Principle and Wiring Method of the PT100 Temperature Probe
Release Date:
2021-11-02
Author:
Pt100 refers to a resistance of 100 ohms at 0°C, PT100 temperature probe The resistance. A resistive temperature sensor made of platinum (Pt) exhibits a positive temperature coefficient, and its resistance varies with temperature according to the following relationship: R = R₀(1 + 10T).
I. PT100 Temperature Probe The main technical parameters are as follows:
PT100 temperature probe measurement range: -200 to 850;
Permissible deviation: Class A (0.15, 0.002t), Class B (0.30, 0, 0.005t); thermal response time less than 30 s.
Minimum installation depth: minimum installation depth for thermal resistance, 200 mm
The allowable current is 5 mA. In addition, the Pt100 temperature sensor features vibration resistance, stability, accuracy, and high-pressure tolerance.
Advantages.
II. Three-wire connection method for PT100 temperature probes.
The PT100 temperature probe has three leads, designated A, B, and C (or black, red, and yellow). The resistance between any two of these leads is as follows: the resistance between A and either B or C is approximately 110 ohms at room temperature, while the resistance between B and C is 0 ohms, indicating that B and C are internally connected in a straight‑through configuration.
A is the fixed terminal on the instrument to which the sensor is connected. B and C are connected to the other two fixed terminals of the instrument; the positions of the B and C leads may be interchanged, but all three must be properly connected. If intermediate extension leads are used, the three conductors must have identical specifications and lengths. The three‑wire and four‑wire connection methods for resistance temperature detectors are primarily determined by the secondary instruments employed—whether they are two‑wire, three‑wire, or four‑wire systems.
Standard display instruments typically offer a three‑wire connection method. A PT100 sensor has one wire at one end and two wires at the other; both ends are connected to the instrument, and an internal bridge compensates for lead‑wire resistance. Most PLCs use a four‑wire configuration, with two wires at each end; the PLC supplies a constant current source via two of these wires and measures the PT100’s voltage through the remaining two. Furthermore, while four‑wire wiring provides higher accuracy by compensating for lead‑wire resistance, three‑wire wiring is also acceptable, whereas two‑wire wiring offers lower accuracy. The choice of wiring configuration should be guided by the required measurement accuracy and cost considerations.
III. PT100 temperature probe Reasons for using the three-wire connection method:
The PT100 temperature probe has a resistance of 100 Ω at 0 °C, with a temperature coefficient of resistance of 0.3851 Ω/°C. Due to its low resistance and high sensitivity, measurement errors caused by lead‑wire resistance can be eliminated as follows.
In a PT100, all three lead wires have the same cross-sectional area and length (i.e., r1 = r2 = r3). The circuit used to measure the platinum resistance typically employs an unbalanced bridge. One lead (R1) is connected to the power supply of the bridge, while the other two leads (R2 and R3) are connected to the bridge arm containing the platinum resistor and to the adjacent bridge arm resistor, respectively.
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