Extech Instruments RHT35 User manual

USER MANUAL
USB Multi-Function Datalogger
Model RHT35
Additional User Manual Translations available at www.extech.com

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Introduction
Thank you for selecting the Extech multi-function, easy-to-use, portable USB datalogger. The
RHT35 offers temperature, humidity, and pressure logging.
The USB datalogger can be configured and customized by the user by plugging it into a PC USB
port, following the on-screen prompts, and making selections on the supplied ‘PDF Logger
Configuration Tool’.
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.
Features
•Plug-and-play datalogger with USB connector. No USB driver required
•User configurable datalogging settings via supplied PC software tool
•Advanced Datalogger functions including delayed start, high/low alarms, bookmarking,
and password protection
•Automatically generate PDF and Microsoft®Excel®datalog reports
•High accuracy thermistor temperature sensor, capacitive humidity sensor, MEMS
pressure sensor
•Compact light-weight design
•Large LCD for easy viewing
•Dual color (red and green) LED status indicator for datalogger progress, PC connection
status, and high/low alarms
•Large memory capacity: 48,000 readings
Descriptions
Datalogger Description
1. Protective cover and swivel stand (remove to expose
USB plug). Rotate the cover for best desktop viewing
angle.
2. LCD display. Refer to the Display Description later in
this section.
3. Status LED indicator (red/green). Refer to the Status
LED Indicator Description later in this section.
4. MAX-MIN button. Refer to the Button Descriptions
later in this section.
5. Sensors (thermistor internal air temperature,
capacitive RH, MEMS pressure).
6. MARK/Battery life button. Refer to the Button Descriptions later in this section.
7. Power and Datalog Start/Stop button. Refer to the Button Descriptions later in this section.

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8. USB plug.
9. Battery compartment (CR2032 x 2) on rear.
10. Wall hanging mount (rear). Mounting screw
supplied.
Button Descriptions
POWER button. Short press to power ON or OFF. Note that the datalogger cannot be
switched OFF while datalogging is in progress.
START/STOP button (same physical button as the Power button above). Press and hold for
5 seconds to start or stop the datalogger. Note that the datalogger will not start unless it has
been configured using the ‘PDF Logger Configuration Tool.exe’ program as described later in this
user manual.
Maximum-Minimum Reading button. At any time, short press to step through the
highest (MX) and lowest (MIN) readings recorded in the current datalogging session.
Bookmark button. Manually place a time-stamped ‘bookmark’ in the datalog report by
pressing and holding the button until the displayed measurement flashes 3 times. Up to eight (8)
bookmarks can be saved.
Battery Status Note: Short press the MARK button to display the approximate number of days
remaining for the battery life.

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Display (LCD) Description
oFoCTemperature unit of measure as programmed by the user
RH% Displayed when showing Relative Humidity reading
T1 Represents the internal sensor (air) temperature
HHigh Alarm triggered
LLow Alarm triggered
REC REC flashes once per second when actively datalogging. When logger is
programmed with a ‘Start Delay’, REC is displayed but does not flash until after
the delay time has elapsed and the logging begins
Battery icon flashes once per second when battery level is critically low
MX Displayed when the maximum recorded reading is selected with the MAX-MIN
button
MN Displayed when the minimum recorded reading is selected with the MAX-MIN
button
inHg Displayed when showing pressure in imperial units
hpa Displayed when showing pressure in metric units
LED Status Indicator Description
The dual color (red/green) LED status indicator is located to the right of the LCD.
•Red (Alarm): Blinks red every 10 seconds in an alarm condition
•Green (Datalogging): Blinks green every 10 seconds while actively datalogging
•Green (PC connection): Glows steady green while establishing connection to PC

