Infrared Thermometer

Each infrared thermometer is designed to measure a specific temperature range. For example, many models are available with measuring ranges from -30 °C to 500 °C, the others cover a temperature range from - 50 °C to 1,850 °C. Within the respective measuring range, there are usually sub-ranges with different accuracy. When comparing different models, it is important to ensure that the accuracy is sufficient for the temperature range relevant to the intended application.

A high measuring rate or a short response time of the infrared thermometers is particularly important when measuring the objects that move out of the field of view or when temperature changes are to be recorded very detailed. If the sensor's measuring rate is high, it must be ensured that the transmission and storage rate is also correspondingly high. Response times of 150 milliseconds are now standard for many types of device.

When measuring temperature with the infrared thermometer, it is important to take into account that the measured value is influenced by the properties of the material and surface of the measured object. This can be compensated for by one factor – the emissivity or emission factor. The infrared thermometers where the emissivity cannot be adjusted are set either to the factor 0.95 or to the factor for the specific application. The instrument models with adjustable emissivity usually offer the possibility of setting the values between 0.1 and 1.0 or 0.3 and 1.0. If the correct factor is not known, it can usually be determined by comparative measurements or taken from tables.

Every infrared thermometer has an optical system with a certain spot ratio. This indicates the distance the optics of the device must be from the measuring point in order to achieve a certain size of the measuring spot. The first number stands for the distance and the second number for the diameter of the measuring spot. A spot ratio of 8:1 means that at a distance of eight centimetres the spot has a diameter of one centimetre. For the measurements of very small parts or measurements from a great distance, there are infrared thermometers with a spot ratio of 50:1, 60:1 but also with 120:1 or even 300:1. Only a few special models offer the possibility to reduce or enlarge the spot at the same distance.

Infrared radiation is not visible. Sighting aids are available to ensure that the surface temperature is measured at the correct spot. Almost all mobile infrared thermometers offer visible laser markings for this purpose. The simplest form is a simple laser dot. Better is a cross laser with two visible points. The two points change their distance to each other when the distance of the thermometer to the measuring point is changed. The distance between the laser points indicates the size of the measuring spot. Circular lasers, as sighting aids, show even more clearly the size of the measuring spot on the surface of the object. The infrared thermometers with a very large measuring spot ratio also have additional control devices such as a telescopic sight and can be mounted on tripods.

Some infrared thermometers offer the possibility to store the measured values in an internal memory or to send them to mobile devices via Bluetooth. The values stored in the device can usually be transferred directly to a computer in electronic form. The data interface is often a USB interface or the data is stored directly on an SD memory card. The infrared thermometers for fixed installation often have analogue or switching interfaces with which the processes can be controlled.

For some applications, it is useful to have additional sensors built into the device. For example, the infrared thermometers are often used that also have a connection for type K thermocouples for the contact temperature measurement. Also the models with additional sensors for measuring air temperature and humidity also offer clear advantages over the use of several devices in some applications.

The infrared thermometers can not only measure but, if they are equipped with appropriate functions, they can also compare the measured value with the predefined or freely selected limit values. If the measured value exceeds or falls below these limits, optical or acoustic alarms or switching interfaces are triggered. Maximum temperatures, minimum temperatures and average values can also be determined and immediately displayed.

For most organic – i.e. carbon-containing – materials, the temperature can be determined with sufficient accuracy by measuring the infrared radiation if the emissivity is set to 0.95. This is why the infrared thermometers that cannot be set to 0.95 have this factor stored. For this reason, the infrared thermometers for which the emissivity cannot be set have this factor stored. For transparent and shiny objects that transmit or reflect the infrared radiation of other objects, the emissivity factor must be adjusted to obtain correct results.

For many materials with deviating emission values, examples have been published in tables. For example, for copper there are the following values: 0.012 (polished at 327 °C), 0.78 (strongly oxidised at 25 °C), 0.91 (strongly oxidised at 527 °C). When adopting such values, it should be noted that they always depend on the surface condition of the object and usually also on the wavelength that is measured. Often the emissivity also changes with the temperature.

Other factors that influence the emissivity are the roughness of the surface, e.g. polished, ground, oxidised, sandblasted, and the measuring angle. In connection with the measuring angle, the surface geometry of the object to be measured must also be taken into account. Whether the surface is flat, curved inwards or outwards or structured has an influence on how many infrared rays reach the detector in the infrared thermometer.

