Guardian 4389 Diagnostic Repair Manual page 14

GENERAL INFORMATION
VISUAL INSPECTION
When it becomes necessary to test or troubleshoot a
generator, it is a good practice to complete a
thorough visual inspection. Remove the access
covers and look closely for any obvious problems.
Look for the following:
Burned or broken wires, broken wire connectors,
damaged mounting brackets, etc.
Loose or frayed wiring insulation, loose or dirty
connections.
Check that all wiring is well clear of rotating parts.
Verify that the Generator properly connected for the
correct rated voltage. This is especially important
on new installations. See Section 1.2, "AC
Connection Systems".
Look for foreign objects, loose nuts, bolts and other
fasteners.
Clean the area around the Generator. Clear away
paper, leaves, snow, and other objects that might
blow against the generator and obstruct its air
openings.
METERS
Devices used to measure electrical properties are
called meters. Meters are available that allow one to
measure (a) AC voltage, (b) DC voltage, (c) AC
frequency, and (d) resistance In ohms. The following
apply:
To measure AC voltage, use an AC voltmeter.
To measure DC voltage, use a DC voltmeter.
Use a frequency meter to measure AC frequency In
"Hertz" or "cycles per second".
Use an ohmmeter to read circuit resistance, in "ohms".
THE VOM
A meter that will permit both voltage and resistance to
be read is the "volt-ohm-milliammeter" or "VOM".
Some VOM's are of the analog type (not shown).
These meters display the value being measured by
physically deflecting a needle across a graduated
scale. The scale used must be interpreted by the user.
Digital VOM's (Figure 1) are also available and are
generally very accurate. Digital meters display the
measured values directly by converting the values to
numbers.
NOTE: Standard AC voltmeters react to the
AVERAGE value of alternating current. When working
with AC, the effective value is used. For that reason a
different scale is used on an AC voltmeter. The scale
is marked with the effective or "rms" value even
though the meter actually reacts to the average value.
That is why the AC voltmeter will give an Incorrect
reading if used to measure direct current (DC).
PART 1
TESTING, CLEANING AND DRYING
Figure 1. Digital VOM
MEASURING AC VOLTAGE
An accurate AC voltmeter or a VOM may be used to
read the generator AC output voltage. The following
apply:
1. Always read the generator AC output voltage only at the
unit's rated operating speed and AC frequency.
2. The generator voltage regulator can be adjusted for
correct output voltage only while the unit is operating at
its correct rated speed and frequency.
3. Only an AC voltmeter may be used to measure AC
voltage. DO NOT USE A DC VOLTMETER FOR THIS
PURPOSE.
DANGER!: GENERATORS PRODUCE HIGH
AND DANGEROUS VOLTAGES. CONTACT
WITH HIGH VOLTAGE TERMINALS WILL
RESULT IN DANGEROUS AND POSSIBLY
LETHAL ELECTRICAL SHOCK.
MEASURING DC VOLTAGE
A DC voltmeter or a VOM may be used to measure
DC voltages. Always observe the following rules:
1. Always observe correct DC polarity.
a. Some VOM's may be equipped with a
polarity switch.
b. On meters that do not have a polarity
switch, DC polarity must be reversed by
reversing the test leads.
SECTION 1.4
Page 1.4-1