Extech RH350 Operating Manual

User's Guide

SuperHeat Psychrometer

Models RH350 and RH355 (kit)

Introduction

Congratulations on your purchase of the Extech RH350 SuperHeat Psychrometer. This
device measures Differential Temperature (T1-T2, Air-T1, T1-DP), Humidity, Air
Temperature, Dew Point and Wet Bulb. Advanced features include built-in memory and
recall of up to 99 data points, Min/MAX/Average readings from the captured data, Data
Hold, selectable Auto Power Off, and an RS-232 interface for capturing readings to a PC
using optional 407752 software. Careful use of this meter will provide years of reliable
service.

Meter Description

1. Humidity Sensor & Air Temperature Sensor

2. Triple LCD Display

3. On/Off; Set Mode

4. Min/Max/Average; Reset Min/Max

5. Air, T1, Air-T1, Dew Point

6. T1 probe input

7. T2 probe input

8. T1-T2, T2, T1-Dew Point, Wet Bulb

9. Store Current Reading; Backlight

10. Hold; Recall Mode

11. RS232 port

Note: The battery compartment is located

on the rear of the instrument

Display Description

1. Air, T1, Air-T1, Dew Point, Low Battery

2. Temperature °C/°F

3. T2, T1-T2, T1-Dew Point, Wet Bulb

4. Temperature °C/°F

5. Date (month, day, year), Time (24 hour clock)

6. Memory Store/Recall Location

7. Relative Humidity %

8. Maximum, Minimum

9. Hold, Average

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Operation

Open the Protective Sensor Cap

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

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 right display along with the date
and time.

4. Air Temperature appears in the top left display.

5. Wet Bulb is in the lower left display.

6. Pressing the [T1
T1 temperature, Air-T1, and DP (Dew Point).

7. Pressing the [T2
T1-T2, T2, and T1-DP (Dew Point).

Selecting temperature units of measure (C/F)

When the meter is off, press and hold the [ON/OFF
enter setup mode. Momentarily press the [T1
display. Press the [MEM] button to toggle between C or F. Press the [T2
confirm the setting and return to normal operation.

Setting the Date/Time (24 hour clock)

When the meter is off, press and hold the [ON/OFF
enter setup mode. Press the [T1
in sequence. Press the [MEM] button to change the settings. After the Minute setting is
complete, press the [T2
operation.

Data Hold

Press the [REC
appear on the upper right-hand side of the display. Press the [REC
return to normal operation.

Minimum (MN) Maximum (MX) Average (AVG) Function

The MIN/MAX/Average mode allows the user to view only the lowest (MN), highest (MX) or
average readings. Press the [M
display is now showing the lowest humidity and temperature readings in memory. Press the

in

/AVRST] button again and MX appears on the display. The display is now showing the

[M

maximum humidity and temperature readings in memory. Press the [M
to display the average (AVG) readings in memory. To exit the MIN/MAX/AVG mode, press

in

/AVRST] button. To clear the current min/max/avg readings in memory, press and hold

the [M

in

the [M

/AVRST] button for more than two seconds.

T/DPSEL] button toggles the top left display between Air temperature,

▲WB] button toggles the lower left display between WB (Wet Bulb),

SET] button for more than one second to

T/DPSEL] button until “unit” appears in the

T/DPSEL] button to select Year, Month, Day, Hour and Minute

▲WB] button to confirm the date/time setting and return to normal

HOLD] button momentarily to freeze the displayed reading. The 'HLD' icon will

in

/AVRST] button once and MN appears on the display. The

SET] button for more than one second to

▲WB] button to

HOLD] button again to

in

/AVRST] button again

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Backlight Display

Press the [M

in

/AVRST] and [MEM] buttons together to turn on the backlight. It will remain on

for ten seconds.

Automatic Power OFF

With the meter off, press and hold down the [ON/OFF

SET] + [RECHOLD] buttons for more than

1 second to enter auto power off settings. Press the [MEM] button to select non-sleep (n) or
2, 5, 10, 20, 40 and 60 minutes autosleep. Press [T2

▲WB] to confirm the selection.

Manual Datalogging

Manual datalogging allows the user to store and recall up to 99 readings with the press of a
button.

1. Press the [MEM] button to manually store a single reading into memory. The display
will flash 3 times and the memory location number will be displayed below the humidity
reading.

2. To view stored readings, press and hold the [REC

HOLD] button for 2 seconds and

“RECALL” will blink next to the memory location number on the display.

3. Press the [MEM] button to manually increment through the stored readings.

4. Press [REC

5. Press [REC

Note: In RECALL mode, pressing the [M

HOLD] + [MEM] for more than 1 second to clear the memory.
HOLD] for more than 1 second to return to normal operation.

in

/AVRST] button for min/max/avg readings will auto

search the stored readings in memory and display the minimum, maximum and
average values of the stored readings.

Note: An infrared printer port is located on the side of the meter. This feature is used on more

advanced models and is not functional on this model.

Warranty

EXTECH INSTRUMENTS CORPORATION (A FLIR COMPANY) warrants this instrument to
be free of defects in parts and workmanship for one year from date of shipment (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 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.

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CALIBRATION

The following verification and calibration procedures require the 33% and 75% RH reference
bottles which are supplied with the Model RH355 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 a minimum of 10 minutes

3. Verify that the reading is within the accuracy specification

Relative Humidity Calibration (33% and 75%)

33% Calibration

1. Turn 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 [M
for 2 seconds to enter calibration mode.

5. “32.8%” (reading may vary depending on operating temperature) will flash on the
LCD screen. 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

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 [M

4. “75.3%” (reading may vary depending on operating temperature) 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: Frequently check the water level in the salt bottles. Both the 33% and 75%
bottles should be completely saturated with some water present. The bottles are
sealed and not refillable.

in

/AVRST] button, press and hold the [ON/OFFSET] button

SET] button will turn the meter off.

in

/AVRST] button for 2 seconds to enter the 75% calibration.

RS-232 PC Communications Interface

The meter is equipped with an RS-232 PC interface jack (3.5mm phono) for connection to
a PC. The cable to connect the meter to the PC is included in the optional 407752 data
acquisition kit. The kit includes Windows
store readings in a text file and display real-time measurements in a series of selectable
formats. For more information or specific operating instructions, refer to the User Guide
included with the 407752 kit or contact Extech Instruments.

TM

compatible software that allows the user to

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Specifications

Function Range and Resolution Accuracy

Humidity 0.0 to 100.0% RH
Temperature (air) -4.0 to 122.0oF (-20 to 50oC) ±1.8oF (±1oC)

Temperature (external K) -40 to 1832oF (-40 to 1000oC) ±(0.3% rdg + 1.8oF (1oC))

Display Triple LCD
Sensor Type Humidity: Precision capacitance sensor

Internal Temperature: Thermistor
External Temperature: K-Type Thermocouple

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)

Low Battery Indicator Yes
Overrange Indicator E2 (air) E5 (T1), E8 (T2)
Underrange Indicator E3 (air), E6 (T1), E9 (T2)

o

Operating Conditions -4 to 122
Storage Conditions -40 to 185

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
Battery Life Approx. 300 hours
Dimensions / Weight 9 x 2.2 x 1.7” (230 x 57 x 44mm); 5.3 oz. (153g )

±3% RH (10 to 90%)

@ 23°C

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 four (4)

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.

Support line [phone]

Copyright © 2008 Extech Instruments Corporation (a FLIR company)

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

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