Patent Publication Number: US-2016231714-A1

Title: System for monitoring and / or controlling equipment in a hazardous area

Description:
This application is a continuation of application Ser. No. 14/186,165, filed Feb. 21, 2014, which itself is a continuation of application Ser. No. 12/938,057, filed Nov. 2, 2010, which claims the benefit of U.S. Provisional Application No. 61/257,247, filed Nov. 2, 2009, and the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD 
     This specification relates to a system for monitoring and/or controlling equipment that is operating in a hazardous environment. 
     INTRODUCTION 
     When operating equipment in a hazardous area it can be desirable to monitor and/or control the equipment from a remote location, outside the hazardous area. Examples of such equipment can include automotive lifts operating in automotive garages and/or other areas that have been designated as hazardous areas by the National Electrical Code Classification. 
     One method of remotely monitoring an automotive lift operating in a hazardous location is to transmit signals from the automotive lift to a device, for example an operator&#39;s console, in a remote location outside the hazardous area. Traditional monitoring and/or control systems use intrinsically-safe electric sensors or other signal generators that are connected by intrinsically-safe cables to intrinsically-safe signal barriers functioning at the boundary or interface between the hazardous and non-hazardous areas. Systems having electrical components within the hazardous area that are not specialized, intrinsically-safe components may not be certified by the National Electrical Code Classification for use in hazardous areas. 
     Specialized, intrinsically-safe electrical components may be expensive (when compared to analogous, non-intrinsically-safe components) and can require specialized installation and maintenance procedures. The failure of an intrinsically-safe electronic component within the hazardous area may present a safety hazard. 
     SUMMARY 
     This summary is intended to introduce the reader to the more detailed description that follows and not to limit or define any claimed or as yet unclaimed invention. One or more inventions may reside in any combination or sub-combination of the elements or process steps disclosed in any part of this document including its claims and figures. 
     In particular, applicants&#39; teachings provide a system for monitoring or controlling equipment in a hazardous area. The system comprising at least one sensor disposed within a hazardous area, each sensor being non-electrical and being adapted to interact with the equipment and generate at least a first non-electric sensor output and a second non-electric second sensor output, the first sensor output being indicative of a first equipment state and the second sensor output being indicative of a second equipment state, a non-electrical communication link extending from the at least one sensor across a boundary between the hazardous area and a non-hazardous area, the non-electric communication link to carry the sensor outputs from the at least one sensor, and at least one controller disposed in the non-hazardous area, the at least one controller coupled to the communication link and operable to generate a controller output signal based on the sensor outputs. 
     Moreover, the system can further include at least one converter communicably linking the at least one sensor and the controller, the at least one converter connected to the communication link to receive the sensor outputs and convert it to a form useable by the at least one controller. 
     The at least one converter can be part of the at least one controller and converts the sensor outputs within the controller. Further, the at least one converter can be disposed in the non-hazardous area between the at least one sensor and the at least one controller. 
     The at least one converter can convert the non-electric sensor outputs to electrical signals. Other types of signals are contemplated, however, and the converter could also convert the non-electric sensor outputs to other suitable signals, including, for example, but not limited to, wireless communications. 
     The controller can be adapted to control the state of equipment based on the converter output signal. 
     The sensor outputs can be optical signals. Further, the sensor outputs can be output fluid flows. Applicants&#39; teachings are not to be limited to just these two examples, however. 
     The system can further comprise a fluid circuit configured to receive a working fluid, each sensor comprising at least one regulator in the circuit, the at least one regulator disposed within the hazardous area and being operatively connected to the equipment, each regulator configured to receive an incoming fluid flow, the first and second sensor outputs comprising, respectively, the first and second output fluid flows downstream of the at least one regulator. Moreover, each converter comprises a pressure switch in communication with the fluid circuit downstream from respective ones of the at least one regulators. Further each regulator comprises a valve, each valve configurable between open and closed configurations, the first output fluid flow being generated when the valve is in the open configuration, the second output fluid flow being generated when the valve is in the closed configuration. 
     Further, the system can comprise at least one trigger member mounted on the equipment, each trigger member corresponding to and adapted to engage at least one valve, each trigger member and corresponding valve connected to the equipment so that changing the equipment from the first equipment state to the second equipment state causes the trigger member to change the configuration of at least one corresponding valve. Each trigger member can comprise a cam and each valve comprises a complimentary cam follower configured to engage the at least one cam. 
     Further, applicants&#39; teachings provide for a lift system for operation in a hazardous area. The lift system comprises a lift mechanism, the lift mechanism being movable between first and second positions, at least one sensor connected to the lift, the at least one sensor being non-electric and being configured to generate at least a first non-electric sensor output and second non-electric sensor output, the first sensor output being indicative of the lift mechanism being in the first position and the second sensor output being indicative of the lift mechanism being in the second position, and a controller disposed outside the hazardous area, the controller in communication with the at least one sensor, and the controller being adapted to control the movement of the equipment based on the sensor outputs. 
     The lift system can further include at least one converter communicably linking the at least one sensor and the controller, the at least one converter to receive the sensor outputs and convert it to a form useable by the at least one controller. The at least one converter can be part of the at least one controller and converts the sensor outputs within the controller. The at least one converter can be disposed in the non-hazardous area between the at least one sensor and the at least one controller. The at least one converter can convert the non-electric sensor outputs to electrical signals. 
     Moreover, the controller is adapted to control the state of equipment based on the converter output signal. The sensor outputs can include optical signals. Further, the sensor outputs can include output fluid flows. 
