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Pulse Measurement problem
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Dave Crabbe
May 28, 2004, 3:55:34 PM5/28/04
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I'm trying to use the Pulse Measurement function in LabVIEW 7 to
measure the period of a periodic wave. Eventually I want to measure
the frequency of any wave I put into my DAQ card, but for now I am
simulating a sine wave signal of 10Hz freq and going between 0 and 4
units. 1000 samples / sec. I expect to simply hook the pulse
measurement canned function to the signal and run it; but I get the
following error: "Error 20308 .. the waveform did not cross the mid
reference level enough times to perform the measurement"
measure the period of a periodic wave. Eventually I want to measure
the frequency of any wave I put into my DAQ card, but for now I am
simulating a sine wave signal of 10Hz freq and going between 0 and 4
units. 1000 samples / sec. I expect to simply hook the pulse
measurement canned function to the signal and run it; but I get the
following error: "Error 20308 .. the waveform did not cross the mid
reference level enough times to perform the measurement"
Guess I am pretty new to LabVIEW.. anyone know what will correct this?
(am using all defaults .. that is I have set no input values)
Dave Crabbe, dave....@nscc.ca
LabVIEWer
Jun 1, 2004, 9:56:07 AM6/1/04
to
You are setting your simulated sine wave to 1000 samples per second.
Have you set the number of samples to something more than 100? To
ensure that you get at least one complete cycle, you should set the
number of samples to put out more than a single cycle. I usually try
to get over 2 complete cycles, but it should work with about 1.5.
Have you set the number of samples to something more than 100? To
ensure that you get at least one complete cycle, you should set the
number of samples to put out more than a single cycle. I usually try
to get over 2 complete cycles, but it should work with about 1.5.
Dave Crabbe
Jun 1, 2004, 10:46:43 AM6/1/04
to
Yes, as I've specified, I am trying 1000 samples per second.. I've
tried from 100 to about 5000, I think.. very easy to duplicate, just
put a simulated sine wave, and then try any of the timing measurement
or pulse measurements VIs and set the freg to less than 15 hz or lower
. seems the measurement VI times out if it doesn't see a cycle within
a certain time frame (absolute). It doesn't seem related to samples ..
I don't know ..
tried from 100 to about 5000, I think.. very easy to duplicate, just
put a simulated sine wave, and then try any of the timing measurement
or pulse measurements VIs and set the freg to less than 15 hz or lower
. seems the measurement VI times out if it doesn't see a cycle within
a certain time frame (absolute). It doesn't seem related to samples ..
I don't know ..
Dave
Yuto Shinagawa
Jun 7, 2004, 5:55:44 PM6/7/04
to
Not sure if you've already solved the problem or not, but I'll post a
reply anyway. Ironically, I came across your post on google when I
encountered the same problem with Labview just yesterday; I'm trying
to make an optical tachometer for a propeller. Anyway, aside from
increasing your sampling interval or increasing the frequency of your
generated waveform, you can just chose to ignore the error message
that would otherwise interrupt your run by simply creating an
indicator for the 'error out' port. Doing this won't hault the
program and prompt you whether or not to continue. If you want to go
one step further, you can unbundle the error cluster output, see if
the error status is true or false (true if it returns an error; false
otherwise), and if true, return infinity as the period. The 'select'
function comes in handy for this.
reply anyway. Ironically, I came across your post on google when I
encountered the same problem with Labview just yesterday; I'm trying
to make an optical tachometer for a propeller. Anyway, aside from
increasing your sampling interval or increasing the frequency of your
generated waveform, you can just chose to ignore the error message
that would otherwise interrupt your run by simply creating an
indicator for the 'error out' port. Doing this won't hault the
program and prompt you whether or not to continue. If you want to go
one step further, you can unbundle the error cluster output, see if
the error status is true or false (true if it returns an error; false
otherwise), and if true, return infinity as the period. The 'select'
function comes in handy for this.
Regards,
Yuto Shinagawa
Keywords: Error -20308 occurred at "ma_ptmFetch.vi" when called from
"Pulse Measurements 1 chan.vi The waveform did not cross the mid
reference level enough times to perform this measurement. Check the
signal length, reference levels, and ref level units.
Dave Crabbe <x...@no.email> wrote in message news:<50650000000500000085...@exchange.ni.com>...
Dave Crabbe
Jun 8, 2004, 8:10:32 AM6/8/04
to
Yuto;
Excellent suggestion. Thanks for your post. Wonder if the LabVIEW team
have an address for 'bugs' or enhancements next time around .. hope
they are monitoring this.
dave
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