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Article: The Wild AC Tachometer

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SparWeb:
This is an article I've been working on for about a month.  I think it's ready to see the light of day. Since the members of this forum have been the inspiration for this idea and the project that it belongs to, Y'all deserve a peek before I submit it for publication.

Wild AC Tachometer: http://www.sparweb.ca/8_Datalog/WACT/Wild_AC_Tachometer_2021-02-16a.pdf

I would like to submit it to the IEEE Spectrum but it's too long for them.  I'm looking for some similar technical or semi-technical publications with an engineering or scientific audience that would understand it.  If any of you have suggestions I'd love to hear some. I have steered away from mathematics to keep it readable.  Without the math, I had to add more text.  I hope it isn't too long.

The story is told in detail in the article, but here just briefly: I spent a lot of time and energy trying to filter noise out of the AC from the motor conversion generator so that I could measure the frequency.  In theory it should be possible to measure the frequency of the AC to get the RPM of the rotor, but it wasn't working.  I tried PICAXE micros, a LM2907, and Arduinos.  I kept getting lots of extra pulses, like the turbine was spinning at 2000 RPM one second and 300 the next.  All the exptra pulses being measured in the micros were just blips of noise, but I couldn't come up with a noise filter that would always work.  Eventually I figured out why the filters weren't working, and I almost gave up on having a good tachometer, when I hit upon the idea that made all the filtering problems go away.  By monitoring all 3 phases from the generator, the tachometer could just monitor the phase-to-phase sequence until it completed a cycle.

It's a 20-page read so hopefully I don't bore you all to death. For those who get the whole idea of homebuilt generators and messy AC, you can "TLDR" to page 15 for the solution.  For a tech journal like IEEE I can easily cut it in half, for other magazines that want the history, it's there.  After it's published (or if I give up submitting it) I'll turn it into a Fieldlines post.  For now, an editor following my tracks and finding all of the content on FL might have to reject the article as already published.  But I think it's safe to link you to a PDF on my home webpage if you want to read it.

I want to give this device a catchy name, but it isn't really a "thing", it's just a simple set of inputs to a microcontroller and a program that uses interrupts instead of pulse-counting to make a tachometer.  For now I call it a "wild AC tachometer" but maybe someone can come up with a better name.

Heres a question for all you sparkies:  Have you ever heard of anything like this before? 

In the article, I refer to similar circuits and programs a little bit, because what I'm doing is very similar to "quadrature" in stepper-motor control and some types of encoders.  On the other hand, when I talk about noisy electronics, everyone answers "filters".  Distortion? Filters.  Spikes? Filters.  Harmonics? Filters.  Always driving the point that I'm supposed to filter the AC to the microcontroller.  Yeah, well, here I am not filtering anything at all, and the tachometer is rock-steady 24/7 for 4 years now.

There was a time when I wondered if this is a patentable idea.  It has all the features of a unique function in a working device that could be patented.  But then I consider what it would take to defend a patent like this...  you can't see anything from the outside (that's the great thing about it) so the only way to know about a patent infringement is to hack the code out of a chip... then go to court... life is too short for that.  I have gained so much from sharing ideas, this site included, I just want to share it out there.

I know I said it already: thank you to everyone on Fieldines for the ideas, advice, and inspiration.  It helps me solve problems all the time.  This is just one example that I've spent a lot of time on.

mbouwer:
New possibilities for a nice active pitch control?

Bruce S:
I like that you used the Polyphase wording instead of just 3-phase.

Have you tested this on a polyphase unit with more than 3-phases?

Still reading :-).

Bruce S

Mary B:
Nice article! I remember the discussion way back when on some for of tachometer.

SparWeb:
I've mentioned it before - but at the time I didn't realize it was special.  Didn't seem that big a deal.
Then I got to looking for improvements, simplification, other uses and such...  ...dead air... 
It was hard to even get the google search terms right to pull up anything related to it.
Then I got excited, thinking I might have an idea I could patent...  :]
That phase passed quickly.

I've tried quizzing other engineers about this.  You know, professional engineers with decades of experience dealing with electronic noise.  None of them suggested side-stepping the problem.  Every one of them told me how to filter.  Some of them suggested some really complicated and expensive equipment to do the filtering, like, thousands of bucks equipment. 

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