Patent Publication Number: US-2023145314-A1

Title: An intrinsically safe multi-drop communication hub

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This international application claims priority from and the benefit of U.S. Patent Application No. 62/991,626, filed Mar. 19, 2020, which application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to an apparatus to establish communications with multiple intrinsically safe devices via a communications port communicatively coupled to a single intrinsically safe barrier. 
     BACKGROUND OF THE DISCLOSURE 
     Hazards can occur during pumping of hazardous liquids, including mechanical seal failures resulting in leaks or fugitive emissions, deadheading, reduced or low flow in centrifugal pumps, over-pressurization, and high temperature. The hazards can result in severe incidents including fires, explosions and toxic releases. Safety measures are required by regulations to prevent the hazards and protect the pumping environment. Generally, safety measures include explosion-proofing or use of intrinsically safe designs. Intrinsically safe (IS) equipment is equipment which is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous atmospheric mixture in its most easily ignited concentration. Intrinsically safe designs often encompass control systems that use processors to monitor sensor signals from sensors including, for example, temperature, pressure, flow, speed, vibration, oxygen, etc. These control systems are subject to electrical limits to ensure they do not release electrical or thermal energy above limits based on the fluid being handled. 
     As technologies advance it may be desirable to provide additional sensors and/or controls to improve monitoring. Additional signals may provide faster detection or detection of previously unmeasurable parameters. The desirability of additional sensors may be tempered by installation costs. Particularly in existing environments, where cables may be buried under concrete, the addition of sensor cables may be prohibitively expensive. 
     Based on the foregoing it is evident that a need exists for the capability to add sensors in a hazardous environment without exceeding regulated limits and at an affordable cost. 
     SUMMARY 
     An intrinsically safe (IS) multi-drop communication hub (IS hub), a method to obtain signals from IS devices, and a method of mounting and connecting the IS hub are provided. The IS hub includes a multiplexer and a controller to control the multiplexer and sample signals from the IS devices in accord with a sequence of commands from the controller to the multiplexer. Responsive to the commands, the multiplexers powers the IS devices according to the sequence and the controller samples the signals of the powered IS device. 
     The IS hub can be mounted on a bracket in a first position and a second position. In the second position an opening of the IS hub is more easily accessible than in the first position and the cables and other components can be connected to the IS hub. The IS hub is then mounted in the first position where the opening is less or not accessible. 
     In some embodiments of the intrinsically safe (IS) multi-drop communication hub (IS hub) operable in a hazardous environment, the IS hub includes a power contact to receive external power therethrough; a controller including multiplexing sequence logic and a first signal input contact; a multiplexer communicatively connected to the controller and having a power input contact; an inductor connected in series between the power contact and the power input contact of the multiplexer; a communication port communicatively connected to the controller to receive signal data therefrom, the signal data corresponding to signals generated by IS devices connected to the IS hub when the IS hub is in use, wherein when executed by the controller the multiplexing sequence logic causes the multiplexer to supply power in a predetermined sequence to a first of the IS devices during a first time interval and, after the first time interval, to a second of the IS devices during a second time interval which does not overlap in time with the first time interval, and wherein during the first time interval the controller samples a signal corresponding to the first of the IS devices and during the second time interval the controller samples a signal corresponding to the second of the IS devices. 
     In some embodiments of a mounting bracket operable with the IS hubs described herein, the IS hub has a housing having a body and a cover covering an access opening of the body. The mounting bracket can support the IS hub in a first position and in a second position. In the second position the access opening faces upward and in the first position the access opening does not face upward. This allows an installer person to connect wires to the IS hub in the second position and to then place the IS hub in the first position for normal operation. 
     In some variations, the mounting bracket has a hinge operable to move the IS hub from the first position to the second position. In other variations, the mounting bracket has first and second mounting features and the IS hub has mounting features operable with the first and second mounting features of the bracket, so that the IS hub can be mounted in the first position with the first mounting features and the second position with the second mounting features. The mounting features can comprise rails sized and shaped to slide within corresponding slots. The mounting bracket or the body can include the rails or the slots. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned embodiments and additional variations, features and advantages thereof will be further elucidated by the following illustrative and nonlimiting detailed description of embodiments disclosed herein with reference to the appended drawings, wherein: 
         FIG.  1    is a perspective view of a fuel dispensing installation; 
         FIGS.  2  and  3    are schematic representations of an installation with and without an IS multi-drop communication hub; 
         FIG.  4    is a schematic representation of an embodiment of an IS multi-drop communication hub; 
         FIG.  5    is a schematic representation of a variation of the embodiment of the hub of  FIG.  4   ; 
         FIGS.  6  and  7    are perspective views of the embodiment of a housing operable to contain any one of the embodiments and variations of the circuits of the IS multi-drop communication hub; 
         FIG.  8    is a schematic diagram of a variation of the embodiment of the hub depicted in  FIG.  4   ; 
         FIGS.  9  and  10    are circuit diagrams of portions of the hub depicted in  FIG.  8   ; 
         FIGS.  11 A and  11 B  are circuit diagrams of a portion of the embodiment of the IS hub depicted in  FIGS.  4 ,  5 , and  8   ; 
         FIGS.  12  and  13    are perspective views of an embodiment of a mounting bracket operable to mount the IS hub on a pipe; 
         FIG.  14    is a perspective view of another embodiment of a mounting bracket operable to mount the IS hub on a pipe; 
         FIGS.  15  and  16    are perspective views of another embodiment of a mounting bracket operable to mount the IS hub on a pipe in a first or a second position; 
         FIGS.  17  and  18    are circuit diagrams of embodiments of current limiters operable in any one of the apparatus depicted in  FIGS.  4 ,  5 ,  8  and  11   ; and 
         FIGS.  19  and  20    are perspective views of examples of embodiments illustrating mounting of the IS hub. 
     
