Emerson 644 manual Pt100 2-wire RTD, Error due to amb. temp. var. of ± 25 C

Rosemount 644

Reference Manual

00809-0400-4728, Rev AA June 2011

Lead wire imbalance seen by the transmitter = 0.5 Ω

Basic error =	0.5 Ω	= 1.3 °C
	(---0.00385------------------------Ω------/----Ω-------°---C-----)----×----(---100------------Ω-----)-

Error due to amb. temp. var. of ± 25 °C

(0.0039 Ω / Ω °C) × (25 °C) × (0.5 Ω)

=------------------------------------------------------------------------------------------------------- = ±0.1266°C

(0.00385 Ω / Ω °C) × (100Ω)

•Pt100 2-wire RTD:

Lead Wire Resistance

Basic Error = ----------------------------------------------------------

(αPt × Ro)

(αCu) × (ΔTamb) × (Lead Wire Resistance) Error due to amb. temp. variation = ----------------------------------------------------------------------------------------------------------------

(αPt) × (Ro)

Lead wire resistance seen by the transmitter = 150 m × 2 wires × 0.025 Ω/m = 7.5 Ω

Basic error =	7.5 Ω	= 19.5 °C
	(---0.00385------------------------Ω-------/---Ω--------°--C-----)----×----(---100-------------Ω-----)

Error due to amb. temp. var. of ± 25 °C

(0.0039 Ω / Ω °C) × (25 °C) × (7.5 Ω)

=------------------------------------------------------------------------------------------------------- = ±1.9 °C

(0.00385 Ω / Ω °C) × (100Ω)

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