Extech Instruments 407445 Instruction Manual page 6

Calibration
Humidity Calibration
Note: Calibration reference solutions are available from Extech (33%: Part No. 407453 and
75%: Part No. 407465).
1. The grid located on top of the sensor must be removed so that it may fit into the
calibration bottles.
2. Prior to calibrating, allow the meter and probe to stabilize to room temperature.
3. Open the battery compartment to access the calibration adjustments (see diagram
below).
4. Place the sensor head into the 33% calibration reference solution. Wait for a stable
reading (up to 30 minutes). Adjust VR3 until the display reads 33.0%.
5. Place the sensor head into the 75% calibration reference solution. Wait for a stable
reading (up to 30 minutes). Adjust VR4 until the display reads 75.0%.
Temperature Calibration
Note that the temperature calibration adjustments are rarely required. However if a
temperature calibration is in order, the user must have access to an environmental
chamber capable of providing 21
the meter sensor to stabilize (30 minutes approx.) and then adjust the appropriate
potentiometer (see below):
• VR7 - Temperature 21
• VR6 - Temperature 50
Test Equipment Depot, 99 Washington Street, Melrose, MA 02176
Page 6
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C and 50
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C adjustment
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C adjustment
781.665.1400 | 800.517.8431 | Fax: 781.665.0780
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C conditions. Allow time for the chamber and
Model 407445 Version 2.2 February 2004