PT100 wiring method: The clear distinction between two-wire, three-wire, and four-wire systems at a glance
An incorrect wiring method for Pt100 Sensors can result in temperature measurement deviations of several degrees—a significant issue in industrial settings. Many engineers simply connect two wires during installation, leading to persistently low measurement accuracy; only after extensive troubleshooting do they realize the problem lies in the wiring approach. This article clearly explains the differences between two-wire, three-wire, and four-wire systems to help you avoid unnecessary complications.
Why does the wiring method affect accuracy?
At 0°C, the resistance of a Pt100 Sensor is only 100 Ω; for every 1°C change in temperature, its resistance varies by approximately 0.385 Ω. If the wire resistance is 1 Ω (for about 10 meters of standard wire), it results in a temperature measurement error of approximately 2.6°C. Therefore,eliminating the influence of lead resistance is the key consideration in PT100 wiring.
Two-line system: simplest, lowest accuracy
Only two wires are connected, with the sensor and instrument connected in series. The advantage is simple wiring; the disadvantage is that the wire resistance is directly added to the measured value and cannot be eliminated. This configuration is suitable only for short distances and applications with low precision requirements (±5°C acceptable).
The Three-Line System: The Most Common Solution in Industry
Connect three wires, one of which is used to compensate for lead resistance. The principle involves introducing a wire of equal length into each arm of the bridge, thereby canceling out the lead resistances. This is the most widely adopted PT100 wiring method in industrial applications, achieving an accuracy of ±0.5°C and a measurement range of several tens of meters.
Four-line system: highest accuracy
Connect four wires: two for the constant current source and two for voltage measurement. Since the current in the voltage measurement circuit is nearly zero, the lead resistance does not induce a voltage drop, completely eliminating lead-related errors. The measurement accuracy reaches ±0.1°C, making it suitable for laboratory and calibration applications.
How to choose among the three wiring methods?
| mode of connection | Number of wires | accuracy | Applicable Distance | Common Scenario |
| two-wire system | 2 pieces | ±5℃ | <5 meters | Simple Alarm |
| three-wire system | 3 pieces | ±0.5℃ | Dozens of meters | industrial process control |
| four-wire system | 4 pieces | ±0.1℃ | hectometre + | Laboratory Calibration |
Selection recommendation: For 90% of industrial applications, a three-wire system is sufficient. A four-wire system is only required for high-precision calibration; avoid using a two-wire system whenever possible.
Before wiring, confirm which wiring system your instrument supports to avoid terminal misalignment after completion. For any selection or wiring inquiries, please consult our technical team for professional solutions.
Schematic comparison of three wiring methods for the PT100 platinum thermal resistance Temperature Sensor