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Circuits designed by David Johnson, P.E.
Last Updated on: Wednesday, October 18, 2017 05:04 AM

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More detail found in DC Magazine

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Corona Monitor

I have a medical client who has been using their corona machine for several years without too many problems.  However, on occasion, the machine might hiccup for a few seconds. 

The glitch lasted long enough to allow sections of the filter plastic sheets to pass through the system without being properly treated.  They needed to have a logic signal that would swing low when no corona is detected.

The light corona monitoring and alarm circuit I designed is pretty simple.  The circuit is powered by +5v and has an on-board voltage regulator as a reference voltage.  The current from a reversed biased photodiode is converted into a voltage using an op Amp circuit.  That output voltage is fed to a voltage comparator circuit.  I included an adjustment in the current to voltage converter.  After setting the gain to produce a one volt output signal for a typical corona discharge, the comparatorís threshold voltage could also be adjusted.  The device then changes states when the corona intensity dropped by about 20%. 

The alarm output of the monitoring circuit is connected to the companyís computer through a three pin connector.  The alarm signal controlled the treatment process.  When the computer sensed the corona alarm signal, it would shut down the system.  A human operator would then back up the plastic film a few feet and rethread it into the take-up rollers.  Finally, he would press the reset button, which told the computer to start up the film treating process again.

Click on Drawing Below to view PDF version of Schematic

More detail found in DC Magazine

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