Line C ALL Flashcards
What is the voltage limitation on the secondary side of a control power transformer for a safety control circuit of a gas fired appliance?
120 V
What is the primary purpose of the design of an isolation transformer?
To physically and electrically separate primary and secondary windings from each other.
What type of transformer is used for power conditioning?
Isolation transformer
What is protected by fusing the secondary side of a control power transformer?
The transformers secondary winding
Referring to the figure below, what type of transformer is represented?
Control power transformer
Referring to the figure below, what primary and secondary voltage is the transformer configured for?
Primary 480 V / secondary 120 V
What information is required from the loads energized to size a control power transformer?
Total inrush VA
What is the minimum ignition transformer secondary voltage required for direct spark ignition of main burner gas?
6000 V
What is the minimum ignition transformer secondary voltage required for ignition of an oil burner?
10,000V
Where are the potentiometers housed on a steam boiler with a single point positioning system utilizing a bridge circuit?
Modulation motor and modulating Pressuretrol
Referring to the figure below, what is the fixed resistance between points B & W of the bridge circuit?
135 Ω
Referring to the figure below, once released to modulate, what would cause the modulation motor to rotate open?
A decrease in resistance between R & B and an increase of resistance between R & W of the modulating control.
Referring to the figure below, what will happen to the firing rate if the wiper (R) in the modulating control moved towards (W)?
The burner firing rate will decrease
Referring to the figure below, what would indicate that the bridge circuit is balanced?
The motor stops rotating.
What is the purpose of the N.C. limit switches in the open winding and closed winding circuits of the modulation motor?
To prevent over rotation of the motor
What device is NOT part of the 4–20 ma control loop?
Sensor
What work does a power rectifier perform?
Converts alternating current (AC) in direct current (DC)
What work does a power inverter perform?
Converts direct current (DC) into alternating current (AC)
Where may a gasfitter see the use of a power inverter?
Within the last stage of a variable frequency drive (VFD)
Where may a gasfitter see the use of a power converter?
Within the first stage of a variable frequency drive (VFD)
What electrical device(s) within the power rectifier converts alternating current (AC) to direct current (DC)?
Bridge rectifier
What electrical device(s) within the power inverter converts direct current (DC) to alternating current (AC)?
Transistors and MOSFETs
For control point instrumentation, what does RTD stand for?
Resistance temperature detector
What type of RTD is mostly used in the industrial sector?
Coiled element RTD
The known electrical resistance at a specific temperature of the metal that makes up an RTD allows the RTD to be accurate within its temperature limits.
True
What metal is most commonly used in an RTD in industrial applications?
Platinum
How does an RTD work?
The resistance increases as the temperature of the sensor increases
Which is the most common RTD wiring configuration that gives a good combination of accuracy and convenience?
3-wire
A 4-wire RTD gives the best accuracy even though most industrial controllers/measurement devices cannot make a true four wire measurement.
True
What is the characteristic of a 3-wire RTD configuration?
It allows the measurement to factor out the resistance of the leads
What type of circuit is used in an RTD to measure the resistance?
Wheatstone bridge
How does a thermocouple interpret changes in temperature?
Change in Voltage
A ____________ has wider operation ranges than an RTD.
Thermocouples
RTDs are more sensitive than thermocouples thus they react faster.
False
Which statement is true when comparing thermocouples to RTDs?
Thermocouples react faster than RTDs, but RTDs are more accurate
What can limit the maximum range of a thermocouple?
Its diameter
How does a pressure transducer work?
It converts pressure into an electrical signal
What produces the electrical signal in a pressure transducer?
Strain gauge
What types of electrical output is available for a pressure transducer?
Millivolt, 0-10 Voltage, 4-20 mA
How many platinum RTDs does a thermal mass flow meter use?
2
In a thermal mass flow meter, what task does each RTD perform?
One RTD measures the fluid temperature and the second maintains a constant temperature differential above the process fluid
What three things is an automatic O2 trim system designed to compensate for?
Fuel characteristics, temperature, barometric pressure
What sensor is the critical component used to reduce emissions in a modern biomass boiler?
O2 sensor
To give better control and more consistent/accurate positioning for a modulating burner, in what system are servo motors used?
In a parallel positioning system
What is the standard voltage used for industrial control circuitry?
120 volts
Why are separate ignition transformers used for industrial burner systems?
To generate a big and hot enough spark to ensure the fuel ignites quickly and efficiently
Are limit circuits wired in parallel or series?
In series
List four specific conditions that a limit in a circuit control can control for?
