National Instruments cFP-RTD-124 User Manual download pdf (Page 8)

FP-RTD-124 and cFP-RTD-124 8 ni.com

Unfortunately, not all TCR values are as well defined by standards

organizations, and the behavior of RTDs with the same TCR value

may vary from vendor to vendor. The variations are usually small,

and the built-in linearization algorithms of the [c]FP-RTD-124 are

appropriate for nearly all applications.

The [c]FP-RTD-124 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

[1 + A × T + B × T

+ C × T

× (T – 100 °C)]

Temperatures above 0 °C:

= R

[1 + A × T + B × T

]

T = temperature in °C

= RTD resistance at temperature T

= RTD nominal resistance at 0 °C

A, B, and 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-124 supports. If you have a

nonstandard RTD that does not match one of these linearization

curves, measure the resistance with the [c]FP-RTD-124 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-124

TCR

mΩ/Ω/°C

(°C)

–1

(°C)

–2

(°C)

–4

3.750 3.81 × 10

–3

–6.02 × 10

–7

–6.0 × 10

–12

3.851 3.9083 × 10

–3

–5.775 × 10

–7

–4.183 × 10

–12

3.911 3.9692 × 10

–3

–5.8495 × 10

–7

–4.233 × 10

–12

3.916 3.9739 × 10

–3

–5.870 × 10

–7

–4.4 × 10

–12

3.920 3.9787 × 10

–3

–5.8686 × 10

–7

–4.167 × 10

–12

3.928 3.9888 × 10

–3

–5.915 × 10

–7

–3.85 × 10

–12

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

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National Instruments cFP-RTD-124 User Manual Page 8

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