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. 

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:

·        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) ar