Product Manual

7526A

Users Manual

2-8

6. To use a different custom RTD curve, push  two times to show the USR_DEF

selection prompt.

The USR_DEF function of the Product uses the Callendar-Van Dusen equation to source

and measure custom RTD's. The C coefficient is only used for the subrange -260 °C to

0 °C. Only the A and B coefficients are necessary for the subrange 0 °C to 630 °C. The

R0 value is the resistance of the probe at 0 °C.

All five of the custom RTD curves are set to PT385 at the factory, as shown in Table 2-1.

Table 2-1. Default Custom RTD Coefficients

Curve Subrange R0 Coefficient A Coefficient B Coefficient C

1 0 to 630 100 3.9083e10-3 -5.775e10-7 0

2 -260 to 0 100 3.9083e10-3 -5.775e10-7 -4.183e10-12

3 0 to 630 100 3.9083e10-3 -5.775e10-7 0

4 -260 to 0 100 3.9083e10-3 -5.775e10-7 -4.183e10-12

5 0 to 630 100 3.9083e10-3 -5.775e10-7 0

Table 2-2 shows the coefficients for RTD types PT391 and PT392. The C coefficient is

only used for temperatures less than 0 °C.

Table 2-2. Other Common RTD Coefficients

RTD Type R0 Coefficient A Coefficient B Coefficient C

PT392 100 3.9848e10-3 -5.87e10-7 -4.0e10-12

PT391 100 3.9692e10-3 -5.8495e10-7 -4.2325e10-12

Standard Platinum Resistance Thermometer (SPRT)

Coefficients

The SPRT function of the Product uses ITS-90 standard coefficients as a basis to measure

a SPRT. The five custom coefficients are keyed in as deviations from the standard

coefficients, and as such, all of them are set to zero at the factory.

The coefficients A- and B- refer to the A4 and B4 coefficient. These are received when

the SPRT is calibrated at the triple points of argon, mercury, and water. This includes the

83.8058 K to 273.16 K subrange. Coefficients A, B, and C refer to different coefficients

based on which subranges of the SPRT were calibrated. For example, if the 273.15 K to

933.473 K subrange was used, A, B, and C would refer to A7, B7, and C7 whereas if the

273.15 K to 692.67 K subrange was used, A and B would refer to A8 and B8 and C=0.

To key in the deviation coefficients for a custom SPRT:

1. Select RTD measure mode as given in the "Resistance Temperature Detector (RTD)

and Ohms Measure" section of this chapter.

2. Push  until the SPRT type is selected.

3. Push E to show the prompt “SET(1)/RECALL(2)”.

4. Push  to select custom SPRT data entry.

5. At the “ENTER MIN TEMP” prompt, key in the minimum temperature limit for the

custom SPRT, and push E.

6. At the "ENTER MAX TEMP" prompt, key in the maximum temperature limit for the