Emerson Rosemount 148 Reference Manual page 19

Reference Manual
00809-0100-4148
Examples of approximate lead wire resistance effect
calculations
Given:
Total cable length:
Imbalance of the lead wires at 20 °C:
Resistance/length (18 AWG Cu):
Temperature coefficient of Cu (α
Temperature coefficient of Pt (α
Change in Ambient Temperature (ΔT
RTD Resistance at 0 °C (R
o
• 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
150 m
0.5 Ω
0.025 Ω/m °C
): 0.039 Ω/Ω °C
Cu
): 0.00385 Ω/Ω °C
Pt
): 25 °C
amb
): 100 Ω (for Pt 100 RTD)
Installation
June 2019
19