Extech Instruments RH355 User 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 for capturing readings to a PC using
HyperTerminal (cable sold separately). Careful use of this meter will provide years of
reliable service.

RH350/355 V1.7 11/04
2
Specifications
Function Range and Resolution Accuracy
Humidity 0.0 to 100.0% RH ±3% RH (10 to 90%)
@ 23°C
Temperature (air) -4.0 to 122.0oF (-20 to 50oC) ±1.8oF (±1oC)
Temperature (external) T1, T2 -328 to 2250oF (-200 to 1370oC) ±0.3% rdg or
±(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 122.0oF (-68 to 50oC) (calculated from RH and Air
temperature measurements)
Wet Bulb -6.88 to 122.0oF (-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)
Operating Conditions -4 to 122oF (-20 to 50oC); < 99% RH non-condensing
Storage Conditions -40 to 185oF (-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)
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

RH350/355 V1.7 11/04
3
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
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 [T1T/DPSEL]button toggles the top left display between Air temperature,
T1 temperature, Air-T1, and DP (Dew Point).
7. Pressing the [T2▲WB]button toggles the lower left display between WB (Wet Bulb),
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/OFFSET] button for more than one second to
enter setup mode. Momentarily press the [T1T/DPSEL]button until “unit” appears in the
display. Press the [MEM] button to toggle between C or F. Press the [T2▲WB]button to
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/OFFSET] button for more than one second to
enter setup mode. Press the [T1T/DPSEL]button to select Year, Month, Day, Hour and Minute
in sequence. Press the [MEM] button to change the settings. After the Minute setting is
complete, press the [T2▲WB]button to confirm the date/time setting and return to normal
operation.
Data Hold
Press the [RECHOLD]button momentarily to freeze the displayed reading. The 'HLD' icon will
appear on the upper right-hand side of the display. Press the [RECHOLD]button again to
return to normal operation.
1
2
3
4
5
6
7
8
9

RH350/355 V1.7 11/04
4
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 [Min/AVRST]button once and MN appears on the display. The
display is now showing the lowest humidity and temperature readings in memory. Press the
[Min/AVRST]button again and MX appears on the display. The display is now showing the
maximum humidity and temperature readings in memory. Press the [Min/AVRST]button again
to display the average (AVG) readings in memory. To exit the MIN/MAX/AVG mode, press
the [Min/AVRST]button. To clear the current min/max/avg readings in memory, press and hold
the [Min/AVRST] button for more than two seconds.
Backlight Display
Press the [Min/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/OFFSET]+[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 [RECHOLD]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 [RECHOLD]+[MEM] for more than 1 second to clear the memory.
5. Press [RECHOLD]for more than 1 second to return to normal operation.
Note: In RECALL mode, pressing the [Min/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.

RH350/355 V1.7 11/04
5
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 [Min/AVRST]button, press and hold the [ON/OFFSET]button
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/OFFSET]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 [Min/AVRST]button for 2 seconds to enter the 75% calibration.
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.

RH350/355 V1.7 11/04
6
RS-232 PC Communications Interface
RS-232 data format
Baud rate; 9600, Parity; none, Data bits; 8, Stop bits; 1, Flow control; none
RS-232 Connection
Connect the optional interface cable from the meter to the communications port of the PC.
Using Windows® Terminal or HyperTerminal program for PC Communication
The Terminal or the HyperTerminal program is included in all Windows® operating systems.
Typically it is located using the following path:
START Menu > Programs > Accessories > Communications > Terminal or HyperTerminal
When in the Terminal or HyperTerminal program, configure as follows:
1. In the Connection Description window, enter a name, select an icon and click OK.
2. In the Connect To window, select COM1 or COM2 (depending on which port is being
used) and click OK.
3. In the Port Settings window, select the following data format: Baud rate 9600, no
parity, 8 data bits, 1 stop bit, and no flow control. Click OK to enter the main
HyperTerminal window.
4. In the File Menu, select Properties > Settings > ASCII SETUP, select “echo typed
characters” and “Send line ends with line feeds”. Click OK twice to return to the main
HyperTerminal window.
Format
Txxx.xC:Hxx.x%:Txxx.xC:Txxx.xC:Txxxx.xC:Txxxx.xCLRCCRLF or
Txxx.xF:Hxx.x%:Txxx.xF:Txxx.xF:Txxxx.xF:Txxxx.xFLRCCRLF
Where: The 1st value is Air Temperature, the 2nd value is Humidity, the 3rd value is Dew
Point, the 4th value is Wet Bulb, the 5th value is T1, the 6th value is T2.
Format for error value: Exxn xx is error code, the unit is n
For example: if T1 is disconnected, then transmit:
Txxx.xC:Hxx.x%:Txxx.xC:Txxx.xC:TE04n:Txxxx.xCLRCCRLF or
Txxx.xF:Hxx.x%:Txxx.xF:Txxx.xF:TE04n:Txxxx.xFLRCCRLF
Error Codes
An error message will appear on the display if the meter fails an internal diagnostic test.
Note: Error messages E4 and E7 will not display on the LCD. They will be transmitted to the
PC via the RS-232 cable and viewed in HyperTerminal.
1. E2: Air temperature is over the range.
2. E3: Air temperature is below the range.
3. E4: T1 Thermocouple not plugged in
4. E5: T1 temperature is over the range.
5. E6: T1 temperature is below the range.
6. E7: T2 thermocouple not plugged in
7. E8: T2 temperature is over the range.
8. E9: T2 temperature is below the range.
9. E11: Temperature of isothermal block is over the range.
10. E12: Temperature of isothermal block is below the range.
11. E21~E23: Circuit error. Repair/replacement necessary
12. E25: Circuit error. If problem persists, repair/replacement necessary
13. E26: Circuit error. If problem persists, repair/replacement necessary

RH350/355 V1.7 11/04
7

Support line [phone]
Technical support: Extension 200; E-mail: [e-mail]
Repair & Returns: Extension 210; E-mail: [email protected]
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
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.
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 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.
Copyright ©2004 Extech Instruments Corporation.
All rights reserved including the right of reproduction in whole or in part in any form.