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Infrared Thermometer

Infrared Thermometer

Introduction

How do infrared thermometers work? The most basic design 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. 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.

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

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 unit. 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 sighting 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.

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.

Infrared Thermometer Types

  • Handheld Infrared Thermometers: Handheld infrared thermometers are one of the most popular types of infrared pyrometer. They are commonly used for portable applications although some models also feature an integral tripod mount. OMEGA offers a large variety of infrared thermometers in various shapes and form factors. Many of OMEGA handheld infrared pyrometers feature OMEGA's patented Circle Dot/Circle Laser sighting which clearly outlines the field of view of the thermometer.
  • Pocket/Stick-Type Infrared Thermometers: Pocket or stick type infrared thermometers are extremely compact. They are normally small enough to be carried in a shirt pocket.
  • Infrared Thermocouples: Infrared thermocouples are small low cost infrared sensors. They are unique in that they are self-powered and produce an output that mimics a thermocouple sensor.
  • Fixed Mount Infrared Thermometer/Transmitters: Fixed mount infrared thermometers are commonly used in industrial processes where the thermometer can be mounted in a stationary position. Read the High Speed Fiber Optic Infrared Transmitter article for information about the OS4000 Series.
  • 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."