All about infrared type thermometers.

Please feel free to use this article without reservation.

Introduction

In the past taking a person’s temperature was slightly invasive in instances of body temperature being measured.It was achieved using contact thermometers that are placed on the forehead or in the mouth, ear, armpit or rectum. The body temperature caused mercury or colored alcohol to expand and indicate temperature on a linear calibrated scale or have a temperature sensor convert the temperature to a voltage and display the result on an analogue or digital screen. Since then there have been many developments and devices to try and make this basic function less invasive more accurate and quicker to get a reading. The tympanic is a minimal contact type instant thermometer that is placed in the ear and it provides an accurate core temperature reading. Non-contact thermometers allow a person’s temperature to be taken with minimal or zero-contact with the patient as in using an infrared thermometer sometimes called a thermometer gun. This means temperature can be measured without the discomfort of having to sit still with a thermometer in the mouth, armpit, or rectum long enough to obtain a correct temperature reading. The lack of contact also means the disinfection process between patients for the thermometers is minimal or unnecessary, allowing for easier and faster use when screening large numbers of people in settings like airports or border crossings.

The main types of non-contact thermometers are non-contact infrared thermometers, tympanic thermometers, and thermal scanners. Non-contact infrared thermometers are held normally about two to twenty cm away from the patient and typically measure temperature on the forehead or temple. Tympanic thermometers measure the thermal radiation from the tympanic membrane and within the ear canal. Handheld thermal scanners can be used to take a person’s temperature from a greater distance than other non-contact thermometers, which may make them a good candidate for use in mass screening situations. The optimal cut-off temperature for determining fever differs for each device. However, not everyone who has an infection or is infectious will have a fever. Additionally, fevers can be lowered by using antipyretic medications. In instances cosmetic makeup applied to the forehead can act as a barrier to the surface temperature and certain suntan creams with additives can result in skewed readings.

The best infrared thermometer for body temperature is a thermometer containing a laser indicator to indicate the target region and manufactured by a reliable company with experience in measuring temperatures. The laser indicates the target of the temperature being measured ad provides for greater accuracy in positioning.

The thermometer gun has become increasingly popular for taking surface temperatures from a distance – there’s no need to come into physical contact with the item or person. The use of thermometer guns has soared since the Corona-virus threat spread to all countries. Many businesses and public institutions use thermometer guns to screen large numbers of people to detect those who might be sick and running a temperature.

Thermometer guns can be highly inaccurate, mostly because of operator mistakes and also due to the mass production by opportunist companies not exercising adequate quality control and high-quality manufacturing standards. There is also the marketing and use of industrial devices for medical purposes that are not designed for medical and can result in inaccurate readings.

People who don’t know how to use thermometers can get inaccurate readings for a number of different reasons. As an example, thermometer guns must be used at the proper distance, too close or too far will result in an inaccurate reading. They are only accurate for reading surface temperatures of patients. Thermal/thermometer guns don’t measure internal temperature like a probe. Environmental conditions can affect surface temperatures. If for example it is freezing cold or very hot the surface temperature of a body varies drastically from the body core temperature. Electromagnetic field and radio frequency interference can also cause inaccurate readings

But if used correctly by trained operators they have their place. In a perfect world they should be used together with for example the tympanic ear thermometers. If a person has a reading that is deemed abnormally high or low then it should be backed up with a more reliable device that measures core temperature to confirm the body core temperature.

The advantages of using a thermometer gun include the ability to monitor the temperature without touching a contagious person. They are lightweight, compact and easy to use and can be used for fast scanning of large crowds as in many places like airports, hospitals, schools, etc.

How does it work, an easy to grasp explanation.

The technology to measure the infrared radiation is simple and you will be amazed as how simple it really is based on physics, yes even for the man in the street and students. After reading this simple explanation you will have some information to impress colleagues while having coffee and discussing the topic of the day.

Explaining the methodology of infrared thermometers need to refer to exactly what is measured and it is a measurement of infrared radiation from a surface, in the instance of medical purposes the surface of a patient’s forehead or temple.

To understand infrared radiation, it is just one type of radiation that exists within the electromagnetic spectrum. Additional types of electromagnetic radiation include microwaves, x-rays and visible light. The illustration below shows wavelength and frequency of the electromagnetic spectrum.

The wavelength of IR rays is longer than that of the visible spectrum’s red rays. If we could see IR rays on the electromagnetic spectrum, they would appear just after red on the visible spectrum.

IR radiation is, quite literally, heat. Although our eyes cannot visibly detect IR, we can feel it and it can be measured. You can feel infrared radiation when you close your eyes and look at the sun or feel warm from a heater.

Infrared thermometers work based on black body radiation (A physics term), according to which any material with a temperature above absolute zero(very cold) has molecules moving within it. The higher the temperature, the faster the molecules move. The molecules emit infrared radiation as they move, and emit more radiation, including visible light, as they get hotter. This is why a heated metal emits a red or white glow. Infrared thermometers detect and measure this radiation

All matter emits energy in the form of IR (heat). If there is a temperature difference between objects, including the surrounding environment, then this gradient can be measured and used. If the object in question is at the same temperature as its surroundings, the net radiation energy exchange will be zero.

IR light works like visible light and it can be focused, reflected or absorbed. Handheld IR thermometers typically use a lens to focus the IR light from one object onto a detector, called a thermopile. The thermopile absorbs the IR radiation and turns it into heat. The more IR energy, the hotter the thermopile gets. This heat is turned into electricity. The electricity is sent to a detector, which uses it to determine the temperature of whatever the thermometer is pointed at. The more electricity, the hotter the object. The higher the temperature, the more electricity sent to the detector, the higher the reading.

Thermopiles depend on the thermocouple principle. Thermocouples first appeared after the discovery of the thermoelectric effect by Thomas Johann Seedbeck in 1821. Seedbeck discovered that a pair of junctions (contact points) between two wires made of different metals creates voltage equal to the temperature difference between the junctions. Basically, a thermocouple consists of two wires made of different metals joined in two places. Heat enters at one end, travels down each wire separately, then re-joins. When it re-joins, it creates electricity. The voltage of the electricity gives an accurate reading of a temperature between the ends of the device.

A thermopile consists of nothing more than a series of interconnected thermocouples. Each additional thermocouple placed in a thermopile increases the device’s ability to produce electricity. For instance, if a thermocouple generates two volts of electricity, and a thermopile contains four thermocouples, it generates two volts of electricity per thermocouple for a total of eight volts When used to measure temperatures, thermopiles and thermocouples must attach to a device that translates the voltage of the wire to a temperature reading

The time taken from a reading to display the temperature if typically, less than one second Maximum measuring distance is determined by the design and quality of the optics the thermopile and surrounding temperature and atmospheric conditions. The accuracy of a device is determined by the distance-to-spot ratio (D/S Ratio). This ratio is the size of the area being evaluated by the IR thermometer as it relates to distance. In other words, the area being measured becomes larger as the distance increases. The smaller the target, the closer you should be to it.

That’s it short and sweet and to the point. Thank you for taking the time to read my article. And now you can share with others.

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