     The lift system can also include a fluid circuit configured to receive a working fluid, each sensor comprising at least one regulator in the circuit, the at least one regulator disposed within the hazardous area and being operatively connected to the lift, each regulator configured to receive an incoming fluid flow, the first and second sensor outputs comprising, respectively, the first and second output fluid flows downstream of the at least one regulator. Each converter can include a pressure switch in communication with the fluid circuit downstream from respective ones of the at least one regulators. Each regulator can include a valve, each valve configurable between open and closed configurations, the first output fluid flow being generated when the valve is in the open configuration, the second output fluid flow being generated when the valve is in the closed configuration. 
     Moreover, the lift system can further include at least one trigger member mounted on the lift, each trigger member corresponding to and adapted to engage at least one valve, each trigger member and corresponding valve connected to the lift so that changing the lift from the first position to the second position causes the trigger member to change the configuration of at least one corresponding valve. Each trigger member can include a cam and each valve comprises a complimentary cam follower configured to engage the at least one cam. 
     Further, the at least one sensor can include at least a first sensor and a second sensor, the first sensor interacting with the lift so that the first sensor is triggered when the lift mechanism is in the first position, the second sensor interacting with the lift so that the second sensor is triggered when the lift mechanism is in the second position. 
     Moreover, the lift mechanism comprises at least one scissor lift, each scissor lift can include a pivotally connected first and second scissor member, and a respective valve connected to each scissor lift, the valve being mounted on one of the first and second scissor members and the cam mounted on the other of the first and second scissor members. 
     Further, the lift can include first and second scissor lifts, the respective valves on each scissor lift being pneumatically linked to an equalization converter, the equalization converter being adapted to provide an equalization converter output signal to the controller, the controller being adapted to equalize the positions of the first and second scissor lifts in response to the equalization converter output signal. 
     Applicants&#39; teachings also provide for a method of monitoring and/or controlling equipment in a hazardous area. The method comprises the steps of sensing an equipment state using at least one sensor within the hazardous area, the at least one sensor being non-electric and being adapted to interact with the equipment, generating at least a first non-electric sensor output and a second non-electric sensor output, the first sensor output being indicative of a first equipment state and a second sensor output being indicative of a second equipment state, transmitting to a controller the non-electric sensor outputs across a boundary between the hazardous area and a non-hazardous area, generating a controller output signal based on the sensor outputs, and monitoring and/or controlling the equipment based on the controller output signal. 
     The method can also include converting in the non-hazardous area the non-electric sensor outputs to at least one corresponding signal for use by the controller. The method can have the step of converting take place within the controller. Further, the method can have the step of converting take place in the non-hazardous area and separate from the controller. 
     The method can include at least one converter to convert the non-electric sensor outputs to electrical signals. The non-electric sensor outputs can include, for example, optical signals and output fluid flows. 
     Moreover, in accordance with the method the equipment state can be at least first and second positions in a lift mechanism. The lift mechanism can include at least one scissor lift. The lift mechanism can also include first and second scissor lifts, where the controller output signal is used to equalize the positions of the first and second scissor lifts. 
    
    
     
       DRAWINGS 
       For a better understanding of the applicant&#39;s teachings, reference will now be made, by way of example only, to the accompanying drawings which show at least one exemplary embodiment, and in which: 
         FIG. 1  is a block diagram of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 2  is a block diagram of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 3  is a block diagram of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 4  is a block diagram of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 5  is a schematic representation of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 6  is a schematic representation of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 7  is a schematic representation of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 8  is a schematic representation of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 9  is a schematic representation of another example of a system for monitoring and/or controlling equipment in a hazardous area; 
         FIG. 10  is an isometric view of a vehicle lift system incorporating a monitoring and/or control system; 
         FIG. 11  is an isometric view of a single scissor lift from the vehicle lift system of  FIG. 10 ; 
         FIG. 12  is a partial cut-away view of the scissor lift of  FIG. 11 ; 
         FIG. 13  is a schematic representation including a monitoring and/or control system that can be used with the vehicle lift of  FIGS. 10-12 ; 
         FIG. 14  is an isometric view of another example of a vehicle lift incorporating an example of a monitoring and/or control system; and 
         FIG. 15  is an isometric view of another example of a vehicle lift incorporating an example of a monitoring and/or control system. 
     
    
    
     DESCRIPTION OF VARIOUS EMBODIMENTS 
     Various apparatuses or processes will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover processes or apparatuses that are not described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or process described below is not an embodiment of any claimed invention. Any invention disclosed in an apparatus or process described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim or dedicate to the public any such invention by its disclosure in this document. 
     Referring to  FIGS. 1 and 2 , examples of a system  10  for monitoring and/or controlling equipment  12  operating in a hazardous area  14  and conveying the signals to a non-hazardous area  16  are illustrated using a schematic block diagram. In this description, the term hazardous area means any area that is classified as hazardous under the National Electric Code (NEC) classification system, and other analogous areas (for example areas classified as hazardous under similar statues or regulations in various regions and countries around the world). 
     Examples of hazardous areas can include, for example, but not limited to, automotive garage areas. The term non-hazardous, as used herein, means any area that has not been classified as hazardous under the NEC or other analogous regulation/statute. In the illustrated examples, the interface or boundary between the hazardous area  14  and the non-hazardous area  16  is represented as boundary line  18 . In some examples the boundary  18  can be, or coincide with, a physical boundary separating the areas  14 ,  16 , for example a wall or door. In other examples, the boundary  18  can be a non-physical boundary, for example a safe operating distance of at least 10 feet from a fuel source or combustion risk. 
