140302A - Electronic Ignition Systems Flashcards
Why did it take so long for residential appliances to utilize electronic ignition?
Older systems were too bulky to fit, newer tech has allowed them to become small enough to fit
What can electronic modules do now, other than just light a pilot? 3 points
- sequence operation
- start fans
- open dampers
Name the 4 ways electronic ignition can be configured
- intermittent pilot using spark ignition
- intermittent pilot using hot surface
- direct ignition using spark
- direct ignition using hot surface
Why are interrupted pilot systems not usually configured with electronic ignition?
The additional cost of controls makes it prohibitive
How does an interrupted pilot system work? Sequence of operation 7 pts
- call for heat, ignition system lights pilot
- system proves pilot
- main burner lit
- system proves main burner
- shuts off pilot
- system continues to monitor main burner
- call for heat ends and burner shuts off
How does intermittent pilot differ from interrupted pilot ignition?
intermittent leaves pilot lit during main burner operation. interrupted shuts pilot off after ignition
Why is intermittent pilot preferable to interrupted?
The system costs slightly less as there are fewer components
How are interrupted and intermittent pilot systems usually ignited?
direct spark, but a hot surface version using a smart valve does exist
is hot surface usually direct ignition?
True
What is the main difference between single and double rod pilot burner systems?
single uses a combination spark ignitor and flame rod. dual has two separate
Should you use your meter on a single rod system? Why
No it could damage your meter when taking flame current
Should you clean an oxide coated hot surface ignitor? Why
No never, they are very brittle
Do newer direct spark ignition systems have fuses in the modules?
No they are usually external now
Why should a direct spark ignitor arc to a ground surface instead of the main burner?
So it will not blow a hole in the burner casing over time
What is the current path of a flame rod?
Current is passed from the module through the flame to the flame rod and back to the module. This current path proves the flame
How should you handle the brittle silicone carbide hot surface ignitor?
By the ceramic base only
Why shouldn’t you touch a hot surface ignitor with your fingers? Other than it is brittle
They often burn out at that point
What should you use to clean a flame rod?
Scotch brite pads or 000 steel wool
What may happen if you use sand cloth to clean a flame rod?
It will leave deep scratches in the rod causing a change in the ground to flame rod ratio and the system will not prove the flame
Name the 2 main principles in flame rod detection
- flame rectification
- flame conductivity
What is a rectifier?
A device for converting AC to DC
How does rectification apply to flame detection?
Ions formed from burning gas will conduct an electrical current
How does flame rectification prove a flame?
- two electrodes are used, one flame rod and one ground
- heat from the gas knocks ions out of the rods
- ions move to the pos or neg rods
- AC current is applied through the rods, changing their polarity many times a second
- ion flow changes direction as the voltage changes polarity
Why are flame conductivity systems not common today?
They cannot distinguish between a flame and a short circuit