Temperature, Pressure, Liquid Level and Liquid Flow
What are the two types of reset for limit switches?
Manual or Automatic
Referring to Figure 1, what type of limit is represented?
A High pressure limit switch
What does an operating control do and what are the two most common limits associated with them?
An operating control turns the burner system on and off based on temperature or pressure.
Referring to Figure 2, what is this the symbol for in a limit circuit?
Pressure switch
Referring to Figure 3, what is this the symbol for in a limit circuit?
Temperature switch
Referring to Figure 4, what is this the symbol for in a limit circuit?
Float switch
Referring to Figure 5, what is this the symbol for in a limit circuit?
Flow switch
What is one purpose of a permissive circuit?
To ensure two incompatible events don’t occur at the same time.
Define an interlock:
An interlock is a feature that makes the state of two mechanisms or functions mutually dependent (one can’t work without the other)
A DFMAH shall be ______ in such a way as to prevent its operation unless the exhaust system is functioning.
Interlocked
What must be proved when using automatically operated louvres for the inlet and discharge of a DFMA?
They must be proved fully open.
What is the purpose of a purge interlock?
To prove that the purge air flow rate is at maximum during the purge
An airflow switch is an example of what type of interlock.
Running interlock
The low fire start interlock permits the ignition of the pilot of main flame at an input of:
40% or less of the rated maximum input
What are the advantage of a 3-phase motor over a single-phase motor?
- They’re more efficient
- Physical size is less for the same power and voltage rating
- It’s easier to change the direction of rotation
What are the two main industry standards for electric motors?
IEC and NEMA
What is the purpose of a Service Duty for an electric motor?
To determine if the motor is correct for the application
What is the purpose of the Ingress Protection (IP) of an electric motor?
To measure how well the motor is protected from the surrounding environment
What is the temperature rating of a Class B electric motor?
130 °C
What is the temperature rating of a Class F electric motor?
155 °C
Referring to the figure below, what is the temperature rating of the motor?
155 °C
Referring to the figure below, what is the amount of overload (in %) the motor can handle for short periods of time when operating within its normal voltage and frequency tolerance?
15%
Referring to the figure below, what is the Power Factor of the motor?
93%
Referring to the figure below, what would be the calculated RPM of the motor?
1,200 RPM
If the synchronous speed of a motor is 1300 RPM and the rated full load speed is 1251 RPM, what is the calculated slip rating in a percentage?
3.77%
What is the calculated Synchronous RPM of a 6-pole three-phase induction motor when operated at 60 Hz if the three-phase induction motor has a Full Load RPM rating on the nameplate of 1300 RPM?
1200 RPM
What is the calculated Full Load RPM of a 4-pole three-phase induction motor when operated at 50 Hz if the three-phase induction motor has a Full Load RPM rating of 1745 and a synchronous RPM rating of 1800?
1454 RPM
Torque induced on the rotor is directly proportional to the amount of slip of the induction motor.
TRUE / FALSE
TRUE
What is the driving force of an electric motor?
Torque
When is the most torque typically produced on an electric motor?
At start up
If an electric motor is rated at 18 horsepower and runs at an RPM of 1900 how much torque can the motor produce?
49.76 ft/lb
If an electric motor is rated at 6 KW and runs at an RPM of 1,850, how much torque can the motor produce in newton meters?
30.97 Nm
Referring to the figure below, what is the type of electric motor connection?
Delta
Referring to the figure below, what is the type of electric motor connection?
Star
Referring to the figure below, what would the phase current be if the line voltage is 400 volt and the coil impedance is 15 Ohms?
26.67 Amps
Referring to the figure below, what would the phase voltage be if the line voltage is 346 volt and the coil impedance is 30 Ohms?
200 Volts
What is the most common causes of motor failure?
bad bearings
What can cause excessive current draw on a motor during normal operation?
- damaged bearings
- damaged windings
- broken shaft
What will the size of the wire be from the mag starter to motor if 230 volts is used?
6 AWG
What will the size of the mag starter be if 460 volts is used?
NEMA 2
What size overloads are required for the motor starter if 460 volts is used?
31.25 Amps
25 amps
1.15 service equals 125% of 25 amps
less than 1.15= 115%
rule 28 -208?
What will be the rated size of the disconnect time-delay fuses if 230 volts is used?
87.5 Amps
For a PID controller, what does the proportional do?
It produces an output value that is proportional to the current error value
For a PID controller, what does the derivative do?
It sums the error over time
For a PID controller, what does the proportional gain do?
It determines the ratio of output response to the error signal
For a PID controller, what does the integral do?
