Thermopile

Thermopiles are thermal radiation detectors that can convert electromagnetic radiation from the infrared spectral range into an electrical signal.

The incoming focused radiation leads to a temperature change in a material with high absorption. As with thermocouples, the Seebeck effect causes a small electrical voltage to arise at the contact points of two different metals when there is a temperature difference between the contact points. If any such thermocouples (e.g., 80) are now connected thermally in parallel and electrically in series, a sufficiently high thermoelectric voltage can be generated, which serves as a measurement signal. Such an arrangement is called a thermoelectric pile or thermopile.

These detectors have time constants of approximately 7 ms to 150 ms. If this technology is used for non-contact infrared temperature measurement, the temperature of a measurement object can be determined significantly faster than with contact measurement. Thermopiles also generate an evaluable signal for a scene that is significantly colder than the detector itself. This means that temperatures below room temperature or the detector’s temperature can also be measured. Measuring ranges starting at -40 °C are possible. Modern thermopiles generate such a strong thermoelectric voltage that their signal can be sent directly, i.e., without amplification, via a signal line several meters long. As the detector itself can withstand temperatures of up to 250 °C, the absence of an amplifier circuit enables the construction of a sensor with an astonishing ambient temperature range, which is not possible with quantum detectors. If amplification is used to maximize the temperature resolution, values of less than 0.1 K (e.g., 0.025 K) can be achieved.