July
2004, Issue 168
Test Your EQ:
Each
month, Test Your EQ presents some basic engineering
problems for you to test your Engineering Quotient.
What's your EQ?
|
Problem
1— A
residential power meter contains two coils that together
produce a torque on the rotor disc that is proportional
to the instantaneous power flowing in the load, and the
mechanical inertia of the disc averages this torque over
several cycles.
Power
factor correction (PFC) circuits come in two flavors,
one that corrects for reactive (inductive or capacitive)
loads, and one that corrects for nonsinusoidal current
waveforms.
If
the load is an inductive load, such as a lightly loaded
motor, what is the effect of adding a PFC of the first
type to it on the power meter reading? In other words,
does the meter run faster, favoring the power company,
or does it run slower, favoring the customer?
Answer
Problem
2— If
the load is a nonlinear load—such as a large capacitor-input
power supply that draws current in relatively narrow spikes
at the peaks of the AC voltage waveform—what is the effect
of adding a PFC of the second type to it on the power
meter reading?
Answer
Problem 3—Each phase of a three-phase power system
is a sine wave, displaced by 120° from the previous one.
If you connect a resistor across two of the phases, what
is the waveform of the current that flows in it?
Answer
Problem
4—Demonstrate Answer 1 mathematically.
Answer
Problem
5— How
can a disassembler distinguish between executable code
and nonexecutable data?
Answer
Problem
6—What is the difference between a digital oscilloscope
and a digital logic analyzer?
Answer
Problem
7—What is a quarter-wave matching section?
