Usually using platinum resistance temperature sensor PT100, temperature coefficient of resistance of 3.9 x103/ C,0 degrees C electric resistance is 100 ohms, resistance change rate is 0.3851 ohms / c.. Platinum resistance temperature sensor has the advantages of high precision, good stability, application of a wide range of temperature, is the temperature area ( the most commonly used a temperature detector, not only widely used in industrial measurement, and is made of a variety of standard thermometer.
According to IEC751 international standards, the temperature coefficient TCR = 0.003851, Pt100( R0= 100 Ohm ), Pt1000( R0 = 1000omega ) for the unified design of platinum resistance.
The sensor structure: two line system:
The change of resistance of the sensor and connected to the resistive wire value constitute the sensor output values, due to the resistance of a wire to bring additional error of the measured value is high, used for measuring precision is not high, and the length of the wire should not be too long.
Three wire system:
The three line will greatly reduce the resistance of a wire to bring additional errors, the industry generally adopts three wire connecting method.
Four wire system:
When the measured resistance value is very small, the test line resistance may introduce significant error, four wire measurement with two additional test line for providing a constant current, the other two test line measurement of unknown resistive voltage drop, the voltmeter input impedance is high enough conditions, current hardly flows through the voltage meter, which can accurately measure the unknown resistance pressure drop, calculates the resistance value.