Note: Descriptions are shown in the official language in which they were submitted.
CA 02614920 2008-01-25
REMOTE OPTICAL CONTROL OF ELECTRICAL CIRCUITS
BACKGROUND
[0001] The present invention relates to safe remote control of electrical
circuits
such as circuits driving electric motors, electric heaters and the like.
[0002] It is known to use an electrical motor starter to remotely start and
stop a
primary motor. Typically, remote actuation is achieved through an electrical
circuit
having a STOP / START actuator at the remote site and an electrical circuit
connecting the STOP / START actuator to a motor energizing circuit at the
primary
motor site. To enable rapid control of the primary motor, the STOP / START
actuator may consist of one or more pushbuttons. When installed in a hazardous
area where there is a risk of explosive gases, the remote START / STOP
actuator
is typically enclosed in a sealed explosion-proof enclosure so as to reduce
the
chance of an explosion occurring if any spark results from arcing between
switch
contacts.
[0003] While this arrangement may be satisfactory in some environments,
further improvements are possible to improve safety and cost.
SUMMARY
[0004] In accordance with the present invention, there is provided a control
system for electrical apparatus, comprising: an electro-optic interface having
a first
optical transmitter for producing an optical output signal in response to an
electrical
input signal, an optical receiver for producing an output electric signal in
response
to an optical input signal, and a second optical transmitter for producing an
optical
output signal in the visible range of light in response to an electric input
signal; a
first optical path extending from said second optical transmitter to said
optical
receiver through a control module and a second optical path extending from
said
second optical transmitter to said control module, said control module
comprising a
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CA 02614920 2008-01-25
mechanical switch arranged for selectively interrupting said first optical
path and a
light magnifying lens terminating said second optical path.
[0005] In accordance with another aspect of the present invention, there is
provided a method of controlling an electrical system with an optical system,
comprising: at a first station connected to said electrical system,
continuously
supplying light to a control station on a first optical path and supplying
light to said
control station on a second optical path only where a given component of said
electrical system is activated.
[0006] Other features and advantages will be apparent from following
description in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] In the figures which illustrate an exemplary embodiment of this
invention,
[0008] FIG. 1 is a schematic diagram of an optically controlled remote motor
starter arrangement in accordance with an embodiment of the present invention,
[0009] FIG. 2 is a front view of a pushbutton control station in accordance
with
an embodiment of the present invention,
[0010] FIG. 3 is a vertical sectional view along the lines III-I11 of FIG. 2,
[0011] FIG. 4 is a sectional view through a STOP pushbutton made in
accordance with an embodiment of the present invention,
[0012] FIGS. 5A and 5B are diagrams showing, respectively, an optical
switching area of the STOP pushbutton when not actuated and the STOP
pushbutton when actuated,
[0013] FIGS. 6A is a side view of a plunger of the STOP pushbutton,
[0014] FIG. 6B is a side view of a plunger of a START pushbutton in accordance
with an embodiment of the present invention, and
[0015] FIG. 7 is a sectional view through a fiber optic indicator light made
in
accordance with an embodiment of the present invention.
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DETAILED DESCRIPTION
[0016] FIG. 1 is a schematic diagram of an optically controlled remote motor
starter arrangement in accordance with an embodiment of the present invention.
The arrangement includes a motor and starter circuit 10, an electro-optic
interface
module 12 and a pushbutton control station 14. Typically, the interface module
12
is in a protected area whereas the pushbutton control station 14 may be
positioned
in a hazardous area.
[0017] The motor and starter circuit 10 has a motor 16 connected to the mains
18 through breaker 20, starter contacts 22, and overload relay 24. Taps 26
from
the mains supply the primary side of a step-down control power transformer 28.
The secondary side of the transformer provides a first current loop through a
normally closed overload contact 29, starter contactor 30, local start button
32, local
stop button 34 and an interface contact 36 of the interface module 12. The
secondary side of the transformer 28 also provides a second current loop
through
overload contact 29, starter contactor 30, a parallel path through either seal-
in
starter contact 38 or interface contact 40, and interface contact 36. The
motor and
starter circuit 10 also has a starter contact 42 that is connected to
interface module
12.
