ControlLogix PID
ControlLogix PID
(OP)
I'm trying to tune a temperature loop using a ControlLogix.
I've used the closed and open loop methods in other PLCs . The other PLCs have given me a procedure and formula to figure out the integral and derivative time constants for their particular PID algorithm. I've looked, but have not seen a formula for the ControlLogix. Would anyone have an answer for this specifically for the ControlLogix?
I've also used the method of increasing the integral until the process variable oscillates and then increase the integral to smooth out the oscillations. What method is best to use and why? (open, closed, increase gain until oscillations occur).
Thanks,
I've used the closed and open loop methods in other PLCs . The other PLCs have given me a procedure and formula to figure out the integral and derivative time constants for their particular PID algorithm. I've looked, but have not seen a formula for the ControlLogix. Would anyone have an answer for this specifically for the ControlLogix?
I've also used the method of increasing the integral until the process variable oscillates and then increase the integral to smooth out the oscillations. What method is best to use and why? (open, closed, increase gain until oscillations occur).
Thanks,





RE: ControlLogix PID
RE: ControlLogix PID
1. Equation Type - Dependent Variables
2. Start with K' = 0.5, I' = 1000, D = 0
3. Increse K until oscillations are seen in response to minor SP changes. You might even want to use OP clamps to limit OP swings. At this point set K = 0.5 K'. Essentially K' is approximately the natural frequency of the system.
4. Decrease I until you see oscillation response to minor SP changes. At this point set I = 0.5 I'.
5. Same agin for D
Having said all this temperature loops generally have large time constants. In this case a combination of dominant P and D terms with low contributionfrom I works a lot better.
There are other more complex (and in some cases better) methods but you should be able to get a reasonable hand tune using the above.
Chris Devine
www.icande.com.au, www.redbusbar.com
RE: ControlLogix PID
See this thread
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