Partlow MRC 7000 Installation & Operation Manual page 12

12
RTD LEAD RESISTANCE
RTD lead length can affect instrument accuracy, since the size (gauge) and length of the wire
affect lead resistance.
To determine the temperature error resulting from the lead length resistance, use the follow-
ing equation:
Terr = TLe * L where; TLe = value from Table 3 if 3 wire RTD or Table 4 if 2 wire RTD
TABLE 3 3 Wire RTD
Error ° C
AWG No.
10 +/-0.04
12 +/-0.07
14 +/-0.10
16 +/-0.16
18 +/-0.26
20 +/-0.41
24 +/-0.65
TABLE 4 2 Wire RTD
Error °C
AWG No.
10 +/-5.32
12 +/-9.31
14 +/-13.3
16 +/-21.3
18 +/-34.6
20 +/-54.5
24 +/-86.5
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 3
Terr = +/-.46 (‡F/1000 ft) * 2000 ft
Terr = +/-0.92°F
L = length of lead wire in thousands of feet
Error °F
+/-0.07
+/-0.11
+/-0.18
+/-0.29
+/-0.46
+/-0.73
+/-1.17
Error °F
+/-9.31
+/-14.6
+/-23.9
+/-38.6
+/-61.2
+/-97.1
+/-155.6