[0018] The interface module 12 has a step-down transformer 44 with a primary
side connected to the secondary side of transformer 28 of motor and starter
circuit
10. The secondary side of transformer 44 powers an AC/DC converter 46. The DC
output of converter 46 is incorporated in a first current loop including
starter contact
42 of motor and starter circuit 10 and a current limiting resistor 48 and a
high
intensity optical transmitter 50 emitting at a visible wavelength (e.g. 650
nm). The
DC output is also incorporated in a second current loop which loop has a
parallel
path through a first current limiting resistor 52a and a first infrared (e.g.,
850 nm)
transmitter 58a and through a second current limiting resistor 52b and a
second
infrared (e.g., 850 nm) transmitter 58b. Transmitters 58a, 58b may be, for
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example, OPTEK type OPF1414 transmitters. The positive side of the DC output
is
also connected to the serial connection of a first DC relay 60a, (noise
cancelling)
Schmitt trigger 62a, and receiver 64a and a second DC relay 60b, (noise
cancelling) Schmitt trigger 62b, and receiver 64b. Receivers 64a, 64b may be,
for
example, OPTEK type OPF2416 receivers. An optical cable 66 connects the
interface module 12 to pushbutton control station 14. DC relay 60a controls
interface module contact 40 and DC relay 60b controls interface module contact
36.
[0019] The pushbutton control station 14 has an indicator light 68 connected
to
high intensity transmitter 50 of interface module 12 through optical fibre 66-
1 of
cable 66. Station 14 also has a STOP pushbutton 70 connected in an optical
loop
between transmitter 58a and receiver 64a of the interface module 12 by optical
fibres 66-2, 66-3 of cable 66 and a START pushbutton 72 connected in an
optical
loop between transmitter 58b and receiver 64b of the interface module 12 by
further optical fibres 66-4, 66-5 of cable 66.
[0020] Station 14 is non-active, that is, it has no components which use
electrical power.
[0021] The pushbutton control station 14, shown in front elevation in FIG. 2
and
in sectional view in FIG. 3, is typically installed in the field and has a
weatherproof
enclosure 74 rated at a National Electrical Manufacturers Association 3R, 4 or
4X
rating. The enclosure 74 houses optical STOP and START pushbuttons 70, 72 and
fiber optic indicator light 68, all of which are designed to limit the ingress
of dust and
other substances to enable deployment in harsh industrial environments. The
enclosure has a front panel 82 at which the START and STOP pushbuttons 70, 72
and the indicator light 68 are accessible. Optical cable 66 enters the bottom
of the
enclosure 74 via a cable connector 88. The enclosure 74 is dimensioned so as
to
accommodate optical fibers 66-1 to 66-5 of cable 66 without their being
subjected
to such a tight bending radius as to cause light loss or damage. The fiber
optic
cable 66 is a standard cable adapted to be deployed in outdoor installations
on
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cable trays, duct banks or to be directly buried (not shown). In one
embodiment of
the invention, the cable has six multimode, step-index optical fibers having a
125
micron diameter cladding and a 62.5 diameter micron core, the fibers being
contained within interlocked steel armoured, tight buffered, single jacket
Canadian
Standards Association rated FT-4 cable.
[0022] Referring to the sectional view of FIG. 4, the optical STOP pushbutton
70
has a cap 90 and a plunger 92 and is mounted for reciprocal motion within a
housing 94. The plunger 92 is shown in elevation view in FIG. 6A. Housing 94
is
mounted to an optical connector shown generally at 96. An 0-ring seal 98 is
held
in place around the plunger 92 by a press fit installed washer 100. A spring
pin
102, sealed at its ends with silicone plugs 104 to prevent ingress of dust, is
mounted in a bore 105 through the housing 94. The spring pin 102 prevents the
plunger 92 from rotating and limits the plunger's travel. A compression spring
106
mounted around a medial portion of the plunger 92 is operable to bias the
plunger
back to a home position after it is depressed. The plunger terminates in a
solid
blade 93. The surfaces of the blade 93 are rough and black to minimize light
back
reflection into the fiber. The optical connector 96 is of a known ST connector
design. Each of the fibers 66-2 and 66-3 connected to the STOP push button has
an end portion mounted within a ferrule 111. Split sleeves 114 align each of
the
ferrules 111 with a respective ball lens 116. A centre split sleeve 118 aligns
the two
split sleeves 114. At each side of the central connector section, 0-rings seal
around the respective fibers 66-2, 66-3 to prevent ingress of dust and other
contaminants into the central connector section. Although FIG. 4 shows the
STOP
button in a vertical orientation, it can be mounted in any convenient
orientation.
[0023] With this arrangement, as illustrated in FIG. 5A, if plunger 92 is in
its rest
position (i.e., it has not been depressed by an operator), blade 93 is not
interposed
in the light path between ball lenses 116. Consequently, light emitted from
the end
of the transmitter fiber 66-2 is collimated at the ball lens 116 on one side
of the ST
connector and is then refocused by an identical ball lens 116 into the
receiver fiber
CA 02614920 2008-01-25
66-3 at the other side of the ST connector. On the other hand, if plunger is
pressed
by an operator, as seen in FIG. 5B, blade 93 blocks the light path between the
ball
lenses.
