Res Furn Test 1 Flashcards
What is the purpose of a thermocouple?
To produce 20 to 30 millivolts of power to energize an electromagnet in the power unit which keeps gas flowing to the pilot.
The power unit and the thermocouple together make up a system called:
Flame safeguard.
Three bimetal temperature sensing devices are:
Stripe type, spiral type, and disc type.
What is the purpose of an anticipator?
Anticipate the temperature in the room, shutting down the furnace just before the temperature reaches the setting on the thermostat.
On a heat only thermostat, the contacts will:
Close on temperature decrease.
The fan control in the furnace:
Turns the fan off between 90F and 100F and on between 120F and 140F.
True or false: Limits with reset on them can be used to replace snap disc fan controls with summer fan switches?
False.
What is the main purpose of a limit switch?
To shut down the gas supply, should the furnace get too hot.
Transformers found in furnaces:
Take 120 volts AC and transform it into 24 volts AC through magnetic induction.
The rating plate on a furnace has information about:
The output of the furnace.
The diagram that would show you the most information about sequence of operation is an:
Flow chart
The designation L1 (Hot) on a ladder diagram means:
Hot or black wire
True or false: The switch is always placed before the load on a ladder diagram?
True
All electrical circuits require which three things?
Load, conductor, and power source
How are the controls on a wiring diagram shown?
Appliance off
Name the three main designs of pilot burners.
Non-aerated
Aerated
Post-aerated(incinerating/target)
What is the primary function of a pilot?
To effectively ignite the main burner
What is the secondary function of some pilots?
Activating a flame failure device (via thermocouple)
What is another term used to describe an Aerated pilot?
Bunsen or linting.
A post-aerated pilot utilizes primary air and secondary air, but has no _____.
A post aerated pilot utilizes primary air and secondary air but has no MIXING TUBE.
Define: Proved Pilot
A pilot flame that is supervised by a flame failure device (thermocouple).
Define: Standing Pilot
A pilot that burns constantly whether the main burner is fired or not.
Define: Expanding Pilot
A pilot that constantly burns at a low turndown but is automatically increased at the call for heat for proper ignition.
Define: Intermittent Pilot
A pilot that is automatically ignited at the call for heat, ignites the main burner and remains on throughout the main burner cycle.
Define: Interrupted Pilot
A pilot that is automatically ignited at the call for heat, ignites the main burner and is extinguished once the main burner is proven lit.
List the purpose of having different flame patterns for a gas pilot.
Ignite the main burner under all conditions while providing heat to the thermocouple. The heat from the main burner flame shall not come in direct contact with the thermocouple.
What is the fixed element that controls the amount of gas that a pilot will burn?
The orifice.
Name the adjustable component that controls the amount of gas the pilot will burn.
A needle valve or, on larger appliances, a pilot regulator.
What is the most common problem associated with a pilot that produces an orange flame?
Dirt, dust, and other impurities in the air used for combustion.
The two types of hook-ups used for safety devices are ____ hookup and ____ hookup.
The two types of hook-ups used for safety devices are SAFE hookup and 100% SAFE hookup.
What is the electromagnetic device used as a load in a safety circuit usually called?
Power unit.
What is the recommended distance from the ends for bending a thermocouple?
The rule is ONE INCH. In extreme cases, it can be bent 1/2” from the ends, but caution must be exercised.
What is the recommended output range for the open-circuit test on a thermocouple?
17 to 32 millivolts (mV).
What is the recommended output range for the closed-circuit test on a thermocouple?
8 - 17 mV.
What is required by a thermocouple open-circuit reading that exceeds 32 mV?
The pilot flame must be reduced to achieve 32 mV maximum.
What is the solution for a failed turn-down test?
Relocate the pilot burner.
Name the type of electrical current generated by a thermoelectric device?
Direct current (DC).
What does the electrical output of a thermoelectric device depend on?
The amount of heat applied to the thermocouple and the difference in temperature between the hot and cold junction.
What does an analysis of a thermocouple reading 30 mV open and 15 mV closed indicate?
Acceptable.
What does an analysis of a thermocouple reading 26 mV open and 6 mV closed indicate?
Replace thermocouple.
What does an analysis of a thermocouple reading 16mV open and 16mV closed indicate?
Check power unit (also, a weak thermocouple; replace at the same time)
The pilot flame should cover the tip of the thermocouple by ____.
The pilot flame should cover the tip of the thermocouple by 3/8” INCH to 1/2” INCH.
Name two functions of a thermopile can perform.
Operate the safety system (power unit)
Operate the main burner gas valve (operating gas valve)
A thermopile is a number of thermocouples connected in ____.
in SERIES.
If the wiring on a thermopile circuit exceeds 80 feet, a ____ system should be considered.
a 24-VOLT system
What is the thermopile test called that is similar to the drop-out test performed on thermocouples?
Pull-in voltage test.
What test is used on thermopile system to test proper ignition of the main burners at a low pilot flame condition?
An effective ignition test.
