In an ideal world, the test system would respond in exactly the way we ask it to. Unfortunately, this is rarely the case. In the old days, when we were using analog controllers, performing sinusoidal, single amplitude loading, we would manually adjust the frequency, amplitude, and mean, until we achieved the response from the system that we were after. Fortunately, there are now many algorithms that are available that automate the process, while minimizing test time. Algorithms are also available for varying amplitudes and time histories. This section discusses the options available for each controller, along with any other goodies that are in the toolbox for awkward control situations.

Pulsar

This controller has a compensation technique they term Compressors. This is a form of amplitude correction, with or without mean. The convergence rate, which increases speed at the expense of accuracy is set in the advanced configuration window. This algorithm is tied to a given actuator and/or added as an external block that can by wired  anywhere in the loop (function generator for example).

 

The pulsar system has the most advanced method of building "modal" control. Using a function Servotest calls "sockets" the user is able to define any algorithm using Matlab® Simulink® . This algorithm can be used to black-box any complex control algorithm that manipulates system variables, and creates command or monitoring signals. A window that is tabbed in the main window provides operator control of the socket. An example of a socket is to control downdraft force on a Formula One car by computing speed, wheel positions, and cornering force.

 

Since this section is a “catch-all” for any features that are not covered in the other sections, it is worth noting that Pulsar allows 3 input signals for each controller. These inputs are all added together using user-defined % weights and applied to the servo loop. An obvious application of this feature is sine-on-sine, or slowly varying mean positions etc.

 

Addition of an auxiliary feedback (such as Delta-P) is straightforward. Gains for this are included in the controller setup.

SIMCON 2100

This controller has a compensation technique they term ACE. This is a form of amplitude and mean correction. The user enters a mechanical gain, the maximum compensation to be applied, and the maximum change per cycle (convergence rate). The mechanical gain is used for situations where the feedback parameter used for the optimization is not the same as the servo control parameter. This gain value relates the voltage difference between the amplitude of the desired transducer response and the requisite servo-loop command. To make this calculation easy, SIMCON 2100 includes a built in calculator to help the user compute the necessary value to enter.

 

SmarTEST ONE

This controller has a compensation technique they term Amplitude Matching. This is a form of amplitude and mean correction. The user simply hits a button when in the function generator to activate.

 

For non cyclic command signals, Adaptive Model-Based Control (AMC) is available. This is a type of Adaptive Inverse Control.  It analyses the system transfer function on the fly, inverts it and uses that inverse model to compensate the command signal in phase and amplitude in order to achieve the desired target.

 

SmarTEST ONE includes Pseudo Channels as part of the standard package. Pseudo channels are user-defined calculations which can use any feedback or parameter to create a virtual channel. Among other things, pseudo channels can be used for control, data acquisition, and/or limit detection. As an example, pseudo channels can be used for modal control. It allows up to four feedbacks and four valve drive signals to be combined to produce “virtual channels.” Any combination, including trigonometric, log etc., can be applied using a programming language that includes conditionals.

 

As I mentioned earlier, FCS-COM has implemented a unique patented control loop that includes a vast array of tunable parameters for the more challenging control scenarios. For more details, see the Servocontrol and Tuning section.

 

Labtronic 8800/8400

The IST controller has an optional amplitude/mean correction technique called Tri – Modal Amplitude Control. It is able to deal with the mixed transducer situation (different response transducer than control transducer) by automatically monitoring the relationship between the two, and adjusting the compensation accordingly.

 

Also optional, is an adaptive control technique that uses a continuously updating system transfer function to adjust the command to meet the desired response. This is a type of Adaptive Inverse Control. This works with full bandwidth signals.

 

Included in the standard package are a few other control tools. The elements in the PIDFL loop can be arranged in series or in parallel, a user-defined filter can be placed in the forward path, and control loops can be cascaded (a load loop is used to command a displacement loop). As the user selects various options, a graphical display of the loop is presented to the user. Clicking on the various elements in the loop brings-up the properties of the box, allowing the user to change the parameters.

 

The 8800 also includes modal control as part of the standard package. This allows up to four feedbacks and four valve drive signals to be combined to produce “virtual channels.” Only linear sum/difference is available, but this meets most requirements.

