How to Choose an Infrared Thermometer and Its Working Principle
How to Choose an Infrared Thermometer and Its Working Principle
1. Why Use an Infrared Thermometer?
Infrared thermometers utilize infrared technology to quickly and conveniently measure the surface temperature of objects without physical contact. By simply aiming at the target and pressing the trigger, temperature readings are displayed on an LCD screen. These devices are lightweight, compact, and easy to use, enabling reliable measurements of hot, hazardous, or hard-to-reach objects without contamination or damage. Infrared thermometers can take multiple readings per second, whereas contact thermometers may require several minutes for a single measurement.
2. How Does an Infrared Thermometer Work?
Infrared thermometers detect invisible infrared energy emitted by all objects above absolute zero. This energy is part of the electromagnetic spectrum, which ranges from radio waves to gamma rays. Infrared wavelengths lie between visible light and radio waves, typically spanning 0.7 to 1000 micrometers (µm), with 0.7–14 µm being the most common range for infrared thermometers
. The thermometer’s optical system focuses this radiation onto a detector (e.g., a thermopile), which converts it into an electrical signal. This signal is then processed and displayed as a temperature reading.
3. Ensuring Measurement Accuracy
Accurate temperature measurement depends on several factors:
Emissivity: This refers to an object’s ability to emit infrared energy. Since materials also reflect and transmit energy, the thermometer must be calibrated to measure only emitted radiation. Emissivity values range from 0 (perfect reflector) to 1 (perfect emitter, or blackbody). Adjustable emissivity settings or surface treatments (e.g., using black tape) can improve accuracy.
Distance-to-Spot Ratio (D:S): This ratio compares the distance from the thermometer to the target (D) and the diameter of the measurement area (S). A higher ratio (e.g., 12:1) allows accurate measurements of small targets from farther away.
Field of View: The target must fully cover the thermometer’s field of view. For precision, the object should be at least twice the size of the spot measured.
Environmental factors like steam, dust, or reflective surfaces (e.g., polished metal) can also affect accuracy. Avoid measuring through glass or on shiny metals without adjustments.
4. How to Use an Infrared Thermometer
To measure temperature, aim the thermometer at the object, press the trigger, and read the LCD display. Key considerations include:
Measuring only surface temperatures (internal temperatures cannot be detected).
Avoiding glass or reflective surfaces unless using an emissivity correction.
Scanning vertically/horizontally to locate hotspots.
Minimizing interference from steam, dust, or smoke.
Allowing the device to acclimate if exposed to sudden temperature changes (e.g., >20°C difference).
5. Common Applications
Infrared thermometers are widely used in:
Automotive: Diagnosing engine cylinders and cooling systems.
HVAC: Monitoring air stratification, furnace performance, and duct temperatures.
Electrical: Inspecting transformers, panels, and connections for faults.
Food Safety: Ensuring proper storage, cooking, and serving temperatures.
Industrial Maintenance: Assessing machinery, pipelines, and energy efficiency.
Key Takeaway
When selecting an infrared thermometer, prioritize emissivity adjustments, optical specifications (D:S ratio), and environmental suitability to ensure accurate, non-contact temperature measurements across diverse applications.