Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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An Optical Switch
Field of Invention
The invention relates to switches used primarily in hazardous environments,
such as
switches used in liquid level detection in tanks or switches to activate
equipment within a
hazardous environment.
Background of the Invention
Many working environments present explosion hazards or present a risk of
electrical shock.
One hazardous environment is a pumping station or a tank that contains
hazardous and/or
flammable or volatile gases or liquids and chemicals to be pumped. Float
switches are commonly
used in applications of this sort to detect level for activation of a pump
(see Figure 2), but float
switches generally have electrical current that passes through wires and a
switch housed within the
float, such as a mercury switch located in the float. Wires from the float
switch run to a control
panel (or other device) located external to the tank or pit and are located
outside the hazardous area.
Some specialty control panels are explosion proof and can be located in the
hazardous area. As
liquids rise in the tank, the float tilts and a ball or conductive liquid,
such as mercury, moves and
makes contact with an electrical switch or contacts of some sort causing the
switch to activate.
Electrical current then passes from the control panel through the wires, to
the switch, completing
the circuit. These all present a spark hazard, and if a breakdown in
insulation occurs along the
electrical path, an explosion can result.
Some tanks containing flammable liquids or gases use ultrasonic level
detection which
sends a sonic burst to the surface of the liquid and then back. The transit
time of the beam is used
to determine the liquid level (some alternative devices use radar or microwave
radiation as an
energy packet instead of a sound wave, and other sensing technologies are used
in level detection,
e.g. magnetostrictive, submersible pressure transducers, bubblers,
capacitance, etc.). No electrical
.current is used within the tank or pit and the transmitter and receiver are
located external to the
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hazardous atmosphere, usually mounted on the external tank surface, with the
sensing device
positioned in the tank. This technique is not generally used to remotely
signal a device, such as a
signal to engage/disengage a pump (such as a dosing pump) at discrete levels,
as these level
detectors will detect all fluid levels requiring additional logic circuits to
select a predetermined
height or level for operation of a pump, thereby raising the complexity and
expense of such as
system.
In some hazardous environments, explosion proof containers are used to contain
equipment
or devices that may present a possible sparking hazard, such as controls,
pumps, motors, etc.
While pumps or other devices located in a hazardous environment may be
contained in an
explosion proof housing, these devices must be activated or deactivated by
electrical signals (e.g.
providing power to the device). Activation is done remotely from the hazardous
environment to
reduce the possibility of explosion. Hence, when an operator is onsite, the
operator cannot
manually activate/deactivate the device within the hazardous area unless the
activation device is in
an explosion proof housing. It would be desirable to have a switch located
within the hazardous
environment that could be used to manually activate/deactivate the powered
device, and have the
switch not present an arcing hazard, and would not have to be located in an
explosion proof
housing.
Summary of the Invention
The invention is an optically activated switch for use in a hazardous
environment, (non-
hazardous environments also are contemplated) and in one embodiment, the
switch activation
components are contained in a floatable housing and used to signal the need to
operate a pump or
other device. As discussed, a switch is a device having a status (on/off,
make/break, open/closed or
other status indicator) that can be used to control an electrical device. The
switch invention uses a
light beam from a transmitter located outside of the hazardous atmosphere
("outside the hazardous
environment" includes a location within an explosion proof container or
housing) which travels
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through a light carrying cable, fiber, tube or light guide (all considered a
"light guide") to a switch
means located in a hazardous area. Based on the position or "status" of the
switch (optical path
interrupted, or optical path complete), the light can travel to a powered
light detector or receiver
located outside the hazardous area, which detects the status of the switch,
and circuitry can act on
the status to activate or deactivate a powered device, such as a pump or
motor. Several means of
breaking or interrupting the light path can be utilized. The controller to
which the switch is
connected can be configured to activate a pump or device upon detection of the
light or detection of
the lack of the light.
Objects of the invention
It is an object of the invention to have a switch that uses no source of
electrical current or electrical
resistance at the switch location.
Brief Description of the Drawings
Figure 1 depicts an optically activated float.
Figure 1 A is a detail of the float of figure 1
Figure 2 depicts a conventional float.
Figure 3 depicts an optically activated float having a damped switch.
Figure 4 is a cross sectional view of the float of figure 3.
Figure 4A is a detail of the separator assembly of the float of figure 4.
