Extech RH305 Instruction Manual

User's Guide

Digital Psychrometer
Models RH300 and RH305 (kit)

ON/OFF

HOLD

T/DP

/WB

T1

T2

oo

C/ F

RESET

RESET

MX/MN

MX/MN

Introduction

Congratulations on your purchase of the Extech RH300 Digital Psychrometer. This device
measures Humidity, Air Temperature, Dew Point temperature and Wet Bulb temperature.
Advanced features include External Temperature Measurement (with optional probe), Data
Hold, selectable Auto Power Off, and MAX/MIN/Average 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 ±3% RH (10 to 90%) @ 23oC
Temperature (internal) -4.0 to 122.0oF (-20 to 50oC) ±1.8oF (±1oC)
Temperature (external) -4.0 to 158.0oF (-20 to 70oC) ±1.8oF (±1oC)

Display Triple LCD
Sensor Type Humidity: Precision capacitance sensor

Temperature: Thermistor

Response Time 60 seconds typical
Dew Point -90.4 to 122.0

o

F (-68 to 50oC) (calculated from RH and Air

temperature measurements)

o

Wet Bulb -6.88 to 122.0

F (-21.6 to 50oC) (calculated from RH and Air

temperature measurements)

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 2 x 1.5V ‘AAA’ batteries
Battery Life Approx. 80 hours
Dimensions / Weight 7 x 1.9 x 1” (178.5 x 48.8 x 25.2mm); 4.9 oz. (140g)

Meter Description

1. Humidity Sensor & Air Temperature Sensor

2. Triple LCD Display

3. ON/OFF button

4. T1-T2/Dew Point/T1 button

5. °F/°C select

6. MIN/MAX/RESET button

7. T2-DP/Wet Bulb/T2 button

8. HOLD button

9. T2 Probe Jack

Note: The battery compartment is located
on the rear of the instrument

1

9

2

/WB

8

7

6

3

ON/OFF

HOLD

T/DP

4

5

2

T2

T1

RESET

oo

MX/MN

C/ F

RH300 V1.4 11/04

Display Description

1. Relative Humidity %

2. T1

3. T1-T2

4. Dew Point

5. Wet Bulb

6. T2-Dew Point

7. °C/°F

8. T2

9. Maximum

10. Minimum

11. Low Battery/Hold

Operation

11

1

2

3

4

6

5

10

9

8

7

Open the Protective Sensor Cap

CLOSE OPEN

Twist the protective sensor cap, located at the top of
the meter, counter-clockwise a quarter of a turn to
expose the sensor

Plug in the optional external temperature probe (if
needed).

Turn Power ON or OFF

Press the ON/OFF button to turn power on or off. The meter will perform a short self-test
when turned on.

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 button toggles the lower left
display between T1-T2 (internal temperature-

T/DP

T1

external temperature), DP (Dew Point), and T1
(internal temperature).

5. Pressing the button toggles the lower right
display between T2-DP (external temperature-

/WB

T2

Dew Point), WB (Wet Bulb), and T2 (external
temperature).

Note: If the external probe is not connected, T1-T2, T2-DP, and T2 measurements will not
be displayed.

Selecting temperature units of measure (C/F)

Press and hold the

oC/o

F button momentarily to toggle the temperature units.

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RH300 V1.4 11/04

Wet Bulb and Dew Point measurements

1. To read the Wet Bulb measurement, press the button until the symbol Wb
appears in the lower right display. Note: T2 will not be displayed unless the external

/WB

T2

probe is connected.

2. Wet Bulb temperature is now displayed.

3. To read the Dew Point measurement, press the button until the symbol DP
appears in the lower left display .

T/DP

T1

4. Dew Point temperature is now displayed.

Minimum (MIN) Maximum (MAX) Function

The MIN/MAX mode allows the user to view only the lowest (MIN) or highest (MAX)
readings. Press the button once and MIN appears on the display. The display is
now showing the lowest humidity and temperature reading in memory. Press the

RESET
MX/MN

RESET
MX/MN

button again and MAX appears on the display. The display is now showing the maximum
humidity and temperature readings in memory. To exit the MIN/MAX mode, press the
button again and the MIN and MAX icons disappear. To clear the current min/max
readings in memory, press and hold the button for more than two seconds.

