RTD Lead Wire Resistance Error Calculator
See how much error the cable adds to an RTD measurement with a 2 wire connection, and why 3 and 4 wire connections are used.
- R lead = length × Ω/km × (1 + 0.00393 (T − 20))
- Error = 2 × R lead ÷ (R0 × 0.00385) = 6.364 °C
Lead Resistance Error
3 wire: lead resistances cancel if matched · 4 wire: no lead error
Conductor resistance from IEC 60228 class 2 at 20 °C (0.5 mm² 36.0, 0.75 mm² 24.5, 1.0 mm² 18.1, 1.5 mm² 12.1 Ω/km).
Worked example
50 m of 0.75 mm² cable adds 1.225 Ω per conductor at 20 °C. A 2 wire Pt100 then reads about 6.4 °C high; a Pt1000 only 0.64 °C.
Frequently Asked Questions
How much error does a 2 wire RTD have?
About 2.6 °C per ohm of total lead resistance for a Pt100.
Why is 3 wire RTD common?
It cancels the lead resistance at low cost, good enough for most industrial measurements.
Is Pt1000 better for long cables?
Yes, its 10 times higher sensitivity makes lead errors 10 times smaller.
Learn more on the blog
What is an RTD and how it works
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
Read Full Article