Extech Instruments 42540A User manual

User’s Manual
High Temperature InfraRed Thermometer
with Laser Pointer
MODEL 42540A
42540
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Introduction
Congratulations on your purchase of the Model 42540A IR Thermometer. The 42540A is capable of
non-contact (infrared) temperature measurements at the touch of a button. The built-in laser pointer
increases target accuracy while the backlit LCD and handy push-buttons combine for convenient,
ergonomic operation. This meter is shipped fully tested and calibrated and, with proper use, will
provide years of reliable service.
Safety
Use extreme caution when the laser pointer beam is on
Do not point the beam toward anyone's eye or allow
the beam to strike the eye from a reflective surface
Do not use the laser near explosive gases or in other
potentially explosive areas
Meter Description
1. Laser pointer beam
2. IR Sensor
3. Measurement Trigger
4. Battery and Switch Compartment
5. LCD Display
6. Push-buttons
7. Handle Grip
8. Temperature Units (ºC/ºF) Switch
9. Test Lock ON/OFF Switch
10. Alarm ON/OFF Switch
Note: There is a tripod mount on the bottom of the handle
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42540
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Operating Instructions
Basic IR Measurements
1. Hold the meter by its handle and point it toward the surface to be measured.
2. Pull and hold the trigger to turn the meter on and begin testing. The temperature reading, the
flashing ‘SCAN’ icon, the emissivity, and the unit of measure will appear. Note: Replace the 9V
battery if the display does not switch on.
3. Release the Trigger and the reading will hold for approximately 7 seconds (HOLD will appear on
the LCD) after which the meter will automatically shut off. The only exception to this is if the
TEST LOCK switch is set to ON.
Note: Select the temperature units (ºF/ºC) using the top switch inside the battery compartment
Backlight/Laser Pointer
1. While pulling the Trigger, push the backlight/laser button once to turn on the backlight.
2. Press it again to turn on the laser pointer. When the laser is ON the laser icon will appear in
the LCD.
3. Press the laser button to turn the backlight off.
4. Pressing it again turns the laser off.
Note: Backlight and Laser settings will be retained after the meter powers down.
Over-range Indication
If the temperature measurement exceeds the specified temperature range, the thermometer will
display dashes in place of a temperature reading.

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The MODE button options
The MODE button is used to access the programming functions of the instrument. The selected
function is displayed on the bottom line of the LCD. Each parameter is listed below with an
explanation for its use. Press the MODE button to step from one parameter to the next.
EMS (Emissivity Value)
To change the emissivity value, use the UP and DOWN arrows (the range is 0.10 to 1.00).
The current emissivity setting is always shown at the top of the LCD display. A setting of
0.95 covers about 90% of all applications and, when in doubt, should be set as such.
Emissivity is discussed in a dedicated section of this manual.
MAX (Maximum function)
In the MAX mode, only the highest reading encountered in the current measurement
session is displayed
MIN (Minimum function)
In the MIN mode, only the lowest reading is displayed
DIF (Max minus Min value)
In the DIF mode, the MAX less the MIN is displayed.
AVG (Average value)
In the AVG mode, all of the readings in the current measurement session are averaged
and the value is displayed.
HAL (High Alarm setting)
The temperature that, when exceeded, causes the audible/visual alarm to trip.
LAL (Low Alarm setting)
The temperature that, when exceeded high to low, causes the audible/visual alarm to trip.
High and Low Alarm Feature
The Model 42540a has an alarm feature whereas a High Alarm setting and a Low Alarm setting can
be programmed by the user. When either Alarm point is reached the meter will alert the user via an
audible beep and LCD display icon. Follow the steps below:
1. Press the MODE button until the HAL (High Alarm) parameter is displayed. Use the UP and
DOWN arrow keys to set the desired High Alarm temperature setting.
2. Press the MODE button until the LAL (Low Alarm) parameter is displayed. Use the UP and
DOWN arrow keys to set the desired Low Alarm temperature setting.
3. When an alarm limit is reached, the audible alarm will sound and the display icon HIGH or
LOW will appear on the LCD.
4. Note that if the bottom switch (located in the battery compartment) is set to OFF, the audible
alarm will be disabled.

