usb 6009 noise

[maxf]

I have a USB-6009 connected with ai3:ai0 in differential mode. I have a 3/4" long jumper wire connected between the +/- terminals of each channel. I am using a range of +/-1 V.  Along with a DC offset of -5.5mV on AI0, I am seeing heavy noise of about 2 mV P/P and an actual P/P noise of over 3mV on all four channels. Am I reading the specs for the USB-6009 wrong and expecting too much or is there something else wrong here?

In summary, USB-6009 with:

   AI4:AI0  in Differential mode

   Signal input range set to +/- 1 V

   Each AI has + shorted to -

Measured DC offset >5mV

Meaured Noise >2mV P/P  (at both 10 S/s and 10k S/s)

[Ali M]

Hello maxf,

To better answer your questions, do you have a signal source that you are trying to measure with the NI 6009? If so, what is the range of this signal?

Best regards,

Ali M

Applications Engineer

National Instruments

www.ni.com/support

[maxf]

There were a few different signal sources that I was trying to measure and I noticed that the noise was much worse than expected for these. Therefore I am simply trying to determine whether or not the channels are in spec.

As mentioned in my original post I am testing two configurations.

1. AI0+ shorted directly to AI0-, AI1+ to AI1-, etc.  (all in differential mode, range of +/-1V).

2. All analog inputs (+ and -) shorted to ground.

In both cases my signal is 0V and should not be affected by bias currents.

[Ali M]

Regarding your noisy signals, in most cases it could be due to ground loops. I would recommend supplying a known voltage signal e.g. from a power supply or battery and observe the readings in Measurement & Automation Explorer (MAX) Test Panels. Also, please review the following field wiring and noise considerations for analog signals document (e.g. Figure 1) to make sure that your signals sources are correctly matched with the correct grounding configurations.

Best regards

Ali M

Applications Engineer

National Instruments

[maxf]

Been there, done that. The noise seems consistant whether I am supplying 0.500 V or a direct ground. I have also tried resistors in a range from 10K to 100K, no difference.

[Sean_F]

Hi Maxf,

The noise levels you're describing do not sound too unreasonable. Rather than specify your noise in pk-pk could you calculate the rms value of your noise? 

Thanks,

Sean