    
    
     In the drawings, corresponding reference characters indicate corresponding parts, functions, and features throughout the several views. The drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the disclosed embodiments. 
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings, which are described below. The embodiments disclosed below are not intended to be exhaustive or limit the disclosure to the precise form disclosed in the following detailed description. 
     IS equipment must have been tested and approved by an independent agency to assure its safety and can be approved either under the system or entity approval concept. The system concept specifies parts that can be used in the system. The entity concept is more general, it specifies parameters of IS equipment and barriers. IS equipment is located in the hazardous environment, IS barriers are located in non-hazardous areas. Signals have to pass through an IS barrier to connect IS equipment to control equipment that must be located in the non-hazardous, or safe, area. The entity concept specifies, for example, that the maximum allowable voltage of apparatus in the hazardous area, V i  must be higher than maximum voltage, V O , produced by the IS barrier. The entity concept also defines limits for current, capacitance, inductance etc., which allows to mix and match IS barriers and is devices based on certain rules. 
       FIG.  1    is a perspective view of a fuel dispensing installation  1  including fuel tanks  2 , fuel pumps  3 , and fuel level gages  4 . As shown, the fuel tanks are underground and sensors and wiring connections are in an underground sump pump housing. 
       FIGS.  2  and  3    are schematic representations of the installation of  FIG.  1    with and without an IS multi-drop communication hub.  FIG.  2    illustrates a junction box  5 , located in a sump housing, and a fuel dispenser controller  6  that receives sensor signals from the installation and transmits control signals to operate the fuel pumps.  FIG.  3    illustrates the installation of  FIG.  2    with the addition of IS hubs  40 ,  70  in the sump housing and, as described below, operable to receive and transmit data from sensors  11 ,  12 , and  13 , which could be, for example, a water sensor, a flow switch, a corrosion sensor, or any other sensor. 
       FIG.  4    is a schematic representation of an embodiment of an apparatus operable to establish communications with multiple intrinsically safe devices in a hazardous environment via a communications port communicatively coupled to a single intrinsically safe barrier.  FIG.  4    shows a hazardous environment  20 , a safe environment  22 , and in safe environment  22  a control system  24 , an IS barrier  26 , and a cable  28  extending from IS barrier  26  into hazardous environment  20 . 
     In hazardous environment  20  there is an IS device  30 , an IS multi-drop communication hub  40  (also shown in  FIGS.  6  and  7   ), and six IS devices depicted as D 1 -D 6 , which may be IS sensors operable to sense characteristics of IS device  30 . In one example, IS device  30  is a sump pump and the IS sensors sense various parameters related to the operation of the sump pump such current, temperature, vibration, and others. IS devices D 1 -D 6  can also be control devices such as actuators. Each IS device D 1 -D 6  may comprise a pair of wires connected to IS multi-drop communication hub  40 , such as a signal wire and a ground wire. Thermocouples, for example, generate an output voltage based on temperature and therefore comprise two wires. Flow and pressure sensors, control devices, and other IS devices connected to IS multi-drop communication hub  40  may comprise power, ground and signal wires or may have just two wires that carry power and communications at the same time. Hazardous environment  20  may be an enclosable space  150  having a lateral wall  152  and a bottom wall  154  ( FIG.  19   ) sized and shaped to enclose the aforementioned components while providing access to them for repair and maintenance, for example. 
     IS multi-drop communication hub  40  (and IS hub  70 ) comprises a housing  60  (shown in  FIGS.  6  and  7   ), and inside the housing a circuit board  42 , a shield  66  (shown in  FIGS.  6  and  7   ) in front of circuit board  42 , and terminals connected to circuit board  42  and the wires from IS devices D 1 -D 6 . Housing  60  has a body  62  including an opening  63  covered by a cover  64  provided to form an enclosed space. The enclosed space may be sealed by inclusion of gaskets or other fitments (e.g. precision contouring, sizing and shaping of matching surfaces) between the cover and the housing. The seal may be liquid-tight or fluid-tight. 
