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.
