How to measure period, V high, V low for any AC signal

[Eng. Salman]

Dears,

i'm new with labview and i just have basicsI and II course. i'm trying to build a VI to control some Electronic Devices Tests ... but

i sticked in one test >>>>

i have PXI 4070 DMM and PXI 5402 FGen and i'm trying to inject AC signal and Measure the output ....

i need to measure the period, Vh (the Upper Limit), Vl (Lower Limit) for the output  AC Voltage signal >>>>

i have tryed to read the DMM help buut i could not find what i need....

one thing more how to measure the Resistance by 4070 DMM ?

could you please help me .....

thanks in Advance

SAlman 

[Jarrod_B.]

Hello Salman,

Thanks for posting to the forums!  We have plenty of example programs to demonstrate exactly how to take the measurements you need.  To find these, open LabVIEW and go to Help >> Find Examples.  In the Example Finder, navigate to Hardware Input and Output >> Modular Instruments >> NI-DMM (Digital Multimeters) >> Single Measurements.  In this category, you will find examples that show how to measure AC Volts and Frequency. 

In order to truly measure the max and min values of an AC signal, you will have to acquire a waveform over at least an entire period, and then take the max/min values of that dataset.  For examples on how to acquire waveforms with your FlexDMM, refer to the Acquiring Waveforms category under NI-DMM.

I hope this information helps! 

Best regards,

[Eng. Salman]

Dear Jarrod,

thank you for your response and it was very useful but i face another problem ....

i'm trying to tel the DMM to read semi period in square waveform which is T if we assume the period is 2T and the square Waveform is 50% duty Cycle ... and some times its T1 and T2 if the duty cycle is not 50% of the square waveform ...

is thewre any way to find the semi periods T, T1 and T2.

thanks

Salman

[Eng. Salman]

sorry but i want to ask about the way to change the duty cycle of the square wavform ....

i just know to change it using FGen Express is there any other easy way to do that?

i mean is there any single  built in sub VI for this job?

[Jarrod_B.]

Hello Salman,

If you need to perform a semi-period measurement on your signal, the only thing you can do with a DMM is to acquire a waveform and then use the signal processing VIs in LabVIEW to calculate the pulse widths.  Typically, in order to perform a semi-period measurement in hardware, we need a counter.  An M Series DAQ board, for instance, has two counters which can be used for semi-period measurements. 

As for your FGEN question, the square wave is one of the standard waveforms available, and you can adjust the duty cycle using the NI-FGEN property node with the following properties selected:



FYI, if you want to see how an express VI is doing something, you can always convert it to a regular VI and then view it's front panel.  To do this, right click on the express VI and select Open Front Panel.  Be careful when doing so, because once you do, you cannot revert to the express form of the VI. 

I hope this helps.  Good luck with your application!

Best regards,

Message Edited by Jarrod B. on 02-22-2007 11:54 AM

[Eng. Salman]

Dear,

thank you again

but what if i don't have M Series DAQ board!

is there any other way?

[Dennis_Knutson]

Go back and read what Jarrod said. You can use the waveform capture function and use the built-in LabVIEW functions (assuming you have the full version of LabVIEW), to analyze a waveform.