how can i trigger a simulated signal generator

[rbalsan1]

I am trying to simulate the functions of a multiplying DAC.  Here is my current setup:  I have a digital lock in amplifier putting out a refference signal.  I have it running to the analogue input on a usb-6251.  I want my DAQ to put out the same wave but alter the amplitude, so that when I run the ouputed signal back into the lock in, I can have it subtract the ouput signal from the input signal cancelling it out.  The problems ive been having are mostly due to a driffting phase in the ouputted signal making it very difficult to cancel out the signal.
 If I could triger this signal i could keep it in phase with the input signal.
Thanks in advance any help is greatly appreciated.

Bob

[Bueller]

Hi Bob,

Given your current setup, I highly recommend taking a look at the " Cont Gen Voltage Wfm-Int Clk-Analog Start.vi" in the example finder in LabView Help.

You can locate that example in Help >> Find Examples >> DAQmx >> Analog Generation >> Voltage.

If you have an external clock, you can also use that clock as a clock source the DAQ devic itself through one of the PFI lines.

Regards,

Faris A

[rbalsan1]

Thanks, That did help a bit, but i found a DAC example that was a little more suited for my needs.  The problem i had when i modified the design to repeat an incoming wave is it would repeat it in phase and the next read it would repeat it a bit out of phase, to the point where the tool isnt very useful.  Is there a vay i can keep the first read and not let it be replaced by the second?  Here it the vi im working with
Bob

[Bueller]

Bob,

A case structure might be your answer. If you place the " DAQmx Write.vi " inside tbe "True" subdiagram of a Case Structure, and in the "True" case set the condition for the Case Structure to "False", so that next time the while loop runs, it will go through the "False"  subdiagram which you can keep empty.

Please feel free to ask any further questions.

Regards,

Faris A

Applications Engineer

National Instruments