are ADC's that are giving off noise broken?

[Alswash]

first off, sorry about badly phrasing the question as there is no way for me to phrase it without explaining everything.

second, I'm currently runing an ADC through labview to get a reading off of a Accelerometer. when I first plugged in the accelerometer I was getting around +/- .2 V of noise. so I naturally thought that the accelerometer was the problem so I checked it on a scope and found out the exact opposite. I tested my ADC quite throughly as to if this noise got worse or better at different voltages but nothing helps and thankfully nothing makes it worse. I'm wondering if there is anyway to reduce the noise. the accelerometer is very sensitive, having it flucuate even .05V is a big spike.

Can anyone help?

Als.

[mallorim]

Hi Als,

Noise doesn't necessarily mean that the analog input card is broken. Are you using one of National Instrument's Data Acquisition or Analog Input cards? If so, what part and module number are you working with, i.e. a PCI-6229? If you are not using NI hardware, what driver are you using in LabVIEW to control your third party analog input card?

I would check the accuracy specifications page for your data acquisition card. This noise might be within the accuracy specification of your card, in which case you will need to look into a more precise card. However, +/- 0.2 V does seem high for any card that you might be working with. I would try a self calibration in Measurement and Automation Explorer (MAX).

What is the frequency of the noise you are seeing? Is the accelerometer sitting on a table or surface that might be seeing a vibration, for instance the fan in your computer? What type of accelerometer are you using?

Regards,

Mallori M.

[Alswash]

malori,

I'm using a National instruments 9201 with DSUB. I know the noise isn't from the accelerometer because it (A) still has the noise without the accelerometer plugged in and (B) the spectrometer I have had the accelerometer on never had noise. The Accelerometer is a Klister K-Beam 8305B2M2, it measures +/-2Gs. the room that I'm doing this in is sheilded from electronical interference.

Thanks for the help,

Als

[mallorim]

Something to make note of is that the 9201 only supports Reference Single Ended Signals. You can look at this Developer Zone article Field Wiring and Noise Considerations for Analog Signals to check what type of source you are trying to read, you might need to upgrade to a NI 9205, 32 single-ended or 16 differential analog inputs.

However, the NI-9201 should not be exhibiting 0.2 V noise. The highest noise value you should be seeing is not greater than that 0.02 V. If the isolation of the channels is not of great importance, connecting the COM terminal to the chassis ground screw on the right side of the cDAQ chassis should clear up all the noise.

I hope this helps,

Mallori M.

[D_Zuo]

I am having similar problems with my NI9201 and NI9205 with accelerometers made by Xbow (TG series +-2g). I am seeing spikes in all the channels also. These accelerometers are supposed to be single ended. I am using the RSE option for NI9201 and the NRES option for NI9205.

[mr_]

Hello D_Zuo--
 
I have a couple of questions to get a better understanding of your situation.  Are you seeing these spikes on both the 9201 and 9205? Have you always seen spikes on these channels or did it just start happening?  If this just started happening, what has changed?  Have you tried taking other measurements (e.g., non-accelerometer measurements)--still the same behavior? Have you tried performing a self calibration?

When are you seeing the spikes?  Is it when the accelerometer is just sitting idle, or is it moving/being exposed to measurable changes?  The reason I ask is because we may need to apply some filtering to your signal depending on the circumstances of the spikes.

Also, what pins are you connecting to for the 9201 and 9205?

One of the previous posts in this thread noted the Field Wiring Considerations tutorial.  It may be a good resource to make sure proper wiring considerations are taken. 

Cheers!