Pause and resume analog waveform output

[SidMayer]

I have a customer who wants to be able to output multiple channels of very long waveform data, and is planning on using an NI DAQ card like the 6703 for example.  They need to be able, on command, to pause the output, zero the D/A channels, and then later resume the waveform whereever it left off.   Presumably that means a pause and resume through the driver, or an abort with information about where in the waveform we left off.

I have seen info about a gated output clock for pausing from a hardware signal (and I suppose we could use a digital output for this), but it does not look obvious that we can then zero the outputs programmatically and later resume the wave output.

The solution can be DAQ-mx or Traditional DAQ, as long as there is a way to do it...

Thanks!

[reddog]

First, the 6703 is a single point DC voltage board.  If you want to generate several waveforms, I would recommend you go with a 671x, 672x, or 673x board depending on your channel count and speed requirements.  For each of these boards, you could accomplish what you want in DAQmx by using a pause trigger and programmatically grounding the DAC reference.  For instance, by using a digital line as your pause trigger, you could raise the line high whenever you wanted to pause the generation and then ground the DAC reference.  Grounding the DAC reference is accomplished by toggling an attribute in the channel property and forces all output channels to be grounded.  When you want to resume the waveform, you can unground the DAC reference and then lower the digital line.  This will resume the generation from the point it was previously.

[SidMayer]

Thanks!   You are right, I misquoted the board number... the customer had that board in mind, and I already pointed out to him that it is a static update board.  The DAC ground attribute sounds like the missing piece.

[Tom_W_[DE]]

Hi Sid-

I have modified a DAQmx LabVIEW shipping example to illustrate what reddog suggested.  Please note that to use this method you will need to provide your trigger signal to both the digital line and a PFI line for full functionality.

I hope this helps!

Thanks-

[Ed W]

Hi,

Analog output does not support a stop trigger, and there isn’t an easy way to achieve this functionality using hardware timing.  The easiest workaround would be to use a digital start trigger to begin generation and software timing to stop generation.

On the other hand, there is an example that ships with LabVIEW that demonstrates analog generation using a pause trigger.  If you had a hardware switch that acted as an ON/OFF switch for the analog generation, you could use this to begin and end generation.  In addition to this, you would be able to restart the analog generation if you then turned the switch on again.  The example can be found by browsing the example finder to Hardware Input and Output >> DAQmx >> Analog Generation >> Cont Gen Voltage Wfm-Int Clk-Pause Trigger.vi.

Best regards,

Ed W.

Applications Engineer
National Instruments