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High resolution & hardware timing

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3 replies to this topic

#1 Gene

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Posted 25 May 2011 - 05:33 PM

Is it possible to use the U6-PRO to get high resolution samples from the sigma-delta converter and take advantage of hardware timing in the Labjack? I'm trying make sure the samples are uniformly spaced in time and not dependant on my software issuing commands at exactly the desired rate. It appears as if streaming mode doesn't allow for high resolution sampling. Thanks - Gene

#2 LabJack Support

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Posted 26 May 2011 - 02:29 PM

No, the hi-res converter in the U6 pro cannot be used in hardware-timed stream mode. The reason is that the way the converter works is different enough that it would be difficult to implement in stream mode, and since the converter speeds are generally in line with command/response rates we have not tried to force the issue. One suggestion is to take normal steps to provide reliable software timing: good software design, avoid running other programs at the same time, and increase the priority of your process in Windows. Another suggestion is to enable a system timer and collect that in the same Add/Go/Get block as your analog input readings. That way you can evaluate how regular your intervals were.

#3 mhopeng

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Posted 14 August 2012 - 04:35 AM

Thats disappointing. I would have appreciated seeing that information on the specifications page (http://labjack.com/u6/specs), somewhere around the sentence: "The U6-Pro has all the features of the normal U6 with the addition of an auxiliary low-speed high-resolution (24-bit) sigma-delta ADC." Its not mentioned in the manual either.

#4 LabJack Support

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Posted 14 August 2012 - 10:42 AM

Sorry about the confusion. It is mentioned on the main U6 product page in the first paragraph of the section "U6-Pro vs. U6", but I did not see it mentioned on the u6/specs page or in the user's guide. I added mention to the u6/specs page, and to sections 3, 3.2, and 5.2.12

Stream mode is typically used for scan rates of 100 scans/s or higher. The fastest speed available from the hi-res converter is about 4 ms/sample, so it just barely crosses into the realm of stream speeds at its lowest resolution setting. Another issue that the U6 returns 16-bit data values in stream mode.

On the soon-available T7-Pro using hardware timing with the hi-res converter is something we should be able to support. It has a much more powerful processor than the U6 so we can do more. Also, stream data is returned as 32-bit values (normally floats actually).

Another thing with the T-Pro is that it will support scripting (likely not promoted at initial release), so rather than using stream mode, you could make a script that collects hi-res data at the desired interval.

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