Electronic – How to implement a closed loop control circuit for slow process

controlcontrol system

Given a slow process Vout = Process(Vcontr) which takes a control voltage Vcontr and produces an output voltage Vout but with some lag of the order of one second.

I am looking for a good way to implement a closed loop control circuit for setting Vout to a target voltage Vtarget.

My starting point is a circuit as follows:

  • op amp
  • inputs: Vout and Vtarget
  • output: connected to Vcontr-input of the slow process but with a capacitor shunted to ground to slow the rise time (or alternatively some analogue filter?)

Is there a better way to do this? How should I setup the feedback for the op amp?

Best Answer

You can do this entirely with analogue components if you want. First, decide how fast and how perfect you really need the control to be. If you don't care if it takes several seconds to reach the target, then you can perform the control with a simple I (integrator) controller.

It works like this:

  • Use a capacitor to hold the Vcontr voltage.
  • Use an amplifier (make sure it has push-pull output) to measure the error between the voltage error.
  • Set up the amplifier so that it charges the capacitor when the error is negative, and discharges the capacitor when the error is positive. (Or vice versa).

You can adjust the speed at which the controller operates by changing the size of the capacitor, or the resistor that feeds it.

I controller with gain resistors

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