adccommunitymod (AutomationDirect) asked a question.
Created Date: July 23,2011
Created By: dieseltwitch
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I need help seeing up a PID loop for controlling a valve. Some back ground info. The valve is located on the output side of a pump. its a 3 way valve with power to open and power to close. I have it wired to two output (Y1 & Y2). One output from the valve leads to a heat source. this heat source is a "wild " heat source and varies its output to that extent I am using the 3 way valve to control its heat production. I have a sensor on both the in let and out the out of the heat source. Im looking for a 15*F rise from inlet to outlet. On the other output of the valve is the heat demand. The valve basically bypasses the heat source to control its out put. to little flow and it over heats, to much flow and i get very little rise in temperature. and because I have no control over its production of heat i figure using a bypass method would be the best way. Cheaper than a VFD and 3P pump. My problem is making the PID loop work. Because the valve is not an analog controlled valve I have to control it in both direction to position it. I was trying to make a PID loop with a bi polar output. if the number was neg it would rotate the valve one way if its pos then the other way. if its zero then no movement. I have yet to get this to work. My goal was to use the SP (15*F) I than subtract the input from the output. let say I get 10. I would then rotate the valve to slow the flow through the heat source. the valve is fairly slow 160 second lock to lock. so Im not to worried about it overshooting to much. if if does end up being to fast i was going todo 5 second pulled every 15 seconds to slow the rate of the valve down. If some one could give me the setting needed to make the PID loop work that would be great. No mater what i tried the output of the PID loop did nothing. I also was having issues working with the data format of the SP and PV. Please help
Created Date: July 24,2011
Created by: Tom Jenkins
The DirectSoft manual has (used to have?) instructions on how to accomplish this in hte PID section. It is often called Heat/Cool control.
Created Date: July 24,2011
Created by: franji1
The DirectSoft manual has (used to have?) instructions on how to accomplish this in hte PID section. It is often called Heat/Cool control.
It's in the PID chapter of the PLC User Manual (not sure which PLC you have). The section is on "Time Proportional Control " and shows how to do PID with a discrete output instead of an analog output (e.g. home heat control). However, I am not sure how the "variable heat source " will affect the PID control or how to tune it.
Created Date: July 24,2011
Created by: dieseltwitch
The DirectSoft manual has (used to have?) instructions on how to accomplish this in hte PID section. It is often called Heat/Cool control.
One issue, I don't have the manual. Can some one help me out with the PDF?
Created Date: July 25,2011
Created by: bcarlton
The section is actually in the manual for the CPU available in PDF at AutomationDirect.
Created Date: July 25,2011
Created by: Shimmy
Make sure your output limit int the PID is not set on 0 (0 is the default).
Created Date: July 23,2011
Created by: dieseltwitch
I need help seeing up a PID loop for controlling a valve.
Some back ground info.
The valve is located on the output side of a pump. its a 3 way valve with power to open and power to close. I have it wired to two output (Y1 & Y2). One output from the valve leads to a heat source. this heat source is a "wild " heat source and varies its output to that extent I am using the 3 way valve to control its heat production. I have a sensor on both the in let and out the out of the heat source. Im looking for a 15*F rise from inlet to outlet. On the other output of the valve is the heat demand. The valve basically bypasses the heat source to control its out put. to little flow and it over heats, to much flow and i get very little rise in temperature. and because I have no control over its production of heat i figure using a bypass method would be the best way. Cheaper than a VFD and 3P pump. My problem is making the PID loop work.
Because the valve is not an analog controlled valve I have to control it in both direction to position it. I was trying to make a PID loop with a bi polar output. if the number was neg it would rotate the valve one way if its pos then the other way. if its zero then no movement. I have yet to get this to work.
My goal was to use the SP (15*F) I than subtract the input from the output. let say I get 10. I would then rotate the valve to slow the flow through the heat source. the valve is fairly slow 160 second lock to lock. so Im not to worried about it overshooting to much. if if does end up being to fast i was going todo 5 second pulled every 15 seconds to slow the rate of the valve down.
If some one could give me the setting needed to make the PID loop work that would be great. No mater what i tried the output of the PID loop did nothing. I also was having issues working with the data format of the SP and PV.
Please help