Such a device works on the principle of the thermoelectric effect, i.e., generating a voltage when its dissimilar metals (thermocouples) are exposed to a temperature difference.
Adding more thermocouple pairs in series increases the magnitude of the voltage output.
The amount of voltage and power are very small and they are measured in milli-watts and milli-volts using controlled devices that are specifically designed for such purpose.
[4] They are also used widely in heat flux sensors and pyrheliometers[5][6] and gas burner safety controls.
[7] As well as increasing the signal level, the device may be used to provide spatial temperature averaging.
Diagram of a differential temperature thermopile with two sets of thermocouple pairs connected in series. The two top thermocouple junctions are at temperature
T
1
while the two bottom thermocouple junctions are at temperature
T
2
. The output voltage from the thermopile,
ΔV
, is directly proportional to the temperature differential,
ΔT
or
T
1
-
T
2
, across the thermal resistance layer and number of thermocouple junction pairs. The thermopile voltage output is also directly proportional to the heat flux,
q"
, through the thermal resistance layer.
Picture of a heat flux sensor that utilizes a thermopile construction to directly measure heat flux. Model shown is the FluxTeq PHFS-01 heat flux sensor. Voltage output is passively induced from the thermopile proportional to the heat flux through the sensor or similarly the temperature difference across the thin-film substrate and number of thermocouple junction pairs. This voltage output from the sensor's thermopile is initially calibrated in order to relate it to heat flux.
Thermopile, composed of multiple thermocouples in series. If both the right and left junctions are the same temperature, voltages cancel out to zero. However, if there is a temperature difference between sides the resulting total output voltage is equal to the sum of junction voltage differentials.
