GS4 VFD Sleep Mode 3 - Reverse Acting PID

This video is basically the same as the previous video except it is Reverse Acting. That is, as the drive output frequency increases and the water level rises … the process variable or sensor level decreases. We are going to use the exact same setup as in the previous video, so we won’t repeat all of the setup discussion here. I did invert the sensor output, so it would behave in a reveres acting sense. On this sensor you just hold the teach button down for 8 seconds and it automatically inverts the output for you. To switch from Forward to Reverse Acting, we only need to change these guys. We need to tell PID the sensor signal is reverse acting by setting parameter 7.00 to a 3. We need to change the setpoint. Let’s say we want the setpoint to be up here at 90% full. The sensor is revered so it will tell us the tank is 10% empty. Ten percent of 60 Hz is 6Hz, so we enter that for our setpoint. You can view the setpoint in Percent by adjusting the parameters in group 8. We’re not going to take the time to do that in this video. We also need to change our wake and sleep setpoints to match the reverse acting sensor. In the previous video we found that the sleep and wakeup levels are relative to the setpoint. So since the setpoint is at 10% and I want to shut the motor down at another 50% of that, then my Sleep level is 150% OF THE SETPOINT. Which would be 9Hz. Wake up is the same thing, BUT, the largest number you can put in for wake or sleep is 200%. So we’ll put that in for our Wakeup – which means the drive should wake up at 200% of our 6Hz setpoint which is 12Hz or 20 percent of full scale. So sleep and wakeup are going to be pretty close to each other in this demo aren’t they? That’s it. That’s all we have to do to switch from Forward to Reverse acting. Otherwise they are identical. Let’s try it. I’ll bring up the GSOFT2 Scope Function. Adjust my analog pots to mark the sleep and wakeup levels we expect. Turn on the water level LEDs and hit RUN. PID sees the tank is empty and cranks up the blue drive frequency to try to fill the tank. We see the yellow sensor feedback falling – remember it FALLS as the water RISES in a reverse acting system – and since Sleep mode is watching that to see when it crosses the RED sleep threshold we set, the motor turns off. I’ll open the valve to simulate demand. The yellow process variable starts to increase telling us the tank level is decreasing. When it crosses the green wake-up level the motor starts back up and fills the tank again. Let’s speed this up and watch a few cycles. The GS4 drive is now automatically controlling cycling of the pump in a reverse acting system. Perfect. We said the thresholds are relative to the setpoint. Let’s change the setpoint to 20% empty which is 12Hz. That would be around here. So the Sleep level should be 150% of that which is roughly here and the Wake level should 200% of that which is roughly here. Run a couple cycles, and sure enough we see the drive wake up the motor after crossing the new wake up level and the drive turned the motor off at the new sleep level. Again, those levels automatically adjusted relative to the new setpoint that we entered. Delays work exactly the same as in the forward acting. I put the setpoint back at 10% empty and set the delays to two seconds each and if we run a couple cycles we see the drive woke up the motor two seconds after the process variable crossed the green wake up threshold and it shut the motor down two seconds after crossing the red sleep threshold. And just like forward acting demo, you get to specify the what frequency you want the motor to hold at while waiting for the sleep delay. Maybe you have a mixing application and you want to mix slowly for a while before shutting down to reduce foaming. Or maybe you have a pumping application and you want the pump to run slowly for a bit to top off the tank with less turbulence before shutting the motor down. Being able to specify that min drive speed during the sleep delay is real handy in those kinds of applications. And just like the previous video, you can change the max PID frequency output. I set it to 75% and ran the drive and got this. Sure enough, the Max output frequency is limited to 45Hz – which is 75% of the drive’s max of 60Hz. Limiting the drives output frequency is a great way to limit the stress on your motor if your application doesn’t need the full output frequency. That ought to be enough to get you started with Sleep Mode 3 when using a Reverse acting system. Click here to learn more about the GS4 Drive. Click here to learn about AutomtionDirect’s free support options. Click here to subscribe to our YouTube Channel so you will be notified when we publish new videos.