Guide to Properly Calibrating Infrared Thermometers

Infrared thermometers have become a ubiquitous tool in our daily lives, especially in the context of public health monitoring. But how reliable are the readings they provide? If this first line of defense is flawed, it could render the entire screening process ineffective. This article will guide you through selecting, using, and even calibrating your infrared thermometer at home to ensure accurate results.

Not all infrared thermometers are suitable for measuring human body temperature. The market offers two main types: industrial-grade and medical-grade. These devices differ significantly in their design and accuracy requirements.

Industrial infrared thermometers are designed for measuring equipment and material surface temperatures. They typically feature a wide measurement range but lower accuracy, making them unsuitable for human temperature screening. These devices often use broader wavelength ranges and are more susceptible to environmental interference.

Medical-grade infrared thermometers, such as the Fluke 67 MAX clinical infrared thermometer, are specifically engineered for human temperature measurement. They operate within narrower wavelength ranges to minimize environmental interference and are calibrated for human skin emissivity.

When choosing a medical-grade infrared thermometer, look for compliance with recognized standards. The ASTM E 1965-98 standard specifies that devices used for skin temperature measurement must maintain accuracy within ±0.3°C (±0.54°F) to reliably detect abnormal body temperatures.

Infrared thermometers measure skin surface temperature rather than core body temperature. Quality medical-grade devices typically offer two modes:

• Adjusted mode: Compensates for the difference between skin and core temperature
• Unadjusted mode: Displays raw skin surface temperature, primarily used for calibration

Several factors can influence temperature readings:

• Individual variations: Differences in forehead circulation affect skin temperature
• Environmental conditions: Ambient temperature, humidity, and airflow
• Physiological factors: Exercise, emotional state, and recent meals
• Measurement technique: Obstructions like hats or hair

Understanding the technology behind infrared thermometers helps identify potential sources of measurement error.

All objects emit infrared radiation, with intensity correlating to temperature. Infrared thermometers measure this radiation to determine surface temperature.

1. The device's optical system collects infrared radiation from the target
2. Sensors convert this energy into electrical signals
3. Internal circuitry processes these signals to display temperature readings

Note that the laser pointer included in many devices serves only to indicate the measurement area and doesn't participate in temperature measurement.

Three critical elements determine measurement precision: emissivity, wavelength, and geometric conditions.

Emissivity describes an object's ability to emit infrared radiation. Human skin typically has an emissivity of 0.98, though it can vary between 0.94 and 0.99. Medical-grade thermometers usually lock this setting at 0.98.

For near-room-temperature objects like the human body, the 8-14 micrometer wavelength range proves most effective, as it's less sensitive to humidity while providing sufficient energy for reliable measurement.

The distance-to-spot ratio (D:S) determines the measurement area. For forehead thermometers, maintain a distance of no more than 4 inches (10 cm) to ensure accurate readings.

Follow these steps to verify your device's accuracy using a Fluke 4180 precision infrared calibrator:

1. Place the calibrator in a stable environment free from drafts
2. Set the calibrator to 37°C (98.6°F) with 0.98 emissivity
3. Allow both devices to stabilize for 10-15 minutes
4. Confirm your thermometer's emissivity is set to 0.98
5. Maintain proper measurement distance (typically 4 inches)
6. Position the thermometer to avoid body heat reflection
7. Record at least five readings from each device
8. Calculate average values and compare results

According to ASTM standards, medical-grade infrared thermometers should maintain accuracy within ±0.3°C (±0.54°F). If your device exceeds this range, consider professional calibration or replacement.

Infrared thermometers serve as valuable tools in health monitoring when used correctly. By understanding their limitations, selecting appropriate devices, and performing regular accuracy checks, we can ensure reliable temperature screening for better health protection.