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Infrared Thermometer

Introduction to Non contact Infrared Thermometers

On its most basic design an infrared sensor consists of a lens to focus the infrared (IR) energy on to a detector, which converts the energy to an electrical signal that can be displayed in units of temperature after being compensated for ambient temperature variation.

This configuration facilitates temperature measurement from a distance without contact with the object to be measured (non-contact temperature measurement). As such, the infrared thermometer is useful for measuring temperature under circumstances where thermocouples or other probe type sensors cannot be used or do not produce accurate data for a variety of reasons.

Some typical circumstances are where the object to be measured is moving; where the object is surrounded by an EM field, as in induction heating; where the object is contained in a vacuum or other controlled atmosphere; or in applications where a fast response is required.
Noncontact Temperature Measurement with an Infrared Thermometer
Noncontact Temperature Measurement

Learn more about Infrared Thermometers

Why should I use an infrared thermometer to measure temperature in my application?

Non-contact pyrometers allow users to measure temperature in applications where conventional sensors cannot be employed. Specifically, in cases dealing with moving objects ( i.e., rollers, moving machinery, or a conveyor belt), or where non-contact measurements are required because of contamination or hazardous reasons (such as high voltage), where distances are too great, or where the temperatures to be measured are too high for thermocouples or other contact sensors.

How to Choose an Infrared Thermometer

  1. Determine the field of view (target size and distance)
  2. Consider the type of surface being measured and its emissivity
  3. Analyze the spectral response for atmospheric effects or transmission through surfaces
  4. Specify the temperature range and the mounting needs
  5. Don't forget: response time, environment, mounting limitations, viewing port or window applications, and desired signal processing

What should I consider about my application when selecting an IR thermometer?

The critical considerations for any infrared pyrometer include field of view (target size and distance), type of surface being measured (emissivity considerations), spectral response (for atmospheric effects or transmission through surfaces), temperature range and mounting (handheld portable or fixed mount). Other considerations include response time, environment, mounting limitations, viewing port or window applications, and desired signal processing.

What is meant by Field of View, and why is it important?

The field of view is the angle of vision at which the instrument operates, and is determined by the optics of the sensor. To obtain an accurate temperature reading, the target being measured should completely fill the field of view of the instrument. Since the infrared device determines the average temperature of all surfaces within the field of view, if the background temperature is different from the object temperature, a measurement error can occur. OMEGA offers a unique solution to this problem. Many OMEGA infrared pyrometers feature patented laser switchable from circle to dot. In the circle mode a built-in laser thermometer creates a 12-point circle which clearly indicates the target area being measured. In the dot mode a single laser dot marks the center of the measurement area.

Choose the right Infrared for your application

OS530E Infrared Thermometer gun with pointing laser Infrared laser thermometer
A infrared thermometer gun is one of the most popular type of pyrometer. They are commonly used for portable applications although some models also feature an integral tripod mount. OMEGA offers a large variety of laser thermometers in various shapes and form factors. Many of OMEGA pyrometers feature OMEGA's patented Circle Dot/Circle Laser infrared thermometer which clearly outlines the field of view of the gun.
OS643 Pocket/Stick-Type Infrared Thermometer is the smallest and simplest IR sensor Pocket Infrared Thermometers
The pocket infrared thermometers are extremely compact. They are normally small enough to be carried in a shirt pocket.
OS36 Infrared Thermocouples provide an thermocouple signal output related to the temperature Infrared Thermocouples
A infrared thermocouple is a small low cost infrared sensor. They are unique in that they are self-powered and produce an output that mimics a thermocouple sensor.
The Fixed Mount Infrared Thermometer is a broadly used model in industry Fixed Mount IR Thermometers
A fixed mount infrared thermometer is commonly used in industrial processes where the thermometer can be mounted in a stationary position. Read the article about High Speed Fiber Optic Infrared Transmitter for information about the OS4000 Series.
IR2 Two Color-Ratio infrared thermometer. It´s able to measure the temperature though any window Two Color-Ratio Thermometry
Given that emissivity plays such a vital role in obtaining accurate temperature data from infrared thermometers, it is not surprising that attempts have been made to design sensors which would measure independently of this variable. The best known and most commonly applied of these designs is the Two Color-Ratio Thermometer. This technique is not dissimilar to the infrared thermometers described so far, but measures the ratio of infrared energy emitted from the material at two wavelengths, rather than the absolute energy at one wavelength or wave band. The use of the word "color" in this context is somewhat outdated, but nevertheless has not been superseded. It originates in the old practice of relating visible color to temperature, hence "color temperature."

Frequently Asked Questions


What is emissivity, and how is it related to infrared temperature measurements?

Emissivity is defined as the ratio of the energy radiated by an object at a given temperature to the energy emitted by a perfect radiator, or blackbody, at the same temperature. The emissivity of a blackbody is 1.0. All values of emissivity fall between 0.0 and 1.0. Most infrared thermometers have the ability to compensate for different emissivity values, for different materials. In general, the higher the emissivity of an object, the easier it is to obtain an accurate temperature measurement using infrared. Objects with very low emissivities (below 0.2) can be difficult applications. Some polished, shiny metallic surfaces, such as aluminum, are so reflective in the infrared that accurate temperature measurements are not always possible.

