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Sample length for ADC212/216

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Sample length for ADC212/216

Postby Roger » Tue Jun 20, 2006 2:12 pm

I find this paragraph in the Picolog-Data Acquisition Software writeup for the ADC212 (and ADC216):

"When used with the ADC-212/3 up to 32 thousand samples per channel can be collected at full speed. At lower speeds up to a million readings can be collected."

What are the lower speeds (sample rates) referred to here? If the samples are being stored in computer memory, why are they limited to a million readings?
Roger
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Postby Michael » Thu Jun 22, 2006 9:32 am

Hello Roger,

The slow sampling rates refer to collecting data in realtime continuous modes. Sampling rates are typically 5-10millisecond intervals. The scope buffer is not being employed here as the data is passed direct to the PC. Higher sampling rate use the buffer as data cannot be passed as fast as the scope can sample.

The 1 million sample limit is currently a restriction of the software. The 1 million samples have to be loaded into memory before thay can be displayed.

I hope this makes sense.

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Michael
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Sample length for ADC212/216

Postby Roger » Thu Jun 22, 2006 1:18 pm

Thanks for the rate estimate. I take you mean only 100 to 200 samples per second can be passed directly to the PC. This seems really slow. Would it be faster with the pp196 USB to parallel adapter?

If I have to rely on the buffer in the ADC212 or ADC216, perhaps you can clear up an inconsistency in the specifications. For the ADC212 the buffer size is given as 32kS (32k samples?). Then in the ADC216 the buffer size is given as 32kB. If this is bytes and the word size is 16 bits, then this would be only half the buffer size of the ADC212. Or is this a missprint? Also it is not clear if the full buffer size is available for both channels are if the two channels have to share the buffer.
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Postby Michael » Fri Jun 23, 2006 9:06 am

Hello Roger,

I need to elaborate on the data transfer modes. The slower sampling mode relies on the PC closk for timing of signals. Every sample interval the PC clock will tell the driver to get a sample. This slows down the sampling rate significantly due to software and security layers embedded within WinXP. In fast sampling modes, the scope determines the sample interval by its internal clock and passes the converted data to ints internal memory. Once the scope has completed the collection, it will transfer the data to the PC.

The buffer memory size description has changed due to inconsistencies in marketing information. The correct unit of measurement is number of samples. So the 32k = 32,000 samples NOT bytes.

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ADC216

Postby Roger » Mon Jun 26, 2006 9:43 am

I appreciate your patience in answering my questions.

This was not covered in the last response.

Is the 32kS rate in the ADC216 for one channel or for both channels at the same time?
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Postby Michael » Mon Jun 26, 2006 9:50 am

Hello,

The buffer is split between the active channels.
So the buffer length for one channel would be 32,000 and 16,000 for two channels.

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ADC2212/50

Postby Roger » Mon Jun 26, 2006 11:34 am

I seem to be narrowing my choices down to the ADC212/50 because of the buffer size. I have one more question, which I hope I can clearly state.

It is important in choosing an anti-aliasing filter to know the sampling rate. Can the sampling rate be selected independently of the scope time base?

For example, can I specify a 10kS rate and expect to collect samples for 6.4 seconds in a 64k buffer? Or is there some fixed relation determined by the scope time base?

With data logging software can I specify any sample rate I choose?
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