Extech RH390 Operating Manual

User's Guide

Digital Psychrometer
Model RH390

MAX

MIN

°F•°C•WBT

Dew Point

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

±2%RH (20% to 90%)

Humidity

Temperature

Display Dual LCD
Response Time: <30 seconds (90% of final value in moving air)
Sensor Type Humidity: Precision capacitance sensor

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

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

Operating Conditions 32 to 122
Storage Conditions -40 to 185
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)

0.0 to 100.0%RH

o

-4.0 to 158.0
(-20 to 70

-22.0 to – 3.9

and 158.1 to 199.0

(-30.0 to -19.9

and 70.1 to 100.0

o

C)

o

o

F

F

C

o

o

C)

F

Temperature: Thermistor

temperature measurements)

temperature measurements)

o

F (0 to 50oC); < 80% RH non-condensing

o

F (-40 to 85oC); <99% RH non-condensing

±3%RH (10% to 20% and 90 to 95%)
±4%RH typical at 1% and 99%

o

F (±1oC)

±1.8

±2.7oF (±1.5oC)

Warranty

EXTECH INSTRUMENTS CORPORATION warrants this instrument to be free

of defects in parts and workmanship for one year from date of shipme nt (a six
month limited warranty applies to sensors and cables). If it should become
necessary to return the instrument for service during or beyond the warranty
period, contact the Customer Service Department at [phone] ext. 210 for
authorization or visit our website www.extech.com for contact information. A
Return Authorization (RA) number must be issued before any product is returned
to Extech. The sender is responsible for shipping charges, freight, insurance and
proper packaging to prevent damage in transit. This warranty does not apply to
defects resulting from action of the user such as misuse, improper wiring,
operation outside of specification, improper maintenance or repair, or
unauthorized modification. Extech specifically disclai ms any implied warranties
or merchantability or fitness for a specific purpose and w ill not be liable for any
direct, indirect, incidental or consequential damages. Extech's total liability is
limited to repair or replacement of the product. The warranty set forth ab ove is
inclusive and no other warranty, whether written or oral, is expressed or implied.

2

RH390 V2.0 03/05

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

1

2

3
6
5

4

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

67

9

10

8

11

3

MAX MIN

°C °F

Dewpoint
WetBulb

5

RH390 V2.0 03/05

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4

2
3