Emerson Rosemount X-well 648, Справочное руководство

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Specifications and Reference Data
July 2016
Reference Manual
00809-0200-4648, Rev BB
62
Specifications and Reference Data
A.1.7 Examples of approximate lead wire
resistance effect calculations
Given:
Total cable length 150 m
Imbalance of the lead wires at 20 °C 0.5

Resistance/length (18 AWG Cu): 0.025

/m
Temperature coefficient of Cu (a
Cu
)0.039

/

°C
Temperature coefficient of Pt (a
Pt
)0.00385

/

°C
Change in Ambient Temperature (DT
amb
)25 °C
RTD Resistance at 0 °C (R
0
)100

(for Pt 100 RTD)

Pt100 4-wire RTD: No lead wire resistance effect

Pt100 3-wire RTD:
Basic Error =
Error due to amb. temperature variation =
Lead wire imbalance seen by the transmitter = 0.5

Basic Error = = 1.3 °C
Error due to amb. temp. var. of ±25 °C =
= ±0.1266 °C

Pt100 2-wire RTD:
Basic Error =
Error due to amb. temp. variation =
Lead wire resistance seen by the transmitter =
150 m
⫻
2 wires
⫻
0.025

/m = 7.5

Basic Error = = 19.5

C
Error due to amb. temp. var. of ±25 °C =
= ±1.9

C
Imbalance of Lead Wires
(a
Pt
⫻
R
0
)
0.5

(0.00385

/

°C)
⫻
(100

)
(0.0039

/

°C)
⫻
(25 °C)
⫻
(7.5

)
(0.00385

/

°C)
⫻
(100

)
(a
Cu
)
⫻
(DT
amb
)
⫻
(Lead Wires Resistance)
(a
Pt
⫻
R
0
)
7.5

(0.00385

/

°C
)
⫻
(100

)
(0.0039
 / 
°C
⫻
(25
°C)
⫻
(7.5
 )
(0.00385
 /  °C
)
⫻
(100
 )
(a
Cu
)
⫻
(DT
amb
)
⫻
(Imbalance of Lead Wires)
(a
Pt
⫻
R
0
)
Imbalance of Lead Wires
(a
Pt
⫻
R
0
)