Because of the many influencing factors, the correct emissivity must be determined in advance by comparative measurements In the cases where an exact measurement result is required. For this purpose, a suitable material sample should be heated and tested at different measuring points in the required temperature range. For the comparison measurements, the infrared thermometer should be used that is also to be used for the later measurements, so that it is certain that the measuring wavelength is the same.

Comparative measurements with a contact probe
Many infrared thermometers are also equipped with a connection for thermocouples or resistance temperature probes for contact measurement. Often these offer the same or an even larger measuring range. This means that the complete measuring range of the infrared sensor can be easily checked by means of the contact measurements. If the comparison values differ, the emissivity is adjusted until the measured values match. Using this method, specific values for the respective emissivity can be determined for certain workpieces at different temperatures and processing conditions.

Comparative measurements with sticker or paint application
For the comparative measurements, the reflective surfaces can also be covered with a suitable thin adhesive tape or sticker with a known emissivity, or coated with a matt varnish the emissivity of which is known. When the cover has assumed the temperature of the object, the measurements are made with the same infrared thermometer on coated and uncoated areas of the object. If necessary, the emission value for the uncoated area is then adjusted until the temperature reading corresponds to that of the coated area.

It is commonly known that many foods do not spoil as quickly if they are stored at certain temperatures or if they are made more durable with the help of a suitable process. There are a number of regulations for the food industry in this regard. Anyone who processes food or trades in food is obliged, among other things, to create an HACCP concept tailored to the conditions in the company. HACCP stands for Hazard Analysis and Critical Control Points.

Many HACCP concepts define time points and places where temperatures are to be monitored randomly, regularly or continuously. In addition to the reliable temperature determination, it is also important that the food is not contaminated because of the contact with the measuring device. For this reason, infrared thermometers are often used for the measurements on the food. These can determine the surface temperature of the material without touching it. Where it is necessary to determine the core temperature, also the contact thermometers with easy-to-clean penetration probes are also used.

For many foods, exact temperature sequences must be maintained during cooking or preservation in order to achieve the desired product properties. The infrared thermometers are ideal for monitoring temperatures in such processes, as they measure very quickly and without contact. For example, the infrared thermometer can also be installed above a belt conveyor and continuously measure the temperature of the parts or substances moving on the belt. Neither materials nor products nor the process are disturbed by the measurement.

So that the foodstuffs last for a long time but lose as few vitamins and flavours as possible as a result of the temperature treatment, the specified temperatures must be maintained as accurately as possible over the intended period of time. The infrared thermometers used during the industrial food processing usually transmit the measured values directly as an analogue or switching signal. This means that heat can be added or dissipated immediately if the measured values exceed or fall below the defined limit values.

In addition, the signals transmitted by the infrared thermometer can be used to record the temperature curves during the entire process. This enables the detailed evaluations to be made in the event of both deliberate and unintentional changes of the output parameters. For example, the product batches that have not been heated sufficiently can be sorted out immediately and retreated or used in a different way.

The examples of the temperature-dependent preservation methods in the food industry that can be easily monitored with the infrared thermometer are drying, pasteurisation and sterilisation. In the drying, which is only suitable for certain foods, the removal of water ensures a longer shelf life. The drying process can be accelerated by selectively adding heat. However, to ensure that only the water is released, the temperature during drying must be limited and good ventilation must also be ensured.

In the pasteurisation, food is heated to less than 100 degrees Celsius for only a short time to kill heat-sensitive undesirable yeasts and moulds. The sterilisation, on the other hand, involves heating to at least 110 degrees Celsius for a longer period of time, which renders other microorganisms harmless. Heat sterilisation is also used to render cleaned tools germ-free.

It is also important to ensure that the correct temperatures are maintained when transporting and storing perishable food. Especially in the case of chilled and frozen goods, each consignment must be checked for temperature and visual abnormalities upon delivery. For some transports, temperature data loggers are placed with the refrigerated goods in order to record the temperatures without interruption.

It is common knowledge that many foods have a limited shelf life and that the length of the shelf life is strongly influenced by the ambient climate. Anyone who processes food and places it on the market must ensure that consumers are not endangered by the offered products. Operators of restaurants, canteens, fast-food restaurants, snack bars and other catering establishments are obliged to set up and comply with hygiene concepts. In addition to protection against contamination, the important contents of these hygiene concepts always include controlling the temperature of the foodstuffs.

