Measuring Current; Measuring Resistance - Guardian 5240 Diagnostic Repair Manual

SECTION 1.4
TESTING, CLEANING AND DRYING
Correct engine and Rotor speed is maintained by an
engine speed governor. For models rated 60 Hertz,
the governor is generally set to maintain a no-load fre-
quency of about 62 Hertz with a corresponding output
voltage of about 124 volts AC line-to-neutral. Engine
speed and frequency at no-load are set slightly high
to prevent excessive rpm and frequency droop under
heavy electrical loading.

MEASURING CURRENT

CLAMP-ON:
To read the current flow, in AMPERES, a clamp-on
ammeter may be used. This type of meter indicates
current flow through a conductor by measuring the
strength of the magnetic field around that conductor.
The meter consists essentially of a current trans-
former with a split core and a rectifier type instrument
connected to the secondary. The primary of the cur-
rent transformer is the conductor through which the
current to be measured flows. The split core allows
the Instrument to be clamped around the conductor
without disconnecting it.
Current flowing through a conductor may be mea-
sured safely and easily. A line-splitter can be used
to measure current in a cord without separating the
conductors.
Figure 2. Clamp-On Ammeter
Figure 3. A Line-Splitter
Page 18
PART 1
NOTE: If the physical size of the conductor or
ammeter capacity does not permit all lines to be
measured simultaneously, measure current flow
in each individual line. Then, add the Individual
readings.
IN-LINE:
Alternatively, to read the current flow in AMPERES,
an in-line ammeter may be used. Most Digital Volt
Ohm Meters (VOM) will have the capability to mea-
sure amperes.
This usually requires the positive meter test lead to be
connected to the correct amperes plug, and the meter
to be set to the amperes position. Once the meter is
properly set up to measure amperes the circuit being
measured must be physically broken. The meter will
be in-line or in series with the component being mea-
sured.
In Figure 4 the control wire to a relay has been
removed. The meter is used to connect and supply
voltage to the relay to energize it and measure the
amperes going to it.
1.00
BATTERY
- +
Figure 4. A VOM as an In-line meter

MEASURING RESISTANCE

The volt-ohm-milliammeter may be used to measure
the resistance in a circuit. Resistance values can be
very valuable when testing coils or windings, such as
the Stator and Rotor windings.
When testing Stator windings, keep in mind that the
resistance of these windings is very low. Some meters
are not capable of reading such a low resistance and
will simply read CONTINUITY.
If proper procedures are used, the following condi-
tions can be detected using a VOM:
• A "short-to-ground" condition in any Stator or Rotor
winding.
• Shorting together of any two parallel Stator wind-
ings.
• Shorting together of any two isolated Stator wind-
ings.
• An open condition in any Stator or Rotor winding.
GENERAL INFORMATION
A
RELAY