Infrared (IR) thermometers measure surface temperature without physical contact by detecting thermal radiation emitted by objects. Calibration verifies the accuracy of the non-contact temperature measurement using a blackbody radiation source with known temperature and emissivity. IR thermometers are essential for electrical inspection, HVAC, food safety, and process monitoring.
Inspect the IR thermometer lens for contamination, scratches, or damage. Clean the lens per manufacturer instructions. Verify the display, laser aiming system, and emissivity setting function correctly. Check battery condition.
Allow the IR thermometer to acclimate to the ambient temperature for a minimum of 20 minutes. Sudden temperature changes cause internal sensor drift. Record the ambient temperature.
Set the blackbody radiation source to the first test temperature and allow it to stabilize (typically 15-30 minutes per set point). Verify the blackbody emissivity is ≥0.95 and the aperture size exceeds the IR thermometer's spot size at the measurement distance.
Test at a minimum of three temperatures spanning the thermometer's range (e.g., 50 °C, 150 °C, 300 °C). Position the thermometer at the manufacturer-specified distance from the blackbody aperture. Record the IR reading and the blackbody reference temperature at each point.
Verify the optical resolution (D:S ratio) by measuring the blackbody at two distances and confirming the spot size scales correctly. An incorrect D:S ratio causes measurement errors when the target is smaller than the spot.
If the thermometer has adjustable emissivity, verify that changing the emissivity setting produces the expected reading change on a known target. This confirms the emissivity compensation algorithm functions correctly.
Record all data including blackbody set points, IR readings, measurement distances, emissivity settings, and ambient conditions. Issue the calibration certificate with measurement uncertainty and apply the calibration label.
Per ASTM E2847, accuracy must be within ±1 °C or ±1% of reading (whichever is larger) for industrial IR thermometers. Medical-grade IR thermometers per IEC 80601-2-59 require ±0.2 °C in the clinical range. Actual tolerance depends on the instrument class and manufacturer specification.
12 months
A blackbody radiation source provides a surface with precisely known temperature and emissivity (≥0.95), eliminating emissivity uncertainty from the calibration. Measuring real surfaces introduces unknown emissivity errors that cannot be separated from instrument errors during calibration.
The D:S ratio defines the measurement area (spot size) at a given distance. A 12:1 D:S ratio means the spot diameter is 1 inch at 12 inches distance. If the target is smaller than the spot, the thermometer averages the target and background temperatures, producing errors.
Emissivity is the ratio of radiation emitted by a surface compared to a perfect blackbody. Low-emissivity surfaces (polished metals, ~0.1-0.3) emit less radiation and appear cooler to an IR thermometer. The emissivity setting must match the target material, or significant measurement errors will result.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
Get Started Free