Goods receipt in catering establishments
Foodstuffs that are delivered already cooled or for which cooling is prescribed or intended are already checked for visible impairments upon delivery. In addition, the temperature of the goods is measured at relevant points. With a suitable mobile infrared thermometer, the temperature on the surface can be determined quickly and without contact at various points. The infrared thermometers for the catering industry usually have an additional stable stainless steel probe that can also be used to measure core temperatures. The insertion probe, which is carefully cleaned after each measurement, is inserted into the delivered material at specified points. The temperature differences determined in this way can provide information about the temperatures during transport and previous storage.

Foodstuffs storage
Foodstuffs are usually stored in separate storage rooms for shorter or longer periods of time. Depending on the type, size and equipment of the rooms, different temperature levels can occur there. With the infrared thermometer, the temperature of the stored food can be measured quickly and without contact at any time. If necessary, the storage place or possibly the room temperature can be changed. In addition, the temperatures determined by the infrared thermometer can be used to determine the right time to remove the food. Many foodstuffs should be brought slowly to room temperature before processing.

Food preparation
Infrared thermometers can also be used for temperature control during food preparation. For example, you can quickly measure how hot a grill surface or the contents of a pot are. Regardless of whether the food is chilled, frozen or cooked, the infrared thermometers measure its current temperature contact-free and hygienically. Some models of the infrared thermometers for the catering sector also immediately display a warning if cooling temperatures are exceeded or if warm food has cooled down too much. These devices are particularly recommended for checking the temperatures at cold and hot buffets.

Body temperatures can provide information about physical activity and the state of health. Not for nothing is it said that athletes should warm up slowly before high loads. During both power and endurance sports, but also during strenuous physical work, the body temperature rises due to muscular activity. On the other hand, the immune system also reacts to infections by raising the temperature. Elevated core body temperatures above 38 ° C in the case of individuals without physical exercising are referred to as fever. Persons diagnosed with fever should rest as much as possible and be isolated from the others.

The accurate measurement of the body temperature is usually performed with a clinical thermometer approved for this purpose. A significant advantage of the devices with infrared measurement is their speed. The measured body temperature can be read almost immediately. In the case of dangerous infectious diseases, the symptoms of which include fever, persons can be easily checked for the elevated body temperature with infrared cameras as they pass by. Suspicious persons can then be quickly separated and examined more closely. Such checks, for example at airports, can slow down the spread of highly contagious diseases.

IR thermometers with medical approval
Fever thermometers with approval as medical devices are available in various versions. While contact thermometers measure under the tongue, under the arm or rectally, the infrared thermometers measure the temperature on the forehead or in the ear. The measuring range, optics and emissivity of these infrared thermometers are designed to measure the body temperature. Nevertheless, it must be taken into account that the measurement result can be influenced by many factors.

In the analogue glass thermometers, the measured temperature can be read on a scale. These clinical thermometers do not require any auxiliary energy and as a rule can usually be sterilized without any problems. Digital contact thermometers and infrared thermometers require batteries to determine and display the reading. With some of the digital contact thermometers and infrared thermometers it is possible to store the measurement values and to signal about abnormal values immediately by optical or acoustic alarms.

Infrared thermal images in medical diagnostics
Infrared thermometers can be used for more than just quick fever measurement. Special devices with thermal imaging show the heat distribution of the specific body regions. This makes it possible, for example, to visualize the location and spread of inflammations without affecting the body with radiation. The thermal images, which are quick and easy to create, make it easier to recognize certain diseases and evaluate their development. The success of a therapy can also be checked and illustrated quickly and easily with the help of the infrared thermal images.

IR thermometers without medical approval
For the quick control of individuals or groups of people for increased body temperature, the infrared cameras or infrared thermometers can also be used, which do not have approval as a medical device. These measurements are made without body contact. When selecting the infrared thermometers, care must be taken to ensure that the accuracy in the critical measurement range is high and that the measurement spot ratio is suitable for the intended measurements on the forehead. When evaluating the measurement results, it must be taken into account that the forehead temperature is usually lower than the core body temperature. In addition, hair, sweat, creams and makeup can influence the measurement of the infrared radiation. Besides, it must generally be considered that the body temperature can increase because of meals or physical exercising.

IR thermometers in veterinary medicine Infrared thermometers and thermal imaging cameras are also very appropriate for the application in the veterinary medicine. The small and lightweight devices can be easily transported and used in the environment the animal is accustomed to. The measurement itself is fast, painless and contact-free and causes no additional stress. Unlike mobile X-ray devices, the infrared thermometers do not emit any radiation. A helper can therefore calm the animal during the measurement, hold it or bring it into the desired position.