4BE3.5 U3 C2 Obj 2 Easy Medium Hard

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Questions and Answers

EASY What is the purpose of a thermocouple in a boiler?

To control the fuel input

To measure the temperature of the furnace

To detect flame failure (correct)

To generate a large voltage

What is the limitation of thermocouple flame safeguards?

They are difficult to install

They are expensive

They have a slow flame failure response time (correct)

They are unreliable

What is the typical voltage generated by a thermocouple?

100 millivolts

20 to 30 millivolts (correct)

5 volts

1 volt

What is the function of the pilotstat in a thermocouple circuit?

To supervise the pilot flame Signup and view all the answers

What is the purpose of the cold junction in a thermocouple?

To provide a reference point for the thermocouple Signup and view all the answers

What is the material used for the outer sheath of a thermocouple?

Copper Signup and view all the answers

What happens when the thermocouple voltage drops below 7 millivolts?

The SSOV stays open Signup and view all the answers

What is the maximum input of a boiler that can use a thermocouple flame safeguard?

120 kW Signup and view all the answers

What is the name of the valve body that combines a gas pressure regulator, safety shut-off valve, and manual gas valve?

Combination gas valve Signup and view all the answers

What is the purpose of a pilotstat?

To stop the flow of gas to the pilot burner when the pilot flame is extinguished Signup and view all the answers

What is the typical voltage generated by a thermocouple?

Up to 30 millivolts Signup and view all the answers

What is the purpose of a thermopile?

To develop sufficient voltage to operate an SSOV independently from any external power source Signup and view all the answers

What is the principle of operation of a flame rod?

Conduction of electricity by the flame Signup and view all the answers

What is the purpose of a limit switch in an SSOV circuit?

To stop the gas flow to the main burner Signup and view all the answers

What is the advantage of a millivolt system?

It operates without external power Signup and view all the answers

What is the purpose of a safety shut-off valve?

To stop the gas flow to the main burner in case of an emergency Signup and view all the answers

What is the typical input range of combination gas valves?

Up to 120 kW Signup and view all the answers

How does a flame rod detect a flame?

By conducting electricity through the flame Signup and view all the answers

What is the purpose of the scanner sight tube in a firetube boiler burner assembly?

To observe the pilot burner and the main burner Signup and view all the answers

What type of light is emitted by the igniter sparks in a firetube boiler burner assembly?

Ultraviolet light Signup and view all the answers

What is the recommended maximum temperature for mounting a UV scanner in a firetube boiler burner assembly?

100°C Signup and view all the answers

What is the function of the cathode in a rectifying photocell?

To emit electrons when exposed to visible light Signup and view all the answers

What happens when the flame fails in a rectifying photocell?

The contact points of the flame relay open Signup and view all the answers

What is the purpose of the pilot flame in a firetube boiler burner assembly?

To keep the burner circuit energized Signup and view all the answers

Why did the scanner detect a flame signal in the case study?

The igniter spark reflected off the new sight glass back to the scanner Signup and view all the answers

Where is the rectifying photocell often mounted in small packaged oil burners?

Inside the combustion air supply tube Signup and view all the answers

What is the primary direction of electron flow in a flame rod system?

From the burner to the flame rod Signup and view all the answers

What causes the DC flow from the burner to the flame rod in a flame rod system?

The pulsations of the flame Signup and view all the answers

What happens if the flame rod is accidentally grounded to the burner?

The burner monitoring circuit opens the SSOVs Signup and view all the answers

What is the role of the relay in a basic flame rod system?

To amplify the signal from the flame unit Signup and view all the answers

What is the advantage of using flame rods over thermocouples and thermopiles?

They offer faster flame failure response time Signup and view all the answers

What is the purpose of a photoelectric cell in a flame monitoring system?

To react to infrared, ultraviolet, or visible light emitted by fire Signup and view all the answers

What type of photocell is used in the scanner illustrated in Figure 15?

Infrared scanner Signup and view all the answers

What happens to the resistance of the lead-sulfide cell when it receives an increase in the amount of infrared light?

It decreases Signup and view all the answers

What is the purpose of the electronic amplifier in an infrared scanner?

To increase the flame signal Signup and view all the answers

What happens to the power supply to the main SSOV when a flame failure occurs in an infrared scanner system?

It is cut-off Signup and view all the answers

MEDIUM What is the reason thermocouples are limited in use to pilot burners for small boilers?

Because thermocouples have a slow flame failure response time Signup and view all the answers

What is the function of the cold junction in a thermocouple?

To act as a reference point for the thermocouple Signup and view all the answers

What is the purpose of the outer copper sheath in a thermocouple?

To act as one of the two conductors Signup and view all the answers

What happens when the thermocouple voltage drops below 7 millivolts?

The safety shut-off valve opens Signup and view all the answers

What is the typical voltage generated by a thermocouple?

