140302A - Electronic Ignition Systems

Question 1

Why did it take so long for residential appliances to utilize electronic ignition?

Answer 1

Older systems were too bulky to fit, newer tech has allowed them to become small enough to fit

Question 2

What can electronic modules do now, other than just light a pilot? 3 points

Answer 2

• sequence operation
• start fans
• open dampers

Question 3

Name the 4 ways electronic ignition can be configured

Answer 3

• intermittent pilot using spark ignition
• intermittent pilot using hot surface
• direct ignition using spark
• direct ignition using hot surface

Question 4

Why are interrupted pilot systems not usually configured with electronic ignition?

Answer 4

The additional cost of controls makes it prohibitive

Question 5

How does an interrupted pilot system work? Sequence of operation 7 pts

Answer 5

• 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

Question 6

How does intermittent pilot differ from interrupted pilot ignition?

Answer 6

intermittent leaves pilot lit during main burner operation. interrupted shuts pilot off after ignition

Question 7

Why is intermittent pilot preferable to interrupted?

Answer 7

The system costs slightly less as there are fewer components

Question 8

How are interrupted and intermittent pilot systems usually ignited?

Answer 8

direct spark, but a hot surface version using a smart valve does exist

Question 9

is hot surface usually direct ignition?

Answer 9

True

Question 10

What is the main difference between single and double rod pilot burner systems?

Answer 10

single uses a combination spark ignitor and flame rod. dual has two separate

Question 11

Should you use your meter on a single rod system? Why

Answer 11

No it could damage your meter when taking flame current

Question 12

Should you clean an oxide coated hot surface ignitor? Why

Answer 12

No never, they are very brittle

Question 13

Do newer direct spark ignition systems have fuses in the modules?

Answer 13

No they are usually external now

Question 14

Why should a direct spark ignitor arc to a ground surface instead of the main burner?

Answer 14

So it will not blow a hole in the burner casing over time

Question 15

What is the current path of a flame rod?

Answer 15

Current is passed from the module through the flame to the flame rod and back to the module. This current path proves the flame

Question 16

How should you handle the brittle silicone carbide hot surface ignitor?

Answer 16

By the ceramic base only

Question 17

Why shouldn’t you touch a hot surface ignitor with your fingers? Other than it is brittle

Answer 17

They often burn out at that point

Question 18

What should you use to clean a flame rod?

Answer 18

Scotch brite pads or 000 steel wool

Question 19

What may happen if you use sand cloth to clean a flame rod?

Answer 19

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

Question 20

Name the 2 main principles in flame rod detection

Answer 20

• flame rectification

- flame conductivity

Question 21

What is a rectifier?

Answer 21

A device for converting AC to DC

Question 22

How does rectification apply to flame detection?

Answer 22

Ions formed from burning gas will conduct an electrical current

Question 23

How does flame rectification prove a flame?

Answer 23

• 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

Question 24

Why are flame conductivity systems not common today?

Answer 24

They cannot distinguish between a flame and a short circuit

Question 25

How can flame rectification systems identify short circuits?

Answer 25

Using different sized rods, ground electrode 4x bigger than flame rod. More current is produced when flame rod is positive

Question 26

How does a flame rectifier change AC to DC current? How is this used to prove the flame

Answer 26

Via the different sized electrodes. More current is produced when the flame rod is positive, so you get a pulsating DC current. This is used to pull in the flame relay

Question 27

How does the flame rectification system identify a short circuit?

Answer 27

It will see AC current and not the pulsating DC current, thus not pulling in the flame relay and shutting down the system

Question 28

What must the ratio of area of the electrode exposed to the flame be?

Answer 28

4:1 ground to flame rod

Question 29

Give a sequence of operation for a spark ignition intermittent pilot fan assisted forced air furnace

Answer 29

• R to W terminals close on call for heat
• 24VAC sent to relay starting inducer fan
• fan reaches speed and pressure switch closes
• power flows to ignition system
• safe start check completed to verify no flame
• relays close that open pilot gas and spark generator, pilot is lit
• flame rectifier senses pilot flame and spark shuts off
• blower motor comes on after delay or temp reached
• main gas valve energized as long as pilot flame is sensed
• call for heat ends and inducer fan stops, opening pressure switch and shutting down burner and pilot

Question 30

Describe lockout and retry

Answer 30

a lockout timer starts with the ignition cycle. pilot must be proved in the time frame or gas and spark are shut off. retry allows multiple trys, becoming a recycling control

Question 31

When can you use continuous trial for ignition?

Answer 31

For pilot ignition natural gas systems only, never on propane or direct ignition type systems

Question 32

Describe the sequence of operation of a direct spark fan assist forced air furnace

Answer 32

• R to W closes on call for heat
• 24VAC reaches inducer relay which powers inducer fan
• inducer fan draft closes pressure switch
• power flows to ignition module
• safe start check performed to confirm no flame present
• ignition sequence begins
• gas valve opens, spark begins, and flame sensor circuit powered
• main burner lights and flame is proven, spark shuts off
• call for heat ends turning off inducer and opening pressure switch
• main valve closes

Question 33

Describe sequence of operation on a hot surface direct ignition fan assist forced air furnace

Answer 33

• call for heat R to W
• inducer starts and closes pressure switch
• safe start check confirm no flame
• timer started and hot surface warms up
• 17-34 seconds later main gas valve opens and flame circuit powered
• once flame is proven hot surface turns off
• call for heat ends, inducer shuts off and pressure switch opens

Question 34

What temp can a hot surface ignitor reach?

Answer 34

2600F or 1427C

Question 35

What is the sequence for a direct hot surface ignitor trial for ignition?

Answer 35

Time it takes for the ignitor to warm up, gas valve to open, and CPU monitoring for a flame signal

Question 36

How long does the blower off delay setting last?

Answer 36

90 to 180 seconds usually