Flame Rectification

[Texanna Slim]

Today, in front of my supervisor, I casually mentioned to a co-worker that a flame rectifier was sort of like a thermocouple. He then had a shocked look about him and insisted we both have a report (due by Monday morning meeting) on how a thermocouple and and a flame rectifier works. Do any y'all have links to solve this great mystery? Muchos gracias!

[dandyme]

better get busy




see if you can search the contracting business web site to give you some insight.............








Don't be like plagerism Joe B.

[Tiger93rsl]

Flame rectification is just too cool.

http://contractingbusiness.com/feature/cb_imp_13002/#

[snewman24]

Amickracing has a good explanation on his website (plus a ton of other info on HVAC):

http://hvac.amickracing.com/Furnace%20Info/Flame%20rectificatoin.pdf

http://hvac.amickracing.com/

[WhoIsThat?]

insisted we both have a report (due by Monday morning meeting) on how a thermocouple and and a flame rectifier works. Do any y'all have links to solve this great mystery? Muchos gracias!
A t'couple generates DC voltage from heat.

A flame [somehow] half-wave-rectifies AC voltage to produce DC current. I don't know who discovered this effect, by accident or on purpose.
If 120 VAC across a flame gives you 5 uADC through the flame then the flame is acting like a diode in series with a 10 Megohm resistor. With no flame, this network should fool the module into thinking there is a flame.

[Tiger93rsl]

A t'couple generates DC voltage from heat.

A flame [somehow] half-wave-rectifies AC voltage to produce DC current. I don't know who discovered this effect, by accident or on purpose.
If 120 VAC across a flame gives you 5 uADC through the flame then the flame is acting like a diode in series with a 10 Megohm resistor. With no flame, this network should fool the module into thinking there is a flame.



Huh, sounds like you should read some of the links that we posted. But your on the right track. :)
:payattention:

[WhoIsThat?]

Huh, sounds like you should read some of the links that we posted.
:payattention:
I did. Not in my whole life have I heard that a flame can do this but there are a bunch of patents covering flame detectors using this method.
http://www.google.com/search?hl=en&safe=off&client=safari&rls=en&q=%22flame+rectification%22+patent&aq=f&oq=&aqi=

Try it. See if you can fool a module into thinking there is a flame present by using a diode (a 1N4004 should work)/resistor network. Your boss's jaw will drop.
The resistor value needs to be adjusted up or down depending on the applied voltage and the DC current required to give a "flame present" indication.

You didn't hear it here. . .

Here's more stuff on "that other thing." :)
http://en.wikipedia.org/wiki/Thermocouple

[Tiger93rsl]

I did. Not in my whole life have I heard that a flame can do this but there are a bunch of patents covering flame detectors using this method.
http://www.google.com/search?hl=en&safe=off&client=safari&rls=en&q=%22flame+rectification%22+patent&aq=f&oq=&aqi=

Try it. See if you can fool a module into thinking there is a flame present by using a diode (a 1N4004 should work)/resistor network. Your boss's jaw will drop.
The resistor value needs to be adjusted up or down depending on the applied voltage and the DC current required to give a "flame present" indication. If the flame has a high resistance then the resistor value can be lower.

You didn't hear it here. . .

You are correct the right dioed and the right sized resistor to drop the current to the correct level can produce a sign wave that will fool the module into thinking there is a flame.

[WhoIsThat?]

You are correct the right dioed and the right sized resistor to drop the current to the correct level can produce a sign wave that will fool the module into thinking there is a flame.
Since I finally did something right today, now I can go to bed. :)

[Bubbleheadski]

You are correct the right dioed and the right sized resistor to drop the current to the correct level can produce a sign wave that will fool the module into thinking there is a flame.

in a rectifier diodes produce dc voltages from ac voltages. Full wave rectification just produces a higher level of dc (due to the smoothness of the dc voltage ie. less ripple) while a half wave rectifier has more ripple due to only half of the ac sine wave being rectified ie. larger ripple {half of the sine wave}.
Typically in a half wave rectifier you could take the ac sine wave and remove the lower half and the resultant wave would be the positive wave then ride zero for the negative wave then back to the positive wave etc etc.
The full wave turns the negative into another positive wave. Both of these rectifiers are then filtered and the dc voltage is a smother dc line at .707 of the ac voltage. -------
It is easier to understand if i could draw a damn picture on here.... but hopefully you get the idea.

Metals when heated can produce a voltage when heated (dependent on the metal and can have a positive or negative coefficient.)
I bet Goosie can clear this up way better than I!

[Tiger93rsl]

in a rectifier diodes produce dc voltages from ac voltages. Full wave rectification just produces a higher level of dc (due to the smoothness of the dc voltage ie. less ripple) while a half wave rectifier has more ripple due to only half of the ac sine wave being rectified ie. larger ripple {half of the sine wave}.
Typically in a half wave rectifier you could take the ac sine wave and remove the lower half and the resultant wave would be the positive wave then ride zero for the negative wave then back to the positive wave etc etc.
The full wave turns the negative into another positive wave. Both of these rectifiers are then filtered and the dc voltage is a smother dc line at .707 of the ac voltage. -------
It is easier to understand if i could draw a damn picture on here.... but hopefully you get the idea.

Metals when heated can produce a voltage when heated (dependent on the metal and can have a positive or negative coefficient.)
I bet Goosie can clear this up way better than I!

