PXI-6259 simultaneous updating of AO

[georgeofthejungle]

Hi, I have PXI6259 M series DAQ cards. Each card having capacity for four analogue outputs with update rate (if using all four) of 1.25MS/s. My overall goal is to be running 11 analogue outputs (using 3 cards) all running at 1.25MS/s. I want to update all channels at the same point in time - I do not want sequential updating of the channels. I have searched the examples but can't seem to find anything that specifically gives me pointers as to how I ensure each channel is updated at the same time. The timing of the updates is important too, so I want to have some kind of hardware timed execution. Currently I'm researching but soon I shall begin to program and measure in the lab. - I'd like to make sure I don't go tearing off down the wrong track! Any hints and tips of what to look out for would be really appreciated. - I'm pretty new to this!

Regards,

George.

[johnsold]

George,

I have not done this so what I am saying is based on my reading of the manual.  If you do not have it, download the DAQ M Series Manual.

Chapter 5 is about AO.  On page 5-10 it says that the AO Sample Clock updates the outputs of all the DACs.  I interpret that to mean simultaneous updating for one board.  It also tells how to use internal and external clocks.  I suggest designating one card as the timing master and then slaving all the others to use the same clock.  That should get you simultaneous samples to within some nanoseconds.

Lynn

[georgeofthejungle]

Lynn, Hi - Thank you. The manual looks good. One thing i am unsure of is the setting of the analog output generation modes. I would like to use buffered finite sample mode. - How is this set? - is it all set in MAX? - the size of the data set will vary so i'd like to set it in LabView, os if it were set via a property node(?) then this would be good.

[johnsold]

George,

I cannot help with that level of detail.  I do most of my work on the Mac where MAX and DAQmx are not available.

Lynn

[niNickC]

Hello George,

Hopefully I can shed some light on this for you. A task such as this would be programmed using VIs which form part of the driver. You probably already have the driver installed - DAQmx.

A great start for getting to grips with DAQmx is this set of tutorials found on ni.com:

http://zone.ni.com/devzone/cda/tut/p/id/5434

You configure settings like finite sampling, sample rate etc in your DAQmx task.

Moving on from there, to ensure all your cards are properly synchronized you have to ensure that each card is using the same sample clock. You will need to route this clock over the RTSI bus. Thank fully DAQmx makes this really easy. See this for a nice example:

http://zone.ni.com/devzone/cda/epd/p/id/5197

Let me know if this is of any help