PID Problem

i want to ask if it possible to make PID temperature controller with one valve single acting and how to do that

as :

i have a problem with my system i suppose to make PID Temperature controller

the input is the Temp (Ai ------> 4-20 ma)

but the output is a valve with single acting (just one digital output)

this valve is to control the hot water that increase the temp

i can not use FB59 as i have only one Digital output all the time taking action even when

Process value = Set point ------> stopping the open command means closing action

i hope someone can help

If you have a long lag time in your process you can open your valve for say 16 seconds and close it for 4 seconds, then repeat, for an output of 80%.

Do some valve life calculations and lag time measurements to work out how large you want to set your duty cycle. (20seconds in the above example).

One approach to this application would be to convert the numerical CV output from your PID to Pulse Width Modulation of the discrete output.

As Bitbucket said. You can use "time proportional" control with the PID CV output. Just be sure that you operate the solenoid for at least the minimum specified time it needs to avoid problems.

If you tell us what PLC hardware you are working with, we can point to code examples.

You may also want to try Sliding Mode Control (SMC) as mentioned in this thread, among others. You can use the search tools to find other threads, but this one was most helpful to me a while back.

What is the temperature tolerances. You may be better off with a simple on-off control
with a deadband. No PID necessary , use compare instructions.