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Electrician - Fourth Period > Welders and Filters > Flashcards

Welders and Filters Flashcards

1
Q

Resistors are divided into two groups,

what are they?

A
  1. Fixed Resistors
  2. Variable Resistors
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2
Q

What are the two most important ratings of a resistor?

A
  1. Power in Watts
  2. Resistance in Ohms
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3
Q

What are the three most important ratings of a capacitor?

A
  1. Capacitance in Farads
  2. Voltage
  3. Tolerance
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4
Q

What are the two most important ratings of a coil?

A
  1. Inductance in Henry’s
  2. Maximum Current Rating
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5
Q

What is often referred to as a choke?

A

An Inductor

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6
Q

What is a Capacitor?

A
  • A component in an electronic circuit that has the ability to store and release electrical charge
  • This is called capacitance (C) and causes opposition to a change in voltage
  • The unit of measurement is the Farad (F)
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7
Q

Describe the construction of a Capacitor

A
  • A capacitor is two conductive plates separated by a dielectric layer
  • This dielectric layer is an insulator that allows the two plates to be brought close together without shorting out
  • The better the insulator is, the closer the plates can be brought together and the greater the capacitance
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8
Q

What three construction characteristics affect the capacitance of a capacitor?

A
  1. The surface area of the plates
    1. Capacitance increases as the surface area of the plates increases
  2. The distance between the plates
    1. Capacitance decreases as the distance between the plates increases
  3. The dielectric constant between the plates
    1. Capacitance increases as the dielectric constant increases
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9
Q

What are some of the common types of dielectric used in capacitors?

A
  1. Paper
  2. Plastic Film
  3. Mica
  4. Ceramic
  5. Electrolytic - Polarity Sensitive
  6. Tantalum - Polarity Sensitive
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10
Q

Which types of capacitors are polarity sensitive?

A
  1. Electrolytic
  2. Tantalum
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11
Q

What does WVDC mean?

A
  • Working Volts DC
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12
Q

How many time constants does it take for a capacitor to charge?

A

Five Time Constants

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13
Q

What is the equation for one time constant?

A

T = R x C

  • ​T = Time in seconds
  • R = Resistance in ohms
  • C = Capacitance in farads
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14
Q

What code rule states that capacitors shall be provided with a means of draining the stored charge?

A

26-222

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15
Q

How do Inductors behave?

A
  • An inductor opposes a change in current
  • As current increases, the inductor opposes the increase and lowers the peak value
  • When the current decreases, the collapsing magnetic field tries to maintain current
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16
Q

What affects the Inductance of a coil?

A
  • The inductance of a coil is affected by the number of turns in the coil and the following factors in the core:
    • The permeability of the core (u)
      • Inductance of the coil increases as the permeability of the core increases
    • cross-sectional area of the core (A)
      • Inductance of the coil increases as the cross-sectional area of the core increases
    • length of magnetic path (l)
      • Inductance of the coil decreases as the length of the core increases
  • L = (N2uA) / l
17
Q

Why are inductors called “Choke Coils”?

A
  • Because they suppress sudden rises in current
  • They also oppose sudden decreases in current
18
Q

What is the formula for Percent Ripple?

A

% Ripple = (VRMS of the Ripple / VDC AVG) x 100

19
Q

What do Filters do?

A
  • When an AC voltage is rectified, the result is pulsating DC voltage
  • Filters are used on the output of rectifiers to produce smooth DC Power
20
Q

How does a Capacitor Filter work?

A
  • This is the simplest filter circuit, it consists of a capacitor connected in parallel with the output terminals of a rectifier and in parallel with the load
  • The amount of ripple at the load depends on the capacitance of the capacitor and the resistance or impedance of the load
  • The greater the load, the faster the capacitor dischargers, and the greater the amount of ripple
  • A capacitor’s filtering effectiveness decreases as the load increases
21
Q

How does a choke filter work?

A
  • Consists of an inductor coil connected in series with the output of a rectifier and in series with the load
  • The coil can have an air core or an iron core
  • Inductors oppose a change in current so they produce a reduced ripple at the load
  • The two factors that determine the effectiveness of a choke filter are:
    • The inductance of the choke
    • The amount of current
  • The filtering effect of a choke coil increases as the load increases
22
Q

How does a L-Section filter work?

A
  • Consists of a capacitor and a choke filter
  • The capacitor is connected across the output after the choke filter, this reduces the possibility of voltage spikes produced by the choke at the load
  • Also called a choke-input filter because the choke imputs to the capacitor
  • These filters are effective over a wider range of loads

Electrician - Fourth Period (24 decks)

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