Specifications

CONAX BUFFALO TECHNOLOGIES TSD 43.021
Rev. ORIG
Page 20 of 28
6.6 CALLENDAR-VAN-DUSEN APPLICATIONS
The Callendar-Van-Dusen formula provides constants for a third order polynomial
equation, which then approximates the actual Pt-100 RTDs resistance to a high
degree of precision. Of course, the specific RTD needs to be precisely
characterized by exact temperature testing, and the coefficients should then be
calculated. See Figure 12.
α Alpha is the nominal coefficient for the RTD, which, for most standard elements will
be in the vicinity of 0.00385 (DIN curve).
β Beta is zero (0) for temperatures >0 °C. It is the significant constant for <0 °C
ranges.
δ Delta is the significant coefficient for the higher temperature ranges.
Figure 12 – RTD Callendar-Van-Dusen Entry
The minimum and maximum values are the temperatures within the values for
which the sensor was supposed to be defined and tested for. The units are always
in °C. If the sensor was tested and defined between -50°C and +450°C, you may
enter any values up to and including -50°C for the minimum value and +450°C for
the maximum value.
You MUST enter a value for Delta or else the program will request it. Typical
values will run in the order of 1.40 to 1.60 for 100 Ω (@ 0°C) elements. For units
with the 0.000385 curve, the typical values are in the order of 1.45 to 1.47.
Once you enter all of the numbers, the configuration software will generate the
linearization table for the particular range of the unit. Upon downloading, this table
will be entered into the transmitter’s memory.