 

Cross coupling compensation is part of the standard package. This allows the servo-valve command to be compensated by a polynomial computation of another response. This helps to eliminate cross-talk caused by kinematics of a test fixture or specimen.

 

Gain scheduling, also standard, provides the ability to control very non-linear systems. Different PIDFL settings can be applied for different parts of a command, so that when a steering rack hits an end stop for example, there is a rapid change in stiffness, and the controller can switch to an alternate gain.

 

Load protect is a control mode where, while in position control, actuator motion is stopped if it sees a force that is higher than a pre-set level. This is especially useful for installing specimens.

 

Motion Isolated Load control (MILC) provides significantly improved accuracy compared to a conventional load control loop when the specimen under test has its own externally excited motion. This is used to control the down-force of a racecar on a four post simulator. The force can be controlled despite to motion of the car body. 

FlexTest SE/GT

MTS provides these command compensation techniques:

·        Peak Valley

·        Null Pacing (static) and (dynamic)

·        Adaptive Inverse Control (AIC)

·        Arbitrary End Level

·        Peak Valley Phase

The last three are optional; they do not come with the standard package but they can be added to GT or SE.

 

Also as an option, you can purchase Calculated Signals, and Calculated Channels. The first one allows you to create a signal in the controller that is any mathematical combination of other signals. A virtual code editor provides the user with the ability to write a set of equations that define the channels. Any system signal is available as a variable in the equation. Calculated channels allows the user to take those calculated signals, and use them as virtual feedbacks, and then take the virtual valve drive signal, and distribute it to multiple actuators via a second set of equations. Through this feature, it is possible to build any modal control channel.

 

Tiab

The Tiab controller does not have command optimization at this time.

 

Function Generation

Commands sent to the control system are usually broken into two levels: Function Generation and Test Programming. For this review I have broken Test Programming into its two major components: Block Programming and Time History Playback. This section focuses on the function generator that is built into the controller itself. This is usually a standard component, vs. the optional test programming layer.

Pulsar

The Signal Generator can be added to the main window. Signal Generators may be instanced multiple times and triggered together. Up to three may be connected to one actuator to produce complex waveforms (see Optimization and Other Algorithms), and one may be hooked to several actuators. By selecting the Signal Generator window, and entering setup, the user can select the following:

·        Sine/Square/Triangle waveform

·        Initial phase angle (for phasing multiple Signal Generators)

·        Cycle count interlock (down to ¼ cycles) or continuous operation

·        Soft start

·        Soft stop

·        Main panel display of frequency or time

·        Frequency sweep

o       Lower frequency

o       Upper frequency

o       Sweep rate

o       Sweep direction

o       Linear/log

o       Single/continuous

·        Actions to be performed in the event of a limit trip or limit shutdown

 

The amplitude of each Generator is set as a span on the global spans window, also weighting in % for each of the three inputs for a given channel can be set.

SIMCON 2100

Function generation is performed from an application called WavePlay Playback. The user enters file names for system tuning, configuration and logs, and selects from the following:

·        Channel (single channel, single instance)

·        Frequency

·        Waveform (sine, square, triangle)

·        Amplitude

·        Time/cycle count duration

SmarTEST ONE

Standard function generation is performed using the "Cycle" button on the main screen. Several channels can be synchronized in any combination and each channel can be phase shifted.

 

the following items can be set for each channel:

·        Frequency

·        Amplitude

·        Offset

·        Phase

·        Time/cycle count duration

 

The application also displays current values  for amplitude and error, phase error, cycle count. These parameters can be set on the following waveforms: 

·        Sine/Cosine

·        Sawtooth (triangle)

·        Block (square) wave

·        Ramp up/down (asymmetrical sawtooth with slow rise, rapid fall, or vice versa)

·        Rounded Ramp (as sawtooth, but with the top 10% and bottom 10% rounded)

·        Random

·        Exponential (as ramp down, but with exponential decay on down slope)

 

According to FCS-COM, the Rounded Ramp function is a very efficient shape for rapid cycle accumulation.

Labtronic 8400

The  function generator is selected from the Waveform button on the main screen. In Position Control, the Pos'n key is highlighted, so that the four keys along the bottom show the position channel waveform details and vise-versa for Load control 

 

When in the waveform screen, you can change amplitude, mean and frequency. The shape of the waveform can only be changed when it is not running. 