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PDF Logger Configuration Tool
Connect the datalogger to PC USB port. The PC will prompt to view files. Open the ‘PDF Logger
Configuration Tool’ from the list of available files. Refer to the Operation Section for additional
details on this tool:
1. CONVERT TO EXCEL: Create a spreadsheet report of the logged data
2. CONVERT TO PDF: Create a PDF report and a trend graph of the logged data
3. CONFIGURATION: Click to configure the logger
4. LANGUAGE SELECTION
5. SAMPLING RATE: Datalogger recording interval
6. START DELAY: Delay period from when START is pressed and datalogging begins
7. UNIT: Imperial or Metric unit selection
8. PASSWORD: Select a 16-character password for tamper protection
9. COMPANY NAME: 20-Character user label for inclusion in logging report
10. SAVE: Press SAVE to confirm the configuration
11. CANCEL: Abort the configuration
12. MANUAL: Open the supplied PDF User Manual
13. ALARM LIMIT: Select the Temperature, %RH, and Pressure low/high alarm limits
14. ALARM DELAY: Datalogger will ignore alarms for the programmed period of time
15. ALARM TYPE: Select Alarm mode
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Operation
NOTES:
1. Adobe Reader® software is required.
2. Ensure the logger is at room temperature before inserting it into a PC port.
3. The executable file for programming is named “PDF Logger Configuration Tool”.
4. A datalogging session cannot start until the datalogger is properly configured.
Configuring the RHT35 for a Datalogging session
At any time before logging is started, the logger can be programmed and re-programmed. The
previous logging session will be deleted once a new session is started.
1. Connect the data logger to a PC via the USB port. The logger will switch ON
automatically. Note that a short press of the power button will also power the logger.
2. The LED will glow green while a connection
with computer is being established.
3. An AutoPlay prompt will appear on the PC
when communication is established.
4. Click on ‘Open folder to view files’ to see the
available files.
5. Open the program "PDF Logger Configuration
Tool.exe".
6. The default language is English; select German, French, Italian, Spanish, or Portuguese as
desired. The generated logging report format will match the language selected.
7. To review the User Manual, click ‘Manual’ to open the User Manual PDF file.
8. The parameters needed to configure the datalogger for logging are defined below. Refer
to the earlier screen shot of the ‘PDF Logger Configuration Tool’ window for reference:
•Datalog Sampling Rate
Select the datalogging sampling rate (recording interval) from 30 seconds ~ 120
minutes. The default setting is 30 seconds.
•Datalog Start Delay
Select a period of time that must elapse before recording can begin after the
Start/Stop button is pressed (select from 0 min to 24 hours). The default setting is
0 minutes.
•Unit of Measurement
Select the Metric or Imperial unit of measurement. When metric is selected the
readings display in °C for temperature and hpa for pressure. When imperial is selected
the readings display oF for temperature and inHg for pressure. The default setting in
Metric.
•Alarm Delay
The preset alarm delay time for the Single Event Alarm mode is always zero.
The adjustable delay time range for the Cumulative Alarm is 5 ~ 120 minutes.

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•Alarm Modes
Single Event Alarm mode: The LED immediately starts flashing red every 10 seconds
when the measured value exceeds the alarm threshold.
Cumulative Alarm mode: The LED begins flashing red only after the average value
exceeds the alarm threshold and also after any programmed Alarm Delay time. See
Alarm Delay parameter above.
Alarm Disable (default): Alarm function disabled.
Alarm Note: The LED will continue flashing red every 10 seconds (once it is triggered by
an alarm) even when the measurement later returns to the normal range. To stop the
LED alarm, plug the logger into the PC USB port to generate a report, or power off the
logger (short press of the power button while it is not connected to the PC).
•Alarm Limits
Select the alarm threshold ranges for air temperature, %RH, or pressure. For example,
if the temperature range is set to 2.0~8.0 oC, when the measurement falls below 2oC or
exceeds 8 oC the LED will flash red every 10 seconds.
Note: If an alarm occurs between two logging points, the logged data will not show the
alarm but the LED may still flash red every 10 seconds, especially in Single Event alarm
mode. If desired, use the Cumulative Alarm mode to minimize this effect.
•Password
A 16 alphanumeric character (max.) password may be used to prevent unauthorized
re-programming.
•User Company Name
Input a company name to be included on the log report (20 characters max.).
•A Note On Time Zones
The logger automatically synchronizes the time zone with the connected PC when
‘SAVE’ is selected. Note: Time zone changes occurring during logging are not taken into
account.
Once all the programming is complete, press ‘SAVE’ to confirm the settings. Close the setup
window, remove the logger from the PC USB port, and start datalogging as described in the
next section.

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Start Datalogging
1. Configure the logger as previously described and then hold the Start/Stop button
for 5 seconds to start logging.
2. Measurements update on the display every 10 seconds. The temperature, %RH, and
pressure measurements toggle every 5 seconds.
3. If the logger is programmed with a Start Delay: After pressing and holding the Start/Stop
button for 5 seconds to start logging, REC will appear on the LCD but will not flash until
the delay time has elapsed and logging has begun.
4. When the datalogger is successfully running, the LED flashes green every 10 seconds (as
long as there is no alarm).
Monitoring Alarms While Datalogging
The LED will flash RED every 10 seconds when there is an alarm. The display also shows ‘L’
for low alarm and ‘H’ for high alarm. To stop the LED from flashing red, plug the logger into a
PC, or power off (short press of the power button).
Placing ‘Bookmarks’ While Datalogging
To place a bookmark manually during datalogging, press and hold the MARK button until the
measured reading flashes 3 times. Up to eight (8) bookmarks can be placed; the bookmarks
will appear in the logging report.
MAX-MIN Readings
Short press the MAX-MIN button to step through the highest (MX) and lowest (MN) readings
stored in memory.
Checking Battery Status
At any time, short press the MARK button to view the approximate number of days
remaining for battery life. If battery power is critically low, the battery icon will blink once
per second on the LCD display.
Downloading Logged Data (PDF and Spreadsheet Datalog Reports)
1. Press and hold the Start/Stop button for 5 seconds to stop the datalogger.
2. Plug the logger into the PC USB port (this also stops the datalogger).
3. Open the ‘PDF logger Configuration tool’ from the list of available files.
4. Choose ‘Convert to PDF’ or ‘Convert to Excel’ to generate a report.
5. Select the PC file location where the report is to be saved.
6. The PDF report includes the recorded data, bookmarks, and a trend graph. The
spreadsheet report contains the same data as the PDF report minus the trend graph.

