Abstract:
A system for measuring at least one parameter is provided. The system includes a control logic arrangement powered by a power source, and an intrinsically safe barrier operatively connected to the control logic arrangement, and also powered by the same power source. The intrinsically safe barrier is adapted to be operatively connected to at least one sensor which is also powered by the same power source. The sensor is configured to communicate data representing a parameter to the control logic arrangement via the intrinsically safe barrier. In one embodiment, the control logic arrangement, the intrinsically safe barrier and the sensor are galvonically isolated from external components and/or provided in one enclosure.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to systems and methods for measuring parameters and process variables within a manufacturing environment and more particularly relates a system and method to measuring parameters and process variables within a hazardous environment in which intrinsically safe barriers are utilized. 
   BACKGROUND OF THE INVENTION 
   In industrial processes where flammable or explosive materials are handled any leak or spill can cause an explosive and dangerous atmosphere. These conditions occur in many industrial environments, most typically in those involving petroleum and other chemicals, process gassers, metal and carbon dust, alcohol, grain, starch, flour, and fibers. To protect both personnel and plant, precautions should be taken within these hazardous areas. In the past, pneumatic controls have been used in these environments to avoid the risk of an electrical spark. Currently, while pneumatic equipment is still utilized, new technologies and engineering advances have created a wide range of electrical controls which allow far greater functionality, and still maintain a safe operating environment within such hazardous areas. 
   Many of these technologies, as they apply to process measurement and control, fall into an area of engineering known as “Intrinsic Safety.” Intrinsic Safety methodology describes a placement of an energy-limiting interface electrically between safe and hazardous areas. This energy-limiting interface and placement thereof restricts the electrical energy in the hazardous-area circuits so that potential electrical sparks or hot spots are too limited and weak to cause any ignition. The interface generally passes signals in both directions, but limits the voltage and current that can reach the hazardous