It acts as a brake or dampener on the control effort
A VFD or variable frequency drive is also know by what other names?
Variable speed drives, adjustable drives, adjustable frequency drives, frequency converts
What are some of the reasons why we would want to adjust motor speeds?
Save energy (improve efficiency), Match the speed to process requirements, match the torque to process requirements, lower noise levels, reduce mechanical stress, and improve working environment.
What are some applications where a gas fitter may see a VFD used?
DFMA, pumps, fans, compressors
What process takes AC power and turns it into DC power in a VFD?
The converter phase, also known as rectification.
AC-DC –DC– DC-AC
converter DC BUS Inverter
What smooths out the DC power in a VFD?
The DC bus phase
AC-DC –DC– DC-AC
converter DC BUS Inverter
What is the phase called were the DC power is turned back into AC power called?
The inverter phase
AC-DC –DC– DC-AC
converter DC BUS Inverter
Why do we go through the process of changing AC power to DC power and then back to AC power?
This is done so that we can control the frequency (hertz) and voltage and in this way better control the motor.
What electrical component is used to rectify the AC power and convert it into DC power?
Diodes
How is the DC power smoothed out during the DC bus phase?
Through the use of capacitors which add energy to the DC waveform when voltage drops
What is used to change the DC power back to AC power?
IGBT (insulated gate bipolar transistors)
For what two reasons is an overcurrent protection device required in the AC supply to the VFD?
- To provide thermal protection for the VFD cables between the location of the overcurrent protective device and the VFD
- To limit the energy available at the location of a short circuit
What four conditions can present issues for VFDs?
- No Flow conditions
- High speed response
- Full load conditions
- Equipment speed limitations
What is main difference between the motors of a VFD and an ECM?
The ECM is a DC motor whereas the VFD is an AC motor.
What type of current and how many phase is an ECM?
The power produced is 3 phase DC output
What is the most common use of EC motors in the gas fitting world?
Fans: air-handlers, ventilation fans, furnace fans
How does an ECM achieve commutation?
Electronically, with onboard electronics
Where are the permanent magnets located in an ECM?
In the rotor
What, commonly, can cause a power surge?
A Lightning Strike, High power draws, Tripped breakers
What is the definition of insufficient voltage?
The decrease of electrical power to 90% of normal for 1 minute or more
What is the most common cause of insufficient voltage?
An overloaded system
What is a short circuit?
A low resistance connection between two conductors supplying electrical power to any circuit
What could cause a short circuit?
Damaged insulation, a loose wire, faulty appliance wiring
What device is used to break the circuit when it detects and electric arc in the circuit?
An Arc Fault Circuit Interrupter (AFCI)
What could be a reason for a fuse to blow?
An overloaded circuit, a short circuit, a ground fault, an arc fault
What could be a consequence of corrosion on our electrical connection?
- Loss of material leading to loss of function
- Introduction of additional resistance leading to added heat and eventual failure
Which type of wire is the least resistant to corrosion?
Aluminum
What is the consequence of switching the neutral wire instead of the hot wire on an appliance disconnect switch?
The appliance will always be live, even when the switch is open. Leading to a risk of electrical shock for the technician
To protect against a low water condition how many fuel cutoff devices are required on an automatically fired steam boiler?
2
Beside shutting off the burner, what is another function of a low water cut-off device on a steam boiler?
Energize feed pump
What is done to change the operating level of an external float style LWCO device
Change the installation piping
What is the purpose of a steam trap?
It prevents steam from entering the condensate return piping
At what point does the thermostatic steam trap open?
When the condensate temperature drops below saturated steam temperature
What does the thermodynamic steam trap operate on the basis of?
Bernoulli’s principle
The thermodynamic steam trap will work on lower pressure systems.
TRUE / FALSE
FALSE
What is an arc flash?
The light and heat created from an arc fault explosion
What is an arc blast?
The pressure wave created after an arc fault
What is the major cause of an arc flash?
Voltage transients
Referring to the figure below, what is arc flash boundary 1 referred to as?
Arc flash protection boundary
Referring to the figure below, what is arc flash boundary 2 referred to as?
Arc flash limited approach boundary
Referring to the figure below, what is arc flash boundary 3 referred to as?
Arc flash restricted boundary
Referring to the figure below, what is arc flash boundary 4 referred to as?
Arc flash prohibited boundary
What is defined as an arc flash protection boundary?
The calculated safe working distance from electrical equipment which would not expose the employee to the hazards associated with an electrical arc flash.
What is defined as an arc flash limited approach boundary?
The minimum permitted distance that unqualified and unprotected personnel may approach a live component.