Figure 5 depicts a switch operated mechanically or manually.
Figure 6 depicts another embodiment of a float switch.
Figure 7 depicts another embodiment of a float switch with a delay ring.
Figure 8 depicts a tether cable for a float embodied switch.
Figure 9 depicts a light and a limit optical switch located in a hazardous
environment.
Figure 10 is a representative circuit diagram incorporating the switch, and
used to power a device.
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Figure 11 depicts a top view of an ampoule with two parallel same side optical
fibers where the two
fibers are optically aligned by position of the reflective bar at position A
and where the two fibers
are optically non-aligned (or optically interrupted) by position of the
reflective bar at position B.
Figure 12 is a cartoon showing a magnet used to delay operation of the switch
through a pre-
selected range of motion.
Figure 13 A depicts the operation of a wide angle float as the pump chamber
fills.
Figure 13B depicts the operation of a wide angle float as the pump chamber is
pumped down.
Figure 14 depicts a float embodiment of the switch using a paddle insert
separator assembly.
Detailed Description of the Invention
Shown in figure 1 is an embodiment of the invention in a float. The invention
includes a
housing 1, two light guides 2 (hereafter described as fiber optic cables), a
light source 3, and a
means to interrupt or modify the alignment, here by interposing an object
between the distal ends.
The housing shown has an interior section. The two cables 2 are positioned
into the housing 1. Each
cable terminates at or within the floating housing 1. The terminal (or distal)
ends of the cables are
positioned in the housing near each other, but separated by a gap 10 (see
figure 1, detail A). The
gap 10 is generally positioned in the separator assembly 6 within the housing
1. The separator
assembly fixes the relationship of the cable terminal ends and maintains the
gap, although this
relationship can be fixed through use of the housing alone. The gap can vary
in size, with 0.01 -
0.5 inch suitable for most applications, but could be larger. Some light
detectors can sense the
presence of light radiation across a gap of up to four inches. The ends of the
two fiber optic cables
should be "optically aligned," that is, light emitted from one terminal end
will travel though the gap
(possibly along a zig-zag path if reflective material, such as mirrors, are
employed to bounce the
emitted beam appropriately) and a portion of the transmitted light will enter
the terminal end of the
second cable. The portion that enters must be sufficient to be able to detect
the presence of light
radiation by the light detector. For instance, the two cables may be parallel
with a 45 degree
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reflective surface positioned at the fiber ends, so the two fibers, while
parallel, are "optically
aligned." The two cable ends can be offset a distance and still be optically
aligned if sufficient light
is captured and transmitted through the cable connected to the light detector
to activate the light
receptor. In part, the degree of offset will depend upon the sensitivity of
the light detector and the
strength of the source. Suitable sources and detectors can be found at
www.fiberopticproducts.com:
with sources such as E97 (red 660 nanometers, bright) and detector D92. Using
these sources and
detectors, the light source can still be detected with an offset of one inch
over a gap of about 1 inch.
As shown in the detail A of figure 1, the separator assembly 6 generally
includes an internal
chamber 6A with one fiber cable 2 terminal end positioned adjacent to, in or
on the wall of the
interior chamber and the other fiber optic cable 2 terminal end positioned on
an opposite wall of the
internal chamber 6A, with the two ends optically aligned. The separator
assembly is generally an
assembly removable from the interior of the float with the cables positioned
on the assembly.
Applicant believes it is more efficient to build the separator assembly with
attached cables and
inserted into the float, than using only a hollow interior with the cables
inserted into or attached to
the interior walls of the float, although such a design is workable and within
the scope of the
invention. The separator assembly is not required, but is preferred. For
instance, shown in figure 4
is a separator assembly 6, comprising a glass or clear plastic ampoule 5.
Ampoule contains a
slidable bar, ball, or cylinder (or other shape) IOA, and has the two light
guides coupled on
opposing sides of the ampoule exterior through use of a yoke or collar 11.
Separator assembly 6
would be positioned in the interior of the float, usually the separator
assembly will be fixedly
positioned in the float interior such as with epoxy or a friction fit. As
shown in Figure 4, a collar 12
is used to fix the ampoule in position in the interior of the float, and in
some cases collar 12
functions as additional weight to modify the buoyancy and center of gravity of
the float as needed.
