Partlow MIC 1161 - Sensor Placement; Thermocouple Lead Resistance

13 MIC 1161 Manual
2.2.2 SENSOR PLACEMENT (Thermocouple or RTD)
Two wire RTD’s should be used only with lead lengths less than 10 feet.
If the temperature probe is to be subjected to corrosive or abrasive condi-
tions, it should be protected by the appropriate thermowell. The probe
should be positioned to reflect true process temperature:
In liquid media - the most agitated area
In air - the best circulated area
THERMOCOUPLE LEAD RESISTANCE
Thermocouple lead length can affect instrument accuracy since the size
(gauge) and the length of the wire affect lead resistance.
To determine the temperature error resulting from the lead length resis-
tance, use the following equation:
Terr = TLe * L where; TLe = value from appropriate table
L = length of leadwire in thousands of feet
TABLE 1
See next page for Table 2
AWG
NO.
10
12
14
16
18
20
24
J
.34
.54
.87
1.37
2.22
3.57
8.78
K
.85
1.34
2.15
3.38
5.50
8.62
21.91
T
.38
.61
.97
1.54
2.50
3.92
9.91
R
1.02
1.65
2.67
4.15
6.76
10.80
27.16
S
1.06
1.65
2.65
4.18
6.82
10.88
27.29
E
.58
.91
1.46
2.30
3.73
5.89
14.83
B
7.00
11.00
17.50
27.75
44.25
70.50
178.25
N
1.47
2.34
3.72
5.91
9.40
14.94
37.80
C
1.26
2.03
3.19
5.05
8.13
12.91
32.64
Thermocouple Type:
Temperature error in °C per 1000 feet of leadwire
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