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how to measure the square wave frequency by 6023E
shh2745
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06-29-2004 02:42 PM
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Hi,
I would like to accurate measure the sinewave input signal frequency(60Hz) which the error is in 0.01hz. I used 6023E DAQ card to do analog input. Since 6023E does not have analog trigger function, I converted the sine input as square wave input signal. I try to use the example: Measure Frequency(DAQ-STC). I have no ideal about how to I/O connection about this example. Can anyone tell me how to do the I/O connection for my 6023E and continuous square wave input for the example. And if I use this method, can I have an accurate frequency measurement result with error in 0.01hz. Thanks for your help.
Fred.
I would like to accurate measure the sinewave input signal frequency(60Hz) which the error is in 0.01hz. I used 6023E DAQ card to do analog input. Since 6023E does not have analog trigger function, I converted the sine input as square wave input signal. I try to use the example: Measure Frequency(DAQ-STC). I have no ideal about how to I/O connection about this example. Can anyone tell me how to do the I/O connection for my 6023E and continuous square wave input for the example. And if I use this method, can I have an accurate frequency measurement result with error in 0.01hz. Thanks for your help.
Fred.
06-29-2004 04:49 PM
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Hi,
I already know how to use the Measure Frequency example to detect the frequency. However, I met another big issue. In the example, they detect the raising edge or falling edge to trig and count. If my input is 60hz, I got about 30khz result in the example program result. I think that my square wave (0v and 5V)is not a perfect and flat square wave, and the noise would affect the result. To overcome this issue, my idea is to detect some magnitude of the input signal other than detect the raising edge. I want to know can I do this way by 6023E and if I can, can anyone tell me how to do. Welcome for any suggestion or idea to this noise issue. Thanks.
Fred.
I already know how to use the Measure Frequency example to detect the frequency. However, I met another big issue. In the example, they detect the raising edge or falling edge to trig and count. If my input is 60hz, I got about 30khz result in the example program result. I think that my square wave (0v and 5V)is not a perfect and flat square wave, and the noise would affect the result. To overcome this issue, my idea is to detect some magnitude of the input signal other than detect the raising edge. I want to know can I do this way by 6023E and if I can, can anyone tell me how to do. Welcome for any suggestion or idea to this noise issue. Thanks.
Fred.
Jeremy_C
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07-07-2004 01:28 PM
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The counters on the E Series boards do not have any filtering, so if your signal is not a clean TTL pulse train, you will get some inaccurate readings. Also, you are limited to detecting an edge for any type of counter operation. You could always acquire this pulse train as an analog input and then do some software analysis to determine the frequency. This way, you wouldn't have to rely on edge detection. You could set up your own analysis to detect a pulse depending upon magnitude. I hope this information helps.
