West Control Solutions MRC 7000 Controller Manual - Manual (Page 13)

13
RTD LEAD RESISTANCE
RTD lead length can affect instrument accuracy. Size (gauge) and length of the wire used
affects lead length resistance.
To determine the temperature error resulting from the lead length resistance, use the following
equation:
Terr = TLe * L where; TLe = value from Table 3 if 3 wire or Table 4 is 2 wire.
L = length of leadwire in thousands of feet.
TABLE 3 3 Wire RTD
AWG No. Error
°
C Error
°
F
10 +/-0.04 +/-0.07
12 +/-0.07 +/-0.11
14 +/-0.10 +/-0.18
16 +/-0.16 +/-0.29
18 +/-0.26 +/-0.46
20 +/-0.41 +/-0.73
24 +/-0.65 +/-1.17
TABLE 4 2 Wire RTD
AWG No. Error
°
C Error
°
F
10 +/-5.32 +/-9.31
12 +/-9.31 +/-14.6
14 +/-13.3 +/-23.9
16 +/-21.3 +/-38.6
18 +/-34.6 +/-61.2
20 +/-54.5 +/-97.1
24 +/-86.5 +/-155.6
Example
An application uses 2000 feet of 18 AWG copper lead wire for a 3-wire RTD sensor. What is
the worst-case error due to this leadwire length?
Terr = TLe * L
TLE = +/- .46 (
°
F/1000 ft) from Table 1
Terr = +/- .46 (
°
F/1000 ft) * 2000 ft
Terr = +/- 0.92
°
F