Extech Instruments RH390 User manual

User's Guide

Digital Psychrometer

Model RH390

MAX

MIN

°F•°C•WBT

Dew Point

RH390-EU-EN V2.2 2/11

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.

Specifications

Function Range and Resolution Accuracy

Humidity 0.0 to 100.0%RH

±2%RH (20% to 90%)

±3%RH (10% to 20% and 90 to 95%)

±4%RH typical at 1% and 99%

Temperature -20 to 70oC

(-4.0 to 158.0oF) ±1oC (±1.8oF)

-30.0 to -19.9oC

and 70.1 to 100.0oC

(-22.0 to – 3.9oF

and 158.1 to 199.0oF)

±1.5oC (±2.7oF)

Display Dual LCD

Response Time: <30 seconds (90% of final value in moving air)

Sensor Type Humidity: Precision capacitance sensor

Temperature: Thermistor

Wet Bulb 0 to 80°C (32 to 176°F) (calculated from RH and Air

temperature measurements)

Dew Point -30 to 100°C (-22 to 199°F) (calculated from RH and Air

temperature measurements)

Operating Conditions 0 to 50oC (32 to 122oF); < 80% RH non-condensing

Storage Conditions -40 to 85oC (-40 to 185oF); <99% RH non-condensing

Power Supply 9 Volt battery

Battery Life Approx. 24 hours

Dimensions / Weight 200 x 45 x 33mm (7.8 x 1.7 x 1.3”); 200g (7 oz.)

RH390-EU-EN V2.2 2/11

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

Dewpoint

WetBulb

°C °F

MAX MIN

RH390-EU-EN V2.2 2/11

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 V2.2 2/11

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 V2.2 2/11

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 to 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 V2.2 2/11

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

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