ADC conversion period

[CMX]

Hi,

I've been building an acquistion interface and while testing I got the following error:

> Error -200019 occurred at DAQmx Read (Analog 2D DBL NChan NSamp).vi

>Possible reason(s):
>ADC conversion attempted before the prior conversion was complete.
>Increase the period between ADC conversions. If you are using an external clock, check your signal for the >presence of noise or glitches.

I'm using M series card (PCI-6229) and the acquisition block is about the same as the example for synchronizing AO/AI. Error occurs when I try to read from 16 channels with 15 kHz sampling rate (continuous mode). I don't get this error when using 10kHz. Am I really hitting the limits of my card or is this just something else? Card specs say 250kS/s but I thought this was a maximum per channel.

Many thanks

[chilly_charly]

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@CMX wrote:
...Error occurs when I try to read from 16 channels with 15 kHz sampling rate (continuous mode). I don't get this error when using 10kHz. Am I really hitting the limits of my card or is this just something else? Card specs say 250kS/s but I thought this was a maximum per channel.

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Unfortunately, this specs are valid for a single channel only. Means that your theoretical max ADC is 15.6 kS/s, NOT taking into account the time required to switch from one channel to the other. That's the cause of vthe error. Remember that the settling time after a channel change is significant, and varies with the source impedance. For full accuracy, and with a low impedance source, it reaches 7 microsecs and the max sampling rate on 16 channels is about 5000 kS/s.

CC