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Battery Replacement
When the battery symbol appears empty or close to empty, replace the meter’s
9V battery. The battery compartment is located behind the panel that surrounds the
meter’s trigger. The panel can be pried open near the trigger and folded down as
shown in the diagram. Replace the 9V battery and close the battery compartment
cover.
IR Measurement Notes
1. The object under test should be larger than the spot (target) size calculated by the field of view
diagram (printed on the side of the meter and in this guide).
2. Before measuring, be sure to clean surfaces that are covered with frost, oil, grime, etc.
3. If an object's surface is highly reflective, apply masking tape or flat black paint to the surface
before measuring. Allow time for the paint or tape to adjust to the temperature of the surface it is
covering.
4. Measurements through transparent surfaces such as glass may not be accurate.
5. Steam, dust, smoke, etc. can obscure measurements.
6. The meter automatically compensates for deviations in ambient temperature. However, it can
take up to 30 minutes for the meter to adjust to extremely wide changes.
7. To find a hot spot, aim the meter outside the area of interest then scan across (in an up and
down motion) until the hot spot is located.
Field of View
The meter’s field of view is 16:1. For example, if the meter is 16 inches from the target (spot), the
diameter of the target must be at least 1 inch. Other distances are shown in the field of view
diagram. Note that measurements should normally be made as close as possible to the device
under test. The meter can measure from moderate distances but the measurement may be affected
by external sources of light. In addition, the spot size may be so large that it encompasses surface
areas not intended to be measured.

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Emissivity and IR Measurement Theory
IR Thermometers measure the surface temperature of an object. The thermometer’s optics sense
emitted, reflected, and transmitted energy. The thermometer’s electronics translate the information
into a temperature reading which is then displayed on the LCD.
The amount of IR energy emitted by an object is proportional to an object's temperature and its
ability to emit energy. This ability is known as emissivity and is based upon the material of the object
and its surface finish. Emissivity values range from 0.1 for a very reflective object to 1.00 for a flat
black finish. For the Model 42540a, the emissivity is adjustable from 0.1 to 1.00. Most organic
materials and painted or oxidized surfaces have an emissivity factor of 0.95. When in doubt, set the
emissivity to 0.95.
Emissivity Factors for Common Materials
Material under test Emissivity Material under test Emissivity
Asphalt 0.90 to 0.98 Cloth (black) 0.98
Concrete 0.94 Skin (human) 0.98
Cement 0.96 Leather 0.75 to 0.80
Sand 0.90 Charcoal (powder) 0.96
Soil 0.92 to 0.96 Lacquer 0.80 to 0.95
Water 0.92 to 0.96 Lacquer (matt) 0.97
Ice 0.96 to 0.98 Rubber (black) 0.94
Snow 0.83 Plastic 0.85 to 0.95
Glass 0.90 to 0.95 Timber 0.90
Ceramic 0.90 to 0.94 Paper 0.70 to 0.94
Marble 0.94 Chromium Oxides 0.81
Plaster 0.80 to 0.90 Copper Oxides 0.78
Mortar 0.89 to 0.91 Iron Oxides 0.78 to 0.82
Brick 0.93 to 0.96 Textiles 0.90

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Specifications
Infrared Thermometer Specifications
Range / Resolution -58 to 1400oF (-50 to 760oC) 0.1oC/F over entire range
Accuracy
(of reading)
± 2% of reading or 4oF (2oC) whichever is greater < 932oF (500oC)
± (2.5% of reading + 5o) > 932oF (500oC)
Note: Accuracy is specified for the following ambient temperature range:
64 to 82°F (18 to 28°C)
Emissivity Adjustable from 0.1 to 1.00 (0.95 default value)
Field of View D/S = Approx. 16:1 ratio (D = distance, S = spot)
Laser power Less than 1mW
Spectral response 6 to 14 m (wavelength)
General Specifications
Display 4½ digit backlit LCD display with function indicators
Display rate 1 second approx.
Operating Temperature 32°F to 122°F (0°C to 50°C)
Operating Humidity Max. 80% RH.
Power Supply 9V battery
Automatic Power Off Approx. 6 seconds after the trigger is released
Safety compliance CE
Weight 10.2 oz. / 290g
Dimensions 3.9 x 2.2 x 9.0” (100 x 56 x 230mm)

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Warranty
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