What’s flame rectification?

Flame Rectification Defined                                                                         

By Gary McCreadie

A jittery pilot flame sits in a moist, poorly lit room.  The one supply of sunshine is a low hanging fixture swaying backwards and forwards on account of a loud air flow system pulling in air from a dirty return air grill.  The room smells of cigarette smoke, stale espresso and deceit.  In walks a gruff trying character who seems to be visibly upset with the scenario.  “So,” he says….”I heard you will have been operating your mouth once more, telling all the nice HVACers of the world that you’re solely accountable for creating the sign required to show flame within the heating cycle????”.  The flame develops a facade of anger and blurts out, “you may’t show a factor, go eat one other donut pig!”  “Okay, have it your approach…Hey Sarge, convey up the hose would yah!”

There’s a false impression on the market that the flame itself generates the sign wanted to show flame and energize the “fundamental valve” of the fuel valve.  The flame does play an integral function, however doesn’t really generate the sign, it merely adjustments an AC present to a DC present via the method of flame rectification.  Again once I was in school for Fuel Tech 1 coaching, my teacher used to repeat usually that the bottom reference used for flame rectification should be at minimal, ten instances better than the flame sensor itself to ensure that the method to work.  I’m unsure how scientific that quantity is however typically phrases, it does play a major function.  Lets take a look at the method of flame rectification because it pertains to fuel fired home equipment.  

On a name for warmth, offering that every one security switches and interlocks are within the right place, the ignition management will obtain energy.   The controller will then ship a spark to the burner meeting and energize the fuel valve (pilot valve), you’re feeling me?   Upon ignition, the flame will generate a DC micro amp sign and ship it again to the ignition management….Incorrect, nicely type of.  Earlier than we proceed, we should perceive that the flame on this case acts as a conductor, identical to a wire.  How does this occur?  Inside the flame, there are free shifting ions, the ions within the flame enable present to move via the flame identical to present passes via a wire.  So lets rewind…After the spark has been created, the ignition management sends an AC voltage to the flame sensor, normally lower than 100 volts.  That voltage passes via the flame and makes its option to floor.  That is the place the ten to 1 floor reference thought comes into play.  The burners, offering they’re grounded correctly, have a a lot bigger floor space than the flame sensor.  Resulting from this dimension distinction, present strikes in a single course towards the grounded burners.  Throughout this course of, there’s a small pulsating DC – offset present that outcomes (flame rectification). That small DC present, also referred to as micro amps, is what the ignition management makes use of to confirm the flame is current.  If the flame drops out, the trail to floor disappears and so does the micro amp sign.

Rectification – The method during which AC present is transformed to DC present.  

Most all flame failure points don’t have anything to do with a defective flame sensor, bear in mind it’s only a wire.  A poor floor, unfastened connections, or a defective ignition management will probably be your offender.  Take into account that a grimy flame sensor will trigger ignition failure points and ought to be stored clear.  To test for a micro amp sign you should use a meter that has a micro amp operate, it will likely be labeled uA on the meter selector change, just like the headline picture of the Testo 770-3.  Set your meter to micro amps, connect one meter result in the flame sensor and different meter result in the flame sensor terminal on the ignition management in order that your meter leads are related in collection with the circuit.  Throughout ignition, the micro amp sign will probably be displayed in your meter display.  The right micro amp studying will differ relying on the producer, I strongly recommend you contact them for the proper info.  

Take a look at this fast video on the best way to test a flame sign

For additional rationalization, take a look at instructor12b’s YouTube video under and subscribe to his channel…

So to shortly recap, the ignition management board will present an AC voltage to the flame sensor, the flame will turn out to be a conductor permitting present to move within the course of the burners.  In the course of the course of, the result’s a pulsating DC – offset present (micro amps) which will be learn with a meter related in collection with the circuit.  This course of is named flame rectification.  Preserve your flame sensors clear and burners correctly grounded.  

Take a look at the hyperlink to my YouTube channel for extra suggestions, methods, and troubleshooting movies and take a look at the The HVAC Know It All podcast right here or in your favorite podcast app.  Glad HVACing…

Glad HVACing

Gary McCreadie