Abstract:
An optical controlling circuit and an electrical controlled circuit such as a motor control circuit are interconnected by an electro-optic interface. A passive optical switch located in the optical circuit at a position remote from the electrical circuit is physically actuated to generate a change in optical transmission state of the optical circuit. At the electro-optic interface, the change in optical transmission state of the optical circuit is detected and triggers a change in the electrical transmission state of the electric circuit. Embodied as STOP and START pushbuttons, a pair of such passive optical switches at a position remote from the electric circuit reduces the risk that actuating motor control circuits and the like will cause arcing and, in hazardous environments, explosion.

Description:
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 starter motor 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 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-III 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]      FIG. 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. 
       
    
    
     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  52   a  and a first infrared (e.g., 850 nm) transmitter  58   a  and through a second current limiting resistor  52   b  and a second infrared (e.g., 850 nm) transmitter  58   b . Transmitters  58   a ,  58   b  may be, for example, OPTEK type OPF1414 transmitters. The positive side of the DC output is also connected to the serial connection of a first DC relay  60   a , (noise cancelling) Schmitt trigger  62   a , and receiver  64   a  and a second DC relay  60   b , (noise cancelling) Schmitt trigger  62   b , and receiver  64   b . Receivers  64   a ,  64   b  may be, for example, OPTEK type OPF2416 receivers. An optical cable  66  connects the interface module  12  to pushbutton control station  14 . DC relay  60   a  controls interface module contact  40  and DC relay  60   b  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  58   a  and receiver  64   a  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  58   b  and receiver  64   b  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 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 O-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&#39;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, O-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  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  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  58   a ,  58   b . 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  64   b . In consequence relay  60   b  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  64   a  which outputs an electrical signal to relay  60   a  thereby energizing the relay. In consequence, the relay  60   a  keeps interface contact  36  closed. Now, if a user presses the START optical pushbutton  72 , light transmitted by the optical transmitter  58   b  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  64   b  receives the light signal and energizes relay  60   b  through Schmitt trigger  62   b . This causes the relay  60   b  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 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  60   b  and open contact  40 . 
         [0027]    With motor  160 N, 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  64   b . The receiver therefore ceases energizing relay  60   a  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  60   a  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 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  60   a ,  60   b  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. Alternatively, 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. 
         [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.