User's Guide
Model 45320
Congratulations on your purchase of the Extech 45320 Hygro-Thermometer. The backlit
LCD displays temperature (in C or F) and relative humidity (%) simultaneously.
Maximum and minimum temperature and relative humidity readings can be stored and
recalled. Careful use of this meter will provide years of reliable service.
Backlit E.L. (Electro-Luminance) LCD
Measurement ranges
Temperature: 5.0 F to 122.0 F (-15.0 C to 49.9 C)
Relative Humidity: 25% to 95%
Temperature: ±1.8 F (1 C)
Sensor types
Temperature: Thermistor
Relative Humidity: ±5%
Relative Humidity: Resistive
Max/Min mode
Record/Recall highest and lowest temperature & relative
humidity readings
Over range indication
Dashes ‘------‘ will appear on the LCD for temperature or
relative humidity if a measurement is out of range
Low battery indication
Displayed battery symbol superimposed with an ‘X’
Power supply
Two (2) ‘AA’ 1.5V Batteries
Battery life
1 year (typical)
Meter: 5.25 x 2.75 x 1.00" (133 x 70 x 25mm)
Probe: 7” (178mm) length; 1” (25mm) width
Sensor cable length
39” (1m)
6.7 oz. (190g) with battery
Meter Description
Backlit LCD display
Push-button keypad
Probe in holder
Tilt stand and Battery compartment (rear)
Meter Operation
Meter Power
1. The 42530 is powered by two (2) ‘AA’ 1.5 V batteries.
2. Remove the protective decal that covers the LCD display by peeling it off by its corner.
3. Press the ON/OFF key to turn the meter on. If the display does not appear, check that
the batteries are installed and fresh. Note that a plastic tab, which must be removed
before use, may be installed in the battery compartment between one of the batteries
and the electrical contact.
4. Press the ON/OFF key again to turn the meter off.
1. Slide the Temperature – Relative Humidity Probe up from its holder and hold it in the
air. Do NOT immerse the probe in liquid. Allow time for the readings to stabilize. Note
that the sensor need not be removed from its holder to operate.
2. The temperature (upper left) and relative humidity (right) measurements will appear on
the LCD.
3. The ‘Comfort Level’ display (Wet, Dry, or Comfort icons) will appear at the center of the
LCD. ‘Wet’ indicates that humidity is above 70%. ‘Dry’ indicates that the humidity is
below 40%; ‘Comfort’ indicates that the humidity is between 40% and 70%.
4. Note that the meter has a tilt stand located on the upper back area. Flip up the tilt stand
from its bottom edge for convenient desktop use.
Display Backlight
1. Press the backlight key (light bulb icon) to activate the display backlight. The backlight
will turn off automatically after approx. 5 seconds to conserve battery life.
2. Note that the backlight feature drains the batteries at a faster rate than normally would
be the case without the backlight turned on.
Selecting oC/oF units of measure
The temperature unit selector switch is located inside the battery compartment (back of
meter). Open the compartment and slide the switch to the desired position ( C or F). The
LCD display will reflect the current selection.
Model 45320 Version 1.6 10/06
MAX / MIN Feature
When the meter is turned on it begins keeping track of the highest (Max) and lowest (Min)
temperature and relative humidity readings. To view these readings at any time, press the
MAX/MIN key.
The maximum temperature and humidity readings will appear along with the MAX display
icon. Press the MAX/MIN key again to view the minimum temperature and relative
humidity readings. The minimum temperature and humidity readings will appear along with
the MIN display icon.
Press MAX/MIN key again to exit this mode.
To Clear the MAX/MIN readings, press the CLEAR key once with the MAX or MIN value in
the display. The meter will clear the existing records and begin storing new MAX/MIN
records. Note that the MAX/MIN records are automatically cleared when the meter is
turned off.
Comfort Level Feature
The Comfort Level display (‘Wet’, ‘Dry’, or ‘Comfort’ icons) will appear at the center of the
For humidity measurements below 40%, the meter displays the ‘DRY’ icon. This region of
humidity can be harmful to furniture and other wood products where splitting and cracking
could occur after prolonged exposure. Electronic equipment is also at risk in this region
from static electricity.
For humidity measurements above 70%, the meter will display the ‘WET’ icon. Humidity
above 70% is not considered safe for dwellings or work areas where mold can form and
wood can swell and warp. In addition, sensitive objects such as artwork, musical
instruments, and paper documents can be damaged by high moisture.
Humidity between 40% and 70% is the most comfortable environment for people, furniture,
paper, artwork, etc. In this region the meter displays the ‘COMFORT’ icon.
Battery Replacement
When the low battery indicator appears (the letter ‘X’ over the battery symbol), replace the
two (2) 1.5V ‘AA’ batteries thusly:
Open the rear battery compartment by sliding the compartment cover to the right, replace
the batteries observing polarity, and close the compartment.
99 Washington Street
Melrose, MA 02176
Phone 781-665-1400
Toll Free 1-800-517-8431
Visit us at
Back to the Extech 45320 Product Info Page
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
FAX 781.665.0780 -
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