Infrared Thermometers are non-contact temperature devices that use infrared radiation to infer the temperature of an object. Infrared thermometers—similar to their conventional cousins—are devices that measure temperature without requiring contact. The thermometers infer temperature from a portion of the infrared radiation emitted from the object being measured. The devices are in the family known as thermal radiation thermometers. They are often referred to as temperature guns or non-contact thermometers to describe their ability to measure temperature from a distance.

 
The history of infrared thermometers is a relatively short one. Radiation was not discovered until the start of the 19th century and not named infrared until the late 1800s. The first radiation thermometer patent was granted in 1901, and the first commercially available model was introduced in 1931. Many developed nations began investing in infrared technologies following World War II and throughout the Cold War, leading to the rise of modern infrared thermometers. By the early 2000s, affordable and accurate handheld infrared thermometers became available and used in a wide variety of applications.

Types of Infrared Thermometers

The three main classes of infrared thermometers include:

• Spot infrared thermometers that measure the temperature of a small area on a surface
• Infrared scanning systems that scan a larger region
• Infrared thermal imaging cameras that measure the temperature of many spots over a large area to generate a thermogram—a two-dimensional image

Spot infrared thermometers are the most widely used and diverse. Their types include:

• Handheld infrared thermometers
• Stick-type or pocket infrared thermometers
• Infrared thermocouples, which are small infrared sensors that are self-powered, low cost and yield an output that imitates the sensor of a thermocouple
• Fixed mount infrared thermometers
• Fixed mount infrared transmitters
• Two color-ratio thermometry, which attempts to account for the accuracy-hindering impacts of emissivity by measuring infrared energy released from the source at dual wavelengths

Infrared thermometers have a lens that focuses infrared light from an object onto a sensor called a thermopile. The thermopile collects a small amount of infrared radiation emitted from the targeted source and turns it into heat. The heat is then turned into an electrical signal that is amplified and converts into voltage output. The thermometer’s central processing unit uses this output to solve a temperature equation based on Planck’s Radiation Law. Before a temperature reading is displayed, it compensates for factors such as ambient temperature and emissivity. Depending on the thermometer, the analysis is ready for display the instant the device’s read button or trigger is pressed.

By reading a sample of the infrared radiation from a source, the thermometer measures temperature from a distance without making any contact with the source object. It is important to note that the temperature taken is the temperature on the surface of the object, not an internal temperature. Most infrared thermometers attempt to account for ambient temperatures and emissivity factors—several include manual or automatic emissivity adjustment functionality. Both factors negatively impact the accuracy of temperature readings taken by the devices. The more a surface reflects light, the more emissivity impacts the accuracy of the temperature evaluation.

Max Planck came up with a mathematical representation of electromagnetic radiation in 1900. The advancement of quantum theory and physics were critical to creating the law. Planck’s equation is seen here:

The equation describes the spectral radiance as part of a body, which defines the quantity of energy produced with distinctive frequencies. Full measurement results use several dynamics, including the power released in each unit section of the body and the individual unit solid angle the radiation gauges throughout (on a frequency of each unit).

Variations of the equation are used to measure distinctive wavelengths as opposed to frequencies. A primary factor in these equations is the inclusion of the speed of light in a vacuum or a material base.

Features

Aside from their shared ability to read the temperature from a distance, infrared thermometers have a wide variety of features. The list of features depends on the model acquired. Several of the most common features include:

• Recording minimum and maximum read values during a defined period of time
• Battery powered
• Memory to record and store data values over a course of time or ranges
• Performing other math and statistical functions
• Self-test, self-calibration and diagnostic capabilities
• Zero-point reset
• Laser spot aiming and sighting with the device’s laser, allowing the source of the measurement to be revealed
• Automatic emissivity adjustment
• Waterproof, submersible and washable
• Explosion proof

Applications

Infrared thermometers are highly valuable for determining temperature and:

• The source object is moving, surrounded by an electromagnetic field or contained in a vacuum
• A fast reading is required
• The temperature of the source object is too high for the use of contact sensors

The devices are popular among meteorologists, laboratory scientists and kitchen workers for their variety of uses. Typical applications include recording temperatures of:

• Mechanical equipment or electrical circuit breaker boxes
• Potential or actual hot spots in firefighting situations
• A variety of research and development or manufacturing quality control circumstances such as examining the temperature of heat-producing devices to test calibration
• Materials that are heated or cooled for monitoring purposes
• People with highly infectious diseases
• A contaminated site
• Hard to reach places such as inside HVAC systems
• Foods such as soup where the surface temperature is imperative
• Cooking oil in a skillet or the surface of the skillet itself

Specifications

Specifications of infrared thermometers include their infrared performance characteristics including:

• Spectral range
• Spot ratio
• Emissivity
• Responsivity
• Detectability

Further specifications of infrared thermometers comprise of Fahrenheit or Celsius display and scale characteristics.

The components of infrared thermometers are similar to those found in computers. There is a CPU, a display screen, and a durable outer shell to protect the fragile interior components. Many devices are equipped with a laser for targeting objects. Materials such conductive metals, durable plastics, fiberglass and glass are also alike.

Emissivity needs are critical factors to selecting the appropriate infrared thermometer. Greater adjustment for emissivity is required when taking temperatures from shinier surfaces. Other considerations include:

• Required response time
• Environment
• Mounted device requirements and the limitations of the mounting feature
• The spectral response of the device
• The temperature range

Field of view aspects and limitations define particular infrared thermometers best fit for the task. This includes the spot size measured on a targeted object as well as the distance from which a measurement is taken. In the food preparation industry, temperatures are taken from small items at close range. In stark comparison, the temperature of a large, moving, intensely hot machine part requires testing from a considerable distance.

Standards

ASTM E1965 - Standard specification for infrared thermometers for intermittent determination of patient temperature

ASTM E2758 - Standard guide for selection and use of wideband, low temperature infrared thermometers

UL 2333 - Infrared thermometers

References

Image Credits:

Cole-Parmer