2-Wire vs 3-Wire vs 4-Wire Pt100: What Is the Difference?
Why wiring matters for Pt100
A Pt100 changes resistance by only about 0.385 Ω per °C. The cable and connection resistance can therefore be a significant part of the measured value, especially on long runs. The wiring method determines how much of that cable resistance is included in the reading.
2-wire connection
The 2-wire connection uses one conductor for each side of the element.
- Advantages: simple, low cost, only two conductors
- Disadvantages: cable resistance adds directly to the reading
- Best for: very short cables, Pt1000 elements, non-critical measurements
A 2-wire Pt100 is acceptable when the cable is short and the accuracy requirement is loose. For long cables, the error can be several degrees.
3-wire connection
The 3-wire connection adds a third conductor to compensate for the resistance of one side of the cable. Most industrial transmitters and controllers support 3-wire Pt100 inputs.
- Advantages: good accuracy for industrial probes, common input type
- Disadvantages: assumes both cable legs have equal resistance
- Best for: general industrial probes, HVAC, process equipment
3-wire is the most common choice for industrial Pt100 probes because it balances cost and accuracy.
4-wire connection
The 4-wire connection uses two current-carrying and two voltage-sensing conductors. The voltage measurement is made directly at the element, so cable resistance is effectively eliminated.
- Advantages: highest accuracy, best for long cables
- Disadvantages: more conductors, more expensive, requires a 4-wire input
- Best for: laboratory, metrology, high-accuracy and long-cable installations
Quick selection guide
- Very short cable, loose accuracy: 2-wire
- General industrial probe: 3-wire
- Laboratory or long cable, high accuracy: 4-wire
Cable length and accuracy
As a rule of thumb, the longer the cable and the tighter the accuracy, the more you should move from 2-wire to 3-wire or 4-wire. The conductor size and temperature also matter; thin cables have higher resistance.
Matching the sensor to the instrument
A 3-wire probe will not deliver its best accuracy on a 2-wire input, and a 4-wire probe needs a compatible 4-wire transmitter or meter. Check the input type before ordering, or ask us to supply the probe and transmitter as a matched pair.
We supply Pt100 probes, high-precision Pt100 sensors and temperature transmitters. Contact us with your cable length and accuracy target and we will recommend the wiring method.