Rosemount 848T, Справочное руководство

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Reference Manual
00809-0100-4848, Rev AA
July 2009
Rosemount 848T Wireless
3-6
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 ( 
Cu
) 0.039

/
 
C
Temperature coefficient of Pt ( 
Pt
) 0.00385  /  C
Change in Ambient Temperature (  T
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 x 2 wires x
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
( 
Pt
x R
0
)
( 
Cu
) x (  T
amb
) x (Imbalance of Lead Wires)
( 
Pt
x R
0
)
0.5 
( 
/
  C) x (100 
)
(0.0039  /   C) x (25  C) x (0.5  )
(0.00385  /   C) x (100  )
Imbalance of Lead Wires
( 
Pt
x R
0
)
( 
Cu
) x (  T
amb
) x (Lead Wires Resistance)
( 
Pt
x R
0
)
7.5 
( 
/

 C
) x (100 
)
(0.0039  /   C) x (25  C) x (7.5  )
(0.00385  /   C) x (100  )