What is the four -line RTD temperature sensor?

A very ancient electrical measurement technology, called the Cairvin or the four -wire method, is a practical method to solve the problem of wire resistance.
It is usually used for accurate resistance measurement of scientific experiments under laboratory conditions. The four -line technology uses four lines to connect to the measurement instrument (RTD in this example). Essence
The two wires transmit the "motivation" current from the current source to the RTD temperature sensor, while the other two wires only fall on the voltage signal on the voltage signal to the voltage meter for only the "induction" RTD resistor element.
RTD temperature sensor resistance uses Ohm's law calculation: The measurement voltage displayed by the voltage meter is divided by the adjustable current value of the current source.
Here is a simple 4 -line RTD temperature sensor circuit for explanation:

The wire resistance is completely irrelevant in the circuit. Two "incentives" cables to the two "incentives" cables to the RTD temperature sensor will decrease some voltage along their length, but this voltage decrease can only be "see" by the current source instead of the voltage meter.
The two "detection" cables that connect the voltage meter to the RTD temperature sensor also have resistance, but their voltage decrease can be ignored because the voltage table is very small by the current absorbed by them.
Therefore, the resistance of the load wire has no effect, because the voltage gauge will never detect their voltage drop, and the resistance of the sensing wire of the voltage meter has no effect because they actually carry zero current.
Please note how the wire color (white and red) indicates which wires are on the RTD temperature sensor on the public line pair. RTD is not sensitive to the temperature sensor, because it is just a resistor. This is why it is positive and which color is negative. It is not important.
The only disadvantage of the four -line method is that there are too many required wires. When many different RTD temperature sensors are installed in a process area, the four lines of each RTD temperature sensor can increase considerable number of lines.