 

The types of waveforms are the same as for the 8800 (although some are optional) and the function generator screens for PC operation of the 8400 are identical to the 8800 (below).

Labtronic 8800

An individual function generator is provided for each channel. These may be slaved to other channels, and linked with a master control. Parameters can easily be copied across several channels by grouping. The user selects from the following:

·        Sensor

·        Sine/Triangle/Square/External/Sawtooth

·        Amplitude and frequency

·        Full cycle or haver cycle

·        Amplitude control

·        Cycle count interlock

·        Master/slave relationship

o       Frequency ratio of master

o       Phase from master

·        Ramp up time

·        Ramp down time

·        Mean

FlexTest SE

The function generator menu is reached from the Function Generator button on the front panel. The user can select from the following:

·        Control mode

·        Monotonic

o       Time or rate definition

o       Absolute or relative end level

·        Cyclic

o       Sine/triangle/square

o       Tapered or non tapered

o       Frequency

·        Sweep

o       Sine/triangle/square

o       Start frequency

o       Stop frequency

o       Linear/log sweep

·        Random

o       Shape

·        Amplitude

·        Mean

·        Action to perform when done (disabled, program stop, or hydraulics off--HSM only or HSM and Pump)

·        Compensation (depending on options, see Optimization and Other Algorithms section)

The user can also select external program or block profiles from this menu. See the  Block programming section. The SE function generator can also be operated from the PC using the same user interface as described in the GT section.

FlexTest GT

The MTS controller has a function generator on the main screen. Spans on individual channels provide function generation on several channels together (all in phase). The user selects from the following:

·        Control mode

·        Cyclic

o       Sine/triangle/square

o       Tapered or non tapered

o       Frequency

·        Sweep

o       Sine/triangle/square

o       Start frequency

o       Stop frequency

o       Linear/log sweep

·        Random

o       Shape

·        Amplitude

·        Mean

·        Compensation (depending on options, see Optimization and Other Algorithms section)

 

FlexTest GT also has an application provided as standard called Basic TestWare that provides further function generation capabilities. This channel-by-channel FG adds monotonic loading capability, data acquisition, test log and test-specific limits.

Tiab

The function generator menu is reached from the main control panel. A separate function generator is provided for each channel that has the following options:

·        Sine/Cosine

·        Triangle

·        Step (Square)

·        Sweep any of above from current running frequency to new frequency.

·        Random

 

Block Programming

This is typically an application that is purchased in addition to the standard controller, to provide the ability to sequence through a test procedure. This procedure might be derived from an existing test specification, or it might have been developed from field data to reproduce fatigue. In most cases, your test requirements are unique to your situation, and so close scrutiny of the capabilities of each controller needs to be in the context of your own specific requirements. If you are unable to establish which controllers can meet your needs, I would be happy to help you.

Pulsar

The paradigm used by this controller is a flow chart called "EZflow". The user adds boxes to the flowchart by dragging them onto the workspace, and selects the boxes to enter the parameters. Flow control is accomplished by using branch blocks. Processes are saved in files, and processes can be nested by nesting files in processes. A process may be setup that includes multiple actions, and the user can decide on the action to perform by pointing the start block at the desired process.

 

The following block types can be added to a test:

·        Start block (always executed at the beginning of the test)

·        Command block (contains a set of commands)

·        Nest block (contains another procedure file)

·        Branch on Iteration (with loop counter)

·        Branch on Signal (with levels)

·        Branch on User Request (waits for user response y/n)

·        Branch on Digital Input

·        Branch on Digital Output

·        Branch on Trend Monitor

·        Finish block (always the last block on the test)

The Command Blocks can contain the following:

·        Add/Edit/Remove over/under-peak limits

·        Data collection synchronized/stop/start

·        Drive file playback and reset (see Time History Playback below)

·        Sine with sweep option

·        Ramp up/down

·        Counter (time/level-crossing/digital-inputs)

·        Mean level and span

·        Selection of up to three actuator inputs with weightings

·        Autotuning

·        Change control mode

·        Set a variable

·        Zero a transducer/encoder

·        Pole digital/analog signals (watch for a change of state or level crossing for analog channels)

·        Run a Data Analysis Package

·        Command digital outputs

·        Pause for a user specified period

·        ASCII log (up to four files with 16 signals in each)

·        User break (presents button and message for operator to respond to)

·        Hydraulics on/off

·        Retain amplitude (at the end of the block, the last amplitude is held, otherwise it is ramped to zero)

 

In each of the blocks, the user decides how each function will behave in the event of tripped or abort limits.

