(3) Duration. The time that a pulse remains at its maximum
amplitude is the duration time (td) of the pulse. If the waveform is
symmetrical and has zero rise and decay times, the pulse will have
two equal duration times. The time duration of a symmetrical
waveform is
Time duration (td) = Period/2
or
Time duration (td) = 1/(2 x Frequency)
(4) Decay. The decay time (tf) of a pulse is the time required
for the pulse to return to zero from its maximum amplitude. In
practical applications, we use 90 percent to 10 percent.
(5) Rest. The time between pulses is the rest time of a
waveform.
Section I. SERIES RL CIRCUIT RESPONSE
2.
GENERAL.
The response of any circuit to a step voltage can be
determined by using Kirchoff's law, which states that the sum of the
voltage drops in any closed circuit is equal to the applied voltage.
In Figure 17, a voltage E is applied to a series RL circuit. The
voltage drop across the resistor ER added to the voltage drop across
the inductor EL must, at all times, be equal to the applied voltage
E. The applied voltage is a rectangular pulse (Figure 17B),
consisting of both a positive and a negative voltage.
3.
POSITIVE STEP VOLTAGE.
a. When the positive step voltage (Figure 17B) is applied to the
series RL circuit, the inductor opposes the flow of current by
building up an instantaneous back or counter emf equal to the applied
voltage. Consequently, at the instant the voltage is applied to the
circuit, there is no current flowing in the circuit (Figure 17C). At
this time, all the voltage is impressed across L (Figure 17E), and
there is no voltage drop across the resistor (Figure 17D). As the
counter emf starts to decrease, current starts to flow and a voltage
ER is developed across the resistor. This voltage represents the
difference between the applied voltage and the voltage drop EL across
the inductor at that instant. As the voltage drop across the
inductor decreases, the rate of current change decreases causing a
less rapid increase in the
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