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THE PRINCIPLE OF RESISTANCE TEMPERATURE DETECTORS

Resistance Temperature Detectors (RTDs) exploit the constant change in electrical resistance of some materials with changing temperature. They are almost invariably made of platinum due to the characteristics such as constant resistance change with changing temperature, interchangeability, and high temperature coefficient.

Only platinum (Pt) is currently adopted by Japanese Industrial Standard (JIS). However, nickel, copper, and other metals are used in the industry.

As the principle of measurement is shown in Fig.1, a constant current (0.5 to 2mA) is flowed through a resistance element (typically Pt 100Ω) and the resistance change with changing temperature is measured.

The three-wire construction is commonly applied to offset resistance in lead wires.

ACCURACY FOR RTD

  1. Note:
  2. 1 L = low temperature, M = medium temperature, H = high temperature
    2 The accuracy of class A is not applied to two-wire structure.
    3 The accuracy of class A is not applied to measurement above 450 for wire wound elements and 300 for thin film elements. in IEC Standard.
    4 MI Sheath RTDs can be used up to 500. Specified currents are 0.5, 1, 2mA.
    5 We do not manufacture RTDs for super high temperature.
    Class Accuracy
    1/3B (0.1+0.0017l t l)
    A (0.15+0.002l t l)
    B (0.3+0.005l t l)
    2B (0.6+0.01l t l)
    Note: | t | is an absolute value.

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