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Servo-Hydraulic Controller Buyers Guide

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Please note that this information is intended as a guide only. This section refers to the PID controller only. For information on the products that are layered onto these controllers, refer to the Analysis and Controls Software review. Individual needs vary, for help with a controller to meet your needs, contact us. Presented in alphabetical order of manufacturer, with no bias.

IST
8800/8400
Performance
Reliability
Value
Pros Cons
  • Scalable architecture with clean integration
  • Easy to use graphical interface
  • Lots of features for difficult load loops
  • Large installed base through Instron
  • Small installed base through IST
  • Expensive
  • Structural testing apps buggy
  • Limited support
Comments
I think it is a shame that IST products are not more widely used in the automotive-structural-fatigue-vibration-component testing sector. My opinion is that they have suffered from insufficient marketing, and the prices are set too high. This controller is sold extensively for materials testing (through Instron), and has a lot of features that are unique and very useful for those difficult control situations. They have a PID loop that can be reconfigured easily, the most accurate calibration in the market with intelligent sensors, very useful filtering features, and this is the only controller in the group with gain scheduling. No other controller comes close. These features must be balanced against their lack of support, and small installed base in this market. IST invented the scalable architecture now used by MTS, which is based on a small one channel instrument-based controller, that can stand alone, or integrate through a PC with larger multi-channel-multi-station towers. The only thing I am not keen on is their use of an old parallel interface standard for interconnection.


Moog
SmarTEST ONE/xX
Performance
Reliability
Value
Pros Cons
  • Up to four channels in small self contained package, expandable to 32 with up to 8 stations (xX)
  • Sophisticated load control loop
  • Many safety limits
  • Lots of customizable functions
  • Efficient function-key operation
  • Inexpensive
  • Hierarchical menu system makes finding functions difficult
  • Architecture is not scalable
  • Screen layout is fixed
Comments
This controller has a lot of promise, and with Moog backing, there are significant development dollars dedicated to improving it. This is evident already. I must admit that I initially found it difficult to use because it didn't speak my language. However, as I have used it more and more, I am getting the hang of it, and can now move through the menus quickly with the function keys. The big news is that they are implementing a touch screen display, which means that now, instead of counting off the function keys, you can just hit the button on the screen. Another change that they made recently is that they have hidden many of those arcane features that never get used behind an "Advanced" button. So now, when you want to set up a simple PID loop, PID is all you see. The controller has scripting capability and pseudo channels that will allow the controller to be used in a lot of applications, and now there is virtually no limit to the number of pseudo channels. I like the packaging, and I think with experience it is possible to navigate through the menus very quickly, and this controller would be faster to setup and operate than any of the others. At one time they had a problem with the box crashing in certain situations. These were with the earlier versions. I ran into it a few times, but it did not cause a problem for me, and I would assume the product is becoming more stable as they work out the kinks. By not scalable I mean that you cannot combine several SmarTEST ONE units to make a single multi-channel test.


MTS
FlexTest
Performance
Reliability
Value
Pros Cons
  • Good integration with RPC
  • Worldwide support
  • Scaleable architecture
  • Industry standard
  • Reliable
  • Limited features for pure PID
  • Expensive
  • No automated scripts
  • Interface is not intuitive
Comments
MTS is the market leader, and they have a lot of experience. The FlexTest products are solid, but not earth shattering.If you have a challenging control situation, the toolbox isn't very deep. Both of the other controllers listed here will provide you with a lot more tools to tame that tough load-control loop. However, for straight displacement control, these boxes have everything you need. You can purchase more "tools" but you have to buy everything you need a la carte, which means trusting the sales folks to understand what you need. One set of useful options is Calculated Variables and Calculated Channels. If you want to use them to build your own modal controller you have to buy them both. MTS has also added Three Variable Control capability. It is the only controller on this page that has that option (yes you have to pay more for it!)


Servotest
Pulsar
Performance
no rating
Reliability
no rating
Value
no rating
Pros Cons
  • Innovative software design
  • Flexible hardware architecture
  • Configurable user interface
  • Small company with limited support
  • Small installed base
Comments
One thing you should know before reading this is that I have not had any field experience with Pulse. I was invited to the Servotest home office a few years ago when they were in the early stages of developing this product, and I do have experience with their older DSC 2000 product. However, unlike the others, I have not used the system to develop and run a test myself, and I am therefore unable to provide a definitive rating. From what I see of the user interface, it is well designed, and their hardware architecture is unique. Each test rig is served by remote boxes that are interconnected via fibre optics. A hub/spoke network. The hubs can also be interconnected to create the most flexible architecture of all. Their software is well laid-out, but as with MTS, the sequencer merely plays-out defined sequences. This prevents the user from being able to define a truly random test (a time history is created offline first).


Shore Western
SC 6000
Performance
Reliability
Value
Pros Cons
  • Servocontrol Block Diagram
  • Customizable
  • Analog loop closure
  • Screens can be modified to meet the needs of a given system
  • Small company with limited support
  • Not recommended for general purposing
  • Small installed base
  • Analog loop closure
Comments
Why is "Analog Loop Closure" both an advantage and a disadvantage? Because it has its plusses and minuses. On the plus side, it has infinite bandwidth and resolution, and the Shore Western electronics seem to have a low noise floor. On the negative side, some of the things we take for granted in a digital controller become a nightmare when you straddle the digital and analog domians. The most notable is data acquisition and command generation. Both of these need to be in the digital domain, but need to be converted. This alone is not a huge issue, except when it comes to time-synchronization, and integration of the SC 6000 with external devices to perform real time simulation. The bright folks at Shore Western have come-up with some cool and unique adaptive control algorithms, and the cost of the controller is low. A big benefit of the SC 6000 is its ability to be configured for custom tests. It has the most feature rich block programmer out there, and user interfaces can be designed and built by the end user so that all the tests can be run from a simple set of push buttons and meters.


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