PID load increases over time

[MostEE]

Great forum! I have a process I need to controls that "drifts" over time and I am not sure if a PID control will be able to compensate. By drift, I meant that the amount of energy, required to maintain the setpoint varies over time i.e. like maintaining the level in a tank with a small leak, where the leak gets bigger over time? Let me explain further: I basically need to maintain voltage (yes, not voltage, it is not being translated to engineering units) and hold that desired setpoint by applying a control value (another voltage). However, the voltage required to maintain the first voltage increases over time. From my understanding, the P part of the PID controller should increase the the control voltage to the correct value but what about the fact that the ratio, or proportion, between the process value and the control value increasing over time? I am not even sure if it isc correct to says that the load increases over time? Thanks in advance for any tips or advice!

 

[IRstuff]

So long as the setpoint is valid, a PID should close the loop on the error signal.

TTFN
faq731-376

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[itsmoked]

Actually the I part would probably be doing the correction for you. A PID will very likely solve your described issue.

Keith Cress
kcress -

http://www.flaminsystems.com