RSLogix 5 PID Bias

eta537

Member
Join Date
Jul 2013
Location
St. Louis
Posts
3
Looking for some help understanding the bias function on a PID insturction. Currently my PV is scaled to 0-4095 (level transmitter) with the PID engineering unit maximum 15 and engineering unit minimum -15 within the PID Insturction.

My setpoint is coming into the PID instruction is in engineering unit (SP = -.5).

Do I need to bring in my bias as a +/- 100%?

How does the bias have an effect on the Control Output?
 
The bias is added to the output. If you are controlling level the bias probably doesn't need to be used. If you are controlling level then you are usually controlling the flow in or flow out of a tank. If you have a flow measuring device you can use that to adjust the bias. For instance, if your pump pumps controls the outflow and it pumps 1 cubic meter per 10% output and you know the inflow is 1 cubic meter you could set the bias to 10% of its range so the output will be 10%. This way the pump can instantly respond to the changes in the inflow without waiting for an error to build up. If the level control is not that critical then don't bother.
 

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