SmarTEST ONE/SIMCON 2100

Block profiles for the SIMCON 2100 and SmarTEST ONE controllers are defined from software running on the PC.

 

First, the user runs the Waveform Editor, to create the block profile waveform, when using the SmarTEST ONE, the waveform is downloaded to the controller and executed, when using the SIMCON 2100 they run the Block Cycle Test Editor, to set the parameters of the test before downloading and executing.

 

In the Waveform Editor, the user can enter information about the following, for each channel:

·        Wave name

·        Author

·        Version

·        Comment

·        Project Name/Number

·        Plot color used in the visual editor

·        Engineering units and full scale (this must coincide with the setup of the test hardware)

 

The Waveform Editor workspace gives a Windows Explorer tree view of the profile. Profiles can be dragged around the workspace and dropped in position. This facilitates nesting and sequencing of both waveforms and events.

 

A waveform is built up with blocks. Blocks can be nested. Blocks contain multiple Segments. The user enters the number of repeats for a block in the Block Properties window. There are six different categories of segments:

·        Ramp

·        Haversine

·        Hold

·        Sine

·        Square

·        Triangle

·        Time History Playback

 

Properties of these segments are entered via the Segment Properties window. The user enters amplitude and phase parameters, or whatever is pertinent to the segment type.

 

Events are created in the Event Properties window, and are associated with either an individual segment, or a block. The user places the event in the relevant location in the profile, and then defines an offset for the event from the beginning of the segment, or block. The event type is selected from a list:

·        Start data acquisition

·        Start Amplitude Matching (optimization)

·        Cycle count

·        Turn on or off digital output

·        Set gain (optimization)

·        Multiply gain (optimization)

 

During this entire Waveform Editor session, a graphical window shows the entire waveform, and the effects that are a result of the operator input. The operator can zoom in and pan to inspect the created waveform in detail.

 

When using the SIMCON 2100, the user runs the Block Cycle Test Editor, picks the channels to be used, the A/D channels to be used for optimization, A/D channels to be used for the data acquisition (any channel selected for optimization is automatically included in the data acquisition list), and the digital I/O channels to be used. In the Block Cycle Test Editor window, the user also selects the data acquisition sample rate, and ramp times for start, stop and interlock.

Labtronic 8400

Block programming functions of the 8400 are setup on the PC using the same software as the 8800 (see below).

Labtronic 8800

The application used to define block profiles is called RS Block. It sits on top of the RS BasLab application that manages all the data in a database structured into projects and specimens. Tests may be defined in isolation from physical systems by means of the Virtual Test Rig (VTR). A library of VTR configurations is available for test definition. Test configurations are checked-out and checked-in to the database, to manage version control etc. The BasLab application also allows you to manage user privileges, create, edit and view data for specimens, create, edit and view data for projects, edit events and actions, manage a signals database, launch the schedule editor (RS BasLab), run the test, and analyze the data.

 

RS Block uses a table format to define block profiles. The columns of the table display the following:

·        Logic (shows looping or sequential operation)

·        Individual channel programs

·        Events

·        Data acquisition tasks

·        Tools ( external applications that are launched to perform functions including scope, meter, and sending an email)

 

Each row of the table represents a block in the sequence. Cells are edited by double-clicking a cell.

 

By double-clicking the loop cell, the user has the ability to enter a name for the loop, begin and end sequences, and a loop count. Loops may be nested four deep.