[0024] The optical START button is identical to the just described STOP button
with one exception: the blade of the plunger of the START button is longer
than the
blade of the STOP button and it has an aperture. The plunger of the START
button
is depicted in FIG. 6B. Turing to FIG. 6B, it will be seen that the plunger
112 of the
START button has a blade 113 with an aperture 115. By comparing FIG. 6A with
FIG. 6B, it will be seen that blade 113 of the START button is longer than
blade 93
of the STOP button. In consequence of the described configuration of the START
pushbutton, the START button is, similarly to the STOP button, normally biased
by
a corresponding compression spring (not shown) to a retracted position. In its
retracted position, the longer blade of the START button bars the passage of
light
from the transmitter fiber to the receiver fiber. However, by pressing the
START
pushbutton, the aperture 115 becomes aligned with the light beam emitted from
the
transmitter fiber so that the light passes from the transmitter fiber into the
receiver
fiber.
[0025] Turning to FIG. 7, the fiber optic indicator light 68 has a body 120. A
locknut 122 fixes the body 120 in the front panel 82 of the enclosure 74 (FIG.
3)
with a sealing gasket 124 preventing ingress of dust and other contaminants. A
standard ST female fiber optic connector 126 is mounted in sealing engagement
with body 120. Optical fiber 66-1 is clamped in place by the elements of the
ST
male connector including a ferrule 132 surrounding an end portion of the fiber
66-1.
The end of the fiber 66-1 faces one end of a hollow cylindrical chamber 134
axially
aligned with the fiber and formed in body 120. The opposite end of chamber 134
is
open and receives a plano-convex lens 136. The lens 136 is dimensioned and
positioned so that its focal point is located on the end face of the optical
fiber 66-1.
A diffuser glass 140 is mounted to the body 120 over lens 136 and acts to
evenly
spread light emitted from the body 120 of indicator light 68 and to protect
the lens
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136. The fiber optic indicator light 68 acts to magnify light produced by the
high
intensity fiber optic transmitter 50 (FIG. 1) of interface module 12 which is
transmitted through optical fiber 66-1 and emit this light through diffuser
glass 140.
[0026] Returning to FIG. 1, if motor 16 is OFF and no button has been pressed,
starter contacts 22, 38 and 42 are open (as is interface contact 40) and no
current
flows in the motor and starter circuit 10. However, DC current does flow in
the
interface module 12 through the current loop including parallel mounted
transmitters 58a, 58b. This powers these optical transmitters such that light
is
directed along fibres 66-2 and 66-4. The long blade of the START pushbutton 72
blocks incoming light from fibre 66-4 so that no light reaches receiver 64b.
In
consequence relay 60b is not energized and contact 40 therefore remains open.
In contrast, the shorter blade of the STOP pushbutton 70 allows light to pass
to
fibre 66-3. This light therefore passes to receiver 64a which outputs an
electrical
signal to relay 60a thereby energizing the relay. In consequence, the relay
60a
keeps interface contact 36 closed. Now, if a user presses the START optical
pushbutton 72, light transmitted by the optical transmitter 58b through fiber
66-4
which was hitherto blocked by the blade 113 (FIG. 6B) of plunger 112 (FIG.
6B), is
now able to pass through the plunger aperture 115 (FIG. 6B) to the receiver
fiber
66-5. The optical receiver 64b receives the light signal and energizes relay
60b
through Schmitt trigger 62b. This causes the relay 60b to close its normally-
open
contact 40 which completes a circuit path allowing current to flow in the loop
containing the overload contact 29, starter contactor 30, now closed contact
40,
and closed contact 36. With the starter contactor 30 energised, it closes the
starter
contacts 22, 42, and 38. With starter contacts 22 closed, the primary motor 16
is
energized. Further, the closing of starter contact 42 completes the circuit
including
transmitter 50. Transmitter 50, once energized, feeds visible light to optical
fibre
66-1. Referencing FIG. 7, this light passes to indicator light 68, emerging
from the
end of fibre 66-1 at the focus of lens 136. The light is therefore magnified
by the
lens and strikes the diffuser plate 140 so that diffuse light emerges from the
open
end of the body 120 of indicator light 68 indicating the RUN status of the
primary
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motor 16. Starter contact 38, when closed, by-passes contact 40. Therefore,
the
starter contact 38 acts as a seal-in contact, maintaining a complete circuit
path
through starter contactor 30 after the START pushbutton is released to cut
power to
relay 60b and open contact 40.
