A thermopile is an electronic device that transforms heat into electricity. It is made up of numerous thermocouples that are normally connected in series or, less frequently, in parallel.

Thermocouples work by monitoring the temperature difference between their junction point and the thermocouple output voltage measurement point. Thermocouples with a connector on either side of a thermal resistance layer can be joined in series as thermocouple pairs. The thermocouple pair’s output will be a voltage proportional to the temperature difference across the thermal resistance layer as well as the heat flux through the thermal resistance layer. The magnitude of the voltage output grows as more thermocouple pairs are connected in series. A single thermocouple pair, two thermocouple junctions, or many thermocouple pairs can be used to make thermopiles.

A thermopile is a serially interconnected array of thermocouples, each of which is made up of two different materials with high thermo-electric power and polarities that are opposing. The thermocouples are installed in a structure’s hot and cold zones, with the hot junctions thermally separated from the cold connections. To create an effective heat sink, cold junctions are often put on the silicon substrate. There is a black body in hot places that absorbs infrared and elevates the temperature proportional to the intensity of the incident infrared. Two distinct thermoelectric materials are used in these thermopiles, which are mounted on a thin diaphragm with low thermal conductivity and capacitance.

A thermopile is a collection of thermocouples that are connected in series. A thermopile containing N thermocouples will create a voltage N times higher than a single thermocouple, improving the transducer’s sensitivity. A meaningful voltage can be generated in the thermopile with enough elements to regulate another operation. Heat is frequently measured with this type of transducer.

Thermopiles produce an output voltage proportionate to a temperature differential or temperature gradient rather than absolute temperature.

Thermopiles are used in temperature measuring devices to provide an output in response to temperature, such as infrared thermometers commonly used by medical professionals to measure body temperature. They’re also commonly utilized in heat flux sensors and safety controls for gas burners.

A thermopile’s output is commonly measured in tens or hundreds of millivolts. The gadget can be used to offer spatial temperature averaging in addition to improving the signal intensity. Thermopiles can also generate electricity from heat generated by electrical components, solar wind, radioactive materials, or combustion. The Peltier Effect (electric current transferring heat energy) is also demonstrated by the process, which transfers heat from hot to cold junctions.


  • Temperature measurement in the process field without contact
  • Scanner Thermal Line is a hand-held device that calculates the non-contact temperature.
  • HVAC and lighting control in industrial buildings
  • For protection, human presence and identity are required.
  • Early detection and warning of black ice
  • Blood Glucose Monitoring
  • HVAC power is turned on automatically.
  • Fire detection in transportation tunnels
  • Aircraft Flame and Fire Detection
  • Automatic exhaust gas analysis

Advantages of Thermopile

  • There is no requirement for an external power supply.
  • Response to DC radiation emitted by temperature sensing bodies is stable
  • Characteristics of a Stable Response

Thermopile sensor

A thermopile sensor is a sensor device that uses non-contact temperature sensing with the use of several thermocouples. It has a higher voltage output than a traditional thermocouple sensor.

It is based on the absorption of infrared radiation by the thing being measured. The thermopile sensor’s electrical output is proportional to its temperature. As a result, it’s called a thermoelectric transducer.

How To Test Thermopiles?

The pilot light in a millivolt gas fireplace warms a sensor, which is generally a thermocouple or thermopile. When heat is applied to the thermopile and thermocouple, electricity is generated. The wall switch receives this modest quantity of voltage.

When the switch is turned on, it returns the electricity to the fireplace and instructs it to turn on the flame.

The connections within the switch can become rusted, corroded, or destroyed with time, causing the switch to lose voltage.

As a result, signalling the fireplace to come on by the time the minimal quantity of electricity is returned to the fireplace is insufficient.

After we’ve ruled out the possibility of a faulty wall switch or a malfunctioning pilot flame, we’ll need to inspect the thermopile.

When heated by the pilot flame, the thermopile produces a voltage in the same way that a thermocouple does. We can measure the voltage that the thermopile emits using a digital multimeter.

We’ll use a fireplace as an example, where you’ll need to inspect the status of a thermopile. The thermopile leads are tested with a multimeter.

Because they’re connected to the gas control valve, the first thing we should do is find it.

In most cases, the main control valve is found beneath the lower grill of the fireplace.

The thermopile sensor is located beneath the main control valve. The pilot assembly will be connected to the main control valve via a wire.

It is made up of two wires that are normally protected by a metal sheath. The thermopile wire’s end splits into two leads, which are commonly red and white in color.

The thermopile’s leads will be connected to the main valve. On the terminals to which the thermopile is connected, we can test the voltage with a digital multimeter set to DC millivolts. On your meter, the DC setting will be indicated by the letters “DC” or a symbol.

Differential Temperature Thermopile

Above is a diagram of a differential temperature thermopile with two thermocouple pairs connected in series. The two thermocouples on top are connected and at temperature T1, while the two thermocouples on the bottom are connected and at temperature T2. The thermopile delta V’s output voltage is proportional to the temperature differential (T1-T2) across the thermal resistance layer and the number of thermocouple junction pairs.

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