 

The individual channel cells provide the ability to enter the following:

·        Controller type

o       Serial PID

o       Parallel PID

o       Cascade

·        Feedback (load, stroke, etc)

·        Program

o       Ramp (relative, absolute, final)

o       (Haver) sine

o       (Haver) triangle

o       (Haver) square

o       Sawtooth

o       Hold at level

o       Time history

·        Optimization (amplitude control)

 

Events and actions are also entered via a table format. The columns of the table are:

·        Type

·        Source/parameter

·        Value(s)

·        Slope

·        Arm in Held Status

·        Armed

·        Firmware action

·        Action list

 

The types can be any of the following:

·        Program

·        Digital input

·        Threshold level and slew-rate

·        User-defined condition

 

Firmware actions possible:

·        Set digital output

·        Actuator off

·        Transfer and hold

·        Unload

·        System unload

·        Dynamic ramp-down

 

The action list is a script that is executed. These action lists can be programmed to trigger external devices, external applications, digital outputs, hydraulic status changes, changes in test loop control (e.g. stepping out of the main sequence and running a side rotine for measurement). The user may define a limitless number of action lists, which are then selected in each block with a drop down menu.

 

Up to three data acquisition tracks may be defined, using three IAC boards (see Hardware Architecture section). Data acquisition may be defined as a circular buffer, as synchronous acquisition, or peak valley (hysteresis) in a defined location. Data acquisition can be triggered by the initiation of the block, via keyboard input, limit value, digital input, program software, or user-defined cycle intervals.

FlexTest SE

If you purchase this option, the SE box allows you to create up to four blocks. For the whole sequence, the user enters the following:

·        Number of passes

·        Level type (blocks defined as amplitude/mean or max/min)

·        Total Count (current cycle count)

·        Action to perform when done (disabled, program stop, or hydraulics off--HSM only or HSM and Pump)

 

For each block, the user enters the following:

·        Wave shape with or without zero taper at beginning/end

o       Square

o       Ramp

o       Sine

·        Control mode

·        End level type (absolute or relative)

·        Amplitude/Mean or Max/Min

·        Frequency

·        Compensator (depending on options, see Optimization and Other Algorithms section)

·        Count

 

FlexTest SE can also be programmed from the PC using the same software that is available for GT. For the operation of this software, see GT below.

FlexTest GT

The application used in FlexTest GT is called Multi Purpose TestWare. A Specimen Editor is used to keep track of all data relating to a given component. The Procedure Editor is used to create the block profiles themselves.

 

A palette is presented with icons that are grouped into the following categories:

·        Command

o       Ramp

o       Hold

o       Cyclic (sine, square triangle)

o       Arbitrary end level

o       Time history file

o       Road surface file (from RPC®—sequence of time history files grouped together with repeats)

·        Data Acquisition

o       Turning points

o       Timed

o       Max-Min

o       Level crossing

o       At defined cycle-counts (eg 10, 50, 100, 500, 1000…)

o       Multi-channel time history

o       Trend

o       Circular file

·        Event

o       Limits

o       Digital input

o       Operator button-push

o       Underpeak

o       Timer

·        External Control

o       Digital output

o       Control of external temperature controller (for environmental chambers)

·        Other

o       Alarm

o       Log message to log file

o       Launch oscilloscope

o       Launch external application

 

Items from this palette are dragged into a workspace in any order. Each item is given a name, a start event, and an interrupt event. Start and interrupt events can be based on the start, end or interrupt of any other process. A limit event can therefore be used to start or interrupt another process for example. Double-clicking the item allows the user to edit its parameters.

 

Processes can be grouped together into a procedure that can be looped. This also allows nesting of procedures.

 

Every process has its own counters, as do procedures, and defined levels within commands can be absolute or relative.

 

MTS also offers an optional profile editor that allows users to enter processes using a spreadsheet. A graphical display of the resulting profile is displayed to show the results of the programming.

Tiab

Tiab does not provide a pre-packaged high-level block programming tool. However, the front-end is developed in an open programming language so that users with LabVIEW knowledge can build routines that automate a test. The full range of system functionality can be executed in a complex test sequence. 

Time History Playback

This section is specific to time histories. Time history Playback typically refers to playback of a single or time-synchronous multiple channel dynamic real time signal that commands the actuators to replicate measured data. While many controllers handle time histories directly in their block-programming section, and deal with them in the same way as they deal with sinusoids, that is not true in all cases.