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Specifications
Display (LCD) 5-digit LCD with multi-function indicators
Status indicator (LED) Dual color multi-purpose LED (red/green) for active logging,
alarms, and PC connection status
Temperature Sensors NTC Thermistors
Temperature Range -30 ~ 70oC (-22 ~ 158oF)
Temperature Resolution 0.1oC/oF
Temperature Accuracy ±0.5oC (0.9oF)
Humidity Sensor Capacitive (Relative Humidity)
Humidity Range 0.1 ~ 99.9%RH
Humidity Resolution 0.1%RH
Humidity Accuracy ±3% at 25oC (10 ~ 90%RH), ±5% all other ranges
Barometric Pressure Sensor MEMS
Barometric Pressure Range 300 ~ 1100 hpa (8.9 ~ 32.5 inHg)
Barometric Pressure Resolution 1 hpa (0.1 inHg)
Barometric Pressure Accuracy ±3hPa (0 ~ 60oC); ±5hPa (-20 ~ 0oC); all other ranges
unspecified
Logger Type Re-usable
Datalogger Capacity 16,000 humidity; 16,000 temp.; 16,000 barometric pressure
Sampling Intervals 30 seconds and 5, 10, 30, 60, 90, 120 minutes
Start Delay Time 0, 5, 30, 45, 60, 90, 120 minutes, and 24 hours
Alarm Ranges Temp: -30~70oC (-22~158oF); Humidity: 1 to 99%RH
Alarm Delay (inhibit) 0, 5, 30, 45, 60, 90, 120 minutes
Alarm Types Single Event, Cumulative, and Disable
Operation Buttons Power/Start-Stop, MARK, MAX-MIN
Operating temperature -30~70oC (-22~158oF) for logging; Allow logger to return to
room temperature before connecting to PC
Operating Relative Humidity < 80% RH
Storage Temperature -40~85oC (-40~185oF)
Storage Humidity < 90% RH
Dimensions 80 (L) x 43 (W) x 2.5 (D) mm (3.2 x 1.7 x 0.1”)
Weight 90g (3.2 oz.)
Battery Two (2) 3.0V CR2032 batteries (pre-installed)
Battery Life Three (3) months
Safety Compliance CE
Warranty One Year

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Maintenance
Battery Replacement
The battery compartment is located on the back of the datalogger as shown in the Descriptions
section. When the battery symbol flashes on the display, replace the batteries promptly.
1. Using a large coin, rotate the battery compartment lid clockwise approximately one
quarter turn to open the compartment
2. Replace the two (2) CR2032 batteries with positive (+) side facing up
3. Replace the battery compartment lid and turn counterclockwise to secure it
4. Dispose of batteries in accordance with country, state, and local regulations
Never dispose of used batteries or rechargeable batteries in household waste.
As consumers, users are legally required to take used batteries to appropriate
collection sites, the retail store where the batteries were purchased, or wherever
batteries are sold.
Disposal: Do not dispose of this instrument in household waste. The user is obligated to
take end-of-life devices to a designated collection point for the disposal of electrical and
electronic equipment.
Battery Status Check
To check the approximate number of days of battery life remaining, short press the MARK button.
The display will show the number of days and the ‘d’ for days (XXd).
Cleaning
Wipe the datalogger with a damp cloth, do not use solvents or abrasives as these may damage
the datalogger finish and display lens.
Error Display Codes
ERROR CAUSE SOLUTION
E02 Measured value below specified range Operate in the specified range
E03 Measured value above specified range Operate in the specified range
E04 Temperature error Contact Extech for service
E11 Humidity calibration failed Contact Extech for service
E31 Microprocessor failed Contact Extech for service
E33 Humidity measurement error Contact Extech for service
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