PID Loops Best Practices

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PID Loops

July 27, 2018 / By meswpadmin

Let’s discuss managing PID loops (Proportional, Integral, Derivative) . Have you ever heard the expression, “a little knowledge is dangerous”?  This is definitely true when tuning PID loops. Understanding how PID loops operate can prevent damage to expensive equipment as well as improve performance.

Proportional gain pushes the output based on how far you are from the setpoint. The issue is that the closer you get to the setpoint, the less it pushes. Eventually it doesn’t push any harder and the output can run continuously close to the setpoint, but never get there. Proportional gain is added first with the other gains zeroed out.

Integral gain looks at the difference between the setpoint and the output and then tries to even out that difference. This will cause the output to move above and below the setpoint evenly. This action compensates for Proportional gain’s inability to get there. Integral gain is added in sparingly after Proportional gain is optimized as Integral gain amplifies the Proportional gain’s efforts and can easily cause a runaway condition.

Most applications work well with just Proportional and Integral gain, but let’s say you are controlling the temperature of an oven. If the oven temperature goes above the setpoint, the product may be ruined or catch on fire. So, how do you get the oven to temperature without overshooting the setpoint? This is where Derivative gain is needed.

Derivative gain acts like a brake on the output. The more the controller tries to change the output, the more it counteracts the effort. Caution must be taken when adding Derivative gain as it opposes the efforts of Proportional and Integral gain and therefore should be added last. If Derivative gain is too high, then the output may not be able to act quickly enough, making the output unresponsive for the application.

If you’d like more info on improving PID Loops performance, please give us a call at 317-844-7328 or you can visit http://www.mesindy.com for more info. We have a staff of helpful electrical engineers ready to answer your questions today!

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