Termopaarien

Termopaarien, also known as thermocouples, are compact temperature sensors based on the Seebeck effect. When two dissimilar metals are joined, a voltage is generated that varies with the temperature difference between the junctions. Measuring this voltage at the hot junction and comparing it to a reference junction yields a temperature reading.

Construction and principle: The sensing junction, placed at the measurement point, is joined to a reference end carried to a known reference temperature. The output is a small millivolt signal whose magnitude depends on the metal pair. Modern instrumentation uses cold-junction compensation to convert the millivolts into an absolute temperature.

Common metal pairs and ranges: Type K (Chromel–Alumel) is widely used and covers about -200 to over 1000°C. Type J (Iron–Constantan) and Type T (Copper–Constantan) are common for lower ranges. Types E, N, S, R, and B cover higher temperatures or specialized environments; S and R employ platinum/rhodium alloys, while B uses platinum–rhodium with higher temperature limits.

Advantages and limitations: Thermocouples are rugged, inexpensive, and operate over a broad temperature range. They provide fast response and simple wiring. Limitations include non-linear output, sensitivity to aging and oxidation, drift with time, and reliance on accurate reference junction compensation and calibration.

Applications and standards: They are used in process control, industrial furnaces, engines, kilns, and gas appliances. Standards include IEC 60584 and related national adapters, with calibration data published by standard bodies and manufacturers.