Relative Humidity Calibration
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8.1 Calibration Overview
The 42280A can be calibrated by the user, or it can be returned to Extech for
service. Field calibration requires the use of optional 33% and 75% calibration
salt bottles. Contact your local distributor, or Extech directly, for information re-
garding the purchase of calibration bottles.
8.2 Calibration Process
1. With the meter OFF, insert the sensor into the 33% Calibration Reference
bottle.
2. Simultaneously long press the START/STOP and SET buttons to enter the
33% Calibration mode. The display ‘32.8%’ will flash on the display.
3. After approximately 60 minutes, the ‘32.8%’ display will stop flashing, indi-
cating that the 33% calibration is complete.
4. Plug the RH sensor into the 75% Calibration Reference bottle.
5. Press and hold the START/STOP button to enter the 75% Calibration
mode. The display ‘75.3%’ will flash on the display.
6. After approximately 60 minutes, the display will stop flashing, indicating
that the entire calibration is complete. The meter will automatically return
to the normal operating mode.
8.3 Calibration Notes
• To abort a calibration, long press the START/STOP button before reaching
step 6 in the procedure above.
• For best accuracy, perform the calibration at room temperature 73.4℉ ±
3.6℉ (23℃ ± 2℃).
• For best accuracy, ensure that the calibration bottles are tightly sealed
around the sensor.
#NAS100123; r. AA/88670/88670; en-US
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