Termopary

Termopary, known in English as thermocouples, are temperature sensors that rely on the thermoelectric effect. When two dissimilar metals are joined at a sensing junction and one end is exposed to a higher temperature than the other, a small voltage is generated. This voltage, typically measured in microvolts per degree Celsius, relates to the temperature difference between the junctions and is converted to a temperature reading using a calibration curve. To determine an absolute temperature, the temperature at the reference junction, or cold junction, must be known or compensated for.

Operation depends on the metal pair used, and different material combinations yield different sensitivities and usable ranges. Base-metal types include K (nickel-chromium/nickel-aluminum), J (iron/constantan), T (copper/constantan), E (nickel-chromium/nickel-silicon), and N (nickel-chromium-silicon/nickel-silicon). Noble-metal types used for higher temperatures include S (platinum–rhodium) and R (platinum–rhodium), with B employing a platinum–rhodium alloy suitable for very high temperatures. Selection depends on required temperature range, environment, and accuracy.

Termopary are typically built as two wires joined at the sensing tip, with insulation and protective sheath. Readout electronics provide cold-junction compensation and, often, linearization, to yield a calibrated temperature. They can be produced as probes, surface sensors, or embedded in cables and devices.

Applications are broad, spanning industrial process control, furnaces and kilns, automotive and aerospace systems, HVAC, and laboratory experiments. Advantages include a wide operating temperature range, robustness, simplicity, and relatively low cost. Limitations include non-linearity, drift over time, material degradation, and the need for compensation and careful installation to minimize errors.