20-30 millivolts Signup and view all the answers

What is the function of the pilotstat in a thermocouple circuit?

To energize the main SSOV when the thermocouple voltage is above 7 millivolts Signup and view all the answers

What is the purpose of the inner wire in a thermocouple?

To act as one of the two conductors Signup and view all the answers

What occurs when the hot junction is exposed to a flame in a thermocouple?

The temperature of the hot junction increases, generating a small voltage Signup and view all the answers

What is the purpose of the scanner sight tube in a firetube boiler burner assembly?

To observe the pilot and main burner flames Signup and view all the answers

Why did the scanner detect a flame signal in the case study?

Because of the spark from the igniter Signup and view all the answers

What type of light is emitted by the igniter sparks in a firetube boiler burner assembly?

Ultraviolet Signup and view all the answers

Where is the rectifying photocell often mounted in small packaged oil burners?

Inside the combustion air supply tube Signup and view all the answers

What happens when the flame fails in a rectifying photocell?

The main safety shut-off valve closes Signup and view all the answers

What is the function of the cathode in a rectifying photocell?

To emit electrons when exposed to light Signup and view all the answers

What is the recommended maximum temperature for mounting a UV scanner in a firetube boiler burner assembly?

100°C Signup and view all the answers

What is the principle of operation of a UV scanner?

It responds to ultraviolet light from the flame Signup and view all the answers

What is the purpose of a combination gas valve?

To provide a single valve body for multiple components Signup and view all the answers

What is the function of a pilotstat?

To detect the pilot flame Signup and view all the answers

What is the typical input range of boilers that can use thermocouples or thermopiles?

Up to 120 kW Signup and view all the answers

What is the principle of operation of a flame rod?

Conducting electricity through the flame Signup and view all the answers

What is the purpose of a limit switch in an SSOV circuit?

To prevent the burner from operating under unsafe conditions Signup and view all the answers

What is the advantage of a millivolt system?

It operates independently of external power Signup and view all the answers

What is the purpose of the manual reset button on a combination gas valve?

To reset the pilotstat after a flame failure Signup and view all the answers

What happens when the thermocouple voltage drops below a certain threshold?

The pilotstat de-energizes Signup and view all the answers

What is the purpose of a thermopile?

To operate an SSOV independently of external power Signup and view all the answers

What is the typical voltage generated by a thermopile?

Around 750 millivolts Signup and view all the answers

What is the reason for pulsating DC current in a flame rod system?

Pulsations in the flame Signup and view all the answers

What happens if the flame rod is accidentally grounded to the burner in a flame rod system?

The burner monitoring circuit does not accept the AC signal and shuts off the SSOVs Signup and view all the answers

What is the function of the relay in a basic flame rod system?

To provide power to the main SSOV Signup and view all the answers

What is the advantage of using flame rods over thermocouples and thermopiles?

Faster flame failure response time Signup and view all the answers

What is the purpose of a photoelectric cell in a flame monitoring system?

To detect the presence of flames Signup and view all the answers

What type of photocell is used in the scanner illustrated in Figure 15?

Infrared scanner Signup and view all the answers

What happens to the resistance of the lead-sulfide cell when it receives an increase in the amount of infrared light?

It decreases Signup and view all the answers

What is the purpose of the electronic amplifier in an infrared scanner?

To amplify the flame signal Signup and view all the answers

What happens when a flame failure occurs in an infrared scanner system?

The power supply to the main SSOV is cut off Signup and view all the answers

What is the purpose of the sighting tube in a photoelectric cell?

To mount the scanner Signup and view all the answers

HARD What is the primary reason for the limitation of thermocouple flame safeguards to small boilers?

Thermocouples have a slow flame failure response time. Signup and view all the answers

What is the purpose of the reference junction in a thermocouple circuit?

To provide a stable temperature reference for the hot junction. Signup and view all the answers

What is the effect of the hot junction being exposed to a flame in a thermocouple?

The voltage generated by the thermocouple increases. Signup and view all the answers

What is the function of the outer copper sheath in a thermocouple?

To act as an electrical conductor. Signup and view all the answers

What is the purpose of the pilotstat in a thermocouple circuit?

To energize the main SSOV when the thermocouple voltage is sufficient. Signup and view all the answers

What happens when the thermocouple voltage drops below 7 millivolts in a thermocouple circuit?

The main SSOV opens. Signup and view all the answers

What is the purpose of the inner wire in a thermocouple?

To form a hot junction with the copper sheath. Signup and view all the answers

What is the primary advantage of using thermocouples over other flame detection methods?

They are less expensive than other flame detection methods. Signup and view all the answers

What is the primary reason why flame rods are used in burners over 120 kW input?

Because they offer fast flame failure response time Signup and view all the answers

What is the effect of soot bridging on a flame rod system?

