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

On Fri, December 19, 2025 1:44 pm, smplx wrote:
>

>
> On Fri, 19 Dec 2025, Brooke wrote:
>
>
>> Hi Bob:
>>
>>
>> I think this is the same system used on my gas stove cook top.
>> PS sometimes there's a problem of not enough spark to light a burner. 
>> Any
>> ideas of why?
>
> immediate thought is air / gas ratio is wrong. check jets are clean.
>
>>
>> --
>> Have Fun,
>>
>>
>> Brooke Clarke
>> https://www.PRC68.com
>> axioms:
>> 1. The extent to which you can fix or improve something will be limited
>> by how well you understand how it works. 2. Everybody, with no
>> exceptions, holds false beliefs.
>>
>> -------- Original Message --------
>>
>>> Date: Fri, 19 Dec 2025 06:37:01 +0000
>>> From: Bob Blick<[email protected]>
>>> To: "Microcontroller discussion list - Public."<[email protected]>
>>> Subject: [EE]: Flame rectification
>>> Message-ID:
>>>
>>>
>> <DS5PR19MB997170D9166D3299975BFE43BDDCA9A@DS5PR19MB997170.namprd19.prod
>> .outlook.com>
>>
>>>
>>> Content-Type: text/plain; charset="iso-8859-1"
>>>
>>>
>>> I was doing a cleaning of my gas-fired forced air furnace, and it got
>>> me
>> thinking about how wonderfully designed it must be. It has a Honeywell
>> S8610U
>> "Intermittent Pilot" module that combines both high(15KV-ish) voltage
>> ignition and low(80VAC-ish) voltage, low(5uA-ish) current flame
>> detection on the same wire and electrode. Fantastic. Especially since
>> this very module has been running since 1997, with very little
>> maintenance, and has not missed a beat.
>>>
>>> Has anyone reverse engineered the in and outs of this device and can
>>>
>> describe the circuitry, and how flame detection doesn't die the first
>> time the high voltage comes on? And how it can toggle between the two
>> modes so quickly and reliably?
>>>
>>> For those who haven't encountered it, the module runs on 24VAC,
>>> generates a
>> recurring high voltage spark at twelve Hz, energizes a pilot gas valve,
>>  senses the pilot ignition on the same wire using flame rectification
>> (in
>> between the high voltage sparks) and energizes the main gas valve if
>> there is a pilot flame present, then stops the HV and continues to
>> monitor the flame. It sounds like bzz-click-bzz-thunk-whoosh when
>> starting. Quite obsolete by today's standards, of course. It was built
>> to last almost forever :)
>>>
>>> Thanks! Bob
>>>
>>
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