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Chapter 9
Taking Standard Measurements
Taking Measurements • Voltage • Voltage
Indicators • DC Voltage Measurement •
Current • Resistance • Temperature • Speed •
Scopes • Scopemeters • Manually-Operated
Controls • Digital Logic Probes
Chapter 9 — Taking Standard Measurements
A test light is a test
instrument with a bulb
that is connected to two
test leads to give a
visual indication when
voltage is present in a
circuit.
Chapter 9 — Taking Standard Measurements
When testing a receptacle,
the test light bulb
illuminates when the
receptacle is properly
wired and energized.
Chapter 9 — Taking Standard Measurements
A receptacle tester is a
device that is plugged
into a standard
receptacle to
determine if the
receptacle is properly
wired and energized.
Chapter 9 — Taking Standard Measurements
Refer to the operating manual
of the test instrument for all
measuring precautions
limitations, and procedures.
Chapter 9 — Taking Standard Measurements
A voltage indicator is a
test instrument that
indicates the presence
of voltage when the test
tip touches, or is near,
an energized hot
conductor or energized
metal part.
Chapter 9 — Taking Standard Measurements
Always follow a voltage
indicator test with a test using
a voltmeter to verify the
voltage indicator
measurement any time the
voltage indicator indicates no
voltage.
Chapter 9 — Taking Standard Measurements
A voltage tester is an
electrical test instrument
that indicates the
approximate voltage
amount and type of
voltage (AC or DC) in a
circuit by the movement of
a pointer (and vibration on
some models).
Chapter 9 — Taking Standard Measurements
Before taking any voltage
measurements using a
voltage tester, ensure the
tester is designed to take
measurements on the circuit
being tested.
Chapter 9 — Taking Standard Measurements
Exercise caution
when measuring
AC voltages over
24 V.
Chapter 9 — Taking Standard Measurements
Exercise caution when
measuring DC
voltages over 60 V.
Chapter 9 — Taking Standard Measurements
Care must be taken
to protect the meter,
circuit, and person
using the meter
when measuring
DC with an in-line
ammeter.
Chapter 9 — Taking Standard Measurements
Clamp-on ammeters measure the current in a circuit
by measuring the strength of the magnetic field
around a conductor.
Chapter 9 — Taking Standard Measurements
An ohmmeter measures
resistance with all power to
the circuit OFF.
Chapter 9 — Taking Standard Measurements
A megohmmeter detects insulation failure or potential
failure of insulation caused by excessive moisture,
dirt, heat, cold, corrosive substances, vibration, and
aging.
Chapter 9 — Taking Standard Measurements
The amount of temperature at a location can be
measured using a contact thermometer or infrared
meter.
Chapter 9 — Taking Standard Measurements
A contact thermometer is an instrument that measures
temperature at a single point.
Chapter 9 — Taking Standard Measurements
An infrared meter is a meter that measures heat
energy by measuring the infrared energy that a
material emits.
Chapter 9 — Taking Standard Measurements
The speed of a rotating object can be measured
using a contact tachometer, photo tachometer, or
strobe tachometer.
Chapter 9 — Taking Standard Measurements
A contact tachometer
is a device that
measures the
rotational speed of an
object through direct
contact of the
tachometer tip with
the object to be
measured
Chapter 9 — Taking Standard Measurements
A photo tachometer is a
device that measures
the speed of an object
without direct contact
with the object.
Chapter 9 — Taking Standard Measurements
A strobe
tachometer is a
device that uses a
flashing light to
measure the
speed of a
moving object.
Chapter 9 — Taking Standard Measurements
The two basic
types of scopes
used in
troubleshooting
are oscilloscopes
and scopemeters.
Chapter 9 — Taking Standard Measurements
A scope displays the voltage under test on the scope
screen.
Chapter 9 — Taking Standard Measurements
A trace is a reference point/line that is visually
displayed on the face of the scope screen.
Chapter 9 — Taking Standard Measurements
Typical manually-operated
scope adjustment controls
include intensity, focus,
horizontal positioning,
vertical positioning,
volts/division, and
time/division.
Chapter 9 — Taking Standard Measurements
The volts/division (volts
per division) control
selects the height of the
displayed waveform.
Chapter 9 — Taking Standard Measurements
The time/division (time per
division) control selects
the width of the displayed
waveform.
Chapter 9 — Taking Standard Measurements
A scope is connected
by a probe on the end
of a test lead. A 1X
probe (1 to 1) is used
to connect the input of
the scope to the circuit
under test when the
test voltage is lower
than the voltage limit of
the scope.
Chapter 9 — Taking Standard Measurements
A scopemeter gives
an adequate reading
in most frequency
measurement
applications.
Chapter 9 — Taking Standard Measurements
To measure AC voltage using a scope, a test probe is
connected to the point in the circuit where the DC
voltage is to be measured.
Chapter 9 — Taking Standard Measurements
A digital logic probe is a
special DC voltmeter
that detects the
presence or absence of
a signal.
Chapter 9 — Taking Standard Measurements
A power supply voltage is checked with voltmeter if
the digital circuit or logic probe has intermittent
problems.