     One example of equipment  12  that can be operated in a hazardous environment and monitored using the system  10  is lifting equipment or lift systems. Examples of lift systems include, for example, materials handling lifts and motor vehicle lift systems operated in automotive garages. If the equipment  12  is a motor vehicle lift system, the hazardous  14  area can be the interior of the garage service bay and the like, and the non-hazardous area  16  can be an office space or operator space that is separated from the service bay. 
     The system  10  includes one or more sensors or transducers  20  located within the hazardous area  14 . The sensors  20  positioned within the hazardous area  14  are non-electrical, which may reduce the risk of electrical arcing, short circuits or other potentially dangerous occurrences within the hazardous area. Providing non-electrical sensors  20  in the hazardous area  14  may also increase the likelihood that the system  10  can be certified or approved under the NEC. The sensors  20  can be any type of suitable, non-electric sensor or transducer, including, for example, regulators, optical sensors, digital and analogue encoders, magnetic sensors and any combination thereof. As used herein, the term regulator is used to generally describe and any type of flow modifying apparatus that can be used in a pneumatic or hydraulic circuit or system, including, for example limit switches, valves, flow control valves, pressure regulating valves, pressure transducers, pneumatic and hydraulic encoders and flow rate monitors. 
     The sensors  20  are connected to the equipment  12  being monitored and/or controlled such that the sensors  20  can obtain desired information about the operation or performance of the equipment  12 . For example, limit switches or proximity sensors can be used to monitor the position or movements of the equipment. In some examples all of the sensors  20  can be the same. In other examples, a variety of different sensor  20  types can be used within a single system  10  (for example the equipment  12  can be monitored using a combination of limit switches and optical sensors). It is understood the nature of the connection between the sensors  20  and the equipment  12  can be selected based on the particular configuration of the equipment  12  being monitored and/or controlled and the sensors  20  used. In some examples the equipment  12  includes one or more trigger members that are adapted to engage the sensors  20  used in the system  10 . The trigger member can be any member that is suitable for engaging or triggering the particular sensor  20  selected. Examples of trigger members include, cams (described below with reference to  FIGS. 6-9 ), magnets, equipment output shafts, structural portions of the equipment (for example a scissor member  84 ,  86  described below, or other portion of a lift system), reflective elements (when used in optical sensing systems) and the like. 
     The system  10  can also include one or more converters  22  located in the non-hazardous area  16  (i.e., anywhere outside the hazardous area  14 ). Each converter  22  is connected to one or more sensor  20  using a non-electrical communication link  24 . The communication link  24  can be any type of connection that is suitable based on the nature of the sensor  20  and converter  22  selected in a particular system. For example, if the sensors  20  are pneumatic limit switches, the communication link  24  can be a pneumatic hose, pipe or other fluid conduit. In pneumatic or hydraulic systems the communication link  24  can comprise a fluid circuit configured to receive and circulate the system working fluid (such as, for example, air, oil, non-air gases and water). Alternatively, if the sensors  20  are optical sensors, the communication link  24  can be optical, for example, fiber optic strands. 
     In use, each sensor  20  can generate or produce at least first and second sensor outputs that are indicative of at least first and second equipment  12  operating conditions. In a pneumatic system, the first sensor output can be a first flow condition, such as a continuous air flow or an “on” condition and the second sensor output can be a second flow condition, such as the absence of airflow or an “off” condition. Such outputs can be described as digital outputs, having discrete “on” and “off” conditions. In other examples, the sensor  20  can be capable of generating more than two discrete sensor outputs. For example, a pneumatic system can include a variable valve or regulator that is operable to provide a plurality of flow rates. In such a system, the first sensor output or first flow condition can be a first flow rate, and the second sensor output or second flow condition can be a second flow rate. Such a system can also be operable to provide a third sensor output or third flow condition that is a third flow rate (different than both the first and second flow rates). A sensor  20  capable of providing a plurality of sensor outputs can be described as an analogue sensor (i.e., a device having an output that is proportional to its input). Optionally, the system  10  can include any desired combination of digital and analogue sensors. 
     Each converter  22  is adapted to receive the sensor outputs from at least one sensor  20  in the system  10  and to convert the sensor output into a converter output signal. Optionally, the converter  22  can include electrical components and the converter output signal can be an electrical signal. In other examples, the converter output signal can be non-electrical, such as a pneumatic air stream used to operate a non-electrical controller, such as, for example, a pneumatic logic controller. For example, if the sensors  20  are pneumatic limit switches and the communication links  24  are pneumatic fluid conduits then the converters  22  can be switch valves that are operable to convert pneumatic signals into electrical output signals. In other examples, the converters  22  can be any suitable apparatus that can convert the non-electrical sensor output signals into the desired converter output signal format. Typically, this would be an electrical signal, however, other types of signals are not to be excluded. For example, but not limited to, the converter could transmit its output signal wirelessly. 
     Optionally, as illustrated in  FIG. 1 , each converter  22  can be communicably linked to a single corresponding sensor  20 . In such examples the converter output signal of each converter  22  can be based on the sensor output of a single sensor  20 . In other examples, as illustrated in  FIG. 2 , a converter  22  can be adapted to be communicably linked to two (or more) sensors  20 . In such examples, the converter output signal of a converter  22  connected to two or more sensors  20  can be based on the sensor output of either sensor  20 , or any suitable combination of the sensor outputs. 
