Can buffered digital edge detection only be performed using an external sample clock?

I am working on an application where I need to measure the speed (rpm) of a motor as it starts up using the output of its built in hall effect sensor. The sensor should output 2 pulses per revolution of the motor. My plan is to count the pulses from when the counter (counter 1) is armed to when it is up to speed. Looking at the M series manual, the CVI (v8.5.1) help, and the examples it appears that this can only be done using an external sample clock. Is there a way to route an internal sample clock to the appropriate terminal on the counter so that I do not need to add additional hardware?
I am currently using a PCI-6289, but the final application will use a CDaq-9188 chassis (using one of the the built in 32-bit counters).
Thank you for your assistance.

Thank you for your input.
However, I did forget to mention one detail of the application. I need to buffer the edge counts so that I can graph the speed of the motor as it starts up. I need to be able to acquire the edge counts at reqular intervals so that I can determine how fast the motor was rotating at each point. So far I have not been able to find an example of doing this without and external sample clock. As I mentioned, in the final application I will be using the 32-bit counters on a CDAQ-9188 chassis. The only thing I can think of at this point is to generate a pulse out of the second counter and use that as the sample clock. Will this work?

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Cedric,
dddsdsds wrote:
[...]In my case, i want to get the data at the rising edge of the external clock signal, so at a frequency of 50 kHz. How can I do that ?[...]
You answered your question already. If you want to use an external clock, you have to configure the timing source of your task to be external. In order of proper buffer configuration, you should enter 50kHz as rate in addition to the external configuration, but this will not influence the speed of the acquisition (since it is "clocked" externally!)
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Basically what I want to do is generate a regular pulse over a (configured) set of lines. The pulse will, typically, be 10ms wide at intervals between 900ms and 1,100ms. The interval will only change occasionally and is usually 1 second (1,000).
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1. First of all this only did something if the selected clock source was /Dev1/Ctr1Source. No other clock would do, even though there are 2 clocks on the board (e.g. /Dev1/Ctr0Source did nothing).
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3. Thirdly the pulse sample rate also seemed to be ignored, e.g. set it to 1 or 1,000 made no difference.
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NumberPulseOfSamples   Interval
========================================
1,000                               9 (ish) seconds
2,000                               18 (ish) seconds
4,000                               36 (ish) seconds
1,500                               6½ (ish) seconds
3,000                               8½ (ish) seconds
800                                   7 (ish) seconds
Setting the number of pulse samples to a low value (500) threw an error (-200016, "device memory underflow") when stopping the task.
Can someone shed some light on what is going on and how I can get what I want?

I only seem able to select Ctr1Source, but this may be because (?) I have some clocked analogue input going on at the same time, so perhaps Ctr0Source is busy with this. Unfortunately, the 2 examples of clocked digital wave forms doing a write use PipelinedSampleClock or BurstHandshake, although there are reads using a "SampleClock". If you try to run the 2 examples you get an error
Property: NationalInstruments.DAQmx.Timing.SampleTimingType
You Have Requested: NationalInstruments.DAQmx.SampleTimingType.PipelinedSampleClock (or SampleTimingType.BurstHandshake)
You Can Select: NationalInstruments.DAQmx.SampleTimingType.SampleClock, NationalInstruments.DAQmx.SampleTimingType.OnDemand, NationalInstruments.DAQmx.SampleTimingType.ChangeDetection
Task Name: _unnamedTask<0>
Status Code: -200077
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Attachments:
encoder with timer.JPG ‏50 KB

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Attachments:
Graph.jpg ‏55 KB

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Solved!
Go to Solution.

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Can buffered digital edge detection only be performed using an external sample clock?

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