Two types of electricity
Direct current (DC)
Alternating current (AC)
Converts mechanical energy into electrical energy.
The process of inducing a voltage in a conductor by passing it through a magnetic field.
Maximum voltage is induced when...
the conductor is moved perpendicular to the lines of flux.
When the conductor is moved PARALLEL to the lines of flux...
NO voltage is induced.
One revolution of an AC generator.
(Also, two complete alternations of voltage with NO reference to time.)
the two halves of an AC cycle. (one positive & one negative)
One cycle per second.
Major parts of an AC generator
AC generator output
Sinusoidal wave form (Sine wave)
Sine wave values (pair of numbers)
Degree of rotation- armature's position in the field.
Amplitude-value in relation to maximum or minimum.
Absolute value (no negative numbers) of the point of greatest magnitude. (The peak of the curve-positive or negative)
Peak to Peak
Max positive to Max negative. (Add the absolute values)
The amount that produces the same degree of heat in a given resistance as an equal amount of DC.
Root Mean Square - same as effective value. Is calculated mathematically.
What value does a multimeter measure?
RMS value. (effective value)
Formula for RMS value
E rms = Ep X .707
The time required to complete one cycle. Measured in seconds.
The number of cycles that occurs in a specific period of time.
(Usually cycles per second)
The unit of frequency is
The period of a sine wave is
inversely proportional to its frequency. (higher freq-lower period)
Other than sine wave.
Square, triangular, saw tooth
(Square wave) The duration that the voltage is at the max or min amplitude. Pulse width is one half of the period-hence square.
Linear rise in value. Positive and negative ramps of equal slope.
Saw tooth wave
(Special triangular wave) Long, linear positive ramp with rapid negative ramp
The repetition rate of the waveform
Higher frequency sine waves that are exact multiples of the fundamental frequency.
Square wave harmonics
Fundamental frequency and all ODD harmonics
Triangular wave harmonics
Fundamental frequency and all ODD harmonics AND all are 180 degrees out of phase.
Sawtooth wave harmonics
ODD and EVEN harmonics. Even are 180 degrees out of phase with odd.
Moving Coil Meter
d'Arsonval meter movement
Moving coil meters are designed to measure..
How is AC current measured with a moving coil meter?
The AC current must first be converted to DC.
The process of converting AC current to DC. Accomplished with diodes.
pulsating DC (sine wave is flipped to all positive alternations)
Clamp on ammeter
A split core transformer. It is clamped around the conductor and uses the voltage induced by the conductors magnetic field
Oscilloscope provides the following data:
Phase relationship (of 2 or more waveforms)
Shape of a waveform
Parts of an oscilloscope:
Cathode Ray Tube
Horizontal deflection amp
Vertical deflection amp
Iron vane meter movement does not require
conversion to DC
Phase relationship such that current and voltage pass through peaks and zeros at the same time.
In Phase relationship
Purely resistive circuits are
IN PHASE. Voltage and current pass through max and zero at the same point.
Current is always ____ in a resistive circuit
In phase with voltage.
Power in a resistive AC circuit. Power is always positive.
Most widely used measurement value for AC
Effective (RMS) value
Does current flow across a capacitor?
NO! The capacitor charging and discharging results in movement of electrons from one plate to the other. This resembles current flow.
Capacitive AC circuit - I >C>E
Capacitive reactance formula
The opposition that a capacitor offers to the applied AC voltage.
Current (I) leads Voltage(E) in a capacitive circuit (C)
I>C>E (Remember ELI the ICE man.)
Capacitive Circuit Operation
Voltage starts from zero. Capacitor is empty. Current becomes max. Capacitor charges. Current drops as voltage becomes max and capacitor nears full charge. At max voltage capacitor is fully charged & current drops to zero. Voltage drops towards negative. Capacitor opposes and negative current flows as capacitor discharges.
Capacitive Reactance in Parallel
1/XCT = 1/XC1 + 1/XC2 + 1/XC3 ... + 1/XCn
Capacitive Reactance in Series
XCT = XC1 + XC2 + XC3 ... + XCn
RC Low Pass Filter
RC Low Pass Operation
Allows low frequencies to pass while attenuating high frequency. At low frequency, capacitive reactance is HIGH so voltage drop is across capacitor.
RC High Pass Filter
RC High Pass Operation
Allows high frequency to pass while attenuating low.
At high frequency, capacitive reactance is LOW so voltage drop is across the resistor.
Low Pass Frequency Response
High Pass Frequency Response
Allows a DC signal to pass while blocking the AC signal.
What type of circuit can be used as a decoupling network?
RC low-pass filter.
Passes the AC signal while blocking the DC
What type of circuit can be used as a coupling network?
An RC high-pass filter
A circuit that discriminates against certain frequencies.
RC circuit uses
Filtering (low/high pass)
RC phase shift networks are used only where
small amounts (less than 60 degrees) are desired.
RC leading output phase-shift network
The opposition to current flow by an inductor in an AC circuit.
Counter Electromotive Force (CEMF)
Voltage induced in an inductor coil which opposes the applied voltage. It is out of phase by 180 degrees.
Factors effecting CEMF
The greater the rate of change of the magnetic field (faster the magnetic field expands or collapses) the greater the CEMF.
Voltage (E) leads Current (I) in an inductive (L) circuit
Inductive Reactance Formula
Decoupling Network - Memory Trick
D-coupling = d C pass
Coupling Network - Memory Trick
C-oupling = a C pass
RC Low pass filter - Memory Trick
Capacitor low = frequency low
(Capacitor low in schematic. Low frequency passes)
RC High pass filter - Memory Trick
Capacitor high=frequency high
(Capacitor high in schematic. High frequency passes)
Leading Output Phase-Shift Network
Look for C. (C slows voltage) C in back - input slow-output leads. Output voltage leads input voltage.
Lagging Output Phase-Shift Network
Look for C. (C slows voltage) C in front-output slow-input leads. Output voltage lags input voltage.
The combined effect of resistive and reactive components.
It is the vector sum.
Why is the capacitive voltage vector (Ec) drawn downward?
It lags current by 90 degrees. This is why it points down (-90 degrees).
Why are current vectors used to analyze a PARALLEL circuit?
Because the VOLTAGE is the SAME across all components.
All are EQUAL and IN PHASE with current, so that vector is the horizontal (X) axis.
Why are voltage vectors used to analyze a SERIES circuit?
Because the CURRENT is the SAME across all components.
All are EQUAL and IN PHASE with voltage, so that vector is the horizontal (X) axis.
The ratio of true power (in watts) to apparent power (in volt-amperes) in a REACTIVE circuit.
Power factor of RESISTIVE circuit
True power EQUALS apparent power so power factor is 1.
The value of capacitive reactance _______ as frequency increases
decreases (inversely proportional)
High freq=low Xc
What is the formula for cutoff frequency in an RC circuit?
Counter electromotive force (cemf)
Voltage induced in an inductor coil by the expansion and collapse of the magnetic field resulting from an applied voltage.
Always opposes applied voltage.
Greater inductance=greater cemf
Always 180 degrees out of phase with applied voltage.
Induced voltage is always _____ than applied voltage
In a purely inductive circuit current ___ voltage.
LAGS - remember ELI the ICE man.
E(voltage) L(inductive circuit) I(current)
Current lags by 90 degrees.
The opposition to current flow by an inductor in an AC circuit is
inductive reactance (Xl) measured in ohms
Inductive reactance formula
Inductive reactances in series
When inductors are connected in series, the total inductive reactance is equal to the sum of the individual inductive reactance values