     The converters  22  can be communicably connected to any suitable equipment in the non-hazardous area  16 , such as controller  26 , using second communication links  28 . The second communication links  28  can be any suitable type of connecting member capable of transmitting the converter outlet signals. Because the second communication links  28  are located in the non-hazardous area  16  they can be electrical wires or cables. However, second communication links need not be physical links, but could also be a form of wireless communication to the controller. 
     The optional controller  26  can be any suitable type of controller, including, for example, but not limited to, a computer and a programmable logic controllers or pneumatic logic controller (PLC), and can include any combination of suitable and appropriate components for receiving and processing the converter output signal, including, for example a microprocessor, a memory storing code executable by the processor, user interface controls and display apparatus. In some examples the controller  26  can be adapted to provide a plurality of controller outputs  30  which can be used, for example, to send controller output signals that can be used for a variety of purposes, including, for example, to control the equipment  12 , provide display information on a monitor, provide user feedback or for any other suitable purpose. 
     Optionally, as illustrated in  FIG. 3 , the converter(s)  22  can be physically incorporated or integrated into controller  26 . In this configuration, the non-electric communication link  24  extends from the sensor  20  to the controller  26 . The controller  26  can include an input that is suitable for connecting to, and receiving sensor outputs from the communication link  24 , including, for example, but not limited to, optical connections. The converter  22  that is integrated into the controller  26  can then convert the non-electric sensor outputs into a converter output signal that is in a format that can be accepted and processed by the controller  26 . Although, for simplicity,  FIG. 3  shows one sensor  20  and one converter  22  within controller  26 , it can be appreciated that more than one sensor and converter can be provided, similar to the examples shown in  FIGS. 1 and 2 . In fact, applicants&#39; teachings can contemplate many arrangements and combinations of sensors and converters from  FIGS. 1, 2 and 3 , as well as others that will be evident to those skilled in the art. 
     Referring to  FIG. 4 , another example of the control system  10  can include a non-electric controller  26   a,  such as, for example, but not limited to, a pneumatic PLC. In this configuration, the controller  26   a  is operable to receive the non-electric sensor output signals directly, and the control system  10  need not include a converter  22  element. In this example, the controller output signals  30  can be in the same format (i.e., pneumatic, optical, etc.) as the sensor output signals. Again, although, for simplicity,  FIG. 4  shows one sensor  20 , it can be appreciated that more than one sensor can be provided, similar to the examples shown in  FIGS. 1 and 2 . In fact, applicants&#39; teachings can contemplate many arrangements and combinations of sensors, converters and controllers from  FIGS. 1, 2, 3 and 4  as well as others that will be evident to those skilled in the art. 
     Alternate examples of a monitoring and control system described herein can be similar to system  10 , and like components are represented using like reference characters indexed by one hundred (i.e., systems  110 ,  210 , etc.). 
     Referring to  FIG. 5 , monitoring and/or control system  110  includes a sensor  120  that is connected to a converter  122  by a non-electrical communication link  124 . The converter  122  is also connected to a controller  126  by a second communication link  128 . Based on the converter output signals the controller  126  is configured to generate a controller output  130 . 
     In this example, the system  110  comprises a pneumatic fluid circuit and the sensor  120  is a variably adjustable (i.e., analogue) flow control valve that is activated by a mechanical process in the hazardous area. Pneumatic fluid can be supplied to the pneumatic fluid circuit using any suitable fluid source, including, for example, a compressor, a pump, a storage tank and an accumulator (not shown). 
     In this example, the mechanical process measured by the sensor  120  is the interaction between a cam (i.e., trigger member) on the equipment  112  that acts on a roller, or other such feature, associated with the flow control valve as the equipment  112  moves. Based on the position of the flow control valve, variable fluid flow is sent along the non-electric communication link  124 , which in this example is a pneumatic conduit or hose, across the boundary  18 , to the converter  122  in the non-hazardous area. 
     In this example the converter  122  is a console flow meter that is configured to measure the flow rate of the pneumatic fluid and to convert the fluid flow rate into a representative or proportional electrical signal (i.e., the converter output signal). The electric converter output signals are carried by wires, acting as second communication links  128 , to the controller  126 . Based on the converter output signals, the controller  126  generates one or more controller outputs  130 . It can be appreciated, however, that in applicant&#39;s teachings, converter  122  can be incorporated into controller  126 , similar to the example shown in  FIG. 4 . 
     Referring to  FIG. 6 , monitoring and/or control system  210  includes a sensor  220  that is connected to a converter  222  by a non-electrical communication link  224 . The converter  222  is also connected to a controller  226  by a second communication link  228 . Based on the converter output signals the controller  226  is configured to generate a controller output  230 . 
     In this example, the sensor  220  is an adjustable pressure regulating valve in a pneumatic or hydraulic circuit  233   a,    233   b  that is connected to a converter that is in the form of a pressure switch  222  (i.e., for example, SMC™ model GP46-P10-N01M-X30), by a suitable fluid conduit communication link  224 , including, for example a hose. The fluid conduit extends across the boundary  18 , from hazardous area  14  to non-hazardous area  16 . 
     The pressure regulating valve  220  is configured to be acted upon by the equipment  212  (e.g., movement of a motor vehicle lift), which can cause the pressure regulating valve  220  to change the pressure in the fluid conduit  224 . Pressure changes in the fluid conduit  224 , for example, across a pre-determined pressure threshold, are registered by the pressure switch  222 , which in turn generates an electric output signal which is carried to the controller  226  by second communication links in the form of wires  228 . 
