Martel Electronics 3001 - Manual (Page 24)

d) Press the numeric key corresponding to the custom RTD curve to be used.
e) At the "SET(1)/RECALL(2)" prompt, press to recall the custom RTD curve
coefficients.
f) To use a different custom RTD curve, press the key twice to display the
USR_DEF selection prompt.
The USR_DEF function of the 3001 uses the Calendar-Van Dusen equation for sourcing
and measuring custom RTD's. The C coefficient is only used for the subrange -260 to 0
degrees Celsius. Only the A and B coefficients are needed for the subrange 0 to 630
degrees. The R0 value is the resistance of the probe at 0 degrees Celsius.
All 5 of the custom RTD curves are set to PT385 at the factory, as shown in Table 2.
Table 2 - 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 3 shows the coefficients for RTD types PT391 and PT392. The C coefficient is only
used for temperatures below 0 degrees Celsius.
Table 3 - 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
4.6 Standard Platinum Resistance Thermometer (SPRT) Coefficients
The SPRT function of the 3001 uses ITS-90 standard coefficients as a basis for measuring
a SPRT. The five custom coefficients are entered as deviations from the standard
coefficients, and as such, all of them are set to zero at the factory.
The coefficients A- and B- represent the A
4
and B
4
coefficient, obtained when the SPRT is
calibrated at the triple points of argon, mercury and water. This covers the 83.8058K to
273.16K subrange. Coefficients A, B and C can represent different coefficients based on
which subranges of the SPRT has been calibrated. For example, if the 273.15K to
933.473K subrange was used, A, B and C would represent A
7
, B
7
and C
7
whereas if the
273.15K to 692.67K subrange was used, A and B would represent A
8
and B
8
and C=0.
To enter the deviation coefficients for a custom SPRT:
a) Select RTD measure mode as described in the preceding section.
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