National Instruments FieldPoint cFP-RTD-122 Operating Instructions Manual page 8

The [c]FP-RTD-122 uses a linearization curve known as the
Callendar-Van Dusen equation to measure the temperature of
RTDs. The equation is as follows:
Temperatures below 0 C:
R = R
T 0
Temperatures above 0 C:
T = temperature in C
R = RTD resistance at temperature T
T
R = RTD nominal resistance at 0 C
0
A, B, C are coefficients given in Table 2.
Table 2 lists the coefficients used in this equation for each of the
TCR values that the [c]FP-RTD-122 supports. If you have a
nonstandard RTD that does not match one of these linearization
curves, measure the resistance with the [c]FP-RTD-122 and
convert the resistance to temperature in the manner suggested by
the RTD vendor.
Table 2. Callendar-Van Dusen Coefficients Used by the [c]FP-RTD-122
TCR
m / / C
a
3.750
b
3.851
c
3.911
d
3.916
e
3.920
f
3.928
Three-Wire Compensation of Lead
Resistance Errors
The [c]FP-RTD-122 uses a three-wire compensation technique to
compensate for the lead resistances. The SENSE lead measures the
resistance of the return COM lead. If the EX+ lead has the same
resistance as the COM lead, the [c]FP-RTD-122 corrects for the
FP-RTD-122 and cFP-RTD-122
[1 + A T + B
R = R [1 + A
T 0
A
–1
( C)
3.81 10
3.9083 10
3.9692 10
3.9739 10
3.9787 10
3.9888 10
2
T + C T
T + B
B
( C)
–3
–6.02
–3
–5.775
–3
–5.8495
–3
–5.870
–3
–5.8686
–3
–5.915
8
3
(T – 100 °C)]
2
T ]
–2
( C)
–7
10 –6.0
–7
10 –4.183
–7
10 –4.233
–7
10 –4.4
–7
10 –4.167
–7
10 –3.85
C
–4
–12
10
–12
10
–12
10
–12
10
–12
10
–12
10
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