Course PEF3006 Process Control

Exercise: Monitoring and control of an air heater using LabVIEW

It is assumed that you have watched the following videos before the exercise:

• The video on the home page of the air heater (the mathematical model presented on the home page will be used in later exercises)
• Analog IO with LabVIEW and NI USB-6008 (only until 27:30)

1. In this task the cables on the IO shall be disconnected from the air heater.
   Make a VI for analog IO. Check the functionality with the loopback test.
2. In this and the subsequent tasks, connect the IO device and the air heater (for heater control and temperature measurement of the air outflow).
   Create a VI for monitoring and control of the air heater according to the following specifications:
• The VI runs with a cycle time of 0.05 s.
• The heater is controlled with a voltage signal which can be adjusted manually from the front panel of the VI. The control signal is plotted continously in a chart.
• The temperature measurement from the Temp1 sensor in units of degrees Celcius is plotted continously in a (second) chart. The transformation of the voltage from the sensor to the corresponding temperature in deg C is implemented in a Formula node. The relation between voltage and deg C is shown on a label on the air pipe.
• A measurement filter for the temperature measurement in the form of a time-constant filter where the time-constant Tf [s] is adjustable on the Front panel. You can use this filter. (As a part of the project of this course, you will implement the filter from scratch by yourself). Tf may initially be set to 1 sec. Both the filtered and the unfiltered (raw) measurement signal shall to be plotted on the same chart.
3. Experiments (you may run the air fan at its maximum speed):
1. Adjust the control signal to the heating element as desired, and observe how the lamp that indicates the pulse-width modulator state (on/off) flashes accordingly.
2. Increase Ts to 1 s. How does this influence on the update rate of the charts? Then set Ts back to 0.05.
3. Observe the noise filtering by the filter. (With autoscaling of the Y-axis, signal variations become clearer.)
4. Adjust Tf to a very large value, for example 20 sec. Vary the control signal to the heater. Is there any benefit of having a large Tf? Any drawbacks?

Updated 11 Sept 2017 by Finn Haugen.