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Timers
A
Timer OperatiOn
D.
ELECTRICAl.
CONTROLS
The timer is the central control point of the electrical components. All timers used on Kenmore Dishwashers are similar
in operation and design. The only difference is in complexity due to the variation
in function and features of the various
models
MOTOR
CAM
SWITCH
FIGURE 54
All electromechanica!
timers consists of two basic components; a motor, and cam switches, assembled into one unit..
(Figure 54). To fully understand the function
and relationship
of these two components
to one another, it is necessary
to examine each component
in more detail
Timer motors may vary slightly in appearance, but each functions in the same manner
It is a synchronous-type
motor,
similar to those used in electric
clocks, with a small pinion which drives a cam through
a gear arrangement.
The cam switches are enclosed in a case to protect
them from damage and contamination
by foreign particles which
may cause a malfunction
The number of switch contacts
and cams varies with the number of functions
the dishwasher
performs
The particular
shape of the cam varies with the number of switch contacts
it controls
and the length of time each
switch contact
is ctosed_ Figure 55 shows a very simple cam that
controls
one switch contact,
which is closed for
two increments
of the timer cycle
Let's assume that this cam is designed for a timer that has an advancement
of
six deglees (6 °) every sixty seconds The cut-out
portion of this cam, therefore,
is twelve degrees, and the cam switch
contacts
are closed for only two minutes during the complete
cycle
CAM----/
CAM----.-/
t
FIGURE55
A single metal strip, called a cam follower,
(Figure 55) is anchored
to each cam switch
arm and as the cam turns,
this metal Strip follows the contour of the outer circumference
of the cam, thus causing the cam switch arm to make
and break contact
at the proper time
In Figure 5B we see a more complicated
cam, This cam was designed to control one or possibly two switch arms that
have dual contacts
You will note
that
this cam has raised, cut-out,
and neutral
portions
The raised portions
force the cam switch arm against the outer contact
and the cut out portions
allow the cam switch
arm to make
contact
with its inner contact.
Both contacts
are open when the cam follower
is on the neutral
section of the cam
SWITCH
ARM
CONTACT
CAM
. NEUTRAL
FOLLOWER
SECTION
CAM
_
CONTACT
INNER
OUT
PORTION
-CAM
FOLLOWER
OUTER
CONTACT
€
FIGURE 56
49
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