acquisition analog voltage Ni USB 6259: inverted signal

[lolo25]

Hello,

I have a USB Ni 6259 BNC
I created an analog voltage acquisition task with NiDAQMX on ways from AL0 to AL8
I deal with DasyLab (acquisition I / O -> display ChartRecorder)

My PB is that the BNC signal (coming here a GBF) shall be reversed on the plug of USB-6259, else, all channels display the same signal (see screen capture)

- BNC mass on the outside, soul on the BNC center -> all channels posters the same signal.

- BNC mass becomes the center and the soul becomes coaxaile outside -> Al0 the way that displays the signal, the others way stay at 0  level

 

on the housing USB 6259 cursors technique are all on FS,

NI DAQmx task is mass differential mode (see attached NI spot).

 

Where is my mistake?

thank you for your expertise

[TomRizzo]

When scanning more than the channels you need, there is always a open status effect on the remaining channels that have a open line.

The way you can correct this is by either not scanning those channels or by grounding them.  In fact you can actually buy BNC plugs designed for that.

[lolo25]

Hi Tom Rizzo,

Actually putting the plug (on center outside the BNC plug) to track ALn
the signal becomes zero from the Aln way.

When I measure cutting forces (Kistler dynamometer Kistler charge amplifier +) I use 8 channels and there I can not put caps and the signals are mixed.

'm limited to just useful track number in NiDaqMX task, but still the problem of "coupling".

thanks for your answer.