Page 15 - September 2020 Track N Times

TECHNICAL TRAINING

Ring It Out By Donald Dougherty, Senior Technician

In a previous article, we talked about the versatile Fluke multimeter and its many capabilities. Today, we will focus on
the continuity function. These tests are performed when trying to determine if wiring is intact, electric motor wind-
ings are okay, or if relay coils, solenoid coils or fuses are good or bad.

A little background regarding the term “ring-out”. This refers to the days when multimeters were still an expen-
sive piece of test equipment. Instead of using a multimeter to test wiring harnesses etc. workers would use a simple
low voltage circuit that would cause a bell to ring anytime a “continuous” circuit was found, thereby verifying the
point to point wiring was correct according to the schematic or the pull charts.

A “Fluke” or Ohmmeter works in a similar fashion by supplying a low voltage signal across the circuit being tested and
reading the voltage drop between the leads. Circuitry inside the unit converts this into the familiar “Ohm’s” value and
is displayed on the screen.

Safety First! Be certain no Power is applied to the circuit/device you are
testing, and that all appropriate Lock Out Tag Out procedures are followed.
Although most multimeters have some built-in protection for this situation, it is
not at all safe to take resistance measurements on a live circuit. Besides, any read-
ings you get will be erroneous.
To use this function on your “Fluke” select the W position and connect the leads
to circuit you wish to test. Motor windings will typically show a very low resistance
between T1-T2-T3 and should show a very high resistance from any of those three
leads to ground.
Another feature on the Fluke meter is the “Continuity” function. With this fea-
ture, a beep or tone will sound any time the measurement is 40 ohms or less. You
can access this function by selecting W and then pressing the yellow button. This is
handy for quick “eyes-free” testing of multiple circuits without looking back and
forth between the meter and the work. Just be careful to confirm a near zero ohm
reading occasionally to ensure true continuity is present.

When it is necessary to check the continuity of wires over a distance beyond the
reach of your meter leads, a long piece of wire can be used to extend the leads. This method provides a known ref-
erence, for testing. Any length of wire can be used, but you’ll need to factor in the added resistance of the test wire
when taking readings.

Devices:
Many times, it is hard to tell if a component is good or bad. Although the smell test may work for a questionable
sandwich from a few days ago, it’s not always conclusive when applied to electrical components. Our friend the Ohm-
meter can separate the wheat from the chafe and help determine if a part is good or bad. 24V Relays and solenoid

Continued Page 15

SEPTEMBER 2020
PAGE 13