What is the difference between the principle of 2-wire, 3-wire and 4-wire thermal resistance temperature measurement?

What is the difference between the principle of 2-wire, 3-wire, 4-wire thermal resistance temperature measurement?

The detection equipment connected to the thermal resistance (temperature control meter, PLC input, etc.) has four terminals. I+, I-, V+, V-.

Among them, the I+ and I- ends are used to provide a constant current to the thermal resistance, and V+ and V- are used to monitor the voltage change of the thermal resistance, and in turn detect the temperature change.

The 4-wire is that 4 wires are drawn from both ends of the thermal resistance and connected to 4 terminals.

The 3-wire is the leading out of the 3-wire, which requires the detection of the I-\V- short-circuit of the device.

2 wire leads to 2 wire, which needs to detect the I-\V-, I+/V+ short-circuit of the device.

The principle of temperature measurement is the same, but the wiring is different.

It should be said that the current loop and the voltage measurement loop are connected separately.

2 lines, the current loop and voltage measurement loop are combined to 1, the accuracy is poor.

3 line, the reference bit of the current loop and the reference bit of the voltage measurement loop are one line. Slightly better accuracy.

4 lines, circuit loop and voltage measurement loop independent separate, high accuracy, but cost line.