by Marc Ward
Clay Times July 2003
There’re two reasons I’m writing an article on flame rectification. Well, I guess there are really three reasons. The third reason is that hardly anyone knows what the hell it is… or if truth is known, hardly anyone cares. The first two reasons are; I’ve been doing some safety systems lately with flame rectification and the most important reason of all…. After almost seven years of articles, the easy topics have been used up. I promise, I’ll give it a shot at making an obscure topic sorta’ semi-interesting. But, someone, somewhere, who has this type of system, might get some answers to their problems.
You ever wonder why your gas stove top starts sparking when you turn it on and then it magically stops sparking when the flame starts. How’s it know? What it knows that most folks don’t is that blue flame is a conductor of electricity. Now, it’s not a great conductor of current like a copper wire, but electrons still flow through it. So, the current that was there when you turned on the stove is still there. It’s just doesn’t have to jump across a gap (spark) like it did before. The current flows through the blue flame. If the flame is too low, yellow, or goes out, the electrons start jumping across the gap again. Now, all this description of your kitchen appliance tells part of our little rectification tale. What happens with your gas stove top is just part of what is known as flame rectification.
Kilns that have a flame rod, are using rectification. Our kitchen example above just helps explain that flame is an electrical conductor. What flame rectification does is measure the type and intensity of the current that is passing from the flame rod through the flame to the pilot burner. This is not the same as a thermocouple/BASO system. A thermocouple gets hot and sends a small amount of electrons to a little electric magnet that holds a valve open. Ok, if you don’t have any “gear head” in you, the rest of this article may very well cause the magazine pages to be turned.
You can only rectify an AC current. The rest of the article deals with explaining the previous sentence. “AC” current means Alternating Current. It’s what you have coming out of the electric plugs at home and in your studio. What it means is that the electrons race one way, and then they turn around and race the other way. They “alternate” their direction back and forth…a bunch, real fast. The other kind of current is DC…Direct Current. The electrons always flow in the same direction. Now, here’s the cool part. Well, at least it’s cool to someone like me who learned to skin wiring insulation before I learned to ride a bike. The cool part is that flame is such a particularly bad conductor of electricity that the “rectified” connection depends on the size of the contact on each side. Another way to say that is this only works if your flame rod is small and your pilot is big. Remember, our current is alternating (AC). The electrons race between our pilot burner and our flame rod that is in the flame. Here lies the secret of rectification. I know, I know, you’ve got goose bumps. When the electrons flow from the skinny flame rod to the pilot, they have plenty of landing area over on the face of the pilot. Now, the current alternates and wants to flow back to the flame rod. Well, our skinny little flame rod doesn’t have near as many places for electrons to land. The current has now been rectified. A regular AC current is BIG one way then BIG the other way. A rectified current is BIG one way then really small the other way. This is what the flame rectification safety system measures; the real small current that is juxtaposed by the BIG current. This tiny current is measured in a couple of microamps (that’s 2/millionths of an amp!… a hair dryer can use 13amps… 650 million% more!!!). (Since the pilot flame is a poor conductor, this type of system works well. But, metal is a great conductor. If you have an itty-bitty crack in some wiring, electrons will easily find passage to the metal and screw up our little rectifying dance. You know what happens next, the kiln shuts down mysteriously or won’t light. The local electrician or the guy in the school’s physical plant department with his name on his shirt probably won’t be able to help “rectify” the problem. If you’re having problems with this type of system, look in the yellow pages under “boiler supply”. They are some of the few people that have the tools and the experience to track down your problem. They are also more expensive than plumbers, small town lawyers, and high-class hookers. If you made it to the end of the article, you’re a real trooper. Thanks….