The weight can be lead or other dense material, for instance, steel particles
encased in a corrosion
resistant (preferably an environmental friendly) material. Yoke I 1 and collar
12 could be combined
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(not shown). A detail of yoke 11 is shown in Figure 4, detail A. In a non-
float embodiment, the
separator assembly may not be preferred.
An alternative separator assembly is shown in figure 14. The separator is a
flat paddle 60,
constructed of flexible plastic. Formed in the paddle are clips 61 to hold the
ampoule and optical
cables. The paddle 60 is inserted in the bottom 1/2 of the housing lA and
fixed into position. The
paddle may be fixed by potting the bottom of the paddle to the housing portion
lA, leaving the top
portion of the paddle free to flex. The top of the housing 1B is then attached
to the bottom lA,
such as by RF welding. As shown, the top of the paddle 60 is not form fitting
to the top of the float
housing 1 B, to allow the top of the paddle (where the ampoule is located) to
flex in response to
shock forces. For instance, operators have been known to "clean" floats by
swinging the float by
the tether and slamming the float into a wall.
In the embodiment shown in figure 1, the housing I is floatable, and the
cables "tether" the
housing I to a fixed point, allowing the float to rise and fall with the media
for a range of
elevations. The two fiber cables 2 are contained in a single cable structure,
later described. One of
the fiber optic cables is connected to a light source 3, and the other cable
is connected to a light
detector 5. The light source 3 can be any suitable source, such as a laser,
incandescent light bulb,
sunlight, a light emitting diode, and light generally refers to any
electromagnetic radiation, but for
fiber optics, preferably the light source will consists of visible light,
infrared light, sunlight, and
ultraviolet light; more preferably, light from about 300 nanometers to about
30,000 nanometers in
frequency. Preferably the light source 3 and light receiver or detector 5 will
be located external to
the hazardous area in a control panel or other device (they do not have to be
located together), and
only the fiber optic cables will travel into the hazardous area to the housing
1.
As shown in the Detail A of figure 1, the internal chamber 6A of the separator
assembly 6
creates the needed gap between the fiber optic cables 2 terminal ends. Located
within the internal
chamber 6A is a means to interrupt optical alignment 10, such as a rollable or
slidable ball or bar or
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cylinder, or an opaque fluid positioned within the internal chamber partially
filling the chamber. If
the housing floats, at a certain level the floating housing will tilt (as it
is tethered by action of the
cable that is tied to an internal or external fixed weight, or the housing is
attached to another
stationary device with a cable or tether) and as it tilts, the means to
interrupt optical alignment will
move within the internal chamber due to gravitational forces. If the degree of
movement is
sufficient, the means to interrupt optical alignment will block (or unblock)
the light path between
the two terminal ends of the fiber optic cables 2. Additionally, if the
housing 1 is a fixed device
(that is, it does not float on the media but is fixed at a desired height),
the means to interrupt optical
alignment can be a floating arm or floating barrier positioned in the internal
chamber 6A of the
housing. As the water level rises up to the level of the housing, the floating
arm or barrier will rise
(much like a floating limit switch) to block the light beam (or unblock the
light beam). In this
instance, the switch will have a means to fix the elevation of the housing,
such as a clamp, to attach
the housing to a structure in the hazardous environment, such as a dosing pump
or to the container
storing the hazardous material. For example, in figure 6 is shown one
embodiment, where the
housing is a cylindrical shell 100 with an center hollow interior 101 that is
open on both ends to
the external environment. The housing would be fixed in position in the
hazardous environment.
Trapped in the interior is an opaque float body 102. The two ends of hollow
interior 101 may have
a mesh filter covering the openings that retains the float body in the hollow
interior. Positioned on
opposing sides of the interior 101 are the two optic cable 104A and B. As the
fluid in the chamber
rises, the float body 102 rises and will block the optical path between the
two cables 104 A and B.
As mentioned above, the cables do not have to be on opposing sides, but must
either be optically
aligned, or be optically alignable.
With a switch in a floatable housing, the optical fibers will bend as the
float rises and falls.
Over a period of time, the bending of the optic fibers can result in fracture
or severing of the fibers,
potentially destroying the functioning of the switch. To help alleviate this,
a fairly stout tether cable
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design is preferred. Shown in figure 8 is one suitable design 250. The twin
fiber optic cables 150
(here shown as 1mm diameter sheathed with a polyvinylchloride (PVC) coating
100) are positioned
in the interior of an outer sheath member 300, here a 0.020 inch thick PVC
extruded watertight
jacket, used for strength. More than two optic fibers may be located in the
cable. The fiber-optic
cables or light guides are deployed in a filler material 160 in the interior
of the extruded sheath 300.