     Mounted on circuit board  42  are a communication port  44  communicatively connected to cable  28 , a controller  46 , and a multiplexer  48 . Multiplexer  48  may be a power multiplexer or a control multiplexer, or a combination of both. A power multiplexer time-shares power to one of many power wires of IS devices D 1 -D 6 . A control multiplexer time-shares a control signal to one of many control wires of IS devices D 1 -D 6 . Thusly, the multiplexer activates one device at the time, either by providing power to one device at the time or by controlling the devices such that only one is active at the time. The other devices may be in an inactive or sleep mode. The power multiplexer can also multiplex signals superimposed on the power conductor. 
     Controller  46  includes logic to command the multiplexer to activate the devices. Because the amount of power sourced by IS barrier  26  is limited and the time-base (sampling frequency) of the parameters being sensed may differ, controller  46  must select the operating order of the devices to maximize utility. For example, it may not be necessary to measure temperature as frequently as pressure, because pressure can change instantly while thermocouples do not react instantly to temperature changes. Thus, pressure can be sampled more frequently and temperature can be sampled less frequently. Similarly, an actuator might not need to be operated on a regular basis, it may be turned on or off and left in that state for a period of time. Controller  46  may be a microcontroller, FPGA, system-on-a-chip (SoC) integrated circuit, or any known circuit capable of executing logic instructions. 
       FIG.  5    is a schematic representation of a variation of IS multi-drop communication hub  40  to illustrate the presence of two multiplexers,  48  and  49 . The multiplexers can be power multiplexers, control multiplexers, or a combination of power and control multiplexers. The presence of two multiplexers may be useful in situations where two IS devices may be activated simultaneously without exceeding the IS barrier characteristics limits. Appropriate circuitry, such as diodes and other known circuit elements, may be used to enable connection of power or control wires from both multiplexers to a single IS device, for example to prevent current leakage. Of course, if two devices may be activated, it may also be possible to structure IS multi-drop communication hub  40  to have a dedicated IS device connection and one multiplexer. 
     Controller  46  is able to digitize analog inputs and to sample the digital data, and to transmit the digital data via communication port  44 . The controller may incorporate a communication port. The controller can have many analog inputs (16 is not unusual). In the present example communications from the multiplexer to the controller occur over a line supplying power to the multiplexer, therefore communications are multiplexed with power. Additional inputs of the controller can be used for sensors that do not require provision of power. 
     In one example, the controller has one input dedicated for a device which is always powered (channel 0), one input for four multiplexed devices (channel 1-4), and one input for a temperature sensor (channel 5). The configuration is flexible, meaning that more or fewer devices can be connected to the controller without passing through the multiplexer, depending on the electrical characteristics of the IS devices and installation factors such as cable length. 
     In one variation of the present embodiment, the maximum current permissibly drawn by the IS hub is I MAX  and the controller is structured to maintain current at or below I MAX . In one example I MAX =100 mA at 9 volts. The current consumption of the IS hub includes current consumed by the IS hub plus current consumed by the IS devices suppled power by the IS hub. A current limiter may be included to ensure current does not exceed I MAX . Example current limiters are described with reference to  FIGS.  17  and  18   . 
     Communication port  44  may comprise a terminal to connect cable  28  and a communication integrated circuit including a communication protocol such as, for example the Modbus protocol. The terminal connection is suited to any desired communication scheme, for example serial or parallel schemes. A preferred communication scheme is the half-duplex RS-485 standard, which is a two-wire differential bi-directional communication scheme. Data may be transmitted in sequence together with a node address corresponding to the respective sensor. Data may also be incoming, for example to control actuators, in which case the address indicates which actuator is to be activated. 