     Referring to  FIG. 7 , monitoring and/or control system  310  includes a sensor  320  that is connected to a converter  322  by a non-electrical communication link  324 . The converter  322  is also connected to a controller  326  by a second communication link  328 . Based on the converter output signals the controller  326  is configured to generate a controller output  330 . 
     In this example, the sensor  320  is a pneumatic encoder in a pneumatic circuit  333   a.  The pneumatic encoder  320  includes a rotating disc  344  that rotates in registration with a rotating output (i.e., trigger member) of the equipment  312 . The rotating disc  344  includes a plurality of recesses or apertures  346  spaced circumferentially around the disc  344 . The precise number and arrangement of apertures  346  can be selected based on user requirements. 
     The pneumatic encoder  320  also includes a dowel  348  having a tapered portion  350  that is sized and shaped be at least partially received within the apertures  346  on the rotating disc  344 . The dowel  348  reciprocates between a first position, in which the tapered portion  350  of the dowel  348  is at least partially received in an aperture  346 , and a second position, in which the tapered portion  350  is free of (i.e., removed from) the apertures  346 , based on the rotation of the disc  344 . As the disc  344  rotates the dowel  348  can move to its first position when it is aligned with a respective one of the apertures  346  and is moved to its second position when disc  344  rotates such that the dowel  348  is not aligned with an aperture  346 . This interaction between the disc  344  and the dowel  348  can translate rotational motion of the disc  344  into periodic, reciprocating motion of the dowel  348 . As the disc  344  rotates the tapered portion  350  of the dowel  348  can serve as a camming or guide surface, facilitating the reciprocating motion of the dowel  348 . In some examples the dowel  348  can be biased toward the disc  344  by a suitable biasing means, such as, for example a spring, an elastic, pneumatic pressure and any combination thereof. This example of a pneumatic encoder may be described as a contact encoder. 
     The reciprocating motion of the dowel  348  can produce a series of pressure pulses (i.e., intermittent periods of relatively high and relatively low pressure) within the pneumatic circuit  333   a.    
     In other examples, the pneumatic encoder  320  may be a non-contact encoder. In place of the dowel  348 , one example of a non-contact encoder may include a nozzle connected to the pneumatic circuit  333   a  that is disposed in close, but non-contacting, proximity to the rotating disc  344 . The nozzle can be configured to allow fluid to escape the fluid circuit  333   a.    
     When the disc  344  rotates such that a tip of the nozzle (i.e., the opening to allow fluid to escape the circuit  333   a ) is facing (i.e., opposed by) a solid portion of the disc  344  a gap is formed between the nozzle tip and the disc  344 . In this configuration, fluid from the circuit  333   a  can escape the circuit  333   a  by flowing through the gap at a first flow rate. Fluid escaping at the first flow rate creates a first pressure in the circuit  333   a.  When the disc  344  rotates such that the tip of the nozzle is facing one of the apertures  346 , fluid exiting the nozzle tip is not opposed by a solid portion of the disc  344  and can exit the nozzle at a second, faster flow rate. Fluid escaping the nozzle at the second flow rate can create a second pressure in the circuit  333   a,  the second pressure can be different than the first pressure. As the disc  344  rotates during use, the nozzle can be aligned with an aperture  346  and a solid portion of the disc  344  in an alternating manner, creating alternating instances of the second pressure and the first pressure, respectively, within circuit  333   a.  This alternating flow rate/pressure condition can produce a series of pressure pulses in the circuit  333   a.    
     These pressure pulses (from either example described above, or any other suitable encoder operation) can act upon a suitable converter  322 , in this example a pressure switch  340 , which is configured to convert the pressure pulses into corresponding electrical output signals. The electrical output signals are then carried by wires  336  (examples of second communication links  328 ) to a controller  326 . 
     Optionally, the controller  326  can be configured to produce an output signal  330 , based on each converter output signal, which corresponds to each pressure pulse. In other examples, the controller  326  can include a counter module  348  that is configured to count the pressure pulses and produce a controller output  330  after a predetermined number of pulses are registered (for example, a controller output  330  can be produced for every 5 or 50 pressure pulses). 
     Referring to  FIG. 8 , monitoring and/or control system  410  includes a sensor  420  that is connected to a converter  422  by a non-electrical communication link  424 , such as an optical link. The converter  422  is also connected to a controller  426  by a second communication link  428 , which can be electrical. Based on the converter output signals the controller  426  is configured to generate a controller output  430 . 
     In this example, the system  410  comprises an optical circuit and the sensor  420  is an optical sensor that is activated by a mechanical process in the hazardous area. In this example, the mechanical process is measured by the sensor  420  on the equipment  412  as the equipment  412  moves. Based on the position of the equipment  412  measured by the optical sensor, an appropriate optical signal is sent along the optical communication link  424 , such as, for example, fiber optics, across the boundary  18 , to the converter  422  in the non-hazardous area. 
     In this example the converter  422  converts the optical signal into a representative or proportional electrical signal (i.e., the converter output signal). The electric converter output signals are carried by wires, acting as second communication links  428 , to the controller  426 . Based on the converter output signals, the controller  426  generates one or more controller outputs  430 . 
     It can be appreciated, however, that in applicant&#39;s teachings, the converter in  FIG. 8  can be incorporated into controller, similar to the example shown in  FIG. 4 . Such an example is shown in  FIG. 9 . 
     Referring to  FIG. 9 , monitoring and/or control system  510  includes a sensor  520  that is connected by a non-electrical communication link  524 , such as an optical link directly to the controller  526 . The controller  526  includes converter  522  to convert the received optical signal to the appropriate signal for use by the controller  526 , for example, an electrical signal. Based on the received signals the controller  526  generates a controller output  530 . 
