Author Topic: PID Loop  (Read 6919 times)

Clinton

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PID Loop
« on: February 23, 2004, 06:18:04 AM »
Can you make a suggestion for an initial setting of the PID values?

I am controlling a 16" water valve with the analog output, with feedback input from a flowmeter and want to maintain a constant flow.

The example in the sample program and the book indicate the PID
settings 10, 20, 0

Can you elaborate on each of these values and how they will effect the output?

Thank you for your help.

Clinton Bailey
Quality Manufacturing Company

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Re:PID Loop
« Reply #1 on: February 25, 2004, 10:30:04 AM »
choice P,I, and D actions and values really depend totally the dynamics of the systems under control and the type of response required and there isn't a hard a fast rule. What you can do is to start off with just the propertional term (P) with I and D both zero, then subject your control system to a step input and measure the output response vs time. Gradually increase the P term until the output response react at a speed that you are satisfied with. Pure proportional control usually will result in a steady state error (small difference between Set point and output) but if that is acceptable then there is no need go further. If not, then start adding in an I term and test again. Integral action will eliminate the steady state error but make sure you start with a small I term and increase gradually. Large Integrator can result in over-correction and oscillation of the output between set point or large overshoot before reaching the steady state value.

Most often P or P+I are sufficient for many control applications. D term is less often use. It is used to anticipate a large "differential" change and provide the corrective action. Please read some control theory regarding the P,I and D for details.
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