       FIGS.  6  and  7    are perspective views of the embodiment of the hub depicted in schematic form in  FIGS.  1 ,  5  and  8   . IS multi-drop communication hub  40 ,  70  comprises a housing  60 , and inside the housing circuit board  42 , shield  66  in front of circuit board  42 , terminals connected to circuit board  42 , and the wires from IS devices D 1 -D 6  extending to the IS barrier. Housing  60  comprises a body and a cover. The cover is removed to connect the IS device wires. 
       FIG.  8    is a schematic representation of a variation of IS multi-drop communication hub  40 , denoted by numeral  70 . As shown, IS hub  70  includes a safety barrier  74  between cable  28  and devices in IS hub  40  and electrical safety barriers  76  between multiplexer  48  and IS devices D 1 -D 6  connected to IS hub  40 . Exemplary electrical safety barriers are shown in  FIGS.  9  and  10   . The exemplary safety barriers comprise Zener diodes and resistors configured to place limits on the voltages incoming on the power line from the communication cable and/or on the power supplied to the IS devices. The safety barriers can take any form know to limit voltage and/or capacitance and/or inductance. The safety barriers can be included with any of the IS multi-drop communication hub embodiments depicted herein and may be based on the number and type of IS devices included in the hub. 
     As indicated above, controller  46  is able to digitize analog inputs, sample the digital data, and to transmit the digital data via communication port  44 . The controller can have many analog inputs (16 is not unusual). Additional inputs of the controller can be used for sensors that do not require provision of power. 
     Referring now to  FIG.  11 A , one variation of the embodiments of the IS hub described above will be described to illustrate the operation of the multiplexer. As shown, controller  46  has one input dedicated for an IS device D 1  that does not require provision of power, e.g. a thermocouple, one input for an IS device D 2  which is always powered, and one input connected to sample the output of multiplexer  48 . Four IS devices D 3 -D 6  are connected to the multiplexer. A first IS device is connected via a contact  86  and a second IS device is connected via a contact  87 . Lines  80  and  81  are selectively powered (e.g. binary commands 00, 01, 10, 11) by controller  46  (e.g. multiplexing logic  47 ) to cause multiplexer  48  to activate one of the four IS devices. A line  82  communicates the data/signal obtained from the IS device to controller  48  via signal input contact  99  and a line  82 ′ communicates the data/signal and address information of the IS device generating the sampled values to communication port  44  so that communication port  44  can output the data and address information over lines A and B. In the present example the input signals are superimposed on the power line and pass through multiplexer  48 , therefore the input signals are sampled via inductor  83  and node  83 ′ by controller  46 . In the present example the input signal from the dedicated IS device D 1  is sampled via inductor  84  and node  84 ′ by controller  46 . Node  84 ′ is a connection between inductor  84  and a power contact  85  to which IS device D 2  is connected when the IS hub is in use. In the present context dedicated means that the IS devices is not connected to the multiplexer. Accordingly, IS devices D 1  and D 2  are dedicated. IS hub  70  (and also IS hub  40 ) has an optional current limiter  90  (discussed below with reference to  FIGS.  17  and  18   ) and four contacts operable to connect external power and a communication cable, denoted by numerals  91 - 94 . Multiplexer  48  has a contact  95  operable to receive power and pass-through a signal from an IS device. Controller  46  has input contacts  96 - 98  to receive, directly or via multiplexer  48 , signals from IS devices. Signals could, optionally be provided directly via line  82  to communication port  44 . Data/signals could, optionally, also be provided to controller  46  by connecting a signal contact of each of devices D 1 -D 6  to a signal input contact of controller  46 , in which case multiplexing logic  47  would sample the data directly from the signal input contacts corresponding to the powered IS device through appropriate safety barriers as disclosed herein.  FIG.  11 B  illustrates that a dedicated input for an IS device D 1  that does not require provision of power or an input for an IS device D 2  which is always powered are optional features. 