RESET
MX/MN

Data Hold

Press the HOLD button momentarily to freeze the displayed reading. The 'HLD' icon will
appear on the upper right-hand side of the display. Press the HOLD button again to return
to normal operation.

Automatic Power OFF

The meter automatically shuts off after a programmed period of time. The default time is 10
minutes. To program the time period, press down the HOLD button while turning the meter
on. Continue to hold down both buttons and the meter will cycle through the selectable
power-off times: n, 2, 5, 10, 20, 40 or 60 minutes. “n” disables the auto power off function.
When the desired power-off time appears in the display, release both buttons to select the
time and return to normal operation.

Error Messages

An error message will appear on the display if the meter fails an internal diagnostic test.

1. ER1: Relative Humidity failure. Repair/replacement is necessary.

2. ER2: Internal temperature failure. Repair/replacement necessary.

3. ER3: Reference resistance failure. Repair/replacement necessary.

4. ER4: Internal temperature is out of range.

5. ER5: External temperature is out of range.

RESET
MX/MN

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RH300 V1.4 11/04

CALIBRATION

The following verification and calibration procedures require the 33% and 75% RH reference
bottles which are supplied with the Model RH305 kit.

Accuracy Verification

Checking the 33% or 75% RH Calibration

1. Insert meter’s sensor into the 33% or 75% salt reference bottle

2. Check the reading after 10 minutes

3. Verify that the reading is within the accuracy specification

Relative Humidity Calibration (33% and 75%)

33% Calibration

1. Ensure that “DP” and “WB” appear in the bottom displays before tu rning the meter
OFF.

2. Insert the meter sensor into the 33% salt reference bottle.

3. Allow the meter one hour to stabilize.

4. While holding down the °C/°F button, press and hold the ON/OFF button for 2 seconds
to enter calibration mode.

5. “32.8%” will flash on the LCD screen and “DP” and “WB” will display “_ _ _ _”. After 30
minutes, the flashing will stop to indicate that the 33% calibration is complete. Note: To
exit from the calibration procedure before completion, pressing the ON/OFF button will
turn the meter off.

6. Proceed to the 75% Calibration below.

75% Calibration

1. Insert the meter sensor into the 75% salt reference bottle.

2. Allow the meter one hour to stabilize.

3. Press and hold the button for 2 seconds to enter the 75% calibration.

4. “75.3%” will flash on the LCD. After 30 minutes, the flashing will stop to indicate that
the 75% calibration is complete.

5. Turn power off. Calibration is now complete.

Note: If the salt at the bottom of the calibration bottles appears dry, the bottles should be
replaced.

RESET

RESET

MX/MN

MX/MN

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RH300 V1.4 11/04

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 symbol will appear on the LCD. Replace the two
(2) 1.5 ‘AAA’ batteries by removing the rear battery compartment cover and accessing the
battery compartment. Observe polarity when placing the batteries in the compartment.
Ensure that the compartment cover is securely fastened when finished.

Warranty

EXTECH INSTRUMENTS CORPORATION warrants the basic instrument to be free of
defects in parts and workmanship for one year from date of shipment (a six month limited
warranty applies on 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] EXTENSION 210 for authorization or visit www.extech.com for
more 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 appl y
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 disclaims any implied warranties or merchantability or fitness for a specific
purpose and will 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
above is inclusive and no other warranty, whether written or oral, is expressed or implied.

All rights reserved including the right of reproduction in whole or in part in any form.

Technical support: Extension 200; E-mail: [e-mail]

Repair & Returns: Extension 210; E-mail: [e-mail]

Product specifications subject to change without notice

For the latest version of this User’s Guide, Software updates, and other

up-to-the-minute product information, visit our website: www.extech.com

Support line [phone]

Copyright © 2004 Extech Instruments Corporation.

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RH300 V1.4 11/04