CLICK PID Tutorial Videos Part 2 - Hardware Setup and Wiring from AutomationDirect

Understanding how your system operates is the first key to getting PID to work. So, we’re going to spend this entire video getting to know our system. This is the hardware we will be using in this series of videos. There’s not much to it. This 500-watt heater is trying to heat things up while this exhaust fan is pulling room temperature air through the enclosure. Our goal is we want to accurately control the enclosure's internal temperature by monitoring this RTD transmitter and controlling the heater's average input power. We’ll do that by configuring a CLICK PLC output to be a Pulse Width Modulated – or PWM - signal. That will control this solid-state relay, which will toggle the 120-volt AC power into the 500-watt resistive fan heater. If the PWM signal is on all the time, the heater is on all the time and we get all 500 watts. If the PWM output is set to a 50% duty cycle, then the heater is only on half the time and we get half the heat. A 25% duty cycle gives us 25% of the heat, etc. I have a small fan pulling air through the box. The sizing of that fan is critical, but a bit of a tangent to what we are doing here, so I put it off to a separate video if you want to learn how to do that yourself. The RTD transmitter provides a 4-20mA signal so we can run it directly into an analog current input on this CLICK CPU which I chose because it has two analog inputs. I added a second RTD transmitter to the other analog input, so I could monitor the room temperature if I wanted to. This schematic shows how all of that is wired and the part numbers I used. You can pause the video to take a closer look and I’ll include a link to the schematic and parts list in the notes below the video. Keep in mind, this is just a quick demo I threw together using parts I happened to have laying around the office. So please, don’t get hung up on the exact part numbers. Inside the CLICK PLC we need to scale the analog input to degrees Fahrenheit to create our raw process variable. We’ll have the option to filter the raw process variable which we will subtract from the Setpoint to get the difference between where our process is and where we want it to be. We call that the error. The PID Math then raises or lowers the output level to try and get the process variable as close to the Setpoint as it can. The PID output ranges from 0-100% so normally you will have to scale the PID output to match whatever your process is. But we are using a PWM output which also ranges from 0-100% so we don’t need scaling in this example. We do need to enable the PWM output This looks a little scary, but the good news is all of this – and a lot more - is done in a single configuration dialog box that walks you step-by-step through the process. So, all we really have to do is configure the analog inputs and set up the one PID configuration dialog. Great, we have our hardware wired up and we know conceptually what we need to configure inside the CLICK PLC. Join us in the next video where we will do the PID configuration. Click here to see all the videos in this playlist. Click here to learn about AutomationDirect’s free support options and click here to subscribe to our YouTube channel so you will be notified when we publish new videos.