     In this example, the system  510  comprises an optical circuit and the sensor  520  is an optical sensor that is activated by a mechanical process in the hazardous area. In this example, the mechanical process is measured by the sensor  520  on the equipment  512  as the equipment  512  moves. Based on the position of the equipment  512  measured by the optical sensor, an appropriate optical signal is sent along the optical communication link  524 , such as, for example, fiber optics, across the boundary  18 , to the controller  526  in the non-hazardous area. 
     In this example the controller  526  converts the optical signal into a representative or proportional electrical signal (i.e., the converter output signal) internally, such as with an internal converter  522 . Based on the converter output signals, the controller  526  generates one or more controller outputs  530 . 
     It can be appreciated that although specific examples are shown, it is applicants&#39; intent that various combinations and arrangements of the examples shown in  FIGS. 1 to 9  can be made as will be appreciated to those of skill in the art. For example, but not limited to, having the converter separate from the controller, or within the controller, or mixing various combinations of types of communication links as appropriate. 
     One example of a type of equipment  12  (or  112 ,  212 ,  312 ,  412 ,  512 —hereinafter generally denoted as  12 ) that can be monitored and/or controlled using the monitoring and/or control systems described above is a motor vehicle lift systems. Motor vehicle lift systems can be used to lift a motor vehicle to a predetermined distance or height above the ground to allow a mechanic or technician to access the underside of a vehicle for inspection or repair. Examples of vehicle lift systems include, two-post lift systems ( FIG. 15 ), four-post lift systems ( FIG. 14 ) and scissor lift systems ( FIG. 10 ). In operation, motor vehicle lift systems can be moveable between a first or lowered position, in which a motor vehicle can be driven or moved onto the lift system, and a second or raised position, in which the motor vehicle is raised to a desired working height. 
     Referring to  FIG. 10 , an example of a motor vehicle lift system  52  incorporating a monitoring and/or control system  610 . In this example the vehicle lift system  52  comprises a pair of spaced apart scissor lifts  54  installed within a hazardous area  14 , such as, for example an automotive garage. Each scissor lift system  54  includes a base  56 , a wheel runway apparatus  58  and a lift mechanism  60 . As used herein, the term “wheel” or “vehicle wheel” refers to the tire and wheel assembly found on a motor vehicle. Such an assembly generally includes a conventional tire that is mounted on a metal wheel or “rim.” 
     In the illustrated example, the scissor lifts  54  are free to move independently as they are not mechanically linked together. When in use, the scissor lifts  54  can be operated in unison (i.e., raised and lowered at substantially the same time and the same rate) so that a vehicle supported on the lift maintains a substantially level configuration at all times, for example when being raised, when being held at a fixed height, when being lowered and when the vehicle lift system  52  is in its lowered position (when a vehicle can be loaded or unloaded off the lift). In the present example, the scissor lifts  54  are the same, and any description of one scissor lift  54  is understood to be applicable to both scissors lifts  54 . In other examples, the scissor lifts  54  can be different. 
     Optionally, the wheel runway apparatus  58  can include a support structure  62 . The support structure  62  includes a top surface  64  for supporting wheels of a vehicle. The support structure  62  includes first and second ends  66 ,  68 , and a length extending between the first and second ends  66 ,  68  defining a longitudinal direction  70 . The support structure  62  further includes inner and outer sides  72 ,  74 , and a width extending between the inner and outer sides  72 ,  74  defining a lateral direction  76 . 
     The wheel runway apparatus  58  can include a first support plate  78  movably mounted on the support structure  62 . The first support plate  78  can be located towards the first end  66  of the support structure  62  and can be referred to as a “slip plate.” The first movable support surface  78  can be a generally rectangular plate mounted on a bearing surface (not shown). The first support plate  78  has topside  80  defining a surface for supporting fixed or rear wheels of a vehicle. The first support plate  78  can be generally rectangular, and the topside  80  can be generally flush with the top surface  64  of the support structure  62 . The first support plate  78  can permit limited motion of the fixed wheels of the vehicle in a horizontal plane, at least in the lateral direction  76 , relative to the support structure  62 . 
     The wheel runway apparatus  58  can also include a second support plate (not shown) movably mounted on the support structure  62 . The second support plate can be located towards the second end  68  of the support structure  62 , received on bearing surface  82  and can be referred to as a “turn plate” or a “turntable.” The second support plate can be a generally round plate mounted on a bearing surface generally flush with the top surface  64  of the support structure  62 . The second support plate can permit the steered or front wheels of a vehicle to be steered from side to side without requiring lifting of the vehicle, and simultaneously permit rotational motion and limited motion in a horizontal plane, in the longitudinal and lateral directions,  70 ,  76 , relative to the support structure  62 . The second support plate can have a topside defining a surface for supporting steered or front wheels of a vehicle. 
     Optionally, the wheel runway apparatus  58  can include at least one lighting module (not shown). The lighting module can be mounted to the top surface  64  of the support structure  62 . The lighting module can be mounted generally flush relative to the top surface  64  of the support structure  62 . The lighting module can extend adjacent the inner side  72  of the support structure  62 . The lighting module can be configured to illuminate an underside region of the vehicle when the vehicle is parked on the wheel runway apparatus  58 . The lighting module can be configured to provide illumination directed generally upwards towards parts of the vehicle that require servicing, and generally not in the mechanic&#39;s eyes. In a vehicle wheel alignment lift system, the lighting module can be disposed adjacent the movable support surface of the wheel runway apparatus  58  to provide illumination during wheel alignment procedures. 
