Title: Why are my readings off at 30⁰C when I use ITS-90 subrange 5 and 7 together?
Applies To: 1560, 2560, 2562
Problem Description: Readings from the 1560 at 30⁰C are off by 0.30⁰C
In the 1560, if Sub-range 5 is selected for the Low range, the A5 and B5 coefficients will also be used above 0 °C, because the definition of Sub-range 5 extends from the mercury point to the gallium point. If the user wants to use Sub-range 5 only up to 0 °C and use Sub-range 7 above 0 °C, the best way to do that is to select Sub-range 4 for the Low range and enter the values of A5 and B5 for A4 and B4. Then it should read the same as the 1502A. Please note, however, that there will be a small error (usually very small) around -30 °C with either product because the form of the deviation functions for Sub-range 5 and Sub-range 4 are slightly different.
If only ITS-90 sub-range 7 data is entered for one probe into both a 1560 and a 1502A the probe will read correctly on both readout devices. However, if you program both the 1560 and 1502A with ITS-90 sub-range 5 and 7 data you will only get an error on the 1560 (0.3 degrees at 30) and not the 1502A.
For the 1502A, to enter the ITS-90 sub-range 5 and 7 together, you will need to enter the ITS-90 sub-range 5 data A5 and B5 into the A4 and B4 data fields as well.