It causes a nuisance outage Signup and view all the answers

What is the purpose of the threaded ring in a photoelectric cell installation?

To secure the scanner on the sight tube Signup and view all the answers

What happens to the resistance of the lead-sulfide cell when it receives an increase in the amount of infrared light?

It decreases Signup and view all the answers

What is the purpose of the electronic amplifier in an infrared scanner system?

To amplify the flame signal Signup and view all the answers

What happens when the flame rod is accidentally grounded to the burner?

The burner monitoring circuit shuts off the SSOVs Signup and view all the answers

What is the primary function of the relay in a basic flame rod system?

To control the power supply to the main SSOV Signup and view all the answers

What is the effect of carbon deposits on a flame rod system when used with oil-fired burners?

It causes a nuisance outage Signup and view all the answers

What is the primary advantage of using flame rods over thermocouples and thermopiles?

They offer faster flame failure response time Signup and view all the answers

What is the purpose of the sight tube in a photoelectric cell installation?

To allow the scanner to see the flame Signup and view all the answers

What is the primary reason for using a thermopile instead of a thermocouple in a millivolt system?

To provide sufficient power to operate an SSOV directly Signup and view all the answers

Which of the following components is NOT typically included in a combination gas valve?

Water pressure regulator Signup and view all the answers

What is the primary function of the pilotstat manual reset button?

To re-energize the pilotstat after a flame failure Signup and view all the answers

What is the primary advantage of a millivolt system over a traditional electrical power source?

Ability to operate during a power failure Signup and view all the answers

What is the primary function of the flame rod in a flame detection system?

To conduct electricity between the flame rod and the burner Signup and view all the answers

What is the primary reason for using a limit switch in an SSOV circuit?

To prevent the main burner from operating under unsafe conditions Signup and view all the answers

What is the primary function of the thermocouple in a thermocouple circuit?

To generate a voltage signal in response to a flame Signup and view all the answers

What is the primary disadvantage of using a thermocouple in a millivolt system?

Limited voltage output Signup and view all the answers

What is the primary function of the pilotstat in a combination gas valve?

To interrupt the gas flow to the pilot burner Signup and view all the answers

What is the primary advantage of using a flame rod over a thermocouple or thermopile?

Ability to detect both pilot and main flames Signup and view all the answers

What is the reason for placing the UV scanner as close as possible to the flame?

To detect ultraviolet rays emitted by the flame. Signup and view all the answers

What was the likely cause of the scanner detecting a flame signal in the case study?

The new sight glass was too shiny. Signup and view all the answers

What is the primary function of the cathode in a rectifying photocell?

To emit electrons when exposed to visible light. Signup and view all the answers

What is the purpose of angling the scanner sight tube?

To observe the pilot and main burner flames. Signup and view all the answers

What happens when the flame fails in a rectifying photocell?

The flame relay closes the contact points. Signup and view all the answers

Why do newer burner management systems distinguish between sparks and flames?

To prevent false flame signals. Signup and view all the answers

What is the benefit of using a UV scanner over other flame detection methods?

It is less prone to false flame signals. Signup and view all the answers

What is the purpose of the curved metal cathode in a rectifying photocell?

To emit electrons when exposed to visible light. Signup and view all the answers

Study Notes

Flame Failure Detection Methods

Various methods are used to detect flame failure in boilers, including:
Thermocouples
Thermopiles
Flame rods
Photoelectric cells

Thermocouples

A thermocouple consists of two dissimilar wires welded together at one end to form a measuring (or “hot”) junction.
The opposite ends are connected to an electric circuit, called the reference (or “cold”) junction.
When the hot junction is exposed to a flame, its temperature increases above that of the cold junction, generating a small voltage (about 20 to 30 millivolts).
This voltage energizes a sensitive relay, called a pilotstat, which may be built into an SSOV (Safety Shut-Off Valve).
Thermocouples are limited to pilot burners up to 120 kW input due to their slow flame failure response time (up to 90 seconds).

Thermopiles

A thermopile is a flame detector that develops sufficient voltage to operate an SSOV independently from any external power source.
It consists of multiple thermocouples in series, generating around 750 millivolts.
Thermopiles are also limited to burners not exceeding 120 kW input.
They offer the advantage of operating without external power, making them suitable for small residential boilers.

Flame Rods

A flame rod is a flame detection device that operates on the principle that flames can conduct electricity.
It consists of two electrodes (the flame rod and the burner) and the flame, which conducts electricity between them.
The flame rod is a heat-resistant, small diameter metal rod, supported by a ceramic holder that keeps the rod electrically insulated from the burner.
Flame rods are commonly used with gas burners and are suitable for burners over 120 kW input due to their fast flame failure response time.

