Analysis of the usage skills of infrared thermometer

The use skills of infrared thermometer (infrared thermal imager/spot thermometer) directly affect the measurement accuracy and efficiency. The following is a systematic analysis based on its working principle and common problems:
I. Core parameter setting skills
1. Emissivity (ε) calibration
Principle: The ability of the surface of an object to emit infrared radiation (ε=0~1), the default value is usually 0.95 (for non-metallic materials).
Tips:
The emissivity of the metal surface needs to be reduced (such as polished aluminum ε=0.1~0.3, aluminum oxide ε=0.8);
The tape method can be used for testing: stick black tape (ε≈0.95) on the surface of the object to be measured, compare the temperature difference between the tape and the surrounding area, and reverse the true emissivity.
2. Ambient temperature compensation
Applicable scenarios: When the temperature difference between the ambient temperature and the object to be measured exceeds 10℃.
Operation:
Enable the ambient temperature compensation function (some high-end devices automatically compensate);
Manually enter the ambient temperature (through a built-in sensor or an external probe).
2. Measurement distance and angle control
1. D:S (distance coefficient ratio) matching
Definition: The ratio of the distance between the thermometer and the target (D) and the spot diameter (S). For example, D:S=30:1 means that the spot diameter at 1 meter is about 3.3cm.
Tips:
Ensure that the target size is ≥ 2 times the spot diameter to avoid background radiation interference;
For small targets (such as electronic components), give priority to devices with a high D:S ratio (such as 100:1).
2. Incident angle control
Optimal angle: perpendicular to the measured surface (0°), allowable deviation ≤30°;
Correction method: When the angle deviates, it needs to be corrected according to the formula (temperature = measured value / (cosθ)), or use a device with angle compensation function.
3. Environmental interference response strategy
1. Reflection radiation suppression
Problem: Reflection sources around high-temperature objects (such as furnaces and flames) will cause the measured value to be higher.
Solution:
Isolate the reflection source with a baffle;
Choose a short-wavelength (<3μm) thermometer (not sensitive to reflection).
2. Ambient humidity and dust
Influence: When humidity > 80% or dust concentration is high, the infrared signal attenuates.
Measures:
Use a thermometer with a purge function;
Shorten the measurement distance to within 2 meters.
IV. Application skills for special scenarios
1. Transparent/translucent materials
Glass: Low emissivity (ε≈0.85), requires tape or special mode;
Plastic film: requires heating to a stable state before measurement.
2. Moving target
Skills:
Choose a high-speed response device (response time < 50ms);
Predict the motion trajectory and aim at the target in advance.
3. Low-temperature measurement (<-50℃)
Note: The emissivity changes significantly at low temperatures, and it is recommended to use liquid nitrogen for calibration.
5. Data recording and analysis
Trend analysis:
Measure the same position regularly to establish a temperature baseline;
Use software to generate a thermal map (applicable to thermal imagers) to quickly locate abnormal areas.
Fault prediction:
When the motor bearing temperature suddenly rises > 10℃, it is necessary to stop the machine for inspection;
The temperature difference of the cable connector > 5℃ indicates poor contact.
6. Maintenance and calibration
Lens cleaning:
Wipe with anhydrous alcohol to avoid scratches;
Do not touch the lens directly with your hands.
Calibration cycle:
Send to a professional organization for calibration every year (once every 6 months when high accuracy requirements);
Use a blackbody furnace for verification (the error should be <±1% or ±1℃).
VII. Typical errors and corrections
Wrong operation Phenomenon Correction method
Emissivity is not set (default 0.95) The measured value of the metal surface is too high Adjust the emissivity according to the material type
The distance is too far and exceeds the D:S ratio The temperature value jumps or is too low Shorten the distance or replace the device with a high D:S ratio
The drastic change in ambient temperature is not compensated The measurement error gradually increases over time Enable the environmental compensation function and wait for the device to stabilize
VIII. Selection recommendations
Industrial high temperature (>1000℃): Choose a two-color infrared thermometer (strong anti-interference ability);
Power inspection: give priority to thermal imagers (support visible light fusion and temperature difference alarm);
Laboratory: High-precision (±0.5℃) and wide-range (-50℃~2000℃) equipment is required.