Module 4 PID Demonstration
Go to the following website in order to complete this activity. It will open a Liquid Flow Rate Controller interactive demo that you will use throughout this activity.
(It may be useful for you to print out these instructions so that you can fill in your responses to the questions and bring them to class)
http://dexautomation.com/pidtutorial.php
Control Loop
Notice the following elements once the page is displayed:
- FRC-200 Controller
- Liquid flow rate controller
- Manual
- Set Point is 0
- Output is 100%
- Direct acting: Air valve is used to control the flow. Valve is closed and controller output is 100%
- OP is white trace
- SP is yellow trace
- PV is green trace
LEAVE PUMP OFF FOR NOW
Proportional Demo
- P is Proportional
- Proportional Band or Gain is expressed as a percent. It represents the amount PV or SP must change to cause the OP to change to 100%
Instructions:
- Put controller in AUTOMATIC by clicking A/M button
- P is set for 100%
- Raising SP has the same effect as on the controller as a falling PV
- Try it changing SP to 0 and then 10
- Change SP to 20, then 40
Describe what happens and be prepared to share your answer with with the class:
- Set SP to 0
- Set P to 50
- Change SP to 10. Does output change by 20%? A change of 10 causes a change of 20 or a gain of 2
- Put controller back to MANUAL.
- Set P to 100
- Set OP to 100%
- Start pump by clicking START
- Put controller back to AUTOMATIC
- Change SP to 20
Does OP change from 100 to 80?
- Then decrease P by small amounts and note change in PV.
Describe what happens if P is set too low and be prepared to share your answer with the class:
- Set P to 50 and change SP by small amounts
- Set P to 100 or put pump back to MANUAL before it blows the seals!!!!!
Integral Demo
- I stands for Integral.
- “Repeats per minute” or “Minutes per repeat”. Repeats per minutes means the number of times per minute I repeats the action of P term. This controller uses “repeats per minutes”
Instructions
- SP to 0, OP set to 100, I set to 0, and D set to 0. Pump is OFF.
- Put controller in AUTOMATIC
- Change SP to 10.OP should change from 100 to 90
- Change SP back to 0
- Change I from 100 to 90. Note that I takes over and move OP from 90 to 80 for next minute. Make sure the controller is working by verifying the OP is changing every 1 minute.
- Put controller in MANUAL
- Then put controller in manual and set OP to 100
- Set I to 2
- Put controller back to AUTOMATIC.
Describe what happens and be prepared to share your answer with the class:
- Repeat the previous steps using the following :
- P=200, I=1
- P=200, I=.5
- P=50, I=1
- P=50, I=5
- Once familiar with how P and I interact, Start pump and try tuning the controller.
- Start with P set to 100 and I set to 0.
Describe your results and be prepared to share your answer with the class:
Derivative Demo
- Never used in a flow controller
- Click here to retrieve TEMPERATURE CONTROLLER. Use the other word document to get the new piece of equipment. This piece of equipment does not use respond to SP changes. Controller is now connected to a SIGNAL GENERATOR.
Instructions
- Put controller in AUTOMATIC
- Click BLUE button up on signal generator to cause controller input to slowly ramp up.
- Note how green and white lines mirror each other. This is the result of the P’s corrective action.
- Click STOP on signal generator. This stops the ramping action.
- Change controller back to 200 degrees by typing 200 into signal generator window and press “ENTER”
- Change D to 0.5
- Click up arrow on generator
Note what happens and be prepared to share you answer with the class (derivative action is a proportional to the rate of change of the process. It is designed to stop the PV from changing and then its job is done):
- Click stop on the signal generator.
Note what happens and be prepared to share you answer with the class:
- Experiment with different values for P and D.
Note what happens and be prepared to share you answer with the class:
Critical thinking Activity
Create a small processing lab. Create a lab that would use the PID to control this process.