Re: [EE]: Flame rectification

Hi Harold,

Thanks for the link to the flame detector patent.

On my gas stove, the ignition switch on one of the knobs doesn't always work. So I'll turn that burner on, then turn on another burner. When it lights, they'll both light. I forget if the spark electrodes are all directly paralleled or if there is a 4-way enclosed spark gap somewhere to distribute the ignition. That would make the system more tolerant of partial shorts of one or more electrodes.

Friendly regards, Bob


________________________________________
From: Piclist <[email protected]> on behalf of Harold
Sent: Friday, December 19, 2025 1:41 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE]: Flame rectification

I was not aware of the use of flame rectification for flame detection. I
see a patent on it at
https://patentimages.storage.googleapis.com/bd/ad/0d/f76a332c6472e8/US4427363.pdf
.

I've seen thermocouples used to control the pilot light gas valve in water
heaters. The patent mentions that thermocouples are slow, so you could end
up with a lot of gas beind dumped into the room before the loss of flame
is detected. The flame rectification is quick. Very clever!

We have a gas stove with electronic ignition. One thing that I thought was
clever is that the igniter causes the spark on all the burners, not just
the one that is turned on. I think this is a clever design simplification.
The burner with gas is ignited. The others just spark. I SUSPECT the spark
gaps are in parallel, so it seems there could be a situation where one
spark gap "hogs" the current with a lower arc voltage causing the others
to not arc. One of our burners seems to ignite less reliably, but I don't
really know why.

We did have an intermittent problem in our gas furnace. The contractor
finally just replaced the control board. It has a microcontroller, the
ignition transformer, a bunch of relays, and other stuff. As mentioned
previously, there is a sequence of operations that it goes through in
starting. It first starts the exhaust fan and ensures it is working (as
mentioned previously, I suspect it uses differential pressure). It then
turns on the pilot gas and the igniter. On detecting the pilot flame, it
turns on the main gas (accurate sound effect given previously). Then after
a few seconds (probably temperature controlled), it turns on the blower
that moves the heated air into the ducts.

There are a LOT of safety features to ensure the house does not blow up or
burn down. I wonder how many furnaces have caught houses on fire. I
suspect it's pretty low.

Google AI says "The most common causes of house fires are cooking (the
leading cause, often from unattended food), followed by heating equipment
(especially portable heaters), electrical malfunctions (wiring,
appliances), smoking materials, and candles, with children playing with
fire and dryers also significant factors, all highlighting risks from
unattended flames, faulty systems, and flammable materials."

Harold