As shown in figure 8, the filler material is very fine hair-like polypropylene
fibers, all contained in
a paper wrap 200. As constructed, the interior of the tether cable 250 is
substantially filled, leaving
very little freedom of movement for the optical fibers within the interior. In
the design shown, it is
preferred that both optic fibers be sheathed to prevent shorting of the switch
in the cable
(particularly for the use of side glow cables (not preferred), for end glow
cables, this may not be
necessary). For long tether lengths, it may be preferred to include a strong
reinforcing cable, such
as a steel, Kevlar, carbon fiber, etc cable within or attached to, the tether
cable structure. Shown in
Figure 8 is a cable that houses two optic fibers. The cable may contain more
than two fibers.
In a float embodiment containing the optical switch, the float may reach a
position where
the switch will "flutter" between an optical path open or "blocked" position
or optical path closed
or "complete" position due to inherent instabilities in a float embodiment.
For instance, the float's
position may jitter due to surface waves in the fluid environment. This float
jitter may cause the
slidable or rollable means to interrupt optical alignment (or the switch
activator) located in the float
interior to move back and forth, causing the switch status to rapidly move
between open and closed
(note, switch "open" can be interpreted as path blocked or path complete,
depending on how the
device connected to the switch circuitry is configured to respond to the
status of the switch). To
reduce switch "flutter" a damped switch can be einployed by including a means
to dampen the
switch activator or the means to interrupt optical alignment. The optical
switch may be damped
through a variety of means. For instance, in the embodiment shown in figure 4,
detail A, the
ampoule may be filled or partially filled with a damping fluid 110, such as
mineral oil or other clear
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or light transmissive fluid. The fluid in the ampoule serves two purposes,
lubrication (to help
prevent the rollable or slidable means to interrupt from scratching the walls
of the ampoule and
possibly modifying the optical characteristics of the ampoule walls) and acts
as a damping force,
creating a drag on the bar or ball reducing sudden movements of the bar or
ball. When a damping
fluid is used, it is preferred to separate the fluid from the light guides
(such as by having the fluid
contained in an ampoule) to avoid contamination of the light guide distal ends
by the damping
fluid. The amount of fluid in the ampoule can vary from a few drops to fully
filled.
Alternatively, a slidable bar, ball. cylinder or other structure could be used
with the sides of
the structure roughened (or the interior walls of the ampoule could be
roughened or have added
ridges) to create additional surface area resulting in additional frictional
forces opposing a sudden
movement of the bar. For instance, shown in figure 7 is a ring or annulus
positioned in the separator
assembly chamber 6. A rollable ball is used as the slidable member. The ring
in the housing
chamber insures that a ball positioned in the chamber will not move from
position A (unblocked) to
position B (blocked) without a sufficiently large enough movement of the
housing to allow the ball
to roll over the ridge created by the ring. The ending position of the ball
would not be altered by
minor fluctuations in the float position. Also, an hourglass shaped vessel may
be used, where the
neck of the hourglass can pass the slidable ball, specially designed segmented
cylinders, other
movable structure, or other light blocking device (e.g. opaque liquid). In
this instance, the shape of
the chamber is used to control switch flutter.
Another means to deal with switch flutter is to allow the light to blink,
flash or pulse
periodically, and a change in status of the switch is detected by the presence
or absence of a
suitable number of pulses. For instance, if the light path is initially
blocked, and the status changes,
the change will be noted after detection of so many consecutive light pulses
(detection of, say 5,
consecutive flashes, detecting the presence or absence of a predetermined
number of flashes over a
predetermine time interval helps reduce switch flutter); if the light path is
not blocked, then a
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change in status would be detected after detection of the absence of a certain
number of pulses or
flashes of light over a predetermined time interval. This is generally not
preferred as it increases
the complexity of the circuitry tied to the switch, but may be useful where
the lifetime of the light
source is an issue.
Another means to deal with switch flutter is not to use a constantly "on"
light source.
