Thermopiles are thermoelectric devices used for non-contact temperature measurement by absorbing infrared radiation emitted by an object’s surface. They consist of thermocouples, which produce a voltage proportional to the temperature difference between hot and cold ends. The hot junctions face the incident IR radiation, while the cold junctions are connected to a heat sink. Thermopiles are used in various industries, including medical, gas sensing, and heat sensing applications. They are also used in gas detectors to measure the concentration of gases in the atmosphere.
A thermopile is a thermoelectric device consisting of a series of thermocouples connected in series. It is widely used in non-contact temperature measurement applications and temperature monitoring systems. Thermopiles sense the temperature of an object by absorbing infrared (IR) radiation emitted by the object’s surface. Most device detectors have a black body surface to effectively absorb IR radiation.
The thermocouples that make up a thermopile consist of two strips of different metals welded at one end. Each thermocouple produces a voltage proportional to the temperature difference between the “hot” and “cold” ends, known as the Seebeck effect. However, the total voltage output of one of these devices is significantly higher than that of a thermocouple.
In a thermopile detector, the “hot junctions” of the thermocouples face the incident IR radiation from the object, while the “cold junctions” are connected to a heat sink, which is usually a silica substrate. Once the detector is pointed at the object, heat flows from the object to the thermopile. This heat flow creates a large temperature difference between the hot and cold junctions, which contributes to an increase in the electrical signal output from the thermopile. To easily measure this output signal, a noise-free output amplifier can be used.
In heat sensors, when IR radiation from an object is absorbed by the thermopile sensor, the individual voltages of the thermocouples add up to generate a high output voltage. Most thermopiles have built-in thermistors. This is because the output signal is proportional to the temperature difference between the object and the thermopile, and a thermistor helps record the temperature.
The advent of silicon-based micromachining technology has led to the easy availability of affordable thermopile detectors. These are used extensively across a range of industries. Among other uses, they are used in medical applications such as ear thermometers, heat sensing applications such as microwave ovens and hair dryers, and gas sensing applications such as CO2 sensors.
Gas detectors use thermopiles to measure the concentration of gases in the atmosphere by IR absorption. For example, CO2 sensors are employed in heating, ventilation and air conditioning (HVAC) applications that control indoor air quality (IAQ), facilitating demand controlled ventilation (DCV). These gas detectors have a wide range of industrial applications, such as gas leak detection, landfill CO2 content measurement, patient exhalation CO2 content monitoring, and fire alarm applications.
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