Michael Lloyd

FFT in a CLX

5 posts in this topic

Has anyone here created an Add On for a Fast Fourier Transform I need to see vibration data in the frequency domain and an FFT seems like a good idea. If you're wonder why... I'm looking for harmonics. I'm not sure if I want to tackle it and I'm not sure if it's even possible. N would be something like 250 at 20ms sample rate. Not too overwhelming but transforming then purging and restarting the routine ... idk. Seems daunting but might not be that bad. Thoughts?

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I'm not sure I would put the effort into it when I can connect an XM-124 vibration analysis module to the ControlLogix and let it do the work. We used XM-124's on a system that evaluated some forced-air fans every time we started them up to do a crucial air-circulated heating process. If a bearing came loose or a fan blade was bent, it would let us know so we could shut down the heating process before it passed the critical temperature. The one time it triggered on a blown bearing, the customer flat out ignored the horn, the strobe, and the big orange warning display in two languages and ran the process anyway. Horses/Water.
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And I'll bet that this was the response from the operators when the alarm went off: "Bloody alarm! Why would they put such a loud alarm on this thing? It's not like we're f***ing deaf! And that f***ing strobe light is annoying as hell! Bloody Ken, he has no idea what it's like to be an operator! And what the f*** is all this French on the HMI? Does he think we're f***ing French? Oi, Robbo, get the f***ing fire hose onto that bloody horn and see if you can shut it up!" "Oh look, there's smoke coming from the bearing of that fan. If it wasn't for this f***ing noisy alarm we might have heard that bearing noise!"
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There's a long and ugly story behind that one, the basic moral of which is "if you ignore a nuisance alarm every time you run the machine, eventually you'll be ignoring a critical alarm and you won't know it." The XM-124s also allowed us to quickly accelerate past a resonant frequency on the machine frame. We could have done a decent job by just ramping up the motor and noting when the frame began to vibrate, but our mechanical engineers and the die builders wanted some more information about exactly how and when the structure resonated, and we wanted to be able to allow for possible different failures of the machine frame (like if something came unclamped or cracked) without shutting down the critical process if we didn't have to.

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None of the PLC's that are sensing vibration have an XM-124 module and in most cases I'd have a hard time selling the idea of putting one in

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