Ground for analog and digital signals

[R_J]

Hi All,

In all NI DAQ card, are all Digital and Analog signal lines share the same ground ?

Regards,

J

[AnalogKid2DigitalMan]

In most cases, yes, but to know for sure can you tell us what model DAQ card did you have in mind?

-AK2DM

[R_J]

USB 6008 , 6009 & 6212 DAQ cards

[Buechsenschuetz]

Even if AGND (analog ground) and DGND (digital ground) are tied together somewhere on the board, i.e. if you measure 0 resistance between these terminals, you should always use AGND as reference for analogue signals and DGND as reference for digital signals. "Mixing" AGND and DGND outside a data acquisition system may generate additional noise and/or offset on analogue signals. Digital signals usually are more immune to noise/offset, so probably mixing AGND and DGND will have little, if any, influence on digital signal quality. 

[AnalogKid2DigitalMan]

It looks like those cards share grounds, as suggested an ohm meter will provide ultimate verification.

-AK2DM

[Hardik.Asawa]

Yes, all the grounds including analog output, input, and digital I/O are tied together to the common ground. This connection occurs after the ADC references the appropriate ground, so the ground line for your incoming signal connections should still be tied to the appropriate ground (AI GND, AO GND, or P1.GND) or you may experience increased noise.

Note: The ground lines are still tied together before being routed to the PCI or PXI ground, and thus can be damaged if there is too great a potential difference between each ground.  Before connecting multiple ground lines, take steps to ensure that the potential is the same at each ground terminal.  If this is not possible, consider taking your readings using Differential mode.  If readings are different from one ground to another on the same card, the cable or card may be damaged or the pins bent.