Thermopiles are used in several industries for temperature sensing without any contact. A thermopile is an electronic device that can convert thermal energy to electrical energy. The prime function of a thermopile is to transfer an object’s heat radiation to a voltage output. When compared to the thermocouple operations, a thermopile can detect significantly low temperatures.
What is a thermopile made of?
A thermopile is made of a wide array of thermocouples linked usually in a series, and rarely parallel. There are two distinct materials with large thermoelectric power and opposite polarities. The thermocouples are situated through the cold and hot areas of the device. Moreover, the hot joints are isolated thermally from the cold joints.
The cold joints are usually situated on the silicon substrate which offers an effective heat sink. In the hot junction, there consists of a black body that absorbs the infrared. The infrared increases the temperature as per the intensity of the incident infrared.
Working principle of a thermopile
In the thermopile, the thermocouples function by determining the differences in the temperature from their hot and cold points to the level at which the thermocouple output voltage is determined. The thermocouple pairs are situated on either side of a thermal resistance layer. The thermocouple pair’s output is considered as the voltage. This is directly proportional to the difference in temperature across the thermal resistance layer. Moreover, it is also directly proportional to the inflow of heat via the thermal resistance layer.
When the number of thermocouple pairs in a thermopile is increased in series, the intensity of the voltage output/outcome also increases. A thermopile can be made either with a thermocouple pair which consists of two different thermocouple joints, or multiple thermocouple pairs are in use in the construction of a thermopile.
In the majority of thermopiles, multiple thermocouples in series are included. When both left and right joints consist of the same temperature levels, the voltage output nullifies to zero. On the other hand, when there is a difference in the temperature between the left and right junctions, the voltage output will be equivalent to the sum of the differences in voltages of the left and right junctions.
Applications of thermopiles
Thermopiles are used to offer a voltage output in exchange for the temperature of a measuring device. For instance, an infrared thermometer is used by healthcare professionals to measure the temperature of the body. Furthermore, a thermal accelerometer is also used to measure the temperature in the sensor’s sealed region. Thermopiles are also used in sensors of heat flux, and safety controls in gas burners. The voltage output of a thermopile ranges from tens to hundreds of millivolts.
Applications of a thermopile in a brief:
- Thermal line scanner
- Security human detection and scanner
- Contactless temperature measurement in the process industry
- Monitoring of blood sugar
- Handheld contactless temperature measurement
- HVAC lighting control in commercial buildings
- Detection and warning for black ice
- Automatic HVAC control
- Detection of fire in transport tunnel
- Analysis of exhaust gas (automatic)
- Detection of fire and flame in aircrafts
Apart from the above-mentioned applications, thermopiles are also used to yield electrical energy in the solar wind, laser radiation, radioactive materials, and so on. Concerning thermopile sensors, which are also known as power meters are based on the principle of optical power converting into heat energy. The outcome is an increase in temperature which can be measured by thermopiles.
Advantages of thermopiles
Some of the common advantages of thermopiles include the following:
- There is no need for any external supply of power
- There are stable response characteristics
- One can expect to have a stable response to DC radiation excluded from temperature measuring or sensing devices
Application in gas-fired unit heaters
Thermopiles are widely used in several gas-fired heating units in residential and small commercial installations. The heat source is the flame of the gas-standing pilot light. The voltage yielded by the heat of the gas-fired unit’s flame offers the power for the gas valve to open and close. The thermopiles generate electric power in a small quantity. Thus, the gas valve is designed in a way to utilize gas pressure and aid in the valve opening. Since the heater will not operate without the flame being ignited, it is also considered a safety control. This also means that the pilot light must remain lit whenever the heater functions.
Thermopile sensors/detectors are thermal detectors. Thermal electromotive force is yielded concerning incident infrared light energy. The thermopile sensors don’t have any wavelength dependence. They have diverse applications like analysis of gas, human body detection, measurement of body temperature.