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Controller design

3/13/2011 9:44 AM	Rate (0)
Dreminee Posts: 58 Rating: (2)	Dear All, I have a question how to solve a control application. It's a flow control and the controller output(LMN) is directly connected to a VFD ( 0/100% = 0 - 500 l/min) by analogue output. On PV the flowsensor is connected(0-500l/min). Now just a single control loop is implemented but what happens is that when SP gets closer to PV the controller output goes down what results in less speed of the drive so immeadiatly my flow goes down. So the controller will never reach the SP flow. Now I solved it like this I put an ADD_R block and connected the SP and the LMN since I need always some output even when SP = PV(i.e example 50% = 250l/min) I set the controller output range between -80% and +80% to react on the difference only. I am sure there are more solutions for this. So if there is a better solution I am all ears. Regards, Dreminee
Dreminee Posts: 58 Rating: (2)
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3/14/2011 11:50 PM	Rate (0)
Phantom75 Posts: 2661 Rating: (279)	Hi Dreminee, Which PID block are you using? Most PID blocks will have parametersto limitthe output. Regards
Phantom75 Posts: 2661 Rating: (279)
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3/22/2011 2:52 PM	Rate (0)
Jazz_M Posts: 1121 Rating: (86)	Hi Well phantom is right you can set the limit for the LMN value for your PID By the way which PID are u using as we can use FB61 or SFB 41.. Have fun..
Jazz_M Posts: 1121 Rating: (86)
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