     In some examples, the lighting module includes an assembly or plurality of light emitting diodes. The light emitting diodes can be high intensity and low voltage. The light emitting diodes can provide lighting of the work area and can increase reliability of lighting. Furthermore, use of an assembly or plurality of light emitting diodes can reduce or substantially eliminate shadow effects in the work area. Optionally, the lighting module, or other accessories used in combination with the lift system  52 , can be controlled by the controller output signals  630  generated by the system controller  626  ( FIG. 13 ). 
     The base  56  of each scissor lift  54  can be any suitable structure, such as the metal frame illustrated, that can be used to adequately secure the lift mechanism  60  to a solid, underlying surface, such as the floor of an automotive garage. The base  56  can be made of any suitable material that can handle the loading and mechanical stresses exerted by the lift mechanism  60 , including, for example, metal, plastic and composite materials. The base material can also be selected to have desired chemical properties so that the base can withstand exposure to substances expected to be present in an automotive garage, such as, for example, oil, paint, gasoline, solvents and automotive battery acid. Optionally, the base  56  can mounted upon the floor, recessed beneath the floor surface or be an integral feature in the floor. 
     Referring to  FIGS. 11 and 12 , the illustrated example of a scissor lift  54  includes a lift mechanism  60  that comprises first and second scissor members  84 ,  86  that are pivotally connected using pin joint  88 . As the scissor lift  54  moves between lowered and raised positions the first and second scissor member  84 ,  86  rotate relative to each other about pin joint  88 . A sensor  620  is mounted to the second scissor member  86  in a predetermined position using mounting bracket  690 . In this example the sensor  620  is a pneumatic limit switch  692  (for example, FESTO™ model no. 12146) connected to a pneumatic circuit (not shown). Alternatively, the sensor  620  can be any other suitable sensor as described above. 
     In the illustrated example the pneumatic limit switch  692  includes a cam follower portion  694  that follows the profile of a cam  696  (i.e., trigger member) that is mounted to the first scissor member  84 . As the lift mechanism  60  is raised and/or lowered the first scissor member  84  rotates relative to the second scissor member  86 , which moves the surface of the cam  696  relative to the cam follower portion  694  of the limit switch  692 . The profile of the cam surface can be selected to engage/disengage the limit switch  692  when the lift mechanism  60  moves past predetermined threshold positions. Examples of such positions include the lowered position (when the scissor lift  54  in the vehicle loading position), a maximum height position, a desired working height position and an accessory (e.g., lighting module) threshold position. 
     In the present example, the sensor outputs generated by the pressure limit switch  692  include an “on” pneumatic flow and an “off” pneumatic flow (i.e., an absence of flow passing through the limit switch  692 ). The output flows from the limit switch  692  are carried in pneumatic conduits  624  from the vehicle lift  52  in the hazardous area  14 , across the boundary  18 , to a corresponding converter  622  in the non-hazardous area  16  ( FIG. 13 ). In this example, as shown in  FIG. 13 , the converter  622  is a pressure switch, but any suitable converter can be used. 
     Optionally, the cam profile can be set so that the outputs from limit switch  692  shown in  FIG. 12  are indicative of the lift mechanism  60  being at a predetermined working height. The outputs from the limit switch  692  are converted by pressure switch  622  into electrical signals that are sent to a controller  626  by electrical communication links in the form of wires  628 . Based on the converter output signals the controller  626  can activate one or more appropriate lift accessories using controller outputs, such as controller outputs  630   b.  For example, the controller  626  can be used to turn on the lighting module when the lift mechanism  60  is at working height and turn off the lighting module when the lift mechanism  60  is below the working height. 
     In other examples, signals from sensors  620  on the vehicle lift  52  can be used to automatically lock the slip plates and/or turning plates in predetermined positions when the scissor lifts  54  are moved to a predetermined location (such as the lowered position). 
     In another example, both scissor lifts  54  can include additional limit switches  620   a  (represented in  FIG. 13 ). In this example the cam profiles in each lift mechanism  60  can be set so that the outputs from limit switch  620   a  are indicative of the lift mechanism  60  being in the lowered position (i.e., completely seated on its respective base  56 ). The sensor outputs from both limit switches  620   a  can be routed to a single pressure switch converter  622   a,  as shown in  FIG. 13 . In this configuration, the monitoring and/or control system  610  can be used to control the vehicle lift system  52  equalization. 
     In this example, when the lift mechanisms  60  of each scissor lift  54  are moved toward the their lowered positions the pressure switch  622   a  can receive a sensor output when each limit switch  620   a  is activated (when each lift mechanism  60  is seated on its base). The sensor outputs are converted to electrical signals for the controller  626  by the pressure switch  622   a.  The controller  626  can be configured to recognize or determine when only one limit switch  620   a  is triggered (for example by the magnitude of the converter output signal) and continue lowering the other lift mechanism  60  until both sides of the vehicle lift system  52  are seated on their bases. Alternatively, or in addition, the pressure switch  622   a  can be configured such that it will only output an electrical signal to the controller  626  when both limit switches  620   a  connected to the pressure switch  622   a  are activated. For example, the pressure required to activate the pressure switch  622   a  can be greater than the pressure output signal produced by one of the limit switches  620   a,  but less than the combined pressure output signals of both limit switches  620   a.    