     As indicated above, more dedicated IS devices can be used. The inputs from the dedicated devices are sampled by controller  46 . Advantageously, the multiplexer ensures via hardware that only one device is powered at any one time, which is a more reliable assurance than is provided via software. 
     The controller includes multiplexing sequence logic  47  which when executed by the controller causes the multiplexer to activate one of the IS devices, for example by providing power to the IS device selected by the controller. If the multiplexer has four outputs, two control lines from the controller to the multiplexer suffice to communicate four binary selection codes (e.g. 00, 01, 10, 11). In one example, multiplexing sequence logic  47  proceeds in order, engaging one of its power output contacts at the time to therefore power the IS devise connected to the respective power output contact. While the power output contact is activated, the controller samples signals on a communication line communicatively coupling the power input contact of the multiplexer and the first signal input contact of the controller. Known techniques may be used to ensure the sampled signal is stable before converting the signal to digital data or to filter the sampled signals, for example by creating an envelope of the sample signals from which to draw a data value. Once a data value, in digital data form, is obtained, the multiplexing sequence logic may deactivate the power output contact and activate, or power, another. The activation time may be a predetermined duration or may be responsive to the acquisition of the data value. 
     The term “logic” as used in this patent application includes software and/or firmware executing on one or more programmable processing devices, application-specific integrated circuits, field-programmable gate arrays, digital signal processors, hardwired logic, or combinations thereof. Therefore, in accordance with the embodiments, various logic may be implemented in any appropriate fashion and would remain in accordance with the embodiments herein disclosed. Logic may comprise processing instructions embedded in non-transitory machine-readable media. 
     The IS hub circuits must be enclosed. An example of a housing for the IS hub circuits is shown in  FIGS.  6  and  7   . In certain embodiments, space is limited and mounting and connecting the housing in small spaces can prove very difficult. Advantageously, the wiring constraints resulting from the limited space can be mitigated by mounting the housing in a flexible manner, as depicted in  FIGS.  12  and  13    showing perspective views of a mounting bracket  110  operable to mount the apparatus depicted in  FIGS.  4 - 11 B  on a pipe  100 . A pipe clamp  102  surrounds pipe  100  and penetrates through apertures on a first wall  112  of mounting bracket  102 . A second wall  114  extends from first wall  112  at an angle between 30 and 80 degrees. On the end of second wall  114  opposite first wall  112  is a hinge  116  connecting second wall  114  to a mounting plate  118 . Hinge  116  allows mounting plate  118  to pivot from a first position, shown in  FIG.  12   , in which IS multi-drop communication hub  40  hangs vertically, to a second position, shown in  FIG.  13   , in which IS multi-drop communication hub  40  is in a horizontal position. The hinged mounting plate allows an installer to put which IS multi-drop communication hub  40  in the second position to provide access to the terminal connections through an opening in the body of the IS hub and then to let IS multi-drop communication hub  40  hang, in which case the opening faces a wall of an enclosure constraining access. This is beneficial in situations where space is limited, for example in sump pumps, particularly considering the protrusion of cables from the housing. Of course the mounting bracket does not have to be attached to a pipe, such mounting with a pipe clamp is depicted to illustrate one way to support the bracket. The bracket can also be attached to any support structure within the enclosed space. 
