Extech Instruments RHT20 User manual

USER MANUAL
Humidity & Temperature Datalogger
Model RHT20

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Introduction
Congratulations on your purchase of this Temperature and Humidity datalogger. With this meter,
you can monitor and log data over long periods of time and then easily transfer the data to a pc for
viewing and evaluation. The LCD display provides current or Max/Min temperature, humidity and
time information. This device is shipped fully tested and calibrated and, with proper use, will
provide years of reliable service. Please visit our website (www.extech.com) to check for the latest
version and translations of this User Manual, Product Updates, Product Registration, and
Customer Support.
Meter Description
1 Record LED
2 Alarm LED
3 LCD Display
4 Temperature –Humidity display selection
5 MAX/MIN display selection
6 Battery Compartment (rear)
7 Temperature and Humidity sensors
8 USB PC port (bottom)
Display Description
Full battery symbol.
Weak battery symbol. Replace battery when this
appears. Battery life is more than 3 months.
DATE: Current date is displayed
TIME: Current time is displayed
Time and Date automatically swap every 10 sec.
MAX: Maximum value during a datalogging session is
displayed
MIN: Minimum value during a datalogging session is
displayed
REC: Recording in progress indicator
FULL: Memory is full indicator
%RH: Humidity value is displayed
°C: Celsius temperature units
°F: Fahrenheit temperature units

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Operation
The display and front panel buttons provide a means to view the status of the datalogger, observe
the current Temperature or Relative Humidity and to view the MAX and MIN values recorded during
a recording session. The datalogger setup conditions such as sample rate, temperature units and
alarm values are programmed via the provided software. Refer to the software Help File on the disk
for those procedures.
1. Press the MAX/MIN button to view the recorded Max and Min values with the time they were
recorded. If, while in this mode, no button is pressed for 40 seconds the display will
automatically return to the real time display.
2. The Time and Date display will automatically toggle every 10 seconds
3. When downloading the data to the PC, “-PC-” will be displayed on the LCD. After the download
is complete, the datalogger will display the last value recorded, but it will stop recording. The
logger needs to be re-set from the software to begin a new recording session.
4. The “REC” LED will flash at the programmed rate when the unit is datalogging.
5. Alarm function: When the measured value exceeds the programmed upper or lower limit and
the LED function is selected in the software, the ALM LED will flash one time per minute.
6. If “-LO-“ is displayed, the temperature and humidity sensors need attention.
7. The datalogger should be placed upright when in use.
8. If used in low temperature, high humidity environment, the datalogger should be placed upright
in a dry area to remove any condensation before downloading the data.
9. Battery life can be extended by leaving the datalogger connected to a pc.
10. Disabling the REC and ALM LED’s will extend battery life.
11. The LCD display will stop functioning at very low temperatures and will become active again
when the unit is returned to higher temperatures.
NOTE: The logger needs to be re-set from the software to begin a new recording session.
Combination Lock
The logger is supplied with a wall mount case and security combination lock. The
lock is shipped with a -0-0-0- code as viewed from the side with the alignment bar.
To change the code:
1. Press the release to open the lock (1)
2. Using a pointed object, press IN and HOLD the locking pin on the bottom of the
lock (2).
3. Set the new code (3) and release the locking pin

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Software Installation
This meter has the capability to connect to and communicate with a PC.
Check the software download page of the website www.extech.com/software for the latest
version of the PC software and its operating system compatibility.
Download, Unzip and install the software. Run ExtechInstaller.exe and then refer to the
instructions provided in the HELP Utility within the software program.
Maintenance
WARNING: To avoid electrical shock, disconnect the meter from any circuit and turn OFF
the meter before opening the case. Do not operate with an open case.
Battery Replacement
1. Remove the green protective cover by pushing the bottom of the meter until it slides through
the opening at the top.
2. Remove the two Phillips head screws that secure the battery compartment at the back of the
meter.
3. Open the battery compartment and replace the 3.6V lithium battery observing correct polarity.
4. Re-assemble the meter before use.
Safety: Please dispose of batteries responsibly; never dispose of batteries in a fire, batteries may
explode or leak. If the meter is not to be used for 60 days or more, remove the battery and store
separately.

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Specifications
Display Multi-function LCD
Measurement ranges 0 to 100% RH
-40 to 158°F , -40 to 70°C
Resolution 0.1°, 0.1RH
Maximum data points 16,350 Temperature and 16,350 Humidity values
Sample rate 1s to 24h selectable
Analysis software Check the software download page of the extech.com website for
the latest version of the PC software and its operating system
compatibility.
Open input indication "LO" appears on the LCD
Low battery indication Empty battery symbol appears on the LCD
Power supply 3.6V Lithium Battery
Battery life 3 months (approximately)
Operating Temperature -40 to 158°F, -40 to 70°C
Operating Humidity 0 to 100% RH
LCD Operating Temperature -13°F to 158°F (-25°C to 70°C)
Dimensions 3.7x1.9x1.2") (94.4x48.9x31.2mm)
Weight 3.2oz (90.7g)
Range
Accuracy
Relative Humidity
0 to 20% and 80 to 100%
±5.0%
20 to 40% and 60 to 80%
±3.5%
40 to 60%
±3.0%
Temperature
14 to 104°F
±1.8°F
-13 to 14°F and 104 to 158°F
±3.6°F
-40 to -13F
±8°F typical
-10 to 40°C
±1°C
-25 to -10°C and 40 to 70°C
±2°C
-40 to -25C
±4°C typical

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Two Year Warranty
Teledyne FLIR LLC warrants this Extech brand instrument to be free of defects in parts and workmanship for
two years from date of shipment (a six-month limited warranty applies to sensors and cables). To view the full
warranty text please visit: http://www.extech.com/support/warranties.
Calibration and Repair Services
Teledyne FLIR LLC offers calibration and repair services for the Extech brand products we sell. We
offer NIST traceable calibration for most of our products. Contact us for information on calibration
and repair availability, refer to the contact information below. Annual calibrations should be
performed to verify meter performance and accuracy. Product specifications are subject to change
without notice. Please visit our website for the most up-to-date product information:
www.extech.com.
Contact Customer Support
Customer Support Telephone List: https://support.flir.com/contact
Calibration, Repair, and Returns: [email protected]
Technical Support: https://support.flir.com
Copyright ©2021 Teledyne FLIR LLC
All rights reserved including the right of reproduction in whole or in part in any form
www.extech.com