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LP Calibration

LP Calibration

Owned by Trevor Carey
Mar 12, 2021
5 min read

Equipment                                                                                                                                        

  • Linear Potentiometers (LPs)

  • Reference LP

  • Computer w/ LabView

  • Metal Calibration Mount

  • Zip Ties

LP Calibration                                                                                                                                  

  1. Login to the computer at the sensor calibration station.

  2. Open LP Configuration File and re-save as a different name using the researcher’s name or initials (i.e. Save as “LP Config_APS”)

  3. Fill out LP Config File using the “Analog” rows for the LP Configuration. The reference LP will be on Analog1-0, all other LPs that need to be calibrated will be on the subsequent Analog rows.

    1. Column C: use drop-down to change cell to “Yes” for all rows that will be used (including Analog1-0 for the Ref. LP)

    2. Column D: Input SN of each LP

    3. Column E: The Ref. LP should say “Ref” all other LPs should have the name of the LP (i.e. “LP 117)

    4. Column F: The sensitivity of the Ref. LP should be 9924 mV/V. All other LPs should begin with a sensitivity of 1000 mV/V.

    5. Column H: Specify the range of the LP in units of mm. The Ref. LP should be 152.4mm. (i.e. a 3in LP should have a range of 76.2mm)

    6. Column J: Set the offset of zero.

    7. Save and close the LP config file.

  4. Connect the Ref. LP to the 12V-DC power in the lower right-hand corner of the DAQ.

  5. Connect the Ref. LP to Analog-Channel 0.

  6. Secure the first LP to the calibration mount in one of the available locations and secure with zip ties.

    1. It is best to ensure the Ref LP and the Calibration LP start at the same location. It is recommended to only calibrate one LP at a time.

  7. Connect one end of the jumper cable to the LP and the other end to the DAQ in the appropriate Channel # that corresponds with Analog1-(Channel #) for that specific LP in the Config File.

    1. Example: if the Config File has LP 107 listed in Analog1-3, then the jumper cable should be plugged into Channel 3 on the DAQ.

  8. Open the most recent version of the Labview program ResDAQ located in C:\\reddaqv5.

  9. Click the “Play” button in ResDAQ

  10. Select the appropriate Config File.

  11. Click “Set” in the Header window.

  12. Verify sampling rate is 2000 Hz, and then click “OK”.

  13. Click the toggle “Show Graph” so that it turns green and the live data is plotted.

  14. Start the LP in the retracted position.

  15. Click “Save Data” and wait for the green light to turn on.

  16. Cycle the bar back and forth 2-3 times such that the LP being calibrated is never fully extended or fully retracted. Finish back at the retracted position.

    1. It can be helpful to pre-determine the distance to cycle the bar before beginning to save the data, so that you know you’re not going to exceed the maximum or minimum thresholds of the LP

  17. Click “Stop” and wait for green light turn off.

  18. Open the most recent version of Plot Fast Data from Labview. Located on the desktop.

  19. Click the “Play” button and open the “data” folder.

  20. Select the most recent BIN file that has “@999.0rpm” at the end of the file name.

    1. This file produces a better fit, as the other file has a smoothing algorithm that can eliminate some valuable data.

  21. Select the “Zoom Page” tab.

  22. Ensure “Time/Data” toggle is set to TIME.

  23. Select the appropriate Analog Channel (HOC #) to plot from the drop down.

  24. Turn on “Zero Offset” for HOC-0 and the LP being calibrated.

  25. Verify results match reasonably well. If the you see moments in time where the LP being calibrated plateaued while the Ref LP kept measuring displacement, then the LP being calibrated had exceeded its displacement threshold. It is recommended to start over at Step 9 and re-calibrate the LP ensuring not to go past the threshold of the LP.

  26. Switch “Time/Data” Toggle to DATA

  27. Ensure “X-axis” dropdown is set to “HOC-0”

  28. Verify the slope of the LP being calibrated is linear. If the slope is non-linear then the LP is faulty and needs to be replaced.

  29. Verify Slop of HOC-0 is 1.

  30. If the slope of the LP being calibrated is accurate to two decimal places (1.00 or .99), then the calibration is complete. Otherwise, the LP sensitivity needs to be adjusted.

  31. Copy the slope of the LP being calibrated.

  32. Open the Config file.

  33. Multiply the old sensitivity by the LP’s slope copied in the previous step. Paste the new sensitivity into the cell for the LP being calibrated. Save and Close the Config file.

  34. Repeat Steps 9 through 30 until the slope of the LP is accurate to within 2 decimal places (1.00 or 0.99).

  35. Once the LP is successfully calibrated, disconnect the LP from the jumper cable and the calibration mount.

  36. If desired, the calibration file can be saved as a .txt file or as a BIN file using the “misc” tab and the Dump Button.

  37. Repeat steps 4 through 35 until all remaining LPs are calibrated.

Photos                                                                                                                                               

Step 8-17

Step 18

Step 26

Step 27

Step 25

Step 25

Step 27

Step 28

Step 29

Step 33

Step 36