With just a single zenner dioed you will get half wave rectification DC pulses at 60 HZ. The full wave or more know as the bridge rectifire will produce pulsating positive and negative DC voltage. A capacitor has to be place in the circuit after the bridge to smooth out the DC sign wave and give you clean DC current. The ingintion controller only sees a half wave rectification like you would see if you were and try and trick it using just a single zener dioed.

[WhoIsThat?]

"
A Zener diode is a type of diode that permits current in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". The device was named after Clarence Zener, who discovered this electrical property.
"

My question is, is the larger plate that's in the pilot flame the cathode or the anode?

If you make a bonfire and use unequal size heated plates can you make a battery charger from household AC?

And, who discovered this effect?

[timebuilder]

Here is a good explanation of why the current will only flow in one direction. It is the difference in the relative size of the two conductors (or, emitters if you prefer) that tends to allow the pulsating DC current (rising and falling value, but only in one direction) when an AC current is applied to the ionized portion of the flame.

http://www.hvacmechanic.com/trouble_shooting/FlameFGR-2.pdf

[WhoIsThat?]

Here is a good explanation of why the current will only flow in one direction. It is the difference in the relative size of the two conductors (or, emitters if you prefer) that tends to allow the pulsating DC current (rising and falling value, but only in one direction) when an AC current is applied to the ionized portion of the flame.

http://www.hvacmechanic.com/trouble_shooting/FlameFGR-2.pdf
The rifle diagram seems to say that the electrons go to the larger surface more easily, so 'conventional current'
http://en.wikipedia.org/wiki/Electric_current
goes from the large surface to the small. Therefore the large surface is the diode's anode.

I didn't get how the inner cone can be unburnt gas. Everything in the flame is burning, unless the gas goes to the outer ionized layer and then gets burned. Also, the hottest part of the flame is supposed to be the point at the top of the inner cone.

[timebuilder]

The rifle diagram seems to say that the electrons go to the larger surface more easily, so 'conventional current' goes from the large surface to the small.
Therefore the large surface is the diode's anode.

I didn't get how the cone can be unburnt gas. Everything in the flame is burning, unless the gas goes to the outer ionized layer and then gets burned.


The idea is the larger positive area that is the burner "catches" more electrons from the ionized gas plasma when they are emitted by the smaller area that is the flame rod during one alternation of the AC current. When the larger area goes negative (remember, electron current flows from negative to positive) and emits electrons into the plasma, the smaller flame rod cannot catch nearly as many, and the predominate current is the current from the negative burner to the positive flame rod.

"Conventional current" is a reference to the direction of electron flow that was imagined by Benjamin Franklin. He had a 50% chance of being right, but it was later shown that currents of electrons flow from negative to positive.

Conventional current is the "arrow direction" of Franklin's imaginary current shown in semiconductor schematics. So, when you look at a diode representation in a schematic, the arrow head points from positive to negative in conventional current, but electron flow is actually in the opposite direction of that representation, i.e., negative to positive.

In order to understand what happens in flame rectification, stick with electron current. For other purposes of understanding circuitry, you can use conventional current, as long as you use it consistently.

[kdocsr05]

it is a flames natural ability to flicker causing the rectification no flicker no flame

my tag is new member yet i should be with the pros

[timebuilder]

it is a flames natural ability to flicker causing the rectification no flicker no flame

my tag is new member yet i should be with the pros

Read the links. Flickering is not a process of rectification.

Sorry.

[Texanna Slim]

Thank you all for your input. Can you believe there is no mention of flame rectification in the NATE yellow book or Modern Refrigeration?

[timebuilder]

Thank you all for your input. Can you believe there is no mention of flame rectification in the NATE yellow book or Modern Refrigeration?

:yes:

[Bubbleheadski]

With just a single zenner dioed you will get half wave rectification DC pulses at 60 HZ. The full wave or more know as the bridge rectifire will produce pulsating positive and negative DC voltage. A capacitor has to be place in the circuit after the bridge to smooth out the DC sign wave and give you clean DC current. The ingintion controller only sees a half wave rectification like you would see if you were and try and trick it using just a single zener dioed.

A zener is a special diode. Any diode will conduct in only one direction.
A single diode will as you say conduct for only one half of the sine wave, A full wave rectifier (2 diodes)will conduct in both halves of the sine wave but a bridge rectifier (which uses 4 diodes) gives the best conversion because it is already smoothed to an extent and therefore easier to remove to ripple. Yes capacitors are used as the filtering device because they shunt the ac component to ground. There are many different ways to use capacitors to filter that ac component.

/\
\/ what a bridge rectifier looks like in a schematic

| -half wave rectifier

| | -full wave rectifier in the last 2 imagine the arrows of the diodes
(last image 1 in each direction. )

[Bubbleheadski]

and to throw a BIG kick into the game.... their is/was a lot of talk about HOLE flow theory.
Thats where current flows from positive to negative because the "holes" travel backwards from conventional thinking!!! Hows them taters?
:P

[Bubbleheadski]

it is a flames natural ability to flicker causing the rectification no flicker no flame

my tag is new member yet i should be with the pros

gets your post count up and you can be with the pros. You can be a student or a 30 yr veteran of the trade... but once you get your post count up to 15 either the student or the veteran can be a pros member!
(I know absolutley nothing and I am in the PROS section!!!) :eek2: