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Sampling Rate on some PC's seems to be too slow...

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Sampling Rate on some PC's seems to be too slow...

Postby Nic » Fri Feb 28, 2003 12:30 pm

Hi
I am having trouble recording a 30Hz sine wave signal using Picolog. I am required to record the demodulated signal (30Hz Sine Wave) from a navigation beacon. I'll be using a Laptop and an ADC-200 in an aircraft and recording the signal for 5 minutes. I have simulated this scenario on the bench by using a signal generator and obtaining a 30Hz sine wave which is being fed into the ADC-200. I have set the Picolog software to the following settings:
-Real-Time Continuous
-1 ms Sampling Interval
On my desktop PC (running Windows 98), this simulated setup works fine; the recorded signal is a smooth sine wave. However, when I loaded the software onto a laptop PC running Windows 2000, the same recorded data was jagged (sampling interval was too slow). Incidentally, the laptop has a faster processor to the desktop. I then tried it on a new machine running Windows XP, and the same jagged waveform occurred (due to slow sampling rate). I then tried the same test on an old Laptop running Windows 95, but the test signal was still incomprehensible.

Why does this signal record perfectly on my PC, but not on other machines? As mentioned above, I have used both faster and slower machines and have also tried Windows 95, 98, XP and 2000. Yet, the only machine that this signal records OK on is my own desktop PC.

I filled in a technical support form about this problem on Werdnesday, but as yet haven't received a reply regarding this problem. Please let me if their is a possible solution to this, as I urgently need to seek out an alternative way of recording this signal should it not be possible to use a Pico Instrument for this.

Thanks...

Nic
Nic
 

Postby matthew » Fri Feb 28, 2003 1:17 pm

Hi,

The reason for the slower sampling is that you are using a slow sampling mode - ie Real Time mode. This mode relies heavily on windows timing which varies from version to version (often regardless of processor speed).

Try using Fast-Block mode, this will overcome all timing issues.

Best Regards,
Matt Everett

Pico Software Engineer
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I tried Fast-Block - Still No Joy

Postby Nic » Fri Feb 28, 2003 2:14 pm

Hi Matthew

Thanks for your reply.

I tried Fast-Block mode, but this made no difference. In fact, my 30Hz signal appeared triangular (which appears to be caused by the slow sampling rate). I seem to get better results with Real-Time Mode. However, this mode only works OK on my desktop; all the other PC's I have tried have given me very jagged traingular signals. Also, I need a recording time of 5 minutes, which is not possible with Fast-Block mode.

Any other ideas on how to record my 30Hz sine wave signal for a 5 minute period?

Thanks...

Nic
Nic
 

More suggestions

Postby Alan » Wed Mar 05, 2003 8:20 pm

You are correct in saying that fast block mode will not work - this will limit the max no of samples to 32,000 which spread over 5 mins will not gve much of a sampling rate.

In real time mode the PC controls the sampling so it is possible to collect more than the 32,000 samples the ADC200 can store internally.

Asking for 1 sample per ms is the correct thing to do, the actual sampling rate you will get will depend on the PC and also te operating system. Try ensuring all non essential programs are shut down, and do not display a graph or spreadsheet whilst collecting.

If this does not work, there are a couple of possible options. One would be to use our USB adapter (let us know if you want us to try if this helps under XP first - I have not tried this out for this sort of application). The other solution would be to use the slower ADC100, although this can only sample at a fraction of the speed of the ADC200, its enough for this application and is better suited to collecting large amounts of data.

Regards
Alan
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Sampling Rate

Postby Nic » Thu Mar 06, 2003 8:46 am

Thanks Alan for your assistance.

Where can I source the USB adapter? I originally purchased the ADC-200 through RS Electronics, but they don't seem to have your accessories listed in their catalogue.

Thanks again...

Nic
Nic
 

Postby matthew » Thu Mar 06, 2003 9:16 am

Hi,

You can order the USB-Parallel Port adapter online from here ... or you can find our contact details here.

Best Regards,
Matt Everett

Pico Software Engineer
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