Instead, the source can remain off until the switch is "polled" for its
status. For instance, the
electronics tied to the switch, such as a controller (e.g. PLC or
microcontroller), may interrogate the
status of the switch every second, and turn the light source on once per
second for a designated
time, and "look" for the return status, e.g either light blocked or light
present on the return optical
fiber. Alternatively, the light may stay on, and the status of the switch
polled at the light detector.
Again, this is not preferred, as it increases the complexity of the circuitry
tied to the switch. To
reduce switch flutter, the change in switch status should be consistent for a
selected period of time.
Another method to reduce switch flutter is to use magnets suitably positioned
in the
separator assembly in conjunction with a cylinder or slidable bar or structure
composed of
magnetably interactive material. Shown in figure 12 is a cartoon depicting the
movement of a
slidable magnetic interactive cylinder or slug (here an 18-8 cold formed 3/16"
D x 1/2" L stainless
steel cylinder (sometimes denoted 300 series stainless steel having
approximately 18% chromium
and 8% nickel)) in an ampoule, and a "horseshoe" magnet positioned in the
interior of the float
where the two ends of the horseshoe near the sides or ends of the ampoule. The
horseshoe magnet
is shown for purposes of explanation and is not preferred. As the float moves
from position A
through position D, rotating "upwardly," the slug "sticks" to ampoule near the
magnet, say near the
N pole of the magnet. Before or at position E, the gravitational force
overcomes the magnetic force
and the slug slides downwardly, thus unblocking the optical path through the
ampoule. As the float
rotates from position E downwardly (not shown), the slug will again stick to
the ampoule near the S
pole of the horseshoe magnet and will release when the float returns to a
position before or at
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position A. As used herein, a weak magnetic interaction means that for a given
magnet and slug or
moveable structure (or vice versa, where the magnet moves), the magnetic force
exerted between
the slug or device and magnet is insufficient to overcome the gravitational
force acting on the slug,
thereby allowing the slug to be released at some point as the position of the
slug approaches
vertical, as shown in figure 12.
The actual release point of the slug can vary by modifying the strength of the
magnet, the
weight of the slug, or the magnetizability of the slug's material. In use, the
location of the magnets
can vary. For instance, in figure 12, detail A, two magnets M 1 and M2 can be
positioned at or near
each end of the ampoule or chamber (either internal or external to the
chamber) (by using two
different strength magnets, the release point of the slug on an upward
rotation can be different for
the release point on a downward rotation). Other configurations are possible,
for instance using a
single donut style magnet positioned around the middle of the chamber or a bar
magnet positioned
near the middle of the chamber, or using a magnet as the slug and positioning
weakly magnetic
material at each end of the ampoule or chamber.
The use of the magnet and magnetically interactive slug allows the switch to
remain in its
last configuration (e.g. complete optical path or interrupted optical path)
over a selected range. This
allows the float to operate as a "wide angle" float switch. Shown in figure 13
is a typical wide angle
pump switch operation. In figure 13 A, the pump chamber fills with fluid and
the pump remains
"off' until the float reaches position B. At position B, the pump turns on. As
shown in figure
13B, the pump remains "on" as fluid is pumped out until position A is reached,
at which time the
pump turns off.
The switch as described uses optically aligned light guides and a means to
interrupt optical
alignment by interposing an object. Alternatively, the light guides may be
optically aligned by a
light path that bounces off a reflective moveable member, such as a reflective
bar. Sufficient
movement of the slidable object destroys the bounce path, and hence, results
in non-alignment of
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the distal ends of the light guides. In this configuration, the switch
activator (the sliding bar,
cylinder, ball, etc) is the means to interrupt optical alignment upon suitable
movement. For
instance, the fibers may be parallel, but offset, positioned on the exterior
of the ampoule, as shown
in figure 11. Positioned in the ampoule is a slidable reflective bar (the
ampoule may have a track
for the bar to slide in, or be suitably shaped (e.g. rectangular prism), to
maintain the orientation of
the bar in the ampoule, however, if the receptor is sensitive, a reflective
cylinder or ball may be
used in a cylindrical ampoule, as some scattered light will be detected by a
sensitive detector, such
as the D92 detector). When the bar is interposed between the distal ends
(position A), the reflective
surface creates optical alignment. When the bar is not interposed, optical
alignment is destroyed
(position B).