     In another embodiment of mounting bracket  120 , the mounting bracket is operable to removably mount the IS hub on pipe  100  using pipe clamp  102  or any other means to connect pipe  100  or any other support structure in the limited space to bracket  120 . Bracket  102  includes first wall  112 , second wall  114  extending from first wall  112  at an angle between 30 and 80 degrees, and a pair of slots  122 . A third wall  126  may be provided to support slots  122 . IS hub housing  60  of IS hub  40 ,  70  has a pair of parallel longitudinal rails  124 , e.g. elongate plate walls protruding from the sides of the body of the IS hub, sized and shaped to slide in slots  122 . A protrusion  128 , shown as a bottom wall, may be provided to stop downward movement of hub  60  as it slides in the slots. Thus, IS hub  40 ,  70  can be slid into mounting bracket  120  and can also be slid out for the purpose of making cable connections accessible. The slots can form part of supporting wall  126 , as shown, extending from second wall  114 . In a variation of the present embodiment, the IS hub includes the slots and the rails are provided by the edges of supporting wall  126 . 
     In another embodiment of mounting bracket  120 , denoted as bracket  120 ′, the mounting bracket is operable to removably mount the IS hub in a first position or a second position. As shown in  FIG.  15   , mounting bracket  120 ′ includes first mounting features  121  and second mounting features  131 . Second mounting features  131  include opposing slots  132  separated by a bracket surface  134 . IS hub  40 ,  70  include corresponding mounting features, e.g. rails  124 . Thus, IS hub  40 ,  70  can be slid into first mounting features  121  in the first position and into second mounting features  131  in the second position. As shown, the first position is vertical and the second position is horizonal. The second position can be any position different from the first position that is suitable to access the interior of the IS hub more easily than in the first position. In a variation of the present embodiment, shown in  FIGS.  19  and  20   , mounting bracket  120 ′ includes first mounting features  121 , second mounting features  131 , and protrusion  128 . Wall  126  includes mounting holes to couple mounting bracket  120 ′ to a U-channel that is supported by pipe clamp  102  to pipe  100 . Use of U-channels is commonly known and facilitates moving housing  60  a desired distance and orientation from pipe  100 , which distance and orientation is determined by the placement of other components in space  20 . 
     Additionally, it may be desirable to limit the current flowing through the cable providing power to the IS hub by including a circuit to limit current, e.g. a current limiting circuit. An example current limiting circuit  90  is shown in  FIG.  17   . R 2  allows Q 2  to turn on and pass voltage and current to the load. When the current through R 1  exceeds the design limit, Q 1  begins to turn on, which in turn begins to turn off Q 2 , thus limiting the load current. Current limiters based on the type of transistor or switch used in the current limiter are known. 
     A current limiting circuit may be connected on the input side of the IS hub or, as shown, between the input side and each power drop, e.g. in series with each sensing inductor. 
     A variation of the current limiting circuit shown in  FIG.  17    is shown in  FIG.  18    and includes the components of current limiting circuit  90  and, additionally, an inductance reducing circuit  90 ′ structured to enable reduction of the inductance of inductor  83 . As shown, inductance reducing circuit  90 ′ is in parallel with inductor  83 . Reducing the size of inductors is beneficial for cost and space reasons. Inductance reducing circuit  90 ′ includes an RC filter connected between the power line and R 1  and including a capacitor C 2  and a resistor R 4 . The output of the RC filter is connected to the base of a transistor Q 3  which has an output connected to the base of transistor Q 2 . The output of the RC filter is also connected to a frequency compensated voltage divider comprising an RC circuit including a resistor R 6  and a capacitor C 4 , connected to the output of inductor  83  and to a capacitor C 4  connected to the base of Q 3 . A resistor R 6  completes the circuit connecting the RC circuit to ground. 
     Further examples in accordance with the description hereinabove provided include: 
     Item 1. An intrinsically safe (IS) multi-drop communication hub (IS hub) operable in a hazardous environment, the IS hub comprising: 
     a power contact to receive external power therethrough;
 
