NI6602 pulse width measurement: Do I have to use an external sample clock?

Hi
In the .NET 4 example 'MeasPulseWidthBuf_SmplClk_Cont' it is stated in the comments that:
An external sample clock must be used.
Counters do not have an internal sample clock available. You can use
the Gen Dig Pulse Train-Continuous example to generate a pulse train on
another counter and connect it to the Sample Clock Source you are using
in this example.
I have an application running without specifying an external clock. The applications is running, but I'm not sure I can trust the recorded data. Here is the channel creation code:
   task.CIChannels.CreatePulseWidthChannel(readTaskCounter,
   "ReadPulswidthTask", 25e-9, 20e-6,
   CIPulseWidthStartingEdge.Rising,
CIPulseWidthUnits.Seconds);
task.CIChannels.All.DataTransferMechanism = CIDataTransferMechanism.Dma;
   task.Stream.Timeout = callbackTimeoutInMilliSeconds;
task.Stream.Buffer.InputBufferSize = 50000;
   task.SynchronizeCallbacks = true;
   task.Timing.ConfigureImplicit(SampleQuantityMode.ContinuousSamples);
   task.Control(TaskAction.Verify);
Note that I'm not specifying any external clock.
1) Which clock is the daq using? -It is obviously using some clock since I can collect data via this task.
2) Do I need to change the configuration to use an external clock to achieve reliable readings - as mentioned in the 'MeasPulseWidthBuf_SmplClk_Cont' example?
/mola
Solved!
Go to Solution.

Hi mola,
That specific example is for sample-clocked pulse width measurements. This type of measurement is only supported on newer hardware such as X Series boards and will not run on the 6602.
Your application that you linked uses Implicit timing, meaning that the signal itself serves as the sample clock. That is, at the end of each pulse width that you measure, the sample is deterministically latched in. So, you end up with a buffered array of every pulse width that is seen by the counter.
Best Regards,
John Passiak

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You said that you were using the Pulse Width Measurement VI. Are you using the Express VI (LabVIEW 7 or higher), the regular VI, or are you trying to use a counter to measure do your PWM?
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Hello Friends,
I am new to Labview. And now I am working on a project where I have to measure the pulse width.
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Attachments:
Pulse width.PNG ‏60 KB

I get this pulse ( as in picture attached), I want to get it on analog or digital pins in such a way in get the pulse width of only 1st edge.
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Hello,
I'm not sure I fully understand the pin-out diagram. At present I have a NI9401 in a NI 9172 chassis.
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Hi Daisy,
If you open your DAQ Assistant properties, and read the Measuring Pulse Width help on the side, you'll see that "You can use the counters on your measurement device to measure pulse width. Pulse-width measurements measure the time between either a rising and a falling edge, or a falling and a rising edge." If you change the Pulse Width Setup Starting Edge setting to Falling edge and look at the picture above, you'll see that the pulse width it's measuring the width from a falling edge to a rising edge (the pulse width while the signal is low). So this measurement will go from the falling edge of your first measurement to the rising edge of your second measurement. If you want to measure the width of the first pulse (while the signal is high) you need to set your Starting Edge to Rising.
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Solved!
Go to Solution.

Hi Uli,
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NI6602 pulse width measurement: Do I have to use an external sample clock?

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