9
If your thermocouple is grounded on the negative lead, as shown in
Figure 5, or grounded on the positive lead, as shown in Figure 6, a
leakage current of approximately 0.5
µ
A (5 V/10 M
Ω
) will flow through
your thermocouple. The resultant measurement error will be 4.4
µ
V for
the example thermocouple, based on the equation:
1 lead x 8.78
Ω
/lead x 0.5
µ
A = 4.4
µ
V
This corresponds to an error of 0.09° C.
4.39
µ
V
0.5
µ
A
10 M
Ω
10 M
Ω
+5 V
+
-
-
+
-
+
V
thermocouple
V
meas
R
lead
R
lead
Figure 5.
Thermocouple with Negative Lead Grounded
4.39
µ
V
0.5
µ
A
10 M
Ω
10 M
Ω
+5 V
+
-
-
+
-
+
V
thermocouple
V
meas
R
lead
R
lead
Figure 6.
Thermocouple with Positive Lead Grounded
