Part 11 of 11
PID Loop Application Demonstration. Productivity3000
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Now that we have our PID loop tuned, let’s check the operation of our example application. Here is our PID Loop application demo unit. We have the Productivity 3000 Programmable Automation Controller, the C-more Touch Panel, the Stack Light Tower with indicators and audible alarm, and the Power ON and Emergency Stop Push Buttons. Mounted through the lid of our Process Tank is our Ultrasonic Sensor, and next to it is our overflow shutdown float switch. Also mounted on the portable relay rack are the Process Tank, the Ball Valve, and the Reservoir Tank. Here on the side is the Primer Bulb, and above it is the Flow Indicator currently showing no flow, and mounted to the Reservoir Tank is the Diaphragm Pump we covered earlier. On the rear of the PID Demo unit are various electrical components including relays, power supplies, motor controller, protective devices, ZipLink modules, and other wiring components. Keep in mind we first started our demo unit by allowing the Diaphragm Pump to run and partially fill the Process Tank. Once we had enough water in the tank above the Process Tank’s siphon tube, we fully opened the Ball Valve, and then used the Primer Bulb to start a flow back to the Reservoir Tank. We then TUNED our PID Loop, first manually, and then automatically, and eventually achieved a fast response whenever the Set Point is changed, with minimum overshoot. Let’s start our demonstration with the process running and maintaining a volume of 3.00 gallons as seen here. We have the Ball Valve opened just enough to allow a slightly slow drainage rate as can be seen with our Flow Indicator. As seen here, the PID Loop is constantly making changes to the Process Output, controlling the Diaphragm Pump, and maintaining the desired volume. First we will change the volume to a greater amount by using the C-more Touch Panel to change our Set Point value. Currently we are maintaining a volume of 3.0 gallons, but our process now says we need to change the volume to 3.1 gallons, while keeping the same mixture ratio. On the C-more Touch Panel press the Numeric Entry button for the Tank Volume, enter 3 point 1, and then press enter. Please keep in mind that in our application we could make a change in volume as small as 0.01 gallons. Because we have changed the Set Point to increase the volume, the PID Loop Control will calculate the Error and immediately call for a Process Output of 100%, causing the Diaphragm Pump to run at the maximum one gallon per minute rate. As we get close to the final amount, we can see and hear the pump slow down. We can monitor the status of the volume by glancing at our Stack Light indicators, or take a look at the PID Parameters Screen on the C-more Touch Panel which also shows the status of the volume. Our status indicators can tell us if our volume is High, Low, or OK. Once the volume has reached our new Set Point, we can see the PID Loop Control constantly adjusting the Process Output. The new volume stays constant as the water in our process is used, which is simulated by the drainage through the Ball Valve. The PID Loop Control will maintain this volume until the Set Point value is changed, or the process is stopped. You may ask where an application for controlling the volume in a tank would be used. One possibility is a process where a solution, such as a brine solution, is being mixed to maintain a certain concentration, such as 72 ounces of sodium chloride mixed with 3 gallons of water. But instead of the entire solution being used after being mixed, the solution is being used at a random rate. And on top of that, we need to constantly maintain a set volume in our process tank that is available at any given instant for use in our process. Therefore we would need to maintain the overall volume while measuring how much solution is used at any given instant, and adjust how much additive needs to be replaced accordingly. This would be another good task for the Math Instruction available in the Productivity 3000! A little over the top, but I think you get the picture of how powerful the programming within the Productivity 3000 can be. That wraps it up for this video series on the Productivity 3000 Programmable Automation Controller by AutomationDirect, and its ability to make programming your application go quicker. I realize we covered a lot of ground in this series of videos, with most of the subject matter geared toward obtaining an understanding of PID Loops in general. But if you look back through the various titles, you will see that the actual PID Loop was done with one fill-in-the-blank instruction, a nice time saver, and from there we were able to monitor our process and automatically tune the loop once we got it going. I hope you have gained some useful information for implementing your next application, not only in using a PID Loop, but also all of the other great features offered by the Productivity 3000. Make sure to check back and look for additional Productivity 3000 videos, and other technical learning videos, here at Learn dot Automation Direct dot Com. Until next time, thank you for watching. Have a great day!