Electrical Controls
Isaac Queen –iqueen@atn.org
www.atn.org
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• Contact blocks include
normally open (NO),
normally closed (NC), or
both NO and NC contacts.
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• A joystick is used to
control many different
circuit operations from
one location.
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• Limit switches are used
to convert a mechanical
motion into an electrical
signal.
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• An actuator is the part
of a limit switch that
transfers the
mechanical force of the
moving part to the
electrical contacts.
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• A foot switch is used to allow hands-free control or an
additional control point.
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• Direct scan is a method
of scanning in which the
target is detected as it
passes between the
transmitter and
receiver.
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• Retroreflective scan
is a method of
scanning in which the
target is detected as
it passes between the
photoelectric sensor
and reflector.
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• Diffuse scan is a
method of scanning
in which the target is
detected when
some of the emitted,
reflected light is
received.
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• Ultrasonic sensors detect
objects by bouncing high-
frequency sound waves off
the object.
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• A reed relay is a
fast-operating,
single-pole, single-
throw switch that is
activated by a
magnetic field.
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• Inductive
proximity
sensors use a
magnetic field to
detect the
presence of a
target.
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• Capacitive
proximity
sensors use a
capacitive field
to detect the
presence of a
target.
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• Capacitive sensors work based on the dielectric of the
material to be sensed.
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• A Hall generator is a
thin strip of
semiconductor material
through which a
constant control current
is passed.
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• Hall effect sensors are available in a variety of
packages for different applications.
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• A line (ladder) diagram consists of a series of
symbols interconnected by lines that are laid out
like rungs on a ladder to indicate the flow of current
through the various components of a circuit.
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• A solenoid is an electric
output device that
converts electrical energy
into a linear mechanical
force.
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• A contactor is a control
device that uses a small
control current to energize or
de-energize the load
connected to it.
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• The electrical operation of a contactor can be
shown using a line diagram, a pictorial drawing,
and/or a wiring diagram.
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• Auxiliary contacts may be added to a contactor to
form an electrical holding circuit.
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• A magnetic motor starter is
an electrically operated
switch (contactor) that
includes motor overload
protection.
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• The electrical operation of a motor starter can be
shown using a line diagram, a pictorial drawing, and/or
a wiring diagram.
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• The three stages a motor
goes through during
normal operation include
resting, starting, and
operating under load.
• An overload relay does
not open a circuit while
a motor is starting, but
opens the circuit if the
motor gets overloaded
and the fuses do not
blow.
• In three-wire control, three wires
lead from the control device to the
starter or contactor.
• A step-down control transformer is used to step
down the voltage to the level required in the control
circuit.
• Contactors have either an AC coil or a DC coil, but
may have either AC or DC contacts.
• A magnetic motor starter
is a contactor with
overload protection
added.
• An electronic overload
has built-in circuitry that
senses changes in
current and
temperature.
• Auxiliary contacts are added to give circuits with
pushbuttons memory.
• Two stop pushbuttons connected in series and two
start pushbuttons connected in parallel are used to
control a motor from two locations.
• Two start/stop stations are used to control two separate
magnetic motor starter coils with a common emergency
stop protecting the entire system.
• Two motors can be started almost simultaneously from one
location to prevent product separation or stretching.
• A pilot light is used with a pressure switch to
indicate when a device is activated.
• A pilot light is used with a start/stop station to
indicate when a device is activated.
• NOT logic is used to indicate when a device is not
operating.
• A sequence control circuit does not let the first conveyor
operate unless the second conveyor has started and is running.
• A selector switch is used to provide a common
industrial jog/run circuit.
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• A magnetic reversing starter may be controlled by
forward and reverse pushbuttons.
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• A PLC simplifies the wiring of inputs and outputs
by eliminating the need for auxiliary contacts on
the starter.
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• Programmable logic relays are versatile and are normally
used for control circuits that require numerous relays
and/or frequent changes.
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