Yesterday i measured some dividers made from Nomca resistor arrays. The arrays give division ratios of
- 13:1 (without external resistor)
- 13.5:1 (with 25K external resistor)
- 14:1 (with 10K external resistor)
I made three 14:1 dividers from 8x 5K Nomca arrays and measured division ratios connecting the dividers to a 10V reference and measuring voltages. Division ratios were 4 ppm, 32 ppm and 60 ppm off nominal value.
In order to determine TC of division ratio i did bridge measurements with one bridge leg in the oven. My 3456A measures difference voltage with 0,1 uV resolution, that is about 0,14 ppm of the 0,714 V divided voltage. So with a temperature change of 25 °C i can determine TC to about 0,01 ppm/°C.
TCs measured were (A) -0,83, (B) 2,40 and (C) -0,57 ppm/°C.
As far as i understand 1 ppm/°C on the division ratio with an industrial part without preselection is a nice result and perfect for a LTZ1000 reference. When i removed the external resistor 10K, (A) improved to -0,49 ppm/°C. The external resistor is a 5 ppm/°C MF, up to 30 ppm/°C different from the 25 ppm/°C of the Nomca array. Its changes get attenuated 21:1.
Next step will be to understand better the result (B). I did not yet observe a certain mixture of the eight resistors.
Regards, Dieter