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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. quick_freq_test_with_ADC.ctl