PID is short for Proportional Integral Derivative control, its how we modulate a valve open and closed as the temperature deviates from the setpoint. We’ll keep it really simple in this example and talk about the P term on its own, in fact this is how many temperature controllers operate as purely proportional controllers because it provides a simple and easy to troubleshoot action for a system.
The P term sets how sensitive the controller is, a small P term means you need a small deviation from setpoint to elicit a response from the system. A large P terms means the temperature will have to deviate a lot from the setpoint before the valve or damper starts to act. Here’s how the system will respond with different values for the P term.
And here’s how a ‘full system’ with heating and cooling plus deadbands will look. We’ll just talk here about the cooling response and how to set that up in the T3000 software.
Here’s teh setup in T3000. First define the inputs, outputs and PID in tabs1, 2, 3. To test it out, set the input temperature to manual mode at Tab1, then gradually step it up in small increments. At each step you can see the PID action increasing from 0%, 25% and so on up to 100% at Tab7. Notice the ‘action’ is set to ‘+’ which is for cooling.
All that remains to do something with this PID is write a simple program for the valve to follow the PID as shown below. And that’s it. There’s a better example in the T3000 help documents on how to set up graphics for the system. From the T3000 software you hit the F1 function key to bring that up.
@maurice
I’m doing a tempering valve for a sink that needs to have the hot water controlled to a certain temperature. Let’s say 40degrees
I have water from hot water boiler, going into a temp well sensor before it goes to the sink , and between the boiler and the temp well, I have a modulating valve injecting cold water based on the final temp through a tee.
So as the temp is too high, it will allow water to flow in and bring the temp down.
I saw a post you had done to explain a PID control. It seems very basic
Do you have the full program posted somewhere ?
Control valve is 0-10v
Temp sensor is 10k thermister
The program is exactly as you see above and its already set for cooling under the ‘Action’ column. A popup will show when you change the Action setting to remind you that + is cooling and - is heating.
That’s really all there is to controlling the valve to maintain the setpoint. Yuu could get fancy with a schedule, there’s many examples on the forum but its also quite simple.
I just finished the set up for this valve and it is working beautifully.
Although instead of going from 0 to 100%, I sent the valve note to be 5% as a minimum And then when the temperature closed and I might setpoint, the PID loop would cut in and bring the temperature back. It works very well and I only get about 1° of water temperature up above my setpoint, which is a very quick reaction.
I do have a 24 V AC relay that I need to trigger with the controller. I believe you mentioned before that I could do that.
Do you have a quick wiring diagram where I could output 24 V to a relay directly from the controller?
Thanks again for everything so far! This system is very easy to use.