a controller including multiplexing sequence logic and a first signal input contact;
 
a multiplexer communicatively connected to the controller and having a power input contact;
 
an inductor connected in series between the power contact and the power input contact of the multiplexer;
 
a communication port communicatively connected to the controller to receive signal data therefrom, the signal data corresponding to signals generated by IS devices connected to the IS hub when the IS hub is in use,
 
wherein when executed by the controller the multiplexing sequence logic causes the multiplexer to supply power in a predetermined sequence to a first of the IS devices during a first time interval and, after the first time interval, to a second of the IS devices during a second time interval which does not overlap in time with the first time interval, and
 
wherein during the first time interval the controller samples a signal corresponding to the first of the IS devices and during the second time interval the controller samples a signal corresponding to the second of the IS devices.
 
     Item 2. The IS hub of item 1, wherein the connection between the inductor and the power input contact defines a signal node, and wherein the signal corresponding to the first of the IS devices and the signal corresponding to the second of the IS devices are sampled at the signal node. 
     Item 3. The IS hub of item 2, wherein the controller includes a second signal input contact, and wherein the IS hub further comprises a dedicated sensor power contact, a second inductor connected between the power contact and the dedicated sensor power contact without the multiplexer therebetween, and a second communication line communicatively coupling the dedicated sensor power contact and the second signal input contact. 
     Item 4. The IS hub of item 1, further comprising a safety barrier connected between the power contact and a ground contact. 
     Item 5. The IS hub of item 1, further comprising a safety barrier connected between an output contact of the multiplexer and an IS device contact operable to provide power to the first of the IS devices. 
     Item 6. The IS hub of item 5, further comprising a safety barrier connected between an output contact of the multiplexer and an IS device contact operable to provide power to the first of the IS devices. 
     Item 7. The IS hub of item 6, further comprising a safety barrier connected between the power contact and a ground contact. 
     Item 8. The IS hub of item 7, wherein the controller includes a second signal input contact, and wherein the IS hub further comprises a dedicated sensor power contact, a second inductor connected between the power contact and the dedicated sensor power contact without the multiplexer therebetween, and a second communication line communicatively coupling the dedicated sensor power contact and the second signal input contact. 
     Item 9. The IS hub of item 1, wherein the controller includes a second signal input contact, and wherein the IS hub further comprises a dedicated sensor power contact, a second inductor connected between the power contact and the dedicated sensor power contact without the multiplexer therebetween, and a second communication line communicatively coupling the dedicated sensor power contact and the second signal input contact. 
     Item 10. The IS hub of item 1, wherein the communication port comprises a serial communication port. 
     Item 11. The IS hub of item 10, wherein the serial communication port is an RS-485 communication port. 
     Item 12. The IS hub of item 10, further comprising a current limiting circuit in series with the first inductor. 
     Item 13. The IS hub of item 12, further comprising an inductance reducing circuit in parallel with the first inductor. 
     Item 14. The IS hub of any of the preceding items, wherein the IS hub comprises a housing having a body and a cover covering an access opening of the body, further comprising a mounting bracket operable to move the IS hub from a first position to a second position different from the first position. 
     Item 15. The IS hub of item 14, wherein in the second position the access opening faces upward to facilitate installation and and in the first position the access opening does not face upward. 
     Item 16. The IS hub of item 15, wherein the IS hub is sized and shaped for installation in an enclosable space and in the first position the access opening faces a lateral wall of the enclosable space. 
     Item 17. The IS hub of any one of items 14-16, wherein the mounting bracket has a hinge operable to move the IS hub from the first position to the second position. 
     Item 18. The IS hub of any one of items 14-16, wherein one of the mounting bracket or the body comprises a pair of opposing slots and the other of the mounting bracket or the body comprises a pair of opposing rails sized and shaped to slide in the pair of opposing slots to removably mount the IS hub to the mounting bracket. 
     Item 19. The IS hub of any one of items 14-16, wherein the mounting bracket has first and second mounting features and the IS hub has mounting features operable with the first and second mounting features of the bracket, wherein the IS hub can be mounted in the first position with the first mounting features and the second position with the second mounting features. 
     Item 20. The IS hub of item 19, wherein first or second mounting features comprise rails sized and shaped to slide within corresponding slots of the other of the first or second mounting features. 
     Item 21. A method of determining values of signals generated by intrinsically safe (IS) devices in a hazardous environment, the method performed by a controller executing processing instructions structed to perform the method, the method comprising, in sequence: 
     transmitting a command to a multiplexer to supply power to a first of the IS devices during a first time interval;
 
sampling a signal corresponding to the first of the IS devices;
 
transmitting a command to the multiplexer to supply power to a second of the IS devices during a second time interval which does not overlap in time with the first time interval; and
 
sampling a signal corresponding to the second of the IS devices;
 
     Item 22. The method of item 21, further comprising sampling a signal corresponding to a dedicated of the IS devices. 
     Item 23. The method of item 22, wherein sampling the signal corresponding to the dedicated of the IS devices is performed during the first time interval or during the second time interval. 
     Described above are several embodiments, variations, and examples of an IS multi-drop hub, or IS hub, including safety circuits positioned in serial therewith and included therein. Also described are a housing and a mounting bracket particularly suitable for applications in which mounting spaces are limited. However, the scope of the disclosure is to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B or C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. 
     In the detailed description herein, references to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. 
     As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.