The millivolt drop test is generally associated with
testing for weld quality on the armature. It is the
best test for verifying armature weld quality.
The millivolt drop test is the ultimate electrical test
for detecting bad welds. Unfortunately, it is
difficult to make on armatures with large diameter
wire and nearly impossible to make on armatures
with small wires.
The difficulty is breaking through the insulation on
the wire as it exits the tang or commutator bar
contact. The one testing contact, usually a sharp
knife edged probe, from the KOM (Kelvin Ohm
Meter) can cut through small wires and destroy
the armature. Contact with the knife-edge probe
needs to be made on each bar. Since this is such
a difficult test to perform, it is only practical as a
laboratory test.
Various test methods have been developed over
the last twenty years that come close to making
this test. These tests make it possible to test
100% of the armatures. However, none of these
tests are as accurate or repeatable as the Millivolt
Drop Test.
ESW's weld test, which uses techniques that have
been developed over the past 20 years, comes
very close to the Millivolt Drop Test. The
repeatability and speed of the test using a
stationary armature test fixture assures that a
reliable test has been performed.
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