Fluke 561 Infrared Thermometer Optics 12/1 -40 to +550 °C 2558118 User Manual

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Infrared thermometers measure the surface temperature of an opaque object. The Thermometer’s optics 
sense infrared energy, which is collected and focused onto a detector. The Thermometer’s electronics then 
translate the information into a displayed temperature reading which appears on the display. The laser is 
used for aiming purposes only.  

The Thermometer turns on when you press the trigger. The Thermometer turns off when no activity is 
detected for 7 seconds. 

To measure temperature, aim the Thermometer at the target, pull and hold the trigger. Release the trigger 
to hold a temperature reading.  

Be sure to consider distance-to-spot size ratio and field of view. The laser is used for aiming only.  

To find a hot or cold spot, aim the Thermometer outside the target area. Then, slowly scan across the area 
with an up and down motion until you locate the hot or cold spot. See Figure 4. 

 

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As the distance (D) from the target being measured increases, the spot size (S) of the area measured by the 
unit becomes larger. The spot sizes indicates 90 % encircled energy. The maximum D:S is obtained when 
the Thermometer is 900 mm (36 in) from the target resulting in a spot size of 75 mm (3 in). See Figure 5.