Re : USB DAQ 6363 measurement bad with several channels

[bourdel]

Antonin,

I only use SignalExpress.

If you want, i can send SignalExpress project by mail?

Regards,

Laurent

[Antonin_G.]

Hi Laurent, 

Could you send me a schema of your system : current and resitor wiring.

Indeed your resistor has to be between AI- and the - of your voltage source.

Here are two interesting links you could see as well to ensure your wiring :

http://digital.ni.com/public.nsf/allkb/82508CD693197EA68625629700677B70

http://www.ni.com/white-paper/7114/en

Regards,

[bourdel]

Antonin,

One setup example (Agilent multimeter is replaced by DAQ USB-6363) :

Laurent

[Antonin_G.]

Laurent,

The NI USB DAQ-6363 is ground-referenced (through your PC), that's why you need to make a conditioning where the shunt resistor will be between the " - " of your power supply and your system.

If the shunt is as on the setup example you gave me, there is a common-mode issue on inputs and a drift in the measurement. To act like your example you would need a NI CompactDAQ configuration with embedded conditioning.

Regards,

[bourdel]

Antonin,

I use DAQ in differential mode, so ground reference is not needed to my mind? Is it false?

Regards,

Laurent

[Antonin_G.]

Hi Laurent,

Even in differential mode the DAQ needs a ground reference.

Let me know,

Cheers

[bourdel]

Antonin,

Ok, I will speak with internal HW team to expose connection problem for differential measurement

You think it can be source of my problem (measuremnt diff following sample rate) ?

Regards

Laurent

[bourdel]

Antonin,

We are doing power optimisation on embedded system.

We measure current on DCDC converter / LDO input & output by adding serial 0.1ohm shunt. (BGA component)

So we can't use advice from your link (http://digital.ni.com/public.nsf/allkb/82508CD693197EA68625629700677B70)

and use common ground mode

I look at “NI CompactDAQ configuration with embedded conditioning” but don’t find what is different compare to USB-6363 ?

Is there a solution to use our USB-6363 DAQ in proper way?

Thanks

Laurent

[Antonin_G.]

Hi Laurent,

Di you try with the configuration I gave you ? What are the results and do you still have similar issues ? 

Let me know please,

Regards

[bourdel]

Antonin,

I use this HW setting. I think it fully comply with NI requirements

To simplify i measured directly voltage on shunt that is load (1Ohm/1%)

Generator output is sinusoidal signal

Measurements:

sample to read=200k, Rate=1M, 1 channel

average = 1.01091mV

sample to read=200k, Rate=1M, 2 channels

average = 1.24767mV => ~0.23mV more (+25%) !!!

sample to read=20k, Rate=100k, 2 channels

average = 1.01031mV => need to lower sample rate to have good results

Regards,

Laurent