Question

1:            Is PID control used in Feed Forward or Feed Back control?

2:            Explain how Open Loop Tuning differs from Closed Loop Tuning.

Answer 1

1). With feed-forward or Feedforward control, the disturbances are measured and accounted for before they have time to affect the system. PID control is used in the Feed forward path.

2). The open loop tuning is done manually and closed loop tuning is done automatically.

Open loop tuning

1).Put the controller in manual mode
2)Wait until the process value (Y) is stable and not changing
· 3)Step the output of the PID controller - The step must be big enough to see a
significant change in the process value. A rule of thumb is the signal to noise
ratio should be greater than 5.

Closed loop tuning:

1. Turn off both integral and derivative action in the controller. This can usually be
   accomplished by putting zeros in the integral and derivative tuning parameters.
2. Set the proportional gain (Kc) to a small value.
3. Put the controller in Auto mode.
4. Make a small step in the controller setpoint.
5. Observe the process response.
6. If the controller does not continually cycle (stability limit), increase the controller
   gain (Kc) and repeat from step 4.
7. Once the controller continually oscillates, the controller gain is the ultimate gain Kcu.
8. Measure the period of the cycle and this is the ultimate period Pu.