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Classification of industrial temperature sensors
Release time:2020-02-22   Clicks:706
Classification of industrial temperature sensors
The three most commonly used temperature sensors are thermocouples, thermal resistance thermometers (RTD), and NTC thermistors.
thermocouple:
Consists of two foreign metal wires welded together to form two nodes. The temperature difference between the nodes creates a thermoelectric potential (voltage) between the two wires. By keeping the reference node at a known temperature and measuring the voltage, the temperature of the detection node can be inferred. Thermocouples have the advantage of operating over a very wide temperature range and being very small. However, they also have the defects of small output voltage, easy to be affected by the noise from the loop and high drift.
Thermal resistance thermometer (RTD):
It is a wound wire or thin film spiral tube that can show the change of resistance with temperature. Although the commonly used metals are copper, nickel and inconel, RTD made of platinum has the best linearity, repeatability and stability. With its excellent linearity and unparalleled long-term stability, platinum RTD firmly establishes itself as the international standard for temperature reference transmission. Although thin film platinum RTD provides performance matching, standard grade wire-wound resistors are superior in cost, form size, and convenience. Early thin film platinum RTD suffered from drift due to their high surface area to volume ratio, making them more sensitive to contamination. Later, improvements in film isolation and packaging eliminated these problems, making thin film RTD the preferred temperature sensor over wire-wound resistance and NTC thermistors.
NTC thermistor:
Composed of metal oxide ceramics, it is a low cost and the most sensitive temperature sensor. They are also the least linear temperature sensors with negative temperature coefficients. Thermistors are available in a variety of dimensions, base resistance values, and resistance-temperature (r-t) function curves to simplify packaging and output linearized circuits. Two thermistors are usually used together to make the output linear. The commonly used thermistors have an interchangeability of 10%-20%. Although it provides an accurate 1 per cent interchangeability, it tends to cost more than platinum RTD. Ordinary thermistors exhibit excellent resistance stability over a limited operating temperature range and moderate stability over a wide temperature range (2%/1000 h at 125 ° c).
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