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Non contact thermometers -- how they work and how to use them for best results

Written By: 
Marc Blitstein / President & CEO

Non-contact body thermometers (NCIT) utilize infrared technology to measure temperature at a distance. They belong to a category that also includes tympanic (inner ear) thermometers.

The Science

Infrared thermometers work based on a phenomenon called black body radiation. Anything at a temperature above absolute zero has molecules inside of it moving around. The higher the temperature, the faster the molecules move. As they move, the molecules emit infrared radiation--a type of electromagnetic radiation below the visible spectrum of light. As they get hotter, they emit more infrared, and even start to emit visible light. That is why heated metal can glow red or even white. Infrared thermometers detect and measure this radiation.

How Infrared Thermometers Work

Infrared light works like visible light--it can be focused, reflected or absorbed. Infrared thermometers usually use a lens to focus infrared light from one object onto a detector called a thermopile. The thermopile absorbs the infrared radiation and turns it into heat. The more infrared energy, the hotter the thermopile gets. This heat is turned into electricity. The electricity is sent to a detector, which uses it to determine the temperature of whatever the thermometer is pointed at. The more electricity, the hotter the object is.

All infrared thermometers measure the temperature of the surface at which they are pointed. But the body’s surface temperature is not the same as it’s core temperature – the temperarture used in medicine To obtain the core temperature, the non contact thermometer must also read the ambient temperature, then use what is referred to as an offset table – essentially proprietary algorithms - to convert surface temperature to an oral equivalent temperature. Each manufacturer has their own algorithms developed by conducting clinical trials. To obtain clearance by the FDA to market the device in the USA, including a 510(k) demonstrating equivalence to predicate devices, the IR thermometer must meet certain performance standards – in this case ASTM 1965-98

Human Body Temperature

While typically 98.6°F (37.0°C) is considered a “normal” temperature, some studies have shown that "normal" body temperature can be within a wide range, from 97°F (36.1°C) to 99°F (37.2°C).

Before NCIT’s are used, it is important to understand the benefits, limitations, and proper use of these thermometers. Improper use of these instruments may lead to inaccurate measurements of temperature.

Benefits of NCIT:

Non-contact approach may reduce the risk of spreading disease between people being evaluated

  • Easy to use
  • Easy to clean and disinfect
  • Measures temperature and displays a reading rapidly
  • Provides ability to retake a temperature quickly

Limitations of NCIT:

  • How and where the non contact thermometer is used may affect the measurement (for example, head covers, environment, positioning on forehead).
  • The close distance required to properly take a person’s temperature represents a risk of spreading disease between the person using the device and the person being evaluated.
  • Typically somewhat less accurate than traditional invasive (oral/rectal) designs. Invasive models are required to be accurate to +/-.2°F, while IR of all types are only required to be accurate to +/-.4°F.

Proper Use of NCIT

The person using the device should strictly follow the manufacturer’s guidelines and instructions for use for the specific thermometer being used. The manufacturer’s instructions for use typically include the following information and recommendations for proper use:

Preparing the Environment, patient and NCIT

The use environment may impact the performance of the NCIT. Instructions will typically include recommendations for optimal use, such as the following:

  • Use in a draft-free space and out of direct sun or near radiant heat sources.
  • Determine if conditions are optimal for use. Typically, the environmental temperature should be between 65-95 ºF (18-35 ºC) and relative humidity below 85 percent.
  • Place the non contact thermometer in the testing environment or room for 10-30 minutes prior to use to allow the NCIT to adjust to the environment.

Preparing the Person being Evaluated:

In preparation for taking a temperature measurement with an NCIT, the person using the NCIT should typically ensure that

  • The test area of the forehead is clean, dry and not blocked during measurement.
  • The person’s body temperature or temperature at the forehead test area has not been increased or decreased by wearing excessive clothing or head covers (for example headbands, bandanas), or by using facial cleansing products (for example cosmetic wipes).
  • The person being evaluated should have acclimated to the test environment room for at least 2-3 minutes and preferably 5 or more. If the person being evaluated came from an environment hotter or colder than the state performance range of the device, the NCIT will typically not obtain accurate results.

Cleaning the NCIT:

For cleaning follow the instructions in the Cleaning and Disinfecting section of the product instructions. Most NCITs should never be immersed in water or other liquids. Cleaning between uses is typically not required but periodic cleaning is recommended, particularly if the unit will be used by different operators.

Using the NCIT:

As previously noted, the person using the device should strictly follow the manufacturer’s guidelines and instructions for use for the specific NCIT being used. In particular, the following are typical instructions for NCIT usage.

  • Hold the NCIT sensing area perpendicular to the forehead and instruct the person to remain stationary during measurement(s). (See Figure 1)
  • The distance between the NCIT and forehead is specific to each NCIT. Consult the manufacturer’s instructions for correct measurement distances.
  • Do not touch the sensing area of the NCIT and keep the sensor clean and dry.


Figure 1: Correct Use – Forehead unobstructed, and NCIT perpendicular to forehead and used at distance identified in manufacturer’s instructions.

Figure 2: Incorrect Use – Not perpendicular to forehead

Figure 3: Incorrect Use – Forehead exposed to direct sunlight outdoors

ADC is one of the world’s leading manufacturers of medical grade human body thermometers. We produce over a dozen models, including digital stick, temporal, IR tympanic and IR non contact. We currently produce two models of NCIT – our 429 handheld unit and 432 mini. A third model is under development.