What is an infrared or IR thermometer? What are non-contact temperature sensors?
Relationship between infrared waves and temperature measurements:
All objects emit a certain color and light at different temperatures, which can be measured by using this light or the same thermal power emitted from an object. In other words, the temperature of objects can be obtained based on the spectrum of light emitted from the object.
The infrared spectrum is the energy emitted at wavelengths of 0.75 to 100 micrometers, also known as infrared or infrared radiation. Infrared is a type of electromagnetic radiation that is produced by the vibration and rotation of atoms and molecules of matter at temperatures above absolute zero. If the radiation source temperature is 1000 K, the emitted energy is visible as red light with a wavelength of 0.75 micrometers. In fact, as the temperature rises, infrared waves with shorter wavelengths but more energy are emitted.
The most important part of infrared thermometers is the infrared or IR detector. In thermal detectors, the temperature of the element is detected according to the absorption of electromagnetic rays; As a result, changes in temperature parameter can be used as a good measure of absorption energy.
In industrial applications, most of the thermal radiation occurs in the infrared (IR) range; Therefore, they are often known as infrared thermometers. In some terms, non-contact thermometers, also called high temperatures (around 1000 degrees and above), are called pyrometers or pyrometers.
This infrared sensor is mostly used in factories and industries to measure continuous temperature as well as to measure high temperatures. Usually the temperature range of these sensors is -50 ° C to 3500 ° C.
In most of these types of sensors, the output is 4-20mA, voltage output or thermocouple, and in some cases they have controllers that have a switch output for on / 0ff of a device such as a pump or valve, etc. An example of a model with a controller is given in the following figure:
Models that measure high temperatures typically use a chamber to prevent the sensor from overheating:
Definitions of some infrared sensor parameters:
The degree to which an object is capable of emitting infrared energy is called sensitivity, which can be used to determine the temperature of an object; More precisely, the ratio of the energy emitted by an object to the energy emitted by a black body at the same temperature is called the ability to propagate. In this definition, a black body is a body that is capable of absorbing all electromagnetic wavelengths. The diffusion parameter can be changed from zero (glossy mirror) to one (black body). For example, the emissivity of some metallic and non-metallic materials is given in the table below.
2- Distance to Spot Ratio or D: S
D: S is the ratio of the distance from the object to the diameter of the area whose temperature is being measured. For example, if D: S is a 12: 1 sensor, that is, 12 inches away from the object is equivalent to the average regional temperature of 1 inch in diameter from the object. D: S is usually different for sensors with higher temperatures. As
Example D: S up to a temperature of 1200 degrees 40: 1.
Important parameters in choosing an infrared sensor: