NI 9219 2wire resistance produce erratic values

[Horst_Emscher]

9219 produces isolated values of about 5 kOhm in an long row of 10 kOhm values (actual, the contact is open and should assign n.c.!).

The setup runs in 8 h shifts to get managable datasets for old hardware. 3 NI9219 run in a 4 slot berth. 6 channels are connected to resitances oszilating between 50 Ohm and 1000 Ohm and the other 6 to open circuits, showing 10. kOhm as a normal (and as I have learned now maximum) value.

There are about 10 erratic and singled values in a continuum of 432000 ordinary values. What does it mean?

The other 6 channels show no aberrations.

[TSE_Expert]

Dear Horst_Emscher,

the NI 9219's has two possible input ranges for 2-wire resistance measurement, 10.5 kOhm and 1.05 kOhm,

as you can see in the datasheet:

http://www.ni.com/pdf/manuals/374473a_02.pdf

When the input is left unconnected, i.e. high impedance, the input is out of range. In such a case the expected behaviour of the output is undefined. The glitch what you see in the reading shows, that the intuitively assumed full scale output might be disrupted by internal and external noises influencing the operation of the circuitry. The most obvious point to think of, is that the current generator cannot function properly when the input is n.c.

Best Regards,

NI TSE