FP-RTD-122 and cFP-RTD-122 8 ni.com
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:
RT = R0[1 + A × T + B × T2 + C × T3 × (T – 100 °C)]
Temperatures above 0 °C:
RT = R0[1 + A × T + B × T2]
T = temperature in °C
RT = RTD resistance at temperature T
R0 = RTD nominal resistance at 0 °C
A, B, C are coefficients given in Table 2.
Table2 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.
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
Table 2. Callendar-Van Dusen Coefficients Used by the [c]FP-RTD-122
TCR
mΩ/Ω/°C
A
(°C)–1
B
(°C)–2
C
(°C)–4
3.750a3.81 × 10–3 –6.02 × 10–7 –6.0 × 10–12
3.851b3.9083 × 10–3 –5.775 × 10–7 –4.183 × 10–12
3.911c3.9692 × 10–3 –5.8495 × 10–7 –4.233 × 10–12
3.916d3.9739 × 10–3 –5.870 × 10–7 –4.4 × 10–12
3.920e3.9787 × 10–3 –5.8686 × 10–7 –4.167 × 10–12
3.928f3.9888 × 10–3 –5.915 × 10–7 –3.85 × 10–12