[00271 With motor 16 ON, pressing the STOP 'optical pushbutton 70 inserts
blade 93 (FIG. 4) between fibres 66-2 and 66-3 thereby interrupting light
transmitted to optical receiver 64b. The receiver therefore ceases energizing
relay
60a so that contact 36 opens. This interrupts the circuit path through starter
contactor 30. Consequently starter contacts 22, 42, and 38 open which shuts
down primary motor 16. When the STOP button is released and interface contact
36 again closes, no current will flow in the motor and starter circuit 10
since the
seal-in contact 38 is now open. Therefore, the motor and starter circuit 10
remains
de-energized waiting for a new START command. Because the STOP relay 60a in
normal state is energized, a fail-safe operation of the STOP circuit is
ensured: if the
electro-optic interface module loses power or becomes defective, or the fiber
optic
cable is accidentally cut, the motor 16 stops.
[0028] It will be apparent that the circuit path including starter contactor
30 may
also be completed by depressing local start button 32 in order to energise the
primary motor 16. And the circuit path including contactor 30 may be
interrupted by
depressing local stop button 34. This provides an alternate method of starting
and
stopping the primary motor. The local start and stop buttons are optional and
are
only advisable where they can be positioned in a non-hazardous area.
[0029] If overload relay 24 senses an overload current, it will open overload
contact 29 which will result in de-energising the starter contactor 30 and,
therefore,
the primary motor 16.
[0030] The pushbutton control station 14 can be installed in hazardous areas
without the need to be rated as explosion proof because there is no risk of
the
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optical STOP and START pushbuttons 70, 72 or indicator light 68 producing
sparks
when actuated. Both the STOP and START pushbuttons 70, 72 and the fiber optic
indicator light 68 have switch and fiber mounting elements which are metallic.
These may be grounded through dedicated grounding conductors (not shown) to
limit any build up of static electricity and so prevent static discharges from
occurring.
[0031] As will be appreciated by those skilled in the art, the control circuit
could
be arranged so that the short bladed switch of FIG. 6A acts as a START switch
rather than as a STOP switch and the long bladed switch of FIG. 6B acts as a
STOP switch. This alternate arrangement might be achieved, for example, by
interposing an inverter between the output of each of relays 60a, 60b and
their
respective contacts 40, 36. However, with this arrangement fail safe operation
is
not achieved.
[0032] Although aspects of the invention have been described in the context of
a
control circuit for starting and stopping a motor, it will be clear to one of
ordinary
skill in the art that the arrangement described can be adapted for electrical
heater
control, motorized valve control, lighting control and similar electrical
circuits.
[0033] While specific arrangements of components have been described for
convenience or expense, it is clear that different forms of fiber, such as
plastic fiber,
may be used. Altematively, for long fiber spans between a controlled
electrical
circuit and a controlling optical circuit, light attenuation within the
transmitter and
receiver fibers can be reduced by using longer wavelength infra-red optical
transmitters and receivers operating at or near a 1550 nanometer wavelength.
Although not shown, the electro-optic interface module 12 can be formed as a
sealed unit with plug and socket connector arrangements on the optical and
electrical sides.
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[0034] It will be clear to one of ordinary skill in the art that other
variations are
also possible without departing from the spirit of the invention. For example,
the
invention has been described in terms of an optical circuit because a
controlling
optical circuit is convenient and inexpensive. However, the risk of electric
arcing
can alternatively be reduced by using a hydraulic or pneumatic circuit as the
controlling circuit. In such embodiments, actuation of operator controlled
remote,
non-electrical STOP and START pushbuttons functions to cause a pressure drop
or
increase in the hydraulic or pneumatic circuit. Pressure changes may be
detected
by pressure sensors occupying positions corresponding to the optical receivers
of
the optical embodiment described above. Valves connected to an hydraulic or
pneumatic pump occupy positions corresponding to the light emitters of the
optical
embodiment described above. In a manner corresponding to that described above,
the hydraulic or pneumatic sensors and valves are connected through a
hydraulic-
electrical or pneumatic-electrical interface to allow a similar remote STOP /
START
actuation of the controlled electrical circuit.
[0035] It will be apparent to those skilled in the art that the disclosed
invention
may be modified in numerous ways and may assume many embodiments other
than the forms specifically set out and described above. Accordingly, it is
intended
by the appended claims to cover all modifications of the invention which fall
within
the true spirit and scope of the invention.
