User's Guide
Digital Psychrometer + IR Thermometer
Model RH401
DP
Introduction
Congratulations on your purchase of the Extech RH401 Digital Psychrometer + InfraRed
Thermometer. This device measures Humidity, Air Temperature, Dew Point and Wet Bulb.
Advanced features include Infrared Non-Contact Surface Temperature Measurement, Data
Hold and programmable Auto Power Off. The retractable probe protects the sensors when
the meter is not in use. Careful use of this meter will provide years of reliable service.
Wb
H
umi
C
%
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
FAX 781.665.0780 - TestEquipmentDepot.com
Specifications
Function Range and Resolution Accuracy
Humidity 0.0 to 100.0% RH ±3% RH (10 to 90%)
Temperature (Air) -4.0 to 122.0oF (-20 to 50oC) ±1.8oF (±1oC)
o
C/6oF
o
C/8oF
Temperature (InfraRed)
(@25ºC ±5ºC)
-4 to 842oF (-20 to 450oC)
o
-40 to -4
-40 to -20
F, 842 to 932oF
o
C, 450 to 500 oC
±3% reading or ±3
whichever is greater
±4% reading or ±4
whichever is greater
Display Triple LCD with backlight
Sensor Type Humidity: Capacitance sensor; Temperature (air): Thermistor
Dew Point -90.4 to 122.0
o
F (-68 to 50oC) (calculated from humidity and
temperature measurements)
o
Wet Bulb -6.9 to 122.0
F (-21.6 to 50oC) (calculated from humidity and
temperature measurements)
IR Emissivity Adjustable from 0.3 to 0.99
IR Spot/Distance Ratio 8:1
IR Response Time 0.5 seconds
Operating Conditions -4 to 122
Storage Conditions -40 to 185
o
F (-20 to 50oC); < 99% RH non-condensing
o
F (-40 to 85oC); <99% RH non-condensing
Power Supply 4 x 1.5V ‘AAA’ batteries or AC adaptor
Battery Life approx. 150 hours (laser inactive); 30 hours (laser active)
Dimensions / Weight 6.8x2.7x1.9” (175x70x50mm); 4.9 oz. (140g)
Meter Description
1. Emissivity adjust indicator
2. Laser pointer on indicator
3. Low Battery indicator
4. IR Surface Temperature button
5. ON/OFF/Setup button
6. Back Light button
7. Laser/Down button
8. °F/°C/Up button
9. Dew Point/Wet Bulb button
10. % Humidity display
11. Air Temperature, Dew Point or Wet Bulb display
12. IR Surface Temperature display
13. Extended probe with Humidity &
Air Temperature Sensors
14. PC interface port
15. AC adaptor jack
Note: The battery compartment is located on the rear of the instrument
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DP
Wb
H
umi
C
%
13
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15
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RH401 V1.4 09/04
Operation
Retractable Humidity and Air Temperature Sensor
Press down on the sensor, located at the top of the meter, to
release it. Humidity and air temperature will not be displayed if the
sensor is not extended.
After use, press the sensor into the stored (protected) position.
Power ON/OFF
Press the (or the button) to turn power on. The
meter will perform a short self-test when turned on.
Press and hold the button for three seconds to turn power off.
Humidity and Air Temperature measurements
1. Hold the meter in the area to be tested.
2. Allow adequate time for readings to stabilize.
3. View the Relative Humidity measurement in the lower display.
4. View the Air (probe)Temperature measurement in the middle display
Wet Bulb and Dew Point measurements
1. To display the Wet Bulb measurement, press and hold the button until the
symbol DP appears in the middle display.
2. Wet Bulb temperature is now displayed.
3. To display the Dew Point measurement, press and hold the button until the
symbol Wb appears in the middle display .
4. Dew Point temperature is now displayed.
5. To display IR temp –DP temp (IR surface temperature-Dew Point), press and hold the
button for more than 2 seconds then press the IR Temp button. The reading
can now be viewed in the top display.
6. Press and hold the button for more than 2 seconds to toggle the display back
to IR temperature.
Non-Contact InfraRed Surface Temperature measurements
1. Point the meter toward the surface to be measured.
2. Press and hold the button.
3. View the temperature measurement in the upper display
4. Release the and the reading will be held on the display until a new reading is
taken.
5. While holding down the button, press the button to toggle the laser
targeting pointer on/off. The symbol will appear in the middle left of the display
indicating that surface temperature measurement is active and the laser pointer is on.
WARNING! The Laser button
enabled, each press of the button turns on the Laser beam. Avoid looking directly
into the path of the Laser or pointing the Laser toward anyone’s eyes. Mirrored surfaces
near a measurement object can redirect the Laser, use extreme caution. Do not allow
the Laser beam to be directed toward explosive gases.
enables/disables the Laser pointer. When
Press Here
Sensor
Extended
Sensor
Stored
3
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
FAX 781.665.0780 - TestEquipmentDepot.com
RH401 V1.4 09/04
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