I'm new to LabVIEW (using it for a subject at university) but I've coded up a short program that counts rising and falling edges of a signal (to be used with input of a quadrature encoder). I've tested it at low frequency using the Simulate Signal block and it works fine, but as soon as I pump it up to anything above 4 Hz, it starts playing up (counting a positive edge as a negative edge). At 10 Hz, it doesn't count any edges at all. Same thing with the encoder - when we turn it very slowly the counts register fine, but turn it at even a moderate speed and it'll start missing. Not sure what the issue is. The code is pretty simple so I'm not sure how that'd cause the problem. Here's a copy of my counter block (the true/false input tells it whether to count up or down).

Are you adjusting the length of your simulated waveform when you vary the frequency? Your subVI appears to only be looking for one transition within a waveform. Your simulated signal Express VI is set up for 1000 Hz sample rate and 100 samples. So the outer loop iterates at 10 Hz. If your frequency is 5 Hz, then you are only going to have 1 transition in the section of waveform and you'll detect it. You go higher in frequency, then you might have multiple transitions in your waveform, but the subVI is only looking for the first one, and it might not even get that one. Remember when I said you need to run your loop twice as fast as the incoming waveform? Well you are now seeing that 2:1 ratio. Adjust you length of your simulated waveform as you adjust the frequency so that you don't get multiple transitions on the waveform you are generating each loop iteration.

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