Synchronise PCI-6224 to GPS receiver

[PEM@ANU]

I have a M-series PCI-6224 DAQ card. I need to be able to synchronise the operation of this card to a GPS receiver. The GPS receiver generates 1-pulse-per-second and 10 MHz reference signal outputs. I'm pretty sure this can be done but the documentation on using external timebases in the M-series manual is not very clear. How might I go about this?

[George M.]

Hi,

I am assuming you are trying to run an AI task based off of this external clock. There is an example in the example finder in LabVIEW that does just this. The example can be found in Help>>Find Examples>>Hardware Input and Output>>DAQmx>>Analog Measurements>>Voltage>>Cont Acq&Graph Voltage-Ext Clk.vi. By default, this vi will accept the external clock into PFI7. So, plug in your clock to PFI7, and you will be up and running. Please let me know if you have any other questions, and have a Great Day!

George

[PEM@ANU]

Hi George,

Thank you very much for your reply! Your answer was very helpful but not quite what I was after. The GPS receiver I have generates a 10MHz sine wave - however I want to actually sample at much lower frequencies (256 and 2048Hz) and I want to be able to control that in software. So I really just want to synchronise the DAQ's internal clock to the 10MHz signal, and use the internal clock to do the actual sampling. There's some references in the DAQ manual to a 10MHz Timebase input (as well as 20MHz and 80MHz) but it doesn't really explain how to use them. Any ideas??

Karl

[George M.]

Hi Karl,

Ok, the first thing is that you will not be able to synchronize to a sine wave. That is, if you want to use an external signal, that signal must be a square wave. All of the timing signals are square waves. Next, the internal timebase (20 MHz, 80 MHz, etc) is determined by DAQmx depending on the rate that you specify. It will choose the most appropriate timebase, given a specific rate. I hope this clears up your questions. Please let me know either way, and have a Great Day!

George

[PEM@ANU]

Hi George,

Thanks for letting me know about the sine wave problem, I'll have to find my way around that. I've been reading the DAQ M-series help files and they refer to the RTSI bus as a way of synchronising the DAQ card to an external clock. Is that right? Do you know anything more about how this RTSI bus works? Many thanks!

Karl

[George M.]

Hey Karl,

Here are three amazing documents that discuss the RTSI bus, as well as how to program synchronized operations with NI-DAQmx:

Timing and Synchronization Features of NI-DAQmx

M Series User Manual

These will answer all of your questions about the RTSI bus. Have a Great Day!

George