McKenzie
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Posts posted by McKenzie
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I am encountering erroneous frequency data when reading frequency with labjack T4. I am using DAQ factory express.
Initially I encountered this in a real application, but I have been able to duplicate it in a simple .ctl, which is attached.
I am reading frquency on FIO4 using the time interval method (time between rising edges). I display the result (after some calculations) and also graph the result. I am also sampling three analog channels. In experimentation I have noticed that the problem seems to go away when I delete the three analog channels. Is there any reason why the analog read operations would interfere with the read to FIO4?As far as my test setup goes, I am testing using a function generator to supply 100 Hz square wave to FIO4. I have probed it with an oscilloscope and it is a very clean signal. I do not suspect noise is any part of the problem.
I have tried it on two T4 devices, and they both behaved the same way.
I also attached a screenshot of the ctl file "in action." RPM is calculated from the FIO4. Basically RPM is proportional to frequency. The correct result SHOULD be 600 RPM. But often I see much higher frequencies (corresponding to shorter intervals) which are not correct.
Any help or suggestions would be much appreciated.
erroneous data when reading frequency with Labjack T4
in Channels, Conversions and general data acquisition
Posted
I have not used Kipling. I will try to do that. I do have the latest LJM Installer (I checked that before I came here to the forum).
In the short term I have switched to using counter instead of timer. I just continuously count the pulses and then reconstruct the frequency in post processing after logging. This may end up being a workable solution for me.
Please be reminded that I ran the program with a function generator as input, and monitored the signal with an oscilloscope to confirm good signal integrity. So I don't see much point in using DAC1 to generate a "known good" waveform. But thank you for the suggestion anyway.