     Using the system  610  in this manner enables the controller  626  to ensure that vehicle lift system  52  is equalized or leveled each time the lift mechanisms  60  are lowered onto the bases. In such a system, the likelihood of lift mechanism  60  positioning errors accumulating over multiple vehicle lift  52  strokes or cycles can be reduced because the positions of the scissor lifts  54  are “equalized” each time the vehicle lift  52  is lowered. A converter  622   a  used in such a system can be referred to as an equalization converter and can produce equalization converter output signals. 
     Optionally, the vehicle lift system  52  can include an additional sensor  20 , for example another limit switch, positioned on the vehicle lift  52  such that the limit switch is triggered when one of the scissor lifts  54  reaches a predetermined maximum height. When this upper limit switch is triggered the sensor output is converted using a corresponding pressure switch converter and the resulting electrical signal can cause the controller  626  to stop the upward movement of one or both of the scissor lifts  54 . 
     Alternatively, or in addition, one or more limit switch can be mounted to the base  56  or floor of the garage so that the limit switch is contacted by at least one of the scissor members  84 ,  86  or the wheel runway supports  58  when the scissor lift  54  reaches its lowered position. In such a configuration, the structural components of the scissor lift  54  (scissor members  84 ,  86  and wheel runway supports  58 ) can act as the trigger member for engaging the limit switch. 
     Referring to  FIG. 13 , an example of a controller  626  that can be used in combination with a vehicle lift system  52  includes inputs  698  for receiving the converter output signals from one or more converters  622 ,  622   a.  The controller  626  also includes inputs  600  for receiving operator commands, such as, for example, up, down and bypass commands from a set of operator controls. 
     The controller  626  also includes a plurality of outputs for controlling a variety of functions such as, for example, outputs  630   a  for controlling the hydraulic pumps and motors used to raise and lower the vehicle lift system  52  and outputs  630   c  for controlling hydraulic flow control solenoids to adjust the lift mechanism position. 
     Optionally, all of the sensors  620 ,  620   a  monitoring the vehicle lift  52  can be pneumatic sensors. In such a system, a lack of pneumatic pressure can result in the vehicle lift  52  sensors  620 ,  620   a  being inoperable. Optionally, the system  610  can be configured so that the “off” or inactive position of the sensors  620 ,  620   a  (such as limit switches) is the open position such that the corresponding converters  622 ,  622   a  are exposed to high pressure (i.e., the selected operating pressure of the pneumatic circuit used in the system  610 ). The controller  626  can be configured so that the vehicle lift  52  can only be operated when system pressure is detected by one or more predetermined converters  622 ,  622   a.  Using such a controller  626 , a loss of system pressure (by leakage or component failure) can cause the controller  626  to shut-down or otherwise immobilize the vehicle lift  52 , which can prevent an operator from moving the vehicle lift  52  when the position monitoring sensors  620 ,  620   a  are inoperable. This may be a desirable safety feature. 
     Referring to  FIG. 14 , an example of a four-post vehicle lift  106  includes four upright posts  108  that cooperate to support a pair of wheel runway supports  58 . The wheel runway supports  58  can be the same as the wheel runway supports  58  described above, or can be any other suitable type of wheel supporting structure. The four-post vehicle lift  106  can be monitored and controlled using a control system of applicants&#39; teachings. 
     In this example, lower limit sensors  720   a  can be installed at suitable locations, such as toward the bottom of each post  108 , on one or more of the posts  108  such that the lower limit sensors are triggered when the wheel runway supports  58  are in their lowered positions (i.e. in a vehicle loading/unloading position). The lower limit sensors  720   a  can be any type of sensor described above, including pressure limit switches  92 . 
     The lower limit sensors  720   a  can be pneumatically connected to a suitable converter  722  using pneumatic hoses  724 , which can in turn be connected to a controller that controls the movement of the wheel runway supports  58 . 
     Similarly, the four-post vehicle lift  106  can include an upper limit sensor  720   b  (such as a limit switch) positioned toward the top of one or more of the posts  108 . The pneumatic flow form the upper limit sensor  720   b  can transported by hose  724   b  and can be converted by a suitable converter and can cause a controller to stop the upward movement of the wheel runway supports  58  when the upper limit sensor  720   b  is triggered. Optionally, hoses  724   a,b  can be combined into a single hose or conduit that is connected to multiple sensors. 
     The signals from both the upper and lower limit sensors  720   a,    720   b  can be carried to their respective converters via communication links  724   a,    724   b  (pneumatic conduits in this example) from the hazardous area  14 , across the boundary  18  and into the non-hazardous area  16 . 
     Referring to  FIG. 13 , an example of a two-post lift  114  includes two generally upright posts  116 , each of which movably supports a pair of vehicle lifting arms  118  configured to contact the frame of a vehicle being lifted on the two-post lift  114 . The two-post lift  114  also includes lower and upper limit sensors  820   a,    820   b  (for example limit switches  92  described above). 
     The lower limit sensors  820   a  are positioned toward the bottom of each post  116  such that the lower limit sensors  820   a  are tripped when the vehicle lifting arms  118  reach their lowered (vehicle loading) positions. The two-post lift  114  can include a controller, like the controller  626  illustrated in  FIG. 11 , that is configured to use the inputs from the lower limit sensors  820   a  (converted by suitable converters  822 ) to equalize the positions of the vehicle lifting arms  118  after each lift. 
     Similarly, the upper limit sensor  820   b  is positioned such that it is triggered when the vehicle lifting arms  118  reach a predetermined maximum height, which causes the controller to stop the upward movement of the vehicle lifting arms  118 . 
     What has been described above has been intended to be illustrative of the invention and non-limiting and it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the invention as defined in the claims appended hereto.