convert period

[Chris95370]

Using the USB-6002 what can I expect for a "convert period" or the 'conversion time delay' between adjacent channel conversions?

Example:    Sampling several channels at 1Khz, (A0,A1,A2)  what is the time delay between adjecent channel samples?

I'm trying to determine the trade-off between synchronous sampling and non-synchronous sampling.

At what sample rate does this delay become significant for a non-synchronous device?

Thank you

[Kevin_Price · Accepted solution]

Several possible answers.  There is probably more detailed info to be found in your device manual or other DAQmx docs.

1. By default, DAQmx will try to pretty much max out the time between the conversions while honoring the overall sample rate.  With 3 channels at 1 kHz sampling, I'd expect the convert interval to be between about 300 and 333 microsec.

2. You can query a DAQmx Timing property node for "AI Convert.Rate" to find out the exact conversion clock frequency.

3. You can choose to *set* that same DAQmx Timing property node if you'd like the convert clock to be faster, with less time between channels within each particular sample.

The *significance* of this channel-to-channel conversion delay is *entirely* application-dependent.  It may be of negligible concern.  It may matter enough that you decide to buy a more expensive simultaneous-sampling device.  There's no general purpose answer.

-Kevin P

[Chris95370]

Thank you Kevin;

Good information.

Significant with respect to just the sample time:

A 1khz sample period is 1000us and a 333us 'convert period'  is a 33% difference (delay)  between 3 sample channels (two adjacent), this is huge and is significant for my application. I want 1Khz sampling period, but I a much smaller conversion period, something like 10% or less. So I guess I need a synchronous converter.

[Kevin_Price]

I can't say for *certain* about your specific device without more research than I have time to put into it, but there's a good chance you can get that 10% if you use my note #3 above.

The USB-6002 is spec'ed for 50 kHz sampling rate on one channel.  This will probably also be the max rate for the convert clock.  You could *probably* set your sample rate for 1 kHz, then explicitly use the DAQmx property node I mentioned to set the convert clock rate at 20 kHz.  Then 2 channel intervals will be only 0.10 msec, only 10% of your 1 kHz sample rate.  (And you could probably cut that in half by setting the convert clock to 40 kHz.)

-Kevin P

[Chris95370]

Thanks for all your input Kevin.