 

Often, time history playback means replaying iterated drive-files (see the Real Time Simulation section below), for this the RPC format developed by MTS has become the defacto-standard and can be read/written by all the controllers. Most of the packages have the ability to convert time history files from different formats to their own native file structure, and vice-versa. It is therefore possible to use third party programs such as SOMAT® INFIELD with all the reviewed systems.

Pulsar

Time histories can be played out seamlessly. If the sample rate does not match the test system rate, a sample rate conversion utility is launched. This replay function can be a part of an EZflow process, which allows the user to enter repeats, nest loops etc.

SmarTEST ONE

The SmarTEST ONE handles time history playback directly in the block sequence program using a “time history playback” segment. Time histories can also be played back directly by the controller. This is a standard feature.

SIMCON 2100

While this software provides the ability to perform single file playback, I am going to focus this review on their Matrix Playback capability.

 

To create a playback matrix, the user launches the Matrix Editor. A spreadsheet is presented. The columns are as follows

·        Filename (drive file to be played out)

·        Ballast

·        File frequency

·        Playback frequency

·        Over sample (checkbox)

·        Phase 1-n

 

For each phase, the user can select a number of repeats (of the phase) and whether there is a pause when the phase is complete (for inspections etc).

 

For each drive file, the user enters the number of repeats at each phase, the ballast level (this is used to control digital outputs that can fill and empty water dummies), the frequency to be used for playback and whether over-sampling is to be used (this is an interpolation algorithm rather than true up-sampling).

 

Above each phase, the software displays the total repeats, total time and total percent of the test.

 

Matrices may be combined into schedules in much the same way that blocks and segments are combined. These, too are viewed in a Windows Explorer type tree view, and can be dragged-around to new locations.

Labtronic 8400/8800

The routine used for time history playback is called RS Replay. It uses the same table as RS Block described above, and seamlessly integrates with it, allowing the user to combine block programs with time histories. The software also includes cross-fading functions to ensure bump-less transfer from one signal to the next, regardless of their individual end points. It also includes monitoring options that will be dealt with later. Drive file channels are mapped to test rig channels, along with the controller mode, controller type, and any smoothing filters to be used.

FlexTest SE/GT

As with most of the controllers, time history playback is an option. It is presented as an icon on the palette, and dragged into a test procedure in the same way as any other process. The user has the ability to map channels, choose control modes and counter types. MTS also has a file type called road surface (RSURF) files. These files contain a sequence of files and repeats. RSURF files can be nested, and they are created in the RPC simulation package.

Tiab

The Replay and Logging control panel is launched from the main control panel. A single data file is played out, with any number of repeats. Up to 8 signals can be logged to disk in a circular buffer. Data generated in either Excel, Matlab or as ASCII files can be used for playback.

 

Real-Time Simulation Packages

This review does not cover simulation packages. I might do this at a later date. It is a large subject of its own. However, I felt it necessary to at least mention the packages that are available to each controller because this might influence your decision. Real time simulation refers to software that uses Fourier techniques to measure the behavior of a test system, then take edited field-measured data and reproduce the data on the test system. The process includes a series of iterations during the test setup phase to compensate for non-linearities. This process is commonly referred to as the RPC process, which was developed by MTS 30 years ago.

 

The Pulsar system uses a package called ICS, a native application written by Servotest.

 

The SmarTEST product family integrates with FasTEST developed by FCS Control Systems. Along with the standard features of real time simulation, FasTEST also includes vibration control (SISO and MIMO), and sine sweep. This is the only controller that I know of that integrates the two formerly disparate worlds of vibration and fatigue.

 

The Labtronic 8800 controller uses a package developed by LMS, called RS TWR, and is a result of the alliance between IST and LMS. This package integrates with all the other software tools developed by LMS, such as modal analysis, rotating machinery analysis, sound intensity and so on.

 

The FlexTest GT integrates with RPC Pro, the current version of Remote Parameter Control software that has seen continuous improvements and development of new innovative control techniques from MTS for more than 30 years. It now comes in many flavors depending on your needs--from a basic package to highly advanced tools for fatigue analysis, road data reduction and demanding simulation requirements.

 

Tiab is in the process of developing their own real-time simulation package.

