NI-5133 noise

[JChec]

Hi,

I'm using a NI-5133 module to acquire data from an ultrasonic sensor. I'm using Signal Express 3.0 to view the data. The problem I have is that any signal coming in from the NI-5133 has a large noise signal which is a lot larger than the signal i'm even acquiring. The sampling rate is set to its max 100MS/s and the noise viewed in signal express is a 50MHz triangular wave. The ampitude of the noise is 200mV pk-pk and is consistant (so doesn't really seem like noise). This noise is there even if there is no signal attached to the inputs.

I've tried this on different computers and away from any other equipment but with no difference.

Has this problem been encoutered before with this device? Any suggestions?

Thanks,

JChec

[Hillman]

Hi JChec,

Thanks for the post and I hope your well today.

Firstly, does the ultrasonic have this noise when you measure it with another peice of equipment?

Secondly, what input configuration are you using for your input, DIFF, RSE or NRSE? this is dependant upon the type of source. For more information please take a read of the following link to a dev zone article:

Field Wiring and Noise Considerations for Analog Signals

http://zone.ni.com/devzone/cda/tut/p/id/3344

It maybe that  you need to introduce bias resistors. 

If its not a setup issue, then maybe we could filter the signal out..please let me know your thoughts and we can try to resolve your issue.

Hope this helps, 

[John_P1]

Hi JChec,

What voltage range do you have set on your card?  If you are using the full 40V range, your resolution would only be 40/(2^8) = ~156 mV.  You can configure the range in LabVIEW using niScope Configure Vertical.vi.  For now, let's try this out in a test panel.  From LabVIEW, go to Tools >> Measurement and Automation Explorer, then find your device under Devices and Interfaces >> DAQmx Devices.  Right-click and select Test Panels.  Make sure to configure the vertical range to the appropriate value for your signal.

If this does not resolve the issue, let me know what range you are using and what the approximate amplitude of the noise is.  Does adjusting the sample rate affect the frequency of the noise?

-John 

[JChec]

Hi James and John

Thanks for your replies. My voltage range was set to 1V to increase the accuracy but found my noise was still too large. Read through your suggestions and I must thank you for them because while going through your suggestions I found what the problem was. When I was setting my voltage range, I found the the device was not actually adjusting to the set value I was giving it. The data sheet says the noise is 0.35% of the FS. So 40V range would yield 140mV noise and I found this noise did not reduce as I reduced the range until I set was setting it in MAX and eventually the device set its range properly and I noticed a significant difference in the noise which correlated to the datasheet. Will just fiddle around to find out why the setting the range was not working 100%

Thanks,

JChec

[John_P1]

Hi JChec,

Do you mean that your LabVIEW code is not setting the range properly, or is MAX doing the same thing?  There are only a finite amount of ranges available on the 5133:

40mV, 100mV, 200mV, 400mV, 1V, 2V, 4V, 10V, 20V, and 40V

If you specify a range in between these values, the actual range will coerce up to the nearest valid range.  So if you chose 25V as your range, it would still set the card to use the 40V range.  All ranges are specified as peak to peak--20V with no offset would mean +/-10V.  You may be able to use an offset to reduce the range required to make your measurement and thus improve performance.  The offsets that are available to you depend on the range you set, more information can be found on page 2 of the 5133 Detailed Specifications.

-John 

Message Edited by John P on 12-17-2008 03:43 PM

Message Edited by John P on 12-17-2008 03:47 PM

[JChec]

In Max it seems to have no problem, but when I set the range in signal express it doesn't seem to set the range properly. I select the correct value according to the ranges given in the datasheet but it only seems to correctly adjust occasionally. Ie. If I select a 2V range, the ADC seems to be still operating over the 40V range quite often... so you can see how the noise now will be majorly effecting my results here.

Only after reseting the range a few times and acquiring data does it correctly adjust.

Thanks,

J

[Hillman]

Hi Jason,

Thanks for your replies.

So in SignalExpress when you click to run the task - the configuration changes such as Range aren't always updated?

Or is it just when your editing them in 'edit' mode that the changes aren't always applied?

Also, which version of SignalExpress are you using?

Thanks,