Extech Instruments RH390-NIST User manual

User's Guide
Digital Psychrometer
Model RH390
MAX
MIN
°F•°C•WBT
Dew Point

RH390-EU-EN V2.3 07/13
2
Introduction
CongratulationsonyourpurchaseoftheExtechRH390DigitalPsychrometer.Thisdevice
measuresHumidity,AirTemperature,DewPointtemperatureandWetBulbtemperature.
AdvancedfeaturesincludeDataHold,AutoPowerOff,andMAX/MINreading.Carefuluseofthis
meterwillprovideyearsofreliableservice.Pleasevisitourwebsite(www.extech.com)tocheck
forthelatestversionofthisUserGuide,ProductUpdates,andCustomerSupport.
Meter Description
1. Humidity & Temperature Sensor
2. LCD Display
3. Power ON/OFF button
4. °F/°C/WBT (wet bulb)/Dew Point button
5. MIN/MAX button
6. HOLD/Backlight button
Note: The battery compartment is located
on the rear of the instrument
Display Description
1. Relative Humidity %
2. Dew Point
3. Wet Bulb
4. °C/°F
5. Temp/WB/DP Display
6. Maximum
7. Minimum
8. Low Battery
9. Hold
10. RH% Display
11. Auto Off
1
2
4
5
3
6
Dewpoint
WetBulb
°C °F
MAX MIN
9
10
8
11
67
1
4
2
3
5

RH390-EU-EN V2.3 07/13
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Operation
Power
Press the power button( ) to turn power on or off.
Taking measurements
1. Hold the probe in the area to be tested.
2. Allow adequate time for readings to
stabilize.
3. The Relative Humidity measurement
appears in the top display.
4. Pressing the °F/°C/WBT/Dew Point button
toggles the lower display between
Temperature (°F), Temperature (°C), Dew
Point (°C), Dew Point (°F), Wet Bulb (°C)
and Wet Bulb (°F).
Dew Point measurements
1. To select the Dew Point
measurement, press the
°F/°C/WBT/Dew Point button until
DEWPOINT (°F or °C) appears in the
lower right.
2. Dew Point temperature is now
displayed.
°C °F
Dewpoint
°C °F

RH390-EU-EN V2.3 07/13
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Wet Bulb measurements
1. To select the Wet Bulb measurement,
press the °°F/°C/WBT/Dew Point
button until WET BULB (°F or °C)
appears in the lower right.
2. Wet Bulb temperature is now
displayed.
Temperature measurements
1. To select the temperature measurement,
press the °F/°C/WBT/Dew Point button
until °C or °F appears in the lower right.
2. Temperature is now displayed.
Data Hold
Press the hold button ( ) momentarily to
freeze the displayed readings.”HOLD” will appear
on the upper left-hand side of the display. Press
the hold button ( ) again to return to normal
operation.
WetBulb
°C °F
WetBulb
°C °F
WetBulb
°C °F
MAX MIN

RH390-EU-EN V2.3 07/13
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Minimum (MIN) Maximum (MAX) Function
The MIN/MAX mode allows the user to view only
the lowest (MIN) or highest (MAX) readings.
Press the MAX/MIN button once and “MAX”
appears on the display. The LCD is now
displaying the maximum humidity in the top
display and the maximum reading of the selected
parameter in the bottom display. The display will
not change until a higher reading is registered.
Press the MAX/MIN button again and “MIN”
appears on the display. The LCD is now
displaying the minimum humidity and the minimum second reading in the bottom display.
The display will not change until a lower reading is registered.
To exit the MIN/MAX mode, press and hold the MIN/MAX button for 2 seconds until the
“MAX” or “MIN” icon disappears.
Note: Readings are automatically reset when switching from one display to the next
(MAX to MIN).
Backlight
Press and hold the light button ( ) until the backlight comes on. To turn the
backlight off press and hold the light button ( ) until the backlight turns off.
Automatic Power OFF
The meter has a default setting that automatically shuts the
meter off after 10 minutes (indicated by the symbol on
the display. This battery saving feature can be disabled. To
disable the auto power off function, simply press and hold
the hold button
( ) while powering on. The symbol will not appear
when auto power off has been disabled. The meter will
revert to the default auto-off mode when powered off.
°C °F
MAX MIN
°C °F
MAX MIN

RH390-EU-EN V2.3 07/13
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Maintenance
Cleaning and storage
1. The meter should be cleaned with a damp cloth and mild detergent when necessary.
Do not use solvents or abrasives.
2. Store the meter in an area with moderate temperature and humidity (refer to the
operating and storage range in the specifications chart earlier in this manual).
Battery Replacement
When the battery power falls low, the battery symbol will appear on the LCD. Replace
the 9 Volt battery by removing the Philips head screw holding the rear battery
compartment cover to access the battery compartment. Ensure that the compartment
cover is securely fastened when finished.
You, as the end user, are legally bound (Battery ordinance) to return all used batteries
and accumulators; disposal in the household garbage is prohibited!
You can hand over your used batteries / accumulators at collection points in your
community or wherever batteries / accumulators are sold!
Disposal: Follow the valid legal stipulations in respect of the disposal of the device at the
end of its lifecycle
Specifications
Function Range and Resolution Accuracy
0.0 to 10.0%RH ±3%RH
10.0 to 90.0%RH ±2%RH
Humidity
90.0 to 100.0%RH ±3%RH
-30.0 to -20.0oC
-22.0 to – 4.0oF
±1.5oC
±2.7oF
-19.9 to 70.0oC
-3.9 to 158.0oF
±1oC
±1.8oF
Temperature
70.1 to 100.0oC
158.1 to 199.0oF
±1.5oC
±2.7oF
Wet Bulb 0 to 80°C (32 to 176°F)
Dew Point -30 to 100°C (-22 to 199°F)
Calculated from RH and air
temperature measurements
Display Dual LCD
Response Time: <30 seconds (90% of final value in moving air)
Operating Conditions 32 to 122oF (0 to 50oC); < 80% RH non-condensing
Storage Conditions -40 to 185oF (-40 to 85oC); <99% RH non-condensing
Power Supply 9 Volt battery
Battery Life Approx. 24 hours
Dimensions / Weight 7.8 x 1.7 x 1.3” (200 x 45 x 33mm); 7 oz. (200g)
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