Instead of moving an object between the optical fiber distal ends, to modify
the optical
alignment, one end (or both ends) of the fibers could be movable between a
first position of optical
alignment of the distal ends and a second position of optical non- alignment,
such as by moving one
end (e.g. having that end mounted on a sliding bar) to move sufficiently so
that the optical
alignment is interrupted, or having both ends move to either align the distal
ends or interrupt the
optical alignment , such as by moving both fibers in unison until a fixed
object is interposed
between the two fiber ends. These arrangements are not preferred, as movement
of the fibers places
stress on the fibers and repeated movement may result in fracturing the
fibers.
A floating housing 1 can be constructed in any number of ways. One such way
would be to
use foam in a two part mold, encasing the separator assembly within (or by
welding two half floats
together). The housing can also could be constructed of two halves fused
together by glue or heat,
with the separator assembly located within the housing. Any object that floats
could be drilled or
carved out and the separator assembly (if employed) could be inserted inside
and then sealed using
any number of means, including plastic injection molding methods
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The receiver or detector 5 can be located external to the hazardous area in a
control panel or
other device and is not required to be located with the light source. Any
number of commercially
available devices that are sensitive to light energy, such as devices
containing a photo eye or photo
transistor, are suitable as a light detector or receiver. The presence or
absence of light, through the
switch, detected at the receiver, is indicative of the position of the
floating housing in the
environment. The status of the switch can be utilized as a signal means to
perform a specific task
such as starting or stopping a pump.
The invention is not limited to a float embodiment. For instance, the switch
components
(housing, light guides, means to interrupt optical alignment and light source
and light detector) can
be used as any type of switch. For instance, shown in figure 5 is a device
switch. The switch has a
housing 200 (here a plate with two upstanding flanges) into which a first 201
and second 202 light
guide are mounted and separated by a gap, but optically aligned. One of the
light guides is
connected to a light source, another to a light detector. Slidably mounted to
the plate is slide 210.
Slide is movable between positions (e.g. position A, blocking transmission,
and position B,
allowing transmission) between the light guides 202 and 201. Figure 5 depicts
a "slide" switch
type, but any type switch device can employ the optical components, including
a toggle type
switch, push button type switch, rotary type switch, rocker type switch, key
activated switch, limit
switch, proximity switch or other type of manually or mechanically operated
switch where the
operation of the switch occults or blocks the light path or otherwise
interrupts optical alignment (or
as later described, modifies the transmitted characteristics of the source
light) between the two light
guides, through manual or mechanical activation (e.g. relay operation of the
switch activator) as
opposed to gravity operation by a float switch.
As a general purpose switch, the optical switch may incorporate a means to
modify the
received characteristics of a light beam, allowing the switch have multiple
"statuses," instead of
simply on or off. Such a switch could be used to control devices with
selectable settings (such as
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selecting the speed of a motor) or if the allowed variation is an analog
variation, the switch can
operate as a "dimmer switch" or continuously variable switch. For instance,
the slidable bar could
be a stepped density filter or a stepped transmission filter, such as
available from Edmund Optics
(www.edmundoptics.com) as model numbers 147-524, 147-525, 147-526 or 147-527.
These
models have eleven regions of different transmission characteristics (e.g
different density, thus
modifying the transmitted lights amplitude characteristics). In this
embodiment, the slidable bar
does not totally block the light path at all positions on the bar, but
generally allows partial
transmission through the bar. Hence, the relative position of the bar with
respect to the cable ends
within the float interior or separator assembly can be determined based upon a
the amount of light
received by the light receptor after passage through the bar. Hence, the
amount of light transmitted
through the bar can be used to allow the device to function as a multiple
position switch, to control
devices having selectable positions.
Instead of modifying the degree of light transmission though the bar, other
parameters could
be used to modify the received characteristics of the source light, such as
polarization or frequency.
For instance, if the bar had four regions of different color, the light
transmitted through the bar will
vary in color or frequency based upon the position of the bar with respect to
the source of light. The
relative position of the bar (as detected by reception of a different color or
frequency of light) can
then be used to perform different functions (e.g, start pump 1, start pump 2,
etc). A continuous or
analog gradation in transmission characteristics could also be used instead of
a stepped bar as a
"dimmer" type of switch to control a variable speed motor. Another type of
dimmer or
continuously variable type switch would two polarization filters, one fixed
and one rotatable, with
the distal ends of the fibers aligned through the polarized lenses. By
rotation of one of the
polarization filters (such as by mechanical or manual activation of the switch
activator), the
amplitude of the transmitted light can be varied in a continuous manner. All
of the above are
considered a means to modify the received characteristics of a light beam.