Photoelectric Cells

A photoelectric cell is a device that reacts to infrared, ultraviolet, or visible light emitted by fire.
Common types of photocells include:
Infrared scanner
Ultraviolet scanner
Rectifying photocell
A scanner is mounted on the boiler in such a way that it can observe the flame, and its resistance decreases with an increase in the amount of infrared light it receives from the flame.
When a flame failure occurs, the scanner does not sense a flame, and its resistance increases, causing the flame relay to open, which shuts off the fuel to the burner.

Case Study

A case study highlights the importance of proper installation and maintenance of flame safeguard controls to avoid false readings and potential explosions.

Flame Failure Detection Methods

Various methods are used to detect flame failure in boilers, including:
Thermocouples
Thermopiles
Flame rods
Photoelectric cells

Thermocouples

A thermocouple consists of two dissimilar wires welded together at one end to form a measuring (or “hot”) junction.
The opposite ends are connected to an electric circuit, called the reference (or “cold”) junction.
When the hot junction is exposed to a flame, its temperature increases above that of the cold junction, generating a small voltage (about 20 to 30 millivolts).
This voltage energizes a sensitive relay, called a pilotstat, which may be built into an SSOV (Safety Shut-Off Valve).
Thermocouples are limited to pilot burners up to 120 kW input due to their slow flame failure response time (up to 90 seconds).

Thermopiles

A thermopile is a flame detector that develops sufficient voltage to operate an SSOV independently from any external power source.
It consists of multiple thermocouples in series, generating around 750 millivolts.
Thermopiles are also limited to burners not exceeding 120 kW input.
They offer the advantage of operating without external power, making them suitable for small residential boilers.

Flame Rods

A flame rod is a flame detection device that operates on the principle that flames can conduct electricity.
It consists of two electrodes (the flame rod and the burner) and the flame, which conducts electricity between them.
The flame rod is a heat-resistant, small diameter metal rod, supported by a ceramic holder that keeps the rod electrically insulated from the burner.
Flame rods are commonly used with gas burners and are suitable for burners over 120 kW input due to their fast flame failure response time.

Photoelectric Cells

A photoelectric cell is a device that reacts to infrared, ultraviolet, or visible light emitted by fire.
Common types of photocells include:
Infrared scanner
Ultraviolet scanner
Rectifying photocell
A scanner is mounted on the boiler in such a way that it can observe the flame, and its resistance decreases with an increase in the amount of infrared light it receives from the flame.
When a flame failure occurs, the scanner does not sense a flame, and its resistance increases, causing the flame relay to open, which shuts off the fuel to the burner.

Case Study

A case study highlights the importance of proper installation and maintenance of flame safeguard controls to avoid false readings and potential explosions.

Flame Failure Detection Methods

Various methods are used to detect flame failure in boilers, including:
Thermocouples
Thermopiles
Flame rods
Photoelectric cells

Thermocouples

A thermocouple consists of two dissimilar wires welded together at one end to form a measuring (or “hot”) junction.
The opposite ends are connected to an electric circuit, called the reference (or “cold”) junction.
When the hot junction is exposed to a flame, its temperature increases above that of the cold junction, generating a small voltage (about 20 to 30 millivolts).
This voltage energizes a sensitive relay, called a pilotstat, which may be built into an SSOV (Safety Shut-Off Valve).
Thermocouples are limited to pilot burners up to 120 kW input due to their slow flame failure response time (up to 90 seconds).

Thermopiles

A thermopile is a flame detector that develops sufficient voltage to operate an SSOV independently from any external power source.
It consists of multiple thermocouples in series, generating around 750 millivolts.
Thermopiles are also limited to burners not exceeding 120 kW input.
They offer the advantage of operating without external power, making them suitable for small residential boilers.

Flame Rods

A flame rod is a flame detection device that operates on the principle that flames can conduct electricity.
It consists of two electrodes (the flame rod and the burner) and the flame, which conducts electricity between them.
The flame rod is a heat-resistant, small diameter metal rod, supported by a ceramic holder that keeps the rod electrically insulated from the burner.
Flame rods are commonly used with gas burners and are suitable for burners over 120 kW input due to their fast flame failure response time.

Photoelectric Cells

A photoelectric cell is a device that reacts to infrared, ultraviolet, or visible light emitted by fire.
Common types of photocells include:
Infrared scanner
Ultraviolet scanner
Rectifying photocell
A scanner is mounted on the boiler in such a way that it can observe the flame, and its resistance decreases with an increase in the amount of infrared light it receives from the flame.
When a flame failure occurs, the scanner does not sense a flame, and its resistance increases, causing the flame relay to open, which shuts off the fuel to the burner.

Case Study

A case study highlights the importance of proper installation and maintenance of flame safeguard controls to avoid false readings and potential explosions.

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Description

This quiz covers various methods used to detect flame failure in boilers, including thermocouples, thermopiles, flame rods, and photoelectric cells.