PIDD - Cybernetic Systems


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- FC6A     PIDD  (PID with derivative decay)

-   This is the best PID instruction in the FC6A family.
   Addition to the the FC6A CPU, you need an analog input and output module/cartridge.
   The next application note on how to use this PIDD instruction.
  Case study:
   In an application, we had to keep the underpessure in an air extraction system constant.
   To do this, we used  2 fans, each connected to a frequency variator (FV).
The FVs are controlled by the analog output of a FC6A-L03CN1.
The second fan is only used when extraction is impossible with 1 fan.
The underpressure sensor is read via an analog input.
Depending on the number of machines in production, connected to the air extraction system, the underpressure is changing, and the PIDD has to adjust this.

Here the result of the PID monitor.

Start : startup from 0 with 1 fan.
1: normal regulation with 1 fan. PID compensates pressure fall & rise.
2: Air admission too high for 1 fan. System goes to 100% but cannot adjust pressure.
3: 2nd fan is switched on and the PID immediately regulate to setpoint (SP).
4: normal regulation with 2 fans active.  PID compensates pressure fall & rise.
5: Sudden closure of air admission. System reacts as expected.

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