Met Sensor – TEMP/RH Audit

 

Purpose:  This should be done along with all other Met Sensor checks. The RH and TEMP checks are done at the same time using the Psychrometer.

 

Required Equipment:  Psychrometer

 

Reference:  SOPMAN

 

  1. Down the Met channels.
  2. Prep your Psychrometer by adding a small amount of water to the wick on the wet bulb thermometer until saturated. Place this inside the case for the Psychrometer and take out to the Met tower.
  3. Lower the tower and remove the TEMP/RH sensor from the cross arm.
  4. Place the Psychrometer and the TEMP/RH sensor close together shaded from the sun and wind if possible. Turn the Psychrometer on.
  5. Wait about 5 minutes until both have equilibrated to the same temperature.
  6. With a pen and paper, go out to the Psychrometer and read the wet and dry bulb temperatures at the same time.
  7. Do this 12 times spaced over a three minute period.
  8. With this information, go to the “Query Data” under “Tools” on the SiteManager screen.
  9. Select TEMP and RH from the drop down boxes. Now hit the “Get Data” button on the right side.
  10. This will give you the data for last three minute from the DAS. Now average these three numbers and record in the “Metchecks” form located under “StatusForms” on the SiteManager screen. The TEMP average will be the “Ambient DAS Temp” value and the RH average will be the “Ambient DAS RH” value.
  11. Average both the wet and dry bulb temperatures (12 for each) collected from the Psychrometer. Using the slide ruler –Humidity calculator, line up the two temperature averages. Note where the arrow at the left side is pointing. (Percent Relative Humidity) This is the RH reading from the Psychrometer. Record this % as the “RH Psychrometer” value.
  12. Dry bulb temperature is the temperature that will be recorded as the “Psychrometer Temp”.
  13. The temperatures for the Psychrometer and DAS should be within +/- 2 degrees.
  14. Next, will be the “Ice Bath Temp” or the zero value.
  15. Place some ice in a container with a small amount of water. Vigorously agitating to lower the temperature of the water to/near zero degrees.
  16. Place the TEMP/RH sensor in a plastic bag to protect from the water and insert in the ice water bath while still vigorously agitating the water. This may take 2-3 minutes.
  17. After you are satisfied that this has brought the temperature down to/near zero, go back inside and get the last (should be lowest) reading from the “Query Data” for TEMP. This will be recorded as the “Ice Bath Temp” in the MetCheck form.
  18. Remove the TEMP/RH sensor from the ice water and return to the cross arm on the Met tower.
  19. Raise the tower and up the Met channels once the temperature has stabilized.