WEG CFW-11 Programming Manual page 278

PID Regulator [46]
Example: Given a pressure transducer with a 4 to 20 mA output and a full scale of 25 bar (i.e., 4 mA = 0 bar and 20
mA = 25 bar) and P0237=2.000. If it is wished to control 10 bar, the following setpoint must be entered:
Setpoint (%) =
In case the setpoint is defined via analog input (AI1 for instance), P0231 must be configured = 0 (AI1 Signal Function:
Speed reference) and P0233 (AI1 Signal Type) according to the type of signal to be read by the input (if current or voltage).
Do not program P0221 and/or P0222 = 7 (E.P .).
6) To set the speed limits: Adjust P0133 and P0134 according to the application.
The readings exhibited automatically when the inverter is powered are:
- Reading 1 – P0041 "PID Setpoint".
- Reading 2 – P0040 "Process Variable".
- Reading 3 – P0002 "Motor Speed".
7) Indication: Refer to the
Those variables can also be visualized at the analog outputs (AOx), provided that the parameters that define
the function of those outputs be programmed accordingly.
Starting up
1) Manual Operation (open DI3): keeping the DI3 open (Manual), check the process variable indication on the
keypad (HMI) (P0040) based on an external measurement of the feedback signal value (transducer) at AI2.
Next, vary the speed reference until reaching the desired value of the process variable. Only then pass it to
the automatic mode.
NOTE!
If the setpoint is defined by P0525, the inverter will set P0525 automatically with the instantaneous
value of P0040 when the mode is changed from manual to automatic (provided that P0536 = 1).
In this case, the commutation from manual to automatic is smooth (there is no abrupt speed change).
2) Automatic Operation (closed DI3): close DI3 and perform the PID regulator dynamic adjustment, i.e., of
the proportional (P0520), integral (P0521) and differential (P0522), verifying if the regulation is being done
correctly. Therefore, it is only necessary to compare the setpoint to the process variable checking if the values
are close. Observe also how fast the motor responds to oscillations in the process variable.
It is important to point out that the PID gain setting is a step that requires attempt and error in order to
get the desired response time. If the system responds rapidly and oscillates close to the setpoint, then the
proportional gain is too high. If the system responds slowly and takes time to reach the setpoint, then the
proportional gain is too low and must be increased. And in case that the process variable does not reach
the required value (setpoint), then the integral gain must be adjusted.
20
20-6
10
x 2 x 100 % = 80 %
25
Chapter 5 PROGRAMMING BASIC INSTRUCTIONS on page 5-1, in this manual.