This article will cover the basic functions of infrared radiation (IR) temperature sensors as well as some frequently asked questions about their operation and technical characteristics.
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What Is IR and How Is It Used to Determine Temperature?
Infrared radiation is part of the electromagnetic spectrum. It’s higher frequency than microwave radiation and lower frequency than visible light (Fig. 1).
Fig. 1: Electromagnetic spectrum
Although not visible, IR can be felt in the form of emitted heat. All matter emits energy in the form of heat (IR) - if there’s a difference in temperature between objects, then a gradient can be measured and used. IR temperature sensors produce a value for the targeted object and sent a signal to represent the temperature value. IR light can be focused, reflected, and absorbed similar to visible light. IR temperature sensors typically use a lens to focus light from one object onto a thermopile. The thermopile absorbs the IR radiation and turns it into heat - more IR energy absorbed means a hotter temperature reading. The heat from the thermopile is transduced into electricity, which can then be sent to a detector to determine the temperature of the object.
Advantages/Disadvantages of Contactless Temperature Sensors
IR temperature sensors are quick, accurate, and ideal for remote monitoring. The non-contact measuring is particularly useful for the safety of the operator and it limits potential contamination. However, IR thermometers are limited to surface temperature readings only and don’t measure through transparent surfaces or liquids. IR sensor readings can also be affected by environmental conditions/air particles such as dust, fog, excess moisture, or smoke.
What Does Resolution Mean for Temperature Sensors?
This specification is the smallest detectable incremental change of input parameter that can be detected in the output signal. Resolution can be expressed either as a proportion of the reading (or the full-scale reading) or in absolute terms. For example, an 11-bit resolution gives a temperature resolution of 0.125 °C. This means the thermal sensor is capable of providing a digital output with a step size of
0.125 °C.
How to Clean and Maintain IR Sensors
Since IR sensors function by focusing IR light, they must be kept clean in order to function properly. To clean, use a soft cloth or cotton swab with water or medical grade rubbing alcohol and carefully wipe the lens of the part. Allow the lens to dry fully before using the part. Never use soap or chemicals and never submerge the sensor or thermometer in water.
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