Test Operation, Replay, and Monitoring Software

Pulsar

First, the user clicks on a Check button on the toolbar to verify that the test is OK, and that there are no errors or omissions. At this point the full distance of the test is calculated for the odometer display. The test must be saved before it can be executed.

 

The toolbar has a play icon that the user clicks to start the test, or the test can be started through the menu system, or by pressing f5. The test is stopped in the same way, or by pressing f10.

 

If a test is stopped, it can be restarted from the beginning of the block it was currently executing, from the end of the block, or from the beginning of the sequence.

 

Once the test is running, an odometer gives an indication of the progress of the test, although if there are a lot of decision branches, the odometer cannot reflect the change in distance if a different branch is taken. A test timer gives the time the test has been executing (not including pauses). If the user has the EZflow editor open, the currently executing block will have be highlighted, and the loop counters decrement as loops are completed.

 

The test status is automatically logged to a text file.

 

Note that when the block programmer has finished executing, it leaves the servocontrol elements in the state they were last in when it was executing, they are not returned to the state they were in when it started.

 

Test data is collected where the user has defined data acquisition (data logger) blocks in the process.

 

Limits are used to shut the test down in the event of failure (see Handling Limits and Events above). 

 

Optional trend monitoring software allows you to monitor and set limits for each time history file on:

·        Min

·        Max

·        Mean

·        RMS

·        Standard Deviation

 

Limits are set as absolute values, with data available from the first pass as reference. Independent limits may be enabled or disabled, and the actual values for the test may be displayed, along with a pass-by-pass graphical display.

 

SIMCON 2100

The playback and monitoring options are different for block cycle playback vs. time history playback. I will deal with one at a time.

Block Cycle Playback

The Block Cycle Playback Window provides run/stop/hold control, and displays a spreadsheet whose rows are the blocks in the program, and the columns are the following:

·        Waveform (file name of the current block)

·        Channel

·        Gain

·        Cycle count

·        Segment type

·        Segment end time

·        Percent complete

 

The window also displays the test length in hrs min sec, and the elapsed time. A peak display tab displays the current value, and two resetable sets of peak readings. These can be reset manually, or at specified time intervals.

 

Test data is collected where the user has defined data acquisition blocks.

Time History (Matrix) Playback

A Trend Monitor provides limits and logging of parameters during the execution of the test. The following limits may be applied individually, or in any combination:

·        Dynamic limit monitoring—a point by point comparison of the current feedback with a first pass reference file. An envelope of allowable variation is drawn around the reference signal

·        Mean monitoring—the mean values are compared against references for frames of data. The user defines a maximum variation

·        RMS monitoring—the RMS values are compared against references for frames of data. The user defines a maximum variation

 

There are two sets of limits, Alarm and Shutdown. Individual values can be entered for each of these limits for each drive file, or they can be based on limits that are globally defined. Limits can be expressed as absolute engineering units, percent of full scale, or percent of the maximum value.

 

Raw data is also acquired for each drive file, and overwritten each pass.

 

To begin playback, the user enters the filenames for the matrix, IO properties, playback log, and trend limits. The files are downloaded to the box, and the test run button is pressed. Odometers are displayed for the current drive file, current phase, current matrix, and overall test progress. A display of the matrix position is also available. A Pause button causes the test to stop at the end of the current file, a Stop button causes an immediate stop. The user can then restart from the current position, or edit the start position via a graphical matrix editor.

SmarTEST ONE

Once the file has been downloaded to the controller (called a simulation), tests are started stopped reset, and paused using the buttons on the front panel. The Screen shows the current block and step, current command, feedback and error. The user can enter a minimum segment time to increase the test speed to the maximum possible. A time multiplier can be used to factor-up the test time if necessary. An amplitude multiplier acts like a span control.

 

SmarTEST ONE allows the user to perform data acquisition directly on the unit itself. The data can be retrieved without the use of proprietary software using an Ethernet connection and a standard Internet browser.

 

The SmarTEST controller provides two sets of limits,  absolute and relative. Three limit values can be entered for each limit: alarm, script and failsafe. Alarm is used as a warning, failsafe is used as a shutdown, and when a script level is activated, the controller executes a user-defined script that can command the controller to go to rest condition, log event into log file, or begin data acquisition.

