Electronics > Projects, Designs, and Technical Stuff
Isolated zero cross detection w/ AC mains
Circlotron:
Or what about just stick a reduced version of the AC voltage through an op amp integrator to phase shift it by 90 deg and then to a normal zero crossing detector. Bonus is the integrator would function as a low pass filter, stopping any noise pulses getting through and causing false triggering.
Or even easier still, just shove the raw AC through an RC network that would reduce the waveform to signal level, give very nearly 90 deg delay, and filter out noise, and then to the ZCD. What’s not to like about that?
TimNJ:
--- Quote from: Circlotron on October 19, 2019, 02:23:59 am ---Or what about just stick a reduced version of the AC voltage through an op amp integrator to phase shift it by 90 deg and then to a normal zero crossing detector. Bonus is the integrator would function as a low pass filter, stopping any noise pulses getting through and causing false triggering.
Or even easier still, just shove the raw AC through an RC network that would reduce the waveform to signal level, give very nearly 90 deg delay, and filter out noise, and then to the ZCD. What’s not to like about that?
--- End quote ---
Sounds good too.
beduino:
--- Quote from: floobydust on October 18, 2019, 08:31:25 pm ---The best systems, for 3-phase power phase control have a software PLL where the MCU synchronizes a timer to mains, so mains noise does not cause a retrigger or upset.
--- End quote ---
Yep, I do something similar in my spotwelder MCU - mains ZC statistics are made, than when we need fire welding pulse train, ZC sensing ISR is disabled and this way we have more spare MPU cycles for other tasks like for example sensing current using galvanic insulated Hall effect sensor, manage pulses power, etc.
BTW: That is interesting if there are any AC mains power grid standards like for example accuracy of clean mains 50Hz/60Hz period?
schmitt trigger:
You will be interested in the following:
http://fnetpublic.utk.edu/index.html
beduino:
I've already found functional specyfication of power grid in my country in europe and one of those documents mention among others that
average frequency mesured within 10 seconds in mains contact should be in the ranges:
1. 50 Hz ± 1% (49,5 Hz - 50,5 Hz) during 99,5% of the week
2. 50 Hz ± 4% /-6% (47 Hz - 52 Hz) during 100% of the week.
This might help detect inrush disturbances in ZC crossing software I believe in, since when looked at realtime country mains grid frequency data available on web site, this frequency does changes now and is something between: 49.990Hz - 50.020Hz at depends on actual demand of power in grid as I know.
That is interesting :o
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