Emerson Rosemount 148, Reference Manual, Page: 19 / 36

Examples of approximate lead wire resistance effect
calculations
Given:
Total cable length: 150 m
Imbalance of the lead wires at 20 °C: 0.5 Ω
Resistance/length (18 AWG Cu): 0.025 Ω/m °C
Temperature coefficient of Cu ( α
Cu
): 0.039 Ω/Ω °C
Temperature coefficient of Pt ( α
Pt
): 0.00385 Ω/Ω °C
Change in Ambient Temperature (ΔT
amb
): 25 °C
RTD Resistance at 0 °C (R
o
): 100 Ω (for Pt 100 RTD)
• Pt100 4-wire RTD: No lead wire resistance effect.
• Pt100 3-wire RTD:
Lead wire imbalance seen by the transmitter = 0.5 Ω
• Pt100 2-wire RTD:
Lead wire resistance seen by the transmitter = 150 m
×
2 wires
×
0.025 Ω/m =
7.5 Ω
Reference Manual Installation
00809-0100-4148 June 2019
19