 

A standard feature of the controller is the "dying seconds buffer." This is a buffer of data that stores the events that lead up to, and just after an event has occurred. The buffer can be stored to disk, and restored later. This can be useful when debugging a specimen or system failure.

 

An ASCII log file keeps track of all the events that occur during the test. Users can add their own entries for test reporting purposes.

 

Labtronic 8400

Once hydraulic pressure is applied, and the test setup, the user hits the run button on the front panel. The display shows the test status via an icon, along with limits and events. The buttons can be used to pause, stop and rewind the test.

 

For PC operation, the software is identical to the 8800 (see below).

Labtronic 8800

Buttons allow the user to adjust the master span, run, pause, stop or hold at level. A camera icon allows the user to take a snapshot of data with a mouse click. This window also displays elapsed time and elapsed duration in user specified units (e.g. miles or km).

 

During operation, the Schedule Editor can be used to view the progress of the test. An arrow indicates the current position, and the status bar displays the total steps, total progress, and number of blocks. Stopped tests can be restarted at any point by moving the pointer.

 

An ASCII log file keeps track of all the events that occur during the process of the test. The user may also enter comments to help in documentation later. All entries, both manual and automatic, are date and time stamped.

 

Test data is collected where the user has defined data acquisition blocks. Optional software is available for the following:

·        RS PSDMon—monitors changes in the Auto Spectral Density (ASD) of selected signals. Detects changes in specimen dynamics

·        RS TrendMon—monitors and sets limits on statistics of the feedback: max, min, mean, standard deviation and RMS

·        RS CalcMon—allows the user to enter an equation for a statistic or value to be monitored

·        RS Rain—monitors changes in the Rainflow Histogram of selected signals. Detects changes in the damage being applied to the specimen

·        RS LifeMon—calculates the damage number caused by selected signals, from a standard S-N curve

FlexTest SE

Tests are started stopped rewound and paused using the buttons on the front panel. Test progress is displayed as run time, and the various counters and presets are displayed. For more advanced monitoring functions, the PC software is used. This is identical to the software provided with FlexTest GT and is described below.

FlexTest GT

Test progress is displayed as run time, and all the user-defined channel and sequence counters are displayed. A master span is on the main screen, and buttons provide run, stop and pause control. If the Procedure Editor is open, progress is shown by highlighting the block that is currently executing. Tests resume from the beginning of the process that last ran.

 

An ASCII log file keeps track of all the events that occur during the process of the test. The user may also enter comments to help in documentation later. All entries, both manual and automatic, are date and time stamped.

 

Optional trend monitoring software allows you to monitor and set limits for each time history file on:

·        Min

·        Max

·        Mean

·        RMS

·        Standard Deviation

 

Limits may be set as absolute values, or as percentage change from the first pass. Independent limits may be enabled or disabled, and the actual values for the test may be displayed, along with a pass-by-pass graphical display.

 

Optional Fatigue Process and Fatigue Monitoring software can be used to monitor and log the damage accumulated on a component. Once the damage exceeds a given value, the test is stopped.

 

Tiab

The Replay and Logging control panel is used to run stop hold and resume tests. The Continuous Logging function provides operators will the facility to "play out" large datasets to up to 4 specified targets from the controller, and also to simultaneously log the signals on 8 channels.

 

A trip logging function allows users to capture data immediately prior to and after a limit trips. The trip logging is started by the operator, just before the limits are enabled. When a trip occurs, the logged data is retrieved for display, and saved to a date/time stamped ASCII file. The logging duration is calculated automatically, based on the user entered number of channels and sample rate. Decreasing the number of logged channels or the sample rate will increase the logging duration, and vice versa. The Log Viewer will launch automatically when the limit trips.

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PULSAR® is a registered trademark of Servotest, SmarTEST ONE® is a registered trademark of FCS-COM, FlexTest®, TestStar®, Remote Parameter Control®, RPC® and TestWare® are registered trademarks of MTS Systems Corporation, MATLAB® and SIMULINK® are registered trademarks of Mathworks Inc., National Instruments® and LabVIEW® are registered trademarks of National Instruments Corporation, Windows® and Visual Basic® are registered trademarks of Microsoft Corp., SOMAT® is a registered trademark of AEA Technology plc.

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