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Using Output Mode
Using Output Mode
2
2-5
Default RTD Coefficients
The USR_DEF function of the calibrator uses the Calendar-Van Dusen equation
for outputting and measuring custom RTDs. 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 is the resistance of the probe at 0 degrees
Celsius. All of the USR_DEF will be set to PT385 as shown in Table 2-1.
Table 2-1. Default RTD Coefficients
Sub range R
0
Coefficient A Coefficient B Coefficient C
USR_DEF1 0 to 630 100 3.908X10-3 -5.775e-7
USR_DEF2 -260 to 0 100 3.908X10-3 -5.775e-7 -4.183e-12
USR_DEF3 0 to 630 100 3.908X10-3 -5.775e-7
USR_DEF4 -260 to 0 100 3.908X10-3 -5.775e-7 -4.183e-12
USR_DEF5 0 to 630 100 3.908X10-3 -5.775e-7
If other types of RTDs are required, Table 2-2 shows the coefficients for types
PT391 and PT392. The C coefficient is only used for temperatures below 0
degrees Celsius.
Table 2-2. Other Commonly Used RTDs
RTD Type Coefficient A Coefficient B Coefficient C
PT392 3.9848X10-3 -5.87X10-7 -4X10-12
PT391 3.9692X10-3 -5.8495X10-7 -4.2325X10-12
The SPRT function of the calibrator uses ITS-90 standard coefficients for
measuring a SPRT. Since the five coefficients are deviations all of them will be set
to 0.
The coefficients A- and B- represent the A4 and B4 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 A7, B7 and C7 whereas if the 273.15K to 692.67K subrange was used, A
and B would represent A8 and B8 and C=0.
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