LeonMötter Posted May 6, 2020 Report Share Posted May 6, 2020 So let begin by stating that i know that there are fast inputs which are specifically designed for these kind of problems but in this instance i could not use them and for that matter i don't think i need to. To explain what i am doing: i have a oven with 2 internal fans that i need to check if they are rotating. If they stop rotating for some reason an alarm goes off. The way i realized this is with a inductive sensor and steel bolt in the axle. Really basic stuff. Then in my program i used the following net to count the number of rising and falling edges: I do that for a set amount of time (for now it is set to 5 seconds) and if after that time if the counter is not zero than the axle is spinning and every thing is oke. really simple and works almost without any problems. I say almost because at one point a thought to myself, hey if i am measuring this over a set time i can calculate the speed at which the axle is rotating and use that troubleshoot performance of my machine when i need to. What i noticed then was when i increased the output too the motor the rpm measurement went down instead of up. My first thought was well i am probably hitting the limit on what i can measure on normal input only that it was only with one of the 2 axles and even weirder is that that axle that was giving me problems started around a 40 hz signal from the sensor, while the axle without problems was running at almost 100hz from the sensor without any difficulty. So now i am really curious about what is happening here. Could there a difference in response time between inputs? Could this somehow be related to programming? Or am i just abusing the PLC to much and should not expect more? I really want to understand what is going on here, not because i need to but because i want to. 🤔 Quote Link to comment Share on other sites More sharing options...
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