Indeed. The "means to
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interrupt optical alignment" is also a "means to modify the received
characteristics of a light beam"
as the modification is the non-transmission or non-reception of the light beam
by operation of non-
alignment of the distal ends or by interposing a light opaque object between
the distal ends.
Further, the optical switch can accommodate "three way switches" or multiple
pole,
multiple throw type switches. Additional light fibers or light
sources/receivers may be needed for a
particular application. For instance, for a three way switch, each switch has
three distal fiber ends
(here denoted the source, the common, and the traveler). The "traveler"
optical fiber is to run
between the two switches. Each three way switch contains a mirror or other
reflective surface that
provides optical alignment within the switch between the "source wire" and
either the traveler or
the common within each switch, and interrupts optical alignment with the non-
selected path. That
is, the light beam in a three way switch has two possible routes through the
switch, and the route
through the switch selects the path (by movement of the switch activator).
Again, instead of moving
a reflective surface, the optical fiber could be moved by operation of the
switch.
Generally, for a switch embodiments described, the housing (or at least that
portion
containing the distal ends of the light guides and the gap therebetween (such
as the separator
assembly) will be substantially lightproof, and it is preferred that the
housing itself be substantially
lightproof with the switch activator or actuator (the slide, pushbutton,
toggle, etc), for manual
operation, extending through the housing. The distal ends of the light guides
are located in the
interior of the housing in order to keep the optical switch components
isolated from external light
sources (such as ambient light) which might provide a false reading. If
ambient light is not an issue
(e.g., the light source is a non-common frequency, or bursts of light are
used, or highly directional
fibers are used, etc), the housing does not need to be light proof, and simply
is used to define a gap
between the distal ends of the light guides, such as shown in figure 5.
The switch as described could be positioned within the hazardous environment,
such
as adjacent to (or attached to) an explosive proof housing containing a device
(e.g. a motor or
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pump within the interior of the explosive proof housing). The light source and
light detector
utilized by the switch can be located in a remote switch panel or other remote
device, and located
separately if desired. Alternatively, the source and detector can be located
in the interior of the
explosive proof housing, and the light guides from the switch (within the
hazardous environment)
routed into the interior of the explosive proof housing through an explosive
proof connector (the
interior of an explosive proof container is considered to be remote from the
hazardous
environment). See figure 9, showing an optical toggle light switch 1000
operating a light fixture
1002 located in a hazardous environment, and is wired 1004, through an
explosion proof conduit or
using explosion proof wire), to a panel 1003 located outside the hazardous
environment (the light
may be wired to an explosion proof panel in the hazardous environment). The
light fixture 1002 is
in an explosion proof housing, but the optical switch 1000 is not. The optical
switch light guides
1005 proximal ends are located in the panel 1003 and connected to the light
source and light
detector. The status of the switch is detected in the panel 1003, such as
through use of a circuit
(one suitable circuit is shown in figure 10), which circuit will power or de-
power the light fixture
based upon the detected switch status. In this fashion, an operator located in
the hazardous
environment can deactivate or activate the electrical device at or near the
device itself, instead of at
a remote switch panel or activation using an expensive explosion proof housing
for the switch.
Figure 9 also shows an optical limit switch 1010. This optical switch can be
connected to panel
1003 using light guides 1005 (not shown). This limit switch is activated by a
level arm 1100 of a
valve or other device that activates or deactivates the optical limit switch
1010.
The circuit in figure 10 shows the light source (E97) and light detector (D92)
with the
corresponding optical fibers connected to a float embodiment of the optical
switch. The circuit is
designed to have the relay de-energized when the return optical fiber is dark,
that is, when the
detector fails to detect light on the return optical fiber. If light is
detected, the relay is energized,
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closing switch 90, which is used to connect power to the light fixture located
in the hazardous
region.
In this fashion, the powered components of the optical switch are electrically
isolated from
the hazardous environment, and the only energy present within the hazardous
environment is a light
beam. In a hazardous environment, such an optical switch presents a safe and
economic alternative
to conventional switches using an electrical contact in the hazardous
environment that present a
potential source of electric spark and ignition within the hazardous
environment.
