New to PLC PID

Hello all,

I've had background in PLC's and PID loops, but never together.

I am using an A/B Micro830 to control water temperature via a 4-20 modulating valve. Very simple. 3-way hot and cold in / mixed out, direct acting PID.

I'm using the PID function block along with an adjustable buffer and averaging block for the buffer coming off of the scaled RTD reading.

What I'm curious about is how the output on the PID block actually correlates to positioning the valve.

Due to our customer's shut downs, we've already had to install many of the components at the site, which gave me no time to bench test at the shop.

Any help getting me prepared as possible before I go up there next would be very beneficial.

Thank you!

What I'm curious about is how the output on the PID block actually correlates to positioning the valve.

Click to expand...

Usually the PID output is passed first to a scaling function or scaling routine, which scales the PID output to whatever the range of the Valve Operator. Then the scaled value is passed to a PLC output that is connected to the valve operator. The valve operator might have a 4 to 20 miliamp input range, or 0 to 10 volts, or similar.

In order to do the scaling from PID to Valve Output, you need to know the range of each, PID Output Max, PID Output Min, Valve Output Min, Valve Output Max.