measure voltage gpib

[BernoulliLizard]

I need to be able to measure peak to peak voltage of an ac signal.  However, the frequency is 40 kHz, which is too high to measure using the Daq (because the sample rate will not go that high).  How can I measure the waveform using a gpib multimeter?  Is there a sample code out there that will help me?

thanks

[BernoulliLizard]

in case it matters, I am using a 34401A Agilent digital multimeter.

[LeifKing]

Well the specifics depend largely on what part of LabVIEW you are using and what communication interface.  For instance I basically only use LabVIEW VIs so I can only help with that.  Agilent (which is the name now of the old measurement equipment portion of Hewlett-Packard/HP) has a lot of good resources for their equipment and even have pre-made drivers and executables sometimes if that is all you want.  They also often have lots of examples and they maintain a lot of the information for even older HP models that were retired before they became "Agilent".  NI's Drivers' page often have stuff for HP/Agilent instruments as well.

I've had to make my own LabVIEW drivers for the HP 3458A as the ones available didn't work for me and it isn't that hard.  The manuals for the instruments are very good at providing all the commands, what they do, what options you can use with them and even related commands so I didn't find it to hard (though I did have to deal with garbage data).  Without more specifics I can't help more than point you to the "drivers and software" page for the 34401A, but while I find Agilent's new site a little harder to navigate than the previous 2 versions again I'd say it is still rather easy to find if they have anything and a good place to look.

If this doesn't help, I could only help with LabVIEW VI specific codes and only really with RS232 Serial Port or GPIB/IEEE 488 communication ports though many of the others are basically the same thing just replacing with the corresponding function from it's pool of functions.

http://www.home.agilent.com/agilent/techSupport.jspx?cc=US&lc=eng&nid=-536902435.536880933&pid=10000...

Hope you find what you need.

-Leif

Leif King

Metrology Engineer

Oak Ridge Metrology Center

[Albert.Geven]

The drivers for this instrument are not yet available on the NI website but it can operate in a FLUKE alternative dialect and that driver exists

 http://sine.ni.com/apps/utf8/niid_web_display.download_page?p_id_guid=01609CFA7F8A1E9CE0440003BA7CCD...

[BernoulliLizard]

None of the examples from the Agilent link actually work.  Half of them do not actually have links to download or see any actuall example, and the files that do download are not openable.

[Dennis_Knutson]

The 34401A has had a driver that ships with LabVIEW for many years and ones from Agilent are not going to provide any extra functionality to the instrument. If the standard AC measurement is not adequate (i.e. rms reading) and since performing mutliple reads is too slow, you are using the wrong instrument. You are welcome to confirm that with Agilent - it's not a LabVIEW issue.

[johnsold · Accepted solution]

BernoulliLizard,

In your original post you indicated that you want to measure peak to peak voltage of a 40 kHz signal.

I do not know of any voltmeter which will do that.

Get an oscilloscope or a DAQ device with a sufficiently high sampling rate.  Depending on the signal bandwidth (not the same as the signal frequency), PCI card devices for around $500 (US$) or a variety of form factors for $1500 or less should be able to do the job.

Lynn

[LeifKing]

Oscilloscopes don't have very good voltage measurement accuracy specifications.  Oscilloscopes are most suited for observations of the shape of waveforms and especially for dealing with more complicated signals.  Basically a multi-meter is almost always better suited at performing a pure voltage measurement.  Most meters will not measure directly in volts peak, but that is when you use the very basic and simple conversion formulas to convert the rms voltage into peak or peak-to-peak voltage.  Basically Vrms / sqrt(2) = Vpk and 2 * Vpk = Vpk-pk.  often people just use .707 for the square root of 2 and your done if it is a sine wave.  If it is a triangle wave Vrms * sqrt(3) = Vpk and again of course 2 * Vpk = Vpk-pk.  A basic multi-meter can often have problems with other waveforms.

That said as the signal is 40kHz and sounds sinusoidal, I think the 34401A is just fine and much simpler than a scope.  Another nice thing about many multi-meters is that if you just set them up for the measurement function you want, the resolution etc., and leave it on auto-trigger like you would if you were just going to take a reading from the display; many automatically and continuall send the most recent reading directly to the GPIB bus that can be retrieved with just a GPIB read function while oscilloscopes require much more.

If you want to do more you simply use GPIB write routines sending the text strings that are discussed in section 4 of the 34401A user manual.  Usually using the direct measurement commands actual make single triggers are start sending readings to memory that you then have to deal with so I usually either program the settings I want or manually configure it and then just use nothing more than plain GPIB read functions.  To manually trigger for an immediate reading you just send a "MEAS:VOLT:AC? DEF,MIN" and the termination characters if relevant as a simple text string command using a GPIB write.  The DEF sets autoranging and the MIN sets the best possible resolution for that function.  This will cause the meter to take one reading on the AC Voltage function and send it to the buffer which you then read with a GPIB read.  For readings you just put it in a look.  The read rate is much slower than using auto-trigger and everything as is.  It basically works the same way as if the GPIB port was like the front panel display which you just retrieve with the GPIB read.  You would use the memory capabilities, math, and other functions if you had a more complex measurement.