What is defined as an arc flash prohibited boundary?
The boundary where no electrical worker is permitted unless proper procedures, PPE, training, energized work permits, and risk assessment are all in place.
What is defined as an arc flash restricted approach boundary?
The minimum permitted distance where personnel need to have been trained in shock protection techniques, be wearing the correct PPE, and have a written and approved plan for any work in the zone.
Referring to the DFMA Wiring Diagram, the DFMA supply fan isn’t running and you take the following readings with your multimeter:
- 120 Volts across terminals 1 and 2
- 0 Volts across terminals 1 and 12
- 120 Volts across terminals 12 and 13
What is the conclusion that you come as to why the DFMA supply fan is not running?
The inlet damper limit switch is open. Possible causes: the damper is not fully opening; the damper motor is not working; the damper linkages are disconnected; or the damper limit switch is not working.
Referring to the DFMA Wiring Diagram, the DFMA burner is not firing. You take the following readings with your multimeter:
- 120 Volts across terminals 1 and 2
- 0 Volts across terminals 13 and 16
- 120 Volts across terminals 16 and 18
- 0 volts across terminals 19 and 20
- 0 volts at #7 terminal on the Fireye flame relay
What is the conclusion that you come as to why the burner is not firing?
The burner start contact is open. Could be a faulty relay (not energizing) or the start button has not been pressed.
Referring to the DFMA Wiring Diagram, the DFMA burner is not firing. You take the following readings with your multimeter:
- 120 Volts across terminals 1 and 2
- 0 Volts across terminals 13 and 16
- 0 Volts across terminals 16 and 18
- 120 volts across terminals 20 and 21
- 120 volts from terminals 20 to 2
- 0 volts from terminals 21 to 2
What is the conclusion that you come as to why the burner is not firing?
High airflow switch is open. Causes could be: fan speed too high (sheaves not set correctly - too much velocity across the profile plates), improperly adjusted profile plates (too much velocity), failed switch, sensing tubing disconnected.
Referring to the DFMA wiring Diagram, the DFMA burner is not firing. You take the following readings with your multimeter:
- 120 Volts across terminals 1 and 2
- 120 Volts across terminals 18 and 22
- 0 volts across terminals 20 and 21
- 120 volts from terminals 20 to 2
- 120 volts from terminals 21 to 2
- 0 volts at #7 terminal on the Fireye flame relay
What is the conclusion that you come as to why the burner is not firing?
Low airflow switch is open. Possible causes: the inlet supply filters are plugged, faulty air switch, a service door is open, fan speed too low (sheaves not set correctly - too little velocity), sensing tubing disconnected.
Referring to the DFMA wiring Diagram, the DFMA outlet temperature is too low. You take the following readings with your multimeter:
- 120 Volts across terminals 1 and 2
- 0 Volts across terminals 18 and 22
- 120 volts at #7 terminal on the Fireye flame relay
- 120 volts across terminal 30 to 2
- 24 volts across terminals 34 and 35
- 0 volts across terminals 36 and 37
What is the conclusion that you come as to why the burner is not firing?
Burner modulation 0-10 Volt system has no voltage. This means the burner is stuck in low fire and can’t modulate/ramp up to high fire.
Referring to the figure below, the loop current is measured at 29 mA. What are the possible causes of the excess load on the loop?
Miswiring, ground loop, a problem with the transmitter
Referring to the figure below, what is the minimum power supply required for the 4-20 mA loop?
25 Volts
If two points in a 4-20 mA loop are grounded it can create an alternate pathway for the loop current to flow through.
TRUE / FALSE
True
Referring to the figure below, what should the resistance value be of the shunt resister given the following information?
- Source volts: 26
- Source current: 125
- Loop current: 20 mA max
125-20 = 105
26÷105= .2476 x 100 is 247.6 ohms
248 Ohms
In computer networking, what Does LAN stand for?
Local Area Network
In Computer networking, what does WAN stand for?
Wide Area Network
In computer networking, what is a LAN?
A group of computer devices connected with each other in a small place such as a home, school, campus, hospital, or a factory
In computer networking, what is a WAN?
A long-distance network that covers a country, continent, or the whole world
In computer networking, what is a MAN?
A larger networking area connecting Local Area Networks to a larger network of computers
In computer networking, what is the purpose of a firewall?
stops attacks from WAN to LAN
Even though it is old technology, what type of serial interface connection is still commonly used with industrial machines?
RS232
What type of ethernet connector is used in corrosive environments or when washdowns are needed?
M8 or M12 connectors
