precision of internal clock of BNC-2110

[AlexJ]

Hello, I am using the BNC-2110 to get some measurement.

I am working with the presion ot 10000 datapoints each second.

But during a measurement of 30 seconds (external clock) I just get 299970 datapoints, insteads of 300000! So there are missing 30 datapoint. During a measurement of 5 seconds there are missing 5 datapoints.

Could it be a inaccuracy of the internal clock of the BNC-2110?

Thank you for your help.

Rest regards, AlexJ

[Wallace_F]

Hello AlexJ,

I understand that you are doing data acquisition using the BNC-2110, and are missing 1 data point for every second that you are acquiring data.  It also seems as if you are sampling at 10 kSamples/sec.  Am I correct in my assumption?  Also, what is your application development environment?  It would also be helpful to know if you were acquiring analog or digital data, and what your acquisition task parameters are, i.e.. sampling mode, sampling rate, and samples per channel. More specific information about your application would be very helpful in trying to duplicate the conditions you are experiencing.

Regards,

Wallace F.

[AlexJ]

Hello, you are right with your assumption.

I did some more measurement and got some interesting results:

I calculated the difference of two sinus-signals of the same frequency. The data-points of one of them I got from MatLab, the other one I measured with the BNC from NI

I used a toolbox from NI for MatLab and used the order

      AcqNUpdates('Dev2/ai0:7', -10, 10, 100000, 10000, 2);

Do you know this toolbox?

The plot of the result of the difference can be seen in the atachment.

I think the sudden changes of the difference every second (t1=0.75 t2=1.75) is the result of the missing datapoint mentioned above.

I got this result with several measurements and with every channel.

Did somebody else already had this problem?

Best regards, AlexJ

[Wallace_F]

Hello AlexJ,

I've been trying to reproduce the problem that you are having with missing data, but as of yet, have been unsuccessful.  I do have a couple of additional questions for you.

1.  What DAQ board is the BNC-2110 connected to?

2.  Are your data arrays indexed from zero or one?

3.  Does the problem occur if you sample only one channel instead of 8 channels (0:7)?

4.  Does the problem occur if you sample at a lower rate?

Regards,

Wallace F.