analog output fluctuation from siemens plc

[balotagi]

Dear sir,
we are getting fluctuated output from plc even though batching controller is showing constant value after batching completion. we are using fc105 for scaling process. Can anybody suggest how to avoid the fluctuation.

Regards,
Balotagi

 

[dchartier]

Hello balotagi;

I do hope this is a typo, and that you are using FC106 ("UNSCALE") to setup your analog output. FC105 ("SCALE") takes an analog input value (from PIWxxx) and transfers it as a scaled REAL value for your program. FC106 takes a REAL value and turns it into a numerical value adequate for a PQWxxx channel on your AO module.

If this was a typo and the output value is not stable, I have often found that it is a question of wiring and grounding of the AO module. Refer to the correct manual for your PLC family (I presume it is a S7-300 or S7-400, because of your mention of FC105).

Hope this helps,
Daniel Chartier