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PID Controller abnormal action.

6/29/2011 5:50 PM	Rate (0)
Shams Posts: 23 Rating: (1)	Dear All, Iam using FM 355 C PID controller in my project to control the pressure control valve in the inlet and in the discharge line I have presssue transmitter with 0-275 psi range. I have manual / auto selection from scada. If the controller is off the external manipulated output istransfered from scada to the PID.When the controller is on then the PID should control but in my case the problem is when i change it to auto there is no PID action no matter what P and I value i set in the range P = 0.2 to 2.5 I= 10 to 60 s D=0 Tried with different setpoint 35, 30, 35, 40, 45 & 50 psi but when i switch on the controller it starts opening/closing the valve in forward or reverse direction from the previous manual output for eg ( 30 % PCV open ). Kindly suggest any additional parameters i need to set apart from MOD_ADD, CHANNEL, COM_RST, LOAD_PAR, SP_RE, LMN_RE, LMN_REON, SP_HLM, SP_LLM, GAIN, TI, TD, LMN_HLM, LMN_LLM. Thanks. Attachment PID_Snaps.zip (290 Downloads)
Shams Posts: 23 Rating: (1)
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6/29/2011 7:05 PM	Rate (0)
hazem Bronze Member Joined: 2/15/2010 Last visit: 1/20/2024 Posts: 329 Rating: (6)	Dear, i can't understand your problem exactly understand your point but i see your pid settings (p,i &d) you set d=0 as per my studying you can set not zero any value else but you have to use output instead of error (error=reference -feedback) if you set it with error may be you get problem with differentiator at the beginning so better to use error and you will get same action without effect of ramp at beginning. Regards,
	Hazem
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6/29/2011 7:12 PM	Rate (0)
hazem Bronze Member Joined: 2/15/2010 Last visit: 1/20/2024 Posts: 329 Rating: (6)	Dear, if you set d=0 you will not get action from D let d work and it can stablize your system . so instead of use error(setpoint-output) if you differentiate the error you will find(setpoint is constant =0) and you will get only differentiate of output. this way to avoid (stating point from zero to setpoint )this will be step and diffrentiate it will cause impulse and cause your system to be in dangerous situation. so use of output to act with D may be will ehnace your system stablization. Regards,
	Hazem
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6/29/2011 10:56 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 8/31/2025 Posts: 6874 Rating: (1368)	Hi Check if the machine (Such as a compressor) not operating in the unsafe region of operation for a short time?Some safety i ssues which is considered in the loop design may cause that. Check the process conditions and track the curves and logic to undrestand the cause of emergency action of the valve. //check the attachment Regards Attachment 2.zip (302 Downloads)
	Demo Channel on Youtube
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