Both thermocouples and resistance temperature detectors (RTDs) are contact temperature measurement devices. Although both are contact temperature measuring instruments, their principles and characteristics are not entirely the same:
A thermocouple, which operates based on the thermoelectric effect, is a temperature sensor primarily used to measure high temperatures; a resistance temperature detector (RTD), which is based on a conductor or semiconductor, is itself a resistor and is mainly used to measure minute temperature changes.
Second, thermocouples generate changes in induced voltage, which change with temperature; while resistance temperature detectors (RTDs) are resistors, causing positive or negative changes in resistance.
Third, their temperature measurement ranges differ. Thermocouples are used in high-temperature environments, typically between 0-1000 degrees Celsius, or even higher; while resistance temperature detectors (RTDs) generally measure temperatures over a lower range.
Fourth, thermocouples have positive and negative poles. Common defects include short circuits, open circuits, poor contact (which can be diagnosed with a multimeter), and deterioration (identified by surface color). During inspection, the thermocouple should be separated from the secondary instrument, and the thermocouple's thermoelectric potential should be roughly estimated using the multimeter's mV range. Short circuits and open circuits in resistance temperature detectors (RTDs) can be diagnosed using a multimeter.
Fifth, a thermocouple is made of two different metal materials and belongs to bimetallic materials; while a resistance temperature detector (RTD) is a metal material and is also a metal material that is sensitive to temperature changes.
