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lvm timing stamp multichannel

Hello

I am using a PCI 6255 acquisition card to measure voltage on 16 channels. The sampling rate is set to 10 kHz and "samples per channel" is set to 50. Futhermore the "sample mode " on my daqmx timing VI is set to "continuous samples". Actually, I want to record data untill I push on the STOP button (I used a while loop).

 

I am writing data on an *.lvm file. As expected, I get for each channel a column with the time and a column with the value of the measurement (total = 32 columns). What I don t understand is that the "time column" is the same for all 16 channels: first measurement point for all 16 channels is recorded at time 0, second measurement at time 0,0001 and so on.... As far as I know, the 6255 PCI card scans channels sequentially. Therefore I don t understand how can I have the same time stamp for several different measurements. Are measurements on different channels running "simultaneously"?

Can any one explain me that?

The second question is about the influence of the factor "samples per channel".

I don t really understand the meaning of this parameter in my case... Am I reading only 50 samples per channel from all available samples in the buffer?

I send you a copy of my vi and a copy of the obtained lvm file 

 

Thanks for your help

Cheers

M

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Hey,

 

The PCI 6255 is using a multiplexer to switch between the channels, so its using sequential sampling, thats right. But, the way it samples is called intervall sampling, which means that the card samples all channels as fast as possible (depends on how fast the multiplexer can switch) and start to scan the channels again after the dt you selected. The delay between channels in this case is in the region of µs, because of that you cannot notice it with the waveform datatype afterwords.

 

When you are using continous sampling, the number of samples is the size of the memory you reserve within the RAM. The default setting is to read all available samples within the buffer.

 

 

Christian

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