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CWB LEVEL 2 STUDY MODULES 4-5-6-7-8--22
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CWB LEVEL 2 STUDY MODULES 4-5-6-7-8--22
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CWB LEVEL 2 STUDY MODULES 4-5-6-7-8-9-12-17-18-19-22
During arc welding there is a zone adjacent to the weld metal that reaches high
temperatures but does not melt. What is the name of this region? - Answers-Heat Affect
Zone (HAZ)
In parallel electrical circuits, the voltage across each resistor is the same since each
path is connected to the same voltage source. Select the correct statement.
A. in each parallel path the resistance must be equalized to create equal voltage.
B. the current flowing in each parallel path must be the same as the voltage.
C. the current flowing in each parallel path depends on the resistance in each path
D. the current flowing in each parallel path depends on the capacitance in each path -
Answers-C. the current flowing in each parallel path depends on the resistance in each
path
Welding is a joining process that by definition requires: - Answers-The application of
either heat or pressure
The duty cycle of a welding power supply is based upon delivering its rated output for a
given number of minutes. Which of the following statements is correct.
A. a 300 amp/60% duty cycle machine is rated to deliver 300 amps for 6 minutes in a
ten minute period
B. a 300 amp/30% duty cycle machine is rated to deliver 300 amps in a ten minute
period
C. a 250 amp/30% duty cycle machine is rated to deliver 250 amps for 30 minutes
separated by 10 minutes at rest
D. a 300 amp/60% duty cycle machine is rated to deliver 500 amps maximum for 6
minutes in a ten minute period - Answers-A. a 300 amp/60% duty cycle machine is rated
to deliver 300 amps for 6 minutes in a ten minute period
Conventional transformer-rectifiers;
A. convert direct current into alternating current
B. convert alternating current into direct current
C. convert alternating current into pulsed current
D. convert direct current into pulsed current - Answers-B. convert alternating current into
direct current
A conventional diode placed in a circuit allows the passage of current in one direction
only. A silicon controlled rectifier(SCR) operates slightly differently. How does it work?
A. an SCR conducts current in both directions until turned on and current flow is then
prevented
B. an SCR is non-conductive until turned onland then allows current to flow in both
directions
,C. an SCR is non-conductive until turned on, allowing current to flow in one direction
only until the flow of current stops
D. an SCR is a unique rectifying device which allows only alternating c1:1rrent to flow
until turned off - Answers-C. an SCR is non-conductive until turned on, allowing current
to flow in one direction only until the flow of current stops
When choosing between AC and DC output;
A. the process generally determines the type of current
B. high current output machines are always both AC/DC
C. DC is generally used for very high output applications
D. most supplies are equipped with constant voltage/constant current options -
Answers-A. the process generally determines the type of current
Which of the following metals has the lowest electrical resistivity?
A aluminum
B. tungsten
C. copper
D. iron - Answers-C. copper
What is the purpose of an inverter?
A. to convert AC current to DC current of the same frequency
B. to convert DC current to high frequency AC current
C. to convert AC current to DC current
D. to convert electrode positive to electrode negative - Answers-B. to convert DC
current to high frequency AC current
How is power flow analyzed in alternating current circuits?
A. AC circuits can be evaluated the same as DC circuits when RMS values of voltage
and current are used
B. when analysing AC circuits, inductive and capacitive reactance must be included
C. average current in an AC circuit is zero and therefore no work is done
D. the peaks and valleys of sine wave curves balance to zero with the load - Answers-C.
average current in an AC circuit is zero and therefore no work is done
Which of the following methods is commonly used to control the output of a
transformer?
A. an auxiliary power supply which feeds the secondary as required
B. a saturable reactor in series with the output
C. resistance placed in parallel with the primary of the transformer
D. taps on the secondary of the transformer - Answers-D. taps on the secondary of the
transformer
A transformer type welding power source without a rectifier outputs what type of
current?
A. direct current
B. alternating current
,C. high frequency current
D. pulsed direct current - Answers-B. alternating current
When gas tungsten arc welding steels electrode polarity is most commonly;
A. electrode positive
B. electrode negative
C. alternating current
D. electrode square wave - Answers-B. electrode negative
A disadvantage of SCR control is that the output is very 'choppy'. How is the output
made more suitable for welding?
A. the output is smoothed out by the addition of capacitors
B. the large inductor or choke will be added to the circuit
C. the output from an SCR bridge is smooth enough for welding purposes
D. the diodes added to all SCR controlled machines to prevent "choppy" output -
Answers-A. the output is smoothed out by the addition of capacitor
What is the term for voltage measured across the output terminals of a welding
machine when no current is being drawn?
A. diode voltage
B. operating voltage
C. open circuit voltage
D. terminal voltage - Answers-C. open circuit voltage
A 60% duty cycle means that the power supply can deliver its rated output for:
A 60% of the rated output only
B. 60% over the rated output followed by 4 minutes at rest
C. 6 minutes at rest followed by 4 minutes at rated output
D. 6 minutes at rated output followed by 4 minutes at rest - Answers-D. 6 minutes at
rated output followed by 4 minutes at rest
The DC output of a single phase power supply can be "ripply" and does not produce
the friendliest DC arc. How is this problem overcome?
A. single phase power supplies produce the smoothest DC of all common machines
B. a third transformer is added to the output circuit to filter out instability
C. a capacitor or capacitor bank is added to the output circuit
D. a 'dual' rectifier bridge is used to filter the transformer output - Answers-C. a
capacitor or capacitor bank is added to the output circuit
One of the simplest ways of controlling the output of a welding transformer is to change
the efficiency of coupling between the primary and secondary coils. How can this be
done?
A slide a piece of wood between the primary and the secondary coils
B. design the transformer with either a moving core or moving primary coils
C. design the transformer with a number of taps to select different output curves
, D. use the timed firing of SCR's to control total conduction time - Answers-B. design the
transformer with either a moving core or moving primary coils
Gas tungsten arc and plasma arc welding power sources are commonly designed with
high frequency units. What does the high frequency unit do?
A. increases heat input due to the increased frequency which increases the total time
at high current flow
B. outputs high voltage, low current to create and maintain a stable conductive path for
the flow of power
C. decreases the cleaning action created by electrode negative polarity present in
alternating current arcs
D. outputs balanced current flow between electrode positive and electrode negative
half cycles - Answers-B. outputs high voltage, low current to create and maintain a
stable conductive path for the flow of power
Gases are not normally electrically conductive. To start an arc;
A. requires high voltage
B. requires high inductance
'C. requires high current
D. requires AC power - Answers-A. requires high voltage
What voltage is required to cause 5 amps of current to flow through a resistance of 22
ohms?
A. 110 volts
B. 0.22 volts
C. 4.4 volts
D. 5 volts - Answers-A. 110 volts
What type of output is usually required for Gas Tungsten Arc Welding?
A. constant voltage
B. high frequency
C. low power factor
D. low duty cycle
E. constant current - Answers-E. constant current
In GTAW, the high frequency unit increases the incoming AC line voltage to several
thousand volts. Select the correct statement.
A. systems are limited to less than 4,000 volts for safety reasons
B. the spark gap needs to be at least 75mm (3") wide for the spark to create the arc
C. high frequency systems output high voltage but only at low current flow
D. high frequency systems only work with inverter based direct current arcs - Answers-
C. high frequency systems output high voltage but only at low current flow
How is a thyrister or SCR (silicon controlled rectifier) turned on?
A. by reversing current through the junction
B. by a signal called a "gate pulse"
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