Høgskolen i Buskerud: Emne EMAR2101 Reguleringssystemer 1

Lab: Temperature control with LabVIEW

General information

Organization of the lab is given in the lecture plan.

A short report must be sent to the teacher via e-mail to finn.haugen@hibu.no no later than 4 pm Friday 14. November 2008. Requirements to the report:

  • It must describe the answers to the tasks (see below). The answers can be in the form of pictures of the PC screen (create a picture with Alt + PrintScrn, and then paste it into your document with Ctrl+V) together with your short comments. Write the report while you are working on the lab!
    (The report is actually more of a lab protocol. Do not write about general theory.)
  • Send the report as a DOC or a PDF file (preferably PDF).

Equipment

Tasks

The teacher will give a short description of the lab station in the beginning of the session.

Try to work effectively because the time is short. It is acceptable not to complete all the tasks given below within the assigned time.

  1. Connect the I/O device to the lab station.
     
  2. Opening and setting of the temperature control LabVIEW program: Download temperature_control.zip to any folder you prefer, then unzip the files, and finally open the LabVIEW program temperature_control.vi which is one of the unzipped files. Set the Setpoint (y_SP) range [C] element with 50 deg C as maximum and 20 deg C as minimum. Controller output (u) range [V] element with 5 V as maximum and 0 V as minimum. Set the measurement filter time constant to 0.5 sec.
     
  3. Configuring the USB-6008 I/O device: Create a task for for control signal writing (analog output, or AO) and a task for measurement signal reading (analog input, or AI) via the task elements on the front panel of the program. How to create a task is described in item 2 here. You can define a voltage range of 1 - 5V for the measurement task, and the voltage range of 0 - 5V for the control task.
     
  4. Calculating the measurement scaling function: Calculate manually the coefficients a and b according to the following information: The temperature measurement in the range of 1 - 5 V corresponds to temperatures in the range of 20 - 50 deg C, with a linear relation between V and deg C. Then enter these a and b values into the front panel of the program.
     
  5. Controller tuning: Tune a PI controller for the process (including the measurement filter) using the P-I-D-method. During the tuning you can apply steps of e.g. 1 deg C in the setpoint to excite the dynamics of the control system. The nominal operating point value of the setpoint is defined as 35 deg C. Remember to manually bring the process to or near the operating point (by manually adjusting the control signal). The process is close enough to the operating point if the temperature does not deviate more than say 1 deg C from the operating point value. Check if the stability of the control system is ok after the tuning by applying a small step of e.g. 1 deg C in the setpoint. (Do not use too much time on tuning the controller, but the control system must of course have ok stability. It is sufficient that you include only the picture of the stability check together with a proper comment in for this subtask in your report.)
     
  6. Steady-state control error:
    1. What is the steady-state control error after a step change (of say 3 degrees C) of the setpoint? (After the experiment, set the setpoint back to its nominal value.)
    2. What is the steady-state control error after a step change of the disturbance, i.e. increasing the fan speed? (After the experiment, set the fan speed back to its nominal value.)
       
  7. Measurement noise:
    1. Does the measurement filter make the control signal smoother compared to not having a filter? To remove the filtering action, set the Tf  = 0 sec. (After the experiment, set Tf back to its default vaue, 0.5 sec.)
    2. Add derivative control action by setting Td to e.g. 4 s. How does this influence the behaviour of the control signal? (After the experiment, set Td back to 0.)
       
  8. Changing the stability of the control system (to clearly observe the concequences of the change of the parameter settings you can apply a setpoint change of e.g. 3 K  after the parameter change):
    1. What happens to the stability of the control system if the controller gain is increased to a relatively large value?
    2. What happens to the stability of the control system if the integral time is decreased to a relatively small value?
    3. What happens to the stability of the control system if you set the PID controller to direct mode (i.e. some negative controller gain)?

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Oppdatert 11.11.08 av Finn Haugen, faglærer. E-postadresse: finn.haugen@hibu.no