how do I trigger an sinusoidal analog input using labview 6i,student edition, and the PCI-1200 board to get the duration of the waveform

[anita]

I am currently an engineering student and am a novice at using labview programming. I need to write a labview 6.0 virtual instrument, to be used in fuse link testing, which should meet the following requirements:

Inputs:

Current signal from a current transformer - 60 Hz signal, range of +5 V to -5 V

Calculation:

Calculate RMS current ( based on peak currents each cycle for long times to melt, or integrating the waveform within a few cycles for fast melt times) and Amp squared seconds to metl (for fast melt times).

Screen Output:

Time to melt, calculated RMS current, and calculated Amp squared seconds to melt. Visual graphic representation of the waveform ( long time to melt display peak voltage for each half cycle, fast times show breakdown of waveform for up to 20 cycles with 50 points per cycle)


Excel Sheet output:

Sample tests may be run on batches of fuse links at different current levels. After each test is run the screen data is to be able to be transferred to a spreadsheet for analysis. After the batch data is completed, the spreadsheet calculations need to be established to statistically analyze the data ( sample mean, variance, max and minimum values) The spreadsheet then needs to plot the batch data Time Current Characteristic of the fuse link.

I am currently using a PCI-1200 legacy DAQ board, connected to a waveform generator, which provides a simple 60 Hz sinusoid to one of the analog channels of the board. I am using the Al Mult Pt.vi , found in the DAQ example vi palette in labview 6.0, to acquire the analog waveform. I am currently using the Max Min.vi to measure peak current, and the Basic DC/RMS.vi to measure RMS current. These VI's are embedded in a while loop which executes until the stop button is pressed.

I am having difficulty measuring the duration of the Sinusoid signal since my current program continuously acquires data, even if there is no sinusoidal input. I know that there needs to be some kind of triggering that will only show the sinusoid part, the part I'm interested in, ( from when the test is initiated, when current is turned on, to when the fuse melts, so that I can measure the duration of the signal.


I know this is pretty basic, but I would really appreciate your help in any way that you can.

[Filipe A.]

Anita;

To accurately measure the time you sine wave takes to go from one point of interest to the next, you will need to use a DAQ board that has Analog Hardware Triggering capabilities.
The PCI-1200 doesn't have that feature.
I'm attaching a VI that does the trick when you use one of those boards.
By using the PCI-1200, the time measurement will be Software timed (controlled by Windows), meaning, not accurate.
Hope this helps.
Filipe

[anita]

Thanks Filipe,
I was hoping to use a software analog trigger in my VI, known as Acquire N Scans SW Analog trigger.vi I'm hoping that this would work. Thanks again for the VI.
Anita