multiplexing rate

[rico1985]

Hi,

I am using Signal Express 3.0.  I used several data cables to connect three channels together. Different sine wave signals with different sampling rates were sent to these channels. When I took a look at the signas in time domain and measuerd the interchannel delay, it showed that the multiplexing rates are differrent. I am wondering whether it is possible to change the multiplexing rate in Signal Express. Is this a problem for data aquisition and the accuracy of the data?

Thanks a lot!

[Jordan F]

You are not able to change the multiplexing rate or in Signal Express.  If you have LabVIEW you can adjust this via a property node.  However, our devices should have a consistant multiplexing rate between the two channels.  How exactly are you measuring this rate?  What device are you using?

[rico1985]

Hi Jordan,

Thank you for your reply. The attached file includes all of the interchannel delay and the multiplexing rates which I measured by looking at the time domain signals. I am sure those values are reliable. I also attached the Signal Express project. I am using Signal Express 3.0, NI USB-6251 and BNC-2110.

Thanks a lot.

[Jordan F · Accepted solution]

Ningyu,

This is normal to see a different interchannel delay or multiplexing rate because this is derived from the frequency you are sampling at.  With a higher sampling frequency you will need a faster convert clock so all of your channels can be sampled before the next sample clock edge occurs.  The documents below discuss what the convert clock is and how the rate is determined.

How is the Convert (Channel) Clock Rate Determined in NI-DAQmx and Traditional NI-DAQ? 

http://digital.ni.com/public.nsf/websearch/42484E84DA98053686256D32006E0494?OpenDocument

Difference Between the Sample Clock (Scan Clock) and the Convert Clock (Channel Clock)

http://digital.ni.com/public.nsf/allkb/4D1435DF82EF494186256D8A006DD6D4