# PID proportional valve

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Hi,

In a control loop I am using a proportional valve with an input -10V to +10V.

With that input the process can be move left and right.

When it has to be go to the right the input has to be positive, depend on the distance between 0 and +10V.

When it has to be go to the left, the input has to be negative between 0 and -10VDC.

Therefor I am using a output -10VDC to +10VDC.

Now I will use a PID loop for it. Only what I find is a positive or negative PID control, so it can just 1 side on. You can switch this between cool and heat.

But I wil not use that switch cool/heat, but just depend on the process value send the control value to negative or positive.

Can somebody help me to explain how to handle with this.

Thanks al for any help

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Maybe use two PID configurations - one is active when the PV is above a set point, the other active when the PV is below. Or maybe just toggle the 'Reverse Action' bit when the (SP > PV) and back when (SP < PV) if the heating/cooling behavior is similar.

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PLC PID is a mathmatic function not hardware based.

Most PLC PID implementations are for regulation 0 - 100%, or reverse for cooling.

100% of 'what' to do 'something' is not realy their bussiness.

This makes the PID function "universal".

It is your job to scale the "footballs per day " PID input to 0-100%,

and then scale the PID output from 0-100% to "footballs".

In your case with the PID output do a simple scaling (PIDX * 2) = 0-200%

then subtract (PID2X -100)  gives a range of -100 to +100

have a good day.

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• 1 month later...

About the PID output scaling 0 - 200%.

It's not clear how this is working in my application.

I.e. when my PV value is 100 and I need it to setpoint 50,  my CV value has to be i.e. -50%.

When my PV value is 50 and I need it to setpoint 100, my CV value has to be i.e. +50%.

When my PV value = setpoint then my CV value = 0%.

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When I will do it by toggle the reverse action bit. How smooth is that going.

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You may also try PID output limits: output low limit = -1000, output high limit = +1000, then scale PID output to your analog output.

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