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Controlling 2 parameters with a PID control.

Created by: xBigGx at: 10/18/2011 9:08 PM (3 Replies)

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10/18/2011 9:08 PM	Rate (0)
xBigGx Advanced Member Joined: 9/14/2011 Last visit: 12/31/2015 Posts: 68 Rating: (0)	Hi, We have for the moment a basic level control with a PID. When the level is higher than the setpoint, the PID opens a valve and corrects the level. This works fine. There is also a Mag5000 that reads the flow and through a totalizer the customer can see the amount of water that has been flushed. But now they ask to limit the maximum flow to x m³/h. Is there any way to put a second PID in cascade or something and limit his output to x m³/h ? I'm working with TIA Basic V11 Update 2, CPU 1214C DC/C/DC. Regards, Gunther.

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10/18/2011 10:11 PM	Rate (0)
Ayman Elotaify Platinum Member Joined: 5/28/2008 Last visit: 11/19/2018 Posts: 4096 Rating: (749)	Hello, I suggest that you make a sketch and upload here. In any case, to limit the flow rate to certain value, then you should have a controlled valve. So, we have now actual flow value from flow meter and PID output will go to control valve. Hope it helps.
	Ayman Elotaify MISC Egypt www.miscegypt.com
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10/18/2011 11:18 PM	Rate (0)
xBigGx Advanced Member Joined: 9/14/2011 Last visit: 12/31/2015 Posts: 68 Rating: (0)	Ayman Elotaify Hello, I suggest that you make a sketch and upload here. In any case, to limit the flow rate to certain value, then you should have a controlled valve. So, we have now actual flow value from flow meter and PID output will go to control valve. Hope it helps. We have a controlled valve, we have the actual flow and we have the level in the tank. The level is now controlled through a PID controller and a valve. There should only be an extra limit on the maximum flow going through the valve ... In the DCS systems I used to work with I would add an extra PID controller (cascade) and limit this PID to x m³/h. But as far as i can see this limitationis notpresent in the S7-1200 PID's. Attachment sketch.jpg (106 Downloads)
	Last edited by: xBigGx at: 10/18/2011 11:22 PM
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3/2/2013 6:30 PM	Rate (0)
tomsov Member Joined: 10/15/2012 Last visit: 3/16/2017 Posts: 6 Rating: (0)	HI I had the same problem. I used two PID in my solution.

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