How can I mount the infrared pyrometer?

The pyrometer can be of two types, either fixed-mount or portable. Fixed mount units are generally installed in one location to continuously monitor a given process. They usually operate on line power, and are aimed at a single point. The output from this type of instrument can be a local or remote display, along with an analog output that can be used for another display or control loop. Battery powered, portable infrared ''guns'' are also available; these units have all the features of the fixed mount devices, usually without the analog output for control purposes. Generally these units are utilized in maintenance, diagnostics, quality control, and spot measurements of critical processes.

What else should I take into account when selecting and installing my infrared measurement system?

First, the instrument must respond quickly enough to process changes for accurate temperature recording or control. Typical response times for infrared thermometers are in the 0.1 to 1 second range. Next, the unit must be able to function within the environment, at the ambient temperature. Other considerations include physical mounting limitations, viewing port/window applications (measuring through glass), and the desired signal processing to produce the desired output for further analysis, display or control.

I want to measure the temperature through a glass or quartz window; what special considerations are there?

Transmission of the infrared energy through glass or quartz is an important factor to be considered. The pyrometer must have a wavelength where the glass is somewhat transparent, which means they can only be used for high temperature. Otherwise, the instrument will have measurement errors due to averaging of the glass temperature with the desired product temperature.

What is spectral response, and how will it affect my readings?

The spectral response of the unit is the width of the infrared spectrum covered. Most general purpose units (for temperatures below 1000°F) use a wideband filter in the 8 to 14 micron range. This range is preferred for most measurements, as it will allow measurements to be taken without the atmospheric interference (where the atmospheric temperature affects the readings of the instrument).

Some units use wider filters such as 8 to 20 microns, which can be used for close measurements, but are ‘‘distance-sensitive’’ against longer distances. For special purposes, very narrow bands may be chosen. These can be used for higher temperatures, and for penetrations of atmosphere, flames, and gases. Typical low band filters are at 2.2 or 3.8 microns. High temperatures above 1500°F are usually measured with 2.1 to 2.3 micron filters. Other bandwidths that can be used are 0.78 to 1.06 for high temperatures, 7.9 or 3.43 for limited transmissions through thin film plastics, and 3.8 microns to penetrate through clean flames with minimum interference.

If a part is moving, can I still measure temperature?

Yes. Use infrared devices or direct contacting sensors plus a slip ring assembly.

Can a two-color infrared system be used to measure low emissivity surfaces?

Only if at high temperature, say, above 700°C (1300°F).

What error will result if the spot size of the infrared pyrometer is larger than the target size?

It would be indeterminate. The value would be a weighted average that wouldn’t necessarily be repeatable.

How is a infrared pyrometer calibrated?

There are basically two types of infrared calibration sources, hot plate blackbody source and cavity type blackbody source. The hot plate style consists of a metal plate (usually aluminium) with or without concentric grooves where the temperature of the-plate is set and controlled using either an inexpensive potentiometer dial or a high-end temperature controller. The temperature of the plate is sensed using either a thermocouple or an RTD probe. The hot plate is usually painted dull black to improve the surface emissivity. The surface emissivity of a hot plate calibration source is typically 0.95.

blackbody source calibrator for Infrared sensors OMEGA's BB703 Model is a high-end hot plate blackbody source with a built-in temperature controller. The calibration source with built-in temperature controller has much better accuracy and stability compared to a potentiometer dial type unit.

The cavity type blackbody source consists of a blind hole in a cylinder or a sphere where the temperature of the cavity is controlled by a temperature controller, using a thermocouple probe. The cavity type blackbody source has a higher surface emissivity than a hot plate blackbody unit. The emissivity of a cavity type blackbody source is typically 0.98 or higher.

The OMEGA's BB705 Model cavity type blackbody typically goes to higher temperatures (over 530°C [1000°F]) than hot plate blackbodies. In addition, having a higher emissivity value makes them ideal for precise calibration tasks.

In order to calibrate an infrared thermometer, a blackbody calibration source is required. There are 3 factors to consider when selecting a blackbody calibration source:

  1. Type of blackbody (hot plate or cavity type) tells us about the construction and overall performance of the unit.
  2. Target area tells us how large of an area we can check our infrared thermometers with. The target area should be larger than the field of view of the thermometer; otherwise the infrared thermometer will be measuring the target area plus some of the surrounding cooler areas. Normally, an infrared thermometer is checked against a blackbody source at a relatively close distance (about 0.15 to 1m), depending on the target area).
  3. The higher the target emissivity, the more ideal is the calibration. At lower emissivity targets, wavelength bandwidth of the infrared thermometer comes into play. Ideally at E=1.00, wavelength bandwidth of the DUT (Device Under Test) is not a factor.