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NI USB 6008 Sampling speed

Hi, I am currently doing a project to record heart signals which can be analysed and the data backed up to an Excel file. I have no problem with the labview program and I am acquiring the heart signal successfully.

When I use the 6008 I appear to be loosing some of the signal, it seems to be chopping the top and bottom of the wave. I am wondering is this because scope is faster than the DAQ? And maybe the DAQ is not suitable.

 

Thanks, any help would be appreciated.

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Message 1 of 7
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Your problem is probably saturation of the ADC, and not speed. In the 6008 manual you can find how to set the gain on the the 6008 PGA. Choosing a lower gain may fix your problem. But post your code anyway as this is the fastest way to a solution.  


Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
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Message 2 of 7
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What sampling rate are you using to digitize the ECG signal?  It could be that your sampling rate is too low to reliably capture the peaks of the of the QRS complex which will result in the captured waveform looking chopped off.  You should use a minimum of 500 samples/sec (per channel) for ECG - even higher if possible.
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Thanks for the prompt replys. I have built an amplifier circuit which also conditions my ECG. It is the output signal from this that I'm feeding into the USB DAQ. I have adjusted the gain of my circuit by changing the gain-resistor value several times but it is still out of range to capture the entire signal. I know that the 6008 can sample up to 10k samples/second so this should be plenty to capture the entire QRS complex. I have read that the 6008 has a poor onboard FIFO which overflows quickly if aquiring data at a high rate so I am wondering could this be the issue? Also I dont know what rate I am sampling at how can i check this?

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deck wrote:

Thanks for the prompt replys. I have built an amplifier circuit which also conditions my ECG. It is the output signal from this that I'm feeding into the USB DAQ. I have adjusted the gain of my circuit by changing the gain-resistor value several times but it is still out of range to capture the entire signal. I know that the 6008 can sample up to 10k samples/second so this should be plenty to capture the entire QRS complex. I have read that the 6008 has a poor onboard FIFO which overflows quickly if aquiring data at a high rate so I am wondering could this be the issue? Also I don't know what rate I am sampling at how can I check this?


 

I think you should post a picture of the a chart showing the error, your code not as a picture, and a schematic showing how you connect to the 6008. Without all that, we are not able to help you. I have never used the 6008, but I am quite sure then a buffer overflow occur you will not get the problems you are talking about.



Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
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Message 5 of 7
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I was reading the signal but was chopped. I am just reading it into a DAQ assist in a while loop for now so the code is basic. However now I am getting this error Error -50405 occurred at DAQ Assistant



Possible Reason(s):

NI Platform Services: No transfer is in progress because the transfer was aborted by the client. The operation could not be completed as specified.
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Message 6 of 7
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If you had posted the items I requested. your problem most would have most probably been solved now. Why you have not done this. Well that is your call


Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
Message 7 of 7
(3,021 Views)