Pt100, that is to say, its resistance value is 100 ohms at 0 degrees. PT100 temperature sensor is a resistance temperature sensor made of platinum (Pt), which belongs to positive resistance coefficient. The relationship between resistance and temperature change is as follows: R = Ro (1 + αT).
The main technical parameters of Pt100 temperature sensor are as follows:
Measuring range: -200 ~850 ℃; Permissible deviation △℃: A grade± (0.15+0.002 │t│) and B grade± (0.30+0.005│t│) and thermal response time (<30s); minimum insertion depth: minimum insertion depth of thermal resistance (≥200mm); permissible current (≤5mA). In addition, Pt100 temperature sensor also has the advantages of anti-vibration, good stability, high accuracy and high voltage resistance.
Connection of three core wires of PT100 temperature sensor:
PT100 platinum resistance sensor has three leads, which can be represented by A, B, C (or black, red, yellow). There are the following rules among the three wires:
The resistance between A and B or C is about 110 Euros at room temperature, and between B and C is 0 Euros. B and C are directly connected internally. In principle, B and C are no different.
There are three fixed terminals connected to the sensor on the instrument: a fixed terminal connected to the sensor on the instrument. B and C are connected to the other two fixed terminals on the instrument. The positions of B and C are interchangeable, but they all have to be connected. If there are lengthened wires in the middle, the specifications and lengths of the three wires should be the same.
3-wire and 4-wire connection method of thermal resistance: 2-wire, 3-wire and 4-wire connection method is adopted, which is mainly determined by the secondary instrument used for making (selecting).
General display instrument provides three-wire connection method, PT100 one end out of a line, the other end out of two lines, are connected to the instrument, instrument interior through the bridge to offset wire resistance.
Generally, PLC is four-wire, with two wires at each end, two of which are connected with the constant current source of PLC. The voltage of PT100 is also measured by two other wires to offset the resistance of the conductor. The accuracy of four wires is the highest, three wires are also the best, and two wires are the lowest. The specific usage should consider the accuracy requirements and cost.
Reasons why PT100 temperature sensor adopts three-wire connection method:
The resistance of PT100 temperature sensor is 100_and the resistance change rate is 0.3851_/ C. Because of its small resistance value and high sensitivity, the resistance value of lead can not be neglected. The measurement error caused by resistance of lead can be eliminated by using three-wire connection method.
The principle is as follows:
The cross-sectional area and length of three conductors drawn from PT100 are the same (r1 = R2 = r3). The circuit for measuring platinum resistance is usually unbalanced bridge. As a bridge arm resistance, platinum resistance (Rpt100) connects one conductor (r1) to the power end of the bridge, and the other two (r2, r3) to the bridge arm where the platinum resistance is located and the adjacent bridge. On the arm, so that both arms introduce the same resistance value of the lead resistance, the bridge is in equilibrium, and the change of the lead resistance has no effect on the measurement results.
Dimension diagram: wiring diagram:
The PT100 temperature sensor is a kind of instrument that converts temperature variables into a standardized output signal that can be transmitted.