schafbo Posted March 9, 2017 Report Share Posted March 9, 2017 I am looking for a PLC to control an electro-pneumatic regulator in a motion control application. I regularly use the V130 PLCs, but for this application 10 ms of sample time seems to be too slow. I was wondering if there were any Unitronics PLCs that had a faster PID sample time capability? I am looking for 2 ms (or ideally 1 ms) sample time. Quote Link to comment Share on other sites More sharing options...
MVP 2021 Joe Tauser Posted March 10, 2017 MVP 2021 Report Share Posted March 10, 2017 PLCs do not do high speed (< 1 ms) motion well, especially if there is analog involved. If you put code in an interrupt routine you can get 1.25 ms. It works with discrete inputs and outputs only and they must be connected to I/O on the main circuit board. What are the details of your I/O? Typically you use an analog output to drive a regulator, and we are limited to the scan time for updating it. Joe T. Quote Link to comment Share on other sites More sharing options...
schafbo Posted March 10, 2017 Author Report Share Posted March 10, 2017 What alternatives are there to PLC? I am using analog input and analog output. Analog input is connected to a voltage position sensor on the actuator. Analog output is connected to an electronic regulator that supplies the pneumatic actuator. I did not consider the conversion time for analog input, according to the spec it is 30 ms. Does this mean my PID actually runs with 30 ms sample time? Quote Link to comment Share on other sites More sharing options...
Gabriel Franco Posted March 10, 2017 Report Share Posted March 10, 2017 Why do you need such PID response speed? As far as I remember, electro-pneumatic actuators are not so fast. You should consider your analog transmitter conversion time, PLC analog input conversion time, actuator response and process response time itself to set appropriate PID sample time. Quote Link to comment Share on other sites More sharing options...
schafbo Posted March 20, 2017 Author Report Share Posted March 20, 2017 Larger pneumatic actuators are generally slower, but this particular actuator has a small cylinder using 3 to 9 bar of pressure. I have used these actuators with data acquisition devices that are capable of sampling at 2 ms and achieved a much better response time and PID loop performance, however these devices are impractical for controller applications. I was really looking for a PLC solution, but if it is true that PLCs are generally limited at 10 ms I will have to look at something else. Quote Link to comment Share on other sites More sharing options...
MVP 2021 Ausman Posted March 20, 2017 MVP 2021 Report Share Posted March 20, 2017 Wondering if you could just have the plc monitor & provide overall "control", but use a simple direct control loop to do the fast work? Or alternatively some sort of converter which changes your position sensing on the actuator to a High Speed Frequency Output, which might make things possible. A quick goggles found this: http://www.redlion.net/product/analog-frequency-converter-module cheers, Aus Quote Link to comment Share on other sites More sharing options...
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