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PID LOOP FORWARD/REVERSE ACTION

Created by: Sindhu at: 6/3/2009 2:05 PM (3 Replies)

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6/3/2009 2:05 PM	Rate (0)
Sindhu Posts: 163 Rating: (0)	Hi All! In PID controller FB41,where shall we set the direction of the controller,i.e forward action or reverse action
Sindhu Posts: 163 Rating: (0)
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6/3/2009 2:20 PM	Rate (0)
Niranjan Prasad Posts: 691 Rating: (36)	Hi Sindhu ........... The FB41 PID function block dosen't explictly have a controller direction as in the Allen-Bradely PID block whether forward or reverse acting controller. The direction of the controller is set by changing the sign of the Gain parameter. If sign of Gain is positive the controller is reverse acting i.e LMN decreseas as PV increases If sign of Gain is negeative the controller is forward acting i.e LMN increases as PV increases
Niranjan Prasad Posts: 691 Rating: (36)
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6/3/2009 2:21 PM	Rate (0)
Gebhardt Karl Platinum Member Joined: 7/16/2006 Last visit: 12/20/2022 Posts: 1502 Rating: (175)	Hi Do you mean as example cooling or heating. If yes, you can turn the direction with P-Parameter. as example: P = 1.0is heating P = -1.0 is cooling or -2,538 ;-)
	Karl
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6/3/2009 8:43 PM	Rate (0)
Pandiani Bronze Member Joined: 10/31/2005 Last visit: 3/7/2023 Posts: 293 Rating: (29)	You need to be careful about this. In FB41, as others stated sign of control action (direct or reverse ) is determined with the sign of gain parameter. FB41 PID block uses the following form: GAIN * (error + 1/Ti * integral (error) + derivation (error) ). Here, it is obvious that sign of controller gain determines both integral and derivative part as well. What is important is that sign of a controller gain should be the same as sign of process gain. For example, if you control temperature with control valve , you need to know if temperature is rising or falling when valve is opening. Some controllers you can find in practice (other manufacturers) have special binary input that specifies controller action.

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