This article will discuss the difference between the two types of sensors (contact and non-contact temperature sensors). It will also discuss their advantages and disadvantages, while providing some of the latest research and developments in the field.
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Contact and non-contact temperature sensors are used in various applications due to their unique capabilities. Contact sensors rely on physical contact with objects and use conduction to monitor temperature changes. On the other hand, non-contact sensors do not require physical contact and are based on optical analysis of infrared radiation to detect temperature changes.
There are several types of contact temperature sensors, including thermocouples, thermistors, and resistance temperature detectors. In a thermocouple, the voltage difference is produced by the temperature difference between two different wires, and the temperature is calculated by measuring the voltage difference.
Thermistors are usually made of ceramics or polymers, and are different from thermocouples by measuring resistance changes. A common type is a negative temperature coefficient thermistor, whose resistance decreases with increasing temperature. Resistance temperature detectors are similar to thermistors and are usually made of platinum.
Non-contact temperature sensors include optical pyrometers, radiation thermometers, thermal imagers, and fiber optic sensors.
The radiation thermometer measures the radiation emitted from the object to measure the temperature difference. A thermal imager is similar to a radiation thermometer. However, they can calculate two-dimensional space instead of measuring temperature based on a given point on the surface of the object. The fiber optic temperature sensor is a variant of the radiation thermometer. The radiation is detected by active sensing devices, processed by the system and converted into temperature readings.
The optical pyrometer has an optical system and a detector to measure the temperature that is too bright that the naked eye cannot see. The optical system focuses the radiation on the detector and provides temperature measurement.
Thermocouples are used in many common applications, including household appliances (such as refrigerators) and engines used to measure exhaust gas temperature, among other purposes. Thermistors are used in fire alarms, ovens and digital thermometers.
Optical pyrometers are vital to the smelting industry because they can measure the temperature of moving objects at extreme temperatures.
The use of temperature sensors in the automotive industry includes resistance temperature detectors for intake air temperature sensors and optical fiber temperature sensors for setting engine temperature limits, helping to avoid overheating.
Thermocouples are inexpensive, easy to use, have a wide temperature range, and are self-powered. However, they suffer in terms of accuracy.
Although thermistors are sensitive and low cost, they are non-linear and self-heat. The radiation thermometer is accurate, repeatable and has long-term stability. However, their response speed is very slow, and the temperature range they can detect is limited. Due to the high cost, radiation thermometers are not as cost-effective as other sensors.
On the other hand, optical pyrometers can measure high temperatures with high accuracy. However, they are expensive and their accuracy can be affected by thermal background radiation, dust and smoke.
The optical fiber temperature sensor is not affected by nearby radiation, is accurate, has a fast response time, but is expensive, and the development of the measurement system is also very complicated. The thermal imager creates a complete heat map of objects that are difficult or inaccessible, but the image may be difficult to interpret.
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Innovation is driving the field forward. Recently, flexible temperature sensors, including flexible thermocouples, flexible thermistors, and flexible thermochromic types have been researched and optimized; active matrix flexible temperature sensors and self-powered flexible temperature sensors are examples.
Printable high-sensitivity flexible sensors have been explored to provide temperature monitoring for patients. It is a trend to develop wearable sensors that can monitor temperature, which can avoid the bulky problems of traditional devices and measurement errors caused by many factors such as the wearer's movement.
Other related research in the field of non-contact infrared thermometers is the most recent work, that is, to create a low-cost and more accurate Arduino-based infrared thermometer for body temperature detection. Arduino is an open source electronic platform that can convert input to output. This research aims to circumvent the inherent problems of non-contact infrared sensors currently on the market.
Other studies include coating the infrared thermopile sensor lens with graphene sheets for ear thermometers, and proposed a novel design for continuous temperature monitoring. A new non-contact temperature algorithm with high specificity for face detection in video sequences has also been developed.
In the sensor industry, non-contact temperature sensors have a growing trend. It is estimated that by 2027, the market will grow to USD 1,350.2 million, which indicates that the future of non-contact and contact temperature sensors is heating up.
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Reg Davey is a freelance writer and editor based in Nottingham, UK. Writing for news medicine represents a fusion of various interests and fields in which he has been interested and involved for many years, including microbiology, biomedical sciences, and environmental sciences.
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