Download Detectors

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Switches are commonly employed as
input devices to indicate the presence
or absence of a particular condition in
a system or process that is being
monitored and/or controlled.
When the switch makes physical
contact with a moving object, a set of
electrical contacts is forced either
open or closed.
Limit switches have two main parts
◦ Electrical contacts usually sealed within an
enclosed body
◦ Actuating mechanism
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The contacts are either normally open
(N.O) , normally closed (N.C)
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Proximity detectors are
electronic sensors that
indicate the presence of
an object without making
the physical contacts.
The detector normally
does not respond by
producing a linear output
signal proportional to the
distance of the object to
the sensor.
The two major types of
proximity detectors are
inductive and capacitive.
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The inductive proximity switch detects
the presence of ferrous metallic
materials.
An Inductive Proximity Sensor consists of
an oscillator, a ferrite core with coil, a
detector circuit, an output circuit,
housing, and a cable or
connector.
The oscillator generates a sine wave of a
fixed frequency. This signal is used to
drive the coil. The coil in conjunction with
ferrite core induces a electromagnetic
field. When the field lines are interrupted
by a metal object, the oscillator voltage is
reduced, proportional to the size and
distance of the object from the coil.
The reduction in the oscillator voltage is
caused by eddy currents induced in the
metal interrupting the field lines. This
reduction in voltage of the oscillator is
detected by the detecting circuit. In
standard sensors, when the oscillator
voltage drops below a present level, an
output signal is generated.
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Capacitive proximity
sensors are similar to
inductive proximity
sensors.
The main difference
between the two types is
that capacitive proximity
sensors produce an
electrostatic field instead of
an electromagnetic field.
Capacitive proximity
switches will sense metal as
well as nonmetallic
materials such as paper,
glass, liquids, and cloth.
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Control valves are used to provide a
number of functions and are typically
selected on the following basis:
- Application function
- Operating conditions
- Construction
- Sizing
Sliding Stem Valves: The basic body
styles are:
- Globe
- Cage
- Angle body
- Y pattern
- Split body
- Three way
- Single seated
- Double seated
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The globe is one of the
most common types of
body style for slidingstem valves
The globe body differs
considerably depending
on the trim used.
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The valve cage is another type of
globe valve that has been very
popular over the last few years.
Its name comes from the shutter
is driven by some kind of cage
immersed in the valve body.
It is used in many applications
replacing the double-entry with
some additional advantage such
as greater capacity, low noise,
good stability, easy change of the
internal organs (trim), use of
small trim in the same shutter
and decreased problems with
erosion.
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The butterfly
valve consists of
a cylindrical body
with a disk the
same size as the
internal diameter
of the valve
body, mounted
on a shaft that
rotates
perpendicular to
the axis of the
body.
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The valve is shown open, and
can be closed by forcing a
flexible membrane down onto a
lower flexible membrane, using
a pincer action.
A flexible membrane also can
be forced down onto a weir.
Diaphragm valves are good lowcost choices for slurries and
liquids with suspended solids,
but tend to require high
maintenance and have poor flow
characteristics.
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The valve is a partial
sphere that rotates,
and the valve tends to
be slow to open.
The ball valve is
available in other
configurations with
various shaped
spheres for different
flow characteristics.
The valve is good for
slurries and liquids
with solid matter
because of its selfcleaning operation.
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Solenoid valves are used to
supply ON – OFF control of
air to the valve actuator.
They are normally mounted
on the valve actuator, but
they can be mounted
remotely as well.
Solenoid valves can be
supplied in different
voltages and configurations
if required.
Solenoid manifolds are
available and used when a
large number of valve
actuators require control or
contain power to a local
area reducing assembly
time.