Incorrect date/time shown at X-axis when using TDMS file viewer

[Dragon_Dragon]

1. I would like to adding 512Mb Ram for our NI PXI-8105 which currently has only 512MB Ram. Possible?

2. Is there any connectors or hardware that allow the PXI-4472 measure signals that over 10V? We want to measure a signal amplitude around 30V.  SMB300?

3. I wrote a VI which recorded signals by PXI-4472 into TDMS file but the x-axis showed incorrect date and time.Attached the VI and screen capture files.

4. What is the best sampling rate and no.of samples for the PXI-4472 to measure signals 1k hz?

Thanks for help!!!!

[RT4CY]

Hi Dragon,

1. I would like to adding 512Mb Ram for our NI PXI-8105 which currently has only 512MB Ram. Possible?
You should be able to upgrade the RAM.  Check page 2-15 of the PXI-8105 User Manual

2. Is there any connectors or hardware that allow the PXI-4472 measure signals that over 10V? We want to measure a signal amplitude around 30V.  SMB300?
This may be very tricky, since most of the time the PXI-4472 is used to measure from sensors that require IEPE excitation.  What sensors are you measuring from?  If you are measuring from an IEPE accelerometer/microphone, then a simple attenuator won't do.  This is because you will remove the required excitation current that the PXI-4472 device is providing.  I don't believe we have a hardware solution for this, but you could possibly design your own circuit.  I will let you know if I find a manufacturer (or possibly if we have a solution available).

3. I wrote a VI which recorded signals by PXI-4472 into TDMS file but the x-axis showed incorrect date and time.Attached the VI and screen capture files.
I could not generate the TDMS file, since the VI requires Untitled 5.vi.  However, you may find success by looking at this developer zone tutorial.

How to Display Absolute Timestamps from a LabVIEW Waveform in DIAdem

I realize you may not be using DIAdem.  But take a look at the LabVIEW Approach section.  This takes you through getting the timestamp information from your waveform data.  If this does not help, please provide the Untitled 5.vi or the actual TDMS file.

4. What is the best sampling rate and no.of samples for the PXI-4472 to measure signals 1k hz?

Nyquist Theorem states that your sampling rate should be at least twice the frequency of the signal you are trying to measure.  I would recommend always sampling 10 times the frequency of  your signal.  So you could sample at 10 kHz, with 1,000 number of samples.  A good rule of thumb for the number of samples input is 10% of your sampling rate.

Let me know if you have additional questions.

Message Edited by RT4CY on 12-15-2008 04:39 PM

[Dragon_Dragon]

Thanks! Here are the missed file:Untitled5.vi.

In fact, I want to show the recorded signals (Y-axis) with respect to time in seconds (X-axis).

[RT4CY]

Hi Dragon,

Thank you very much for providing that VI!  I did some experimenting with your VI, and I found the issue to be with the Merge Signals.  The problem is that your resulting data type is not waveform, so it does not contain the time stamp information.  If you replace the Merge Signals with a Build Array function, then you should see the correct time stamps.

Message Edited by RT4CY on 12-19-2008 06:32 PM