6254 Counter stops counting as frequency increases

I'm counting tach pulses (CI cnt edges) with a 6254. The DAQmx read is in a timed loop and passes the counter value to an indicator in another lower priority loop using shared variables. The counter counts correctly when the tach is turning slowly but stops counting when the tach speed increases. As the tach slows down the counter begins to count again. I think the maximum tach rate is about 4K..

Please refer to your other forum for more information and questions.
Regards,
Jordan F
National Instruments

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We found that the best way of obtaining speed measurement from a pulse generator is to use the buffered period measurement and scan some period (more than one), then eliminate the first measure (first period measurement may be incorrect due to the uncertainty in the start of measurement with respect to the slope of the signal), next average the measures obtained.
The next step is to divide base time used (internal base time of 20 mhz for example) by the average measure obtained in the preceding step: this is the average period measurement and must be multiplied by 60 and divided by n. of pulses per round: this gives you the rpm value.
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i realise why Apple has changed this behavior....
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Hello Pramod,
You could follow the suggestion from Joel, you could firstly comment out the “DoSomeDbOperation()” method to see if it then would work find without increasing the handle count. This would help narrow down this issue.
And with your description, this issue seems to be a handle leak, then you could also check this blog below which would help you find what type handles leak:
How to troubleshoot a handle leak
Regards.
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Help Counting high frequency voltage spikes

Equipment: NI USB-6229 (250 kS/sec Analog In., 16 bit DAC, 32 bit Counters and internal clocks <= 80 Mhz)
LabView 14
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I have an experimental application where I need to count voltage spikes (integer #) caused by electrons hitting a sensor. These spikes can be as frequent as 500,000 Counts/sec. The spikes are not going to be the same voltage everytime, but they will be visible above the noise so I need to allow the user to select a Threshold Voltage that triggers a real count rather than noise spikes.
Attempts:
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I have a program that uses the Count Edges channel and it is accurate within 3% of the expected # of counts. I was just testing it with a function generator and the program doesn't count unless the signal's voltage is above 2-3 V which won't work for my application. I will post what I have. Does anybody know of a way to trigger off only at selected Voltage levels using counters, or know of a way to filter through the noise to get real spikes?
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Go to Solution.
Attachments:
ElectronCountsTest.vi ‏29 KB

Thanks for the reply johnsold. I didn't think to use a comparator but that is good to know that I have that option. I was and still am hoping for some kind of trick to do this programmatically. One other idea that I was playing with is offsetting two or three different Reads on the same signal to read the signal at different times. If this is a possibility, it may be able to double or triple my sample rate to 500k or 750kS / sec. Anyone else have any ideas on this solution?

6120 counter max frequency

I am trying to set the max frequency for PCI-6120 counter. By the card specification, the counter's max source frequency is 20MHz. However, on MAX software test panel, if the counter frequency is set greater than 5MHz, program pops up an error stating the max valid value is 5e6 MHz.. Attached is the error message. Did I do anything wrong? Or special card setting is needed. Please help. Thanks very much.
Attachments:
NI 6120 counter error message.jpg ‏36 KB

Hi windwalker,
The max source frequency is 20 MHz. The source is an input to the counter which is divided down to produce the output signal:
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The other mode is "pulse" mode, where the counter will count to N and then a pulse its output. You can end up getting a pulse every 2 ticks of the source, which could give you a 10 MHz clock. You can't set this mode in the test panels, but here's an example in LabVIEW showing how to get a 10 MHz output (the "External Clock" can be the 20 MHz timebase).
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Minimum Frequency for counter Pulse Frequency Generation

Hello,
What is the Minimum Frequency that the Counter Output Pulse Frequency VI can generate?
If I need to generate a REALLY low frequency pulse train can I do that?
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Hi Dan,
If you don't explicitly specify a timebase, DAQmx will choose a default depending on the initial parameters you set up for CO Pulse Frequency. For example, the following code should work on any DAQ device with a 32-bit counter and a 100 kHz timebase available (from my first post, 11.64 uHz is the minimum frequency in this scenario).
So... your 10-100 second periods should be more than achievable. The inverse of 12uHz is about 23.15 hours.
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I'm developing an optical tacometer for a model gas turbine engine. I have a boolean signal in labview which is switching at a frequency between 4 and 26Hz. I need a live readout of the frequency of this signal.
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Go to Solution.

This vi should work for you
Tim
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Attachments:
Calculate Frequency from boolean.vi ‏11 KB

How do you count the frequency of a booloen signal?

Hi, I'm new to LabVIEW, so I suspect this is propbably quite a simple problem.
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littlejim4 wrote:
Hi all,
I'm very new to Java, only a few months into it. I am working on a program that compresses a file, thread, string. Firstly it takes a string of undetermided length as input and using the delimiter splits the string, then places that string into a list. Then from that list I take out the recurring words with another list and return the index of where the words are, this has been done without any problems.
Next I want to get the word frequency and return the most common word into the first index following onto the next and so on. I am not sure how best to go about this. I did use a map but that just gives the frequency of the words without any ordering. Can anybody give me any suggestions that I could try bearing in mind that java is my first language so this is also a confidence building exercise.
Many thanks to anybody who responds.Okay, so you have a Map with the 'word' as keys, and the 'frequency' as values, right?
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Frequency Simulator.vi ‏63 KB

Hello marco73
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Message Edited by Ravens Fan on 07-30-2009 10:27 PM
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6254 Counter stops counting as frequency increases

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