Simultaneous acquisition of 2 counters and several (up to 8) AI channels on DAQcard 6036E (PCMCIA) - maximum acquisition rates

[welding_rob]

Hello there,

This is my first post using this forum so please bear with me...

I am currently using a NI DAQCard-6036E 16input/2 output, 200kS/s, 16-bit Multifunction I/O coupled to a NI BNC-2110 breakout box to simultaneously acquire two incremental rotary encoder inputs (as edge counters - one pulsing at every degree, the other once per revolution) and up to 8 analogue inputs.

I am trying to get them to aquire synchronously and as quickly as I can (as a guide - ideally around 50kS/s for two counters and a single AI input).

Now, the limited Labview knowledge I have is self tauglt through 'playing around' so I am sure I have many 'bad habits' and am currently fighting to obtain the quickest sample rate that is possible.

The current vi attempts to set the various daqmx tasks to aquire synchronously. If I create a system simply to aquire on the AI channels, I can achieve capture rates which come close to that of the cards capabilities. However as soon as I implement the counters, this drops - as a rough guide I can only obtain in the order of between 18 - 20kS/s when I have the two counters and a single AI channel running.

I am therefore trying to establish whether this is an inherent limit, or whether I am making various blunders which are restricting me. My other issue is that I am not entirely sure that the AI data and counter samples a are synchronised as I can't see where the common clock is being defined to trigger simultaneous capture of the analogue sample and reading of the two counter registers.

I have uploaded a copy of the current vi (though from a computer without daqmx installed so apologies if it does not load properly... let me know and when I am in front of the correct computer I will re-upload )

Any advice would be very much appreciated!  

[JTG_Wilson]

Hi Welding_Rob,

As I understand it, you want a VI where you have an analogue input and 2 counter inputs that aquire data synchronously.

I've found a tutorial that may be of help to you about timing and synchronization.

I've also found a Community Example that is very similar to what you are trying to do and so should also be of help.

I think the problem is that you have not included the DAQmx timing (sample clock).VI in the setup of the counter channels, also you have to make sure that the DAQmx tasks are started one after the other, you have done this just before you start the analogue voltage task but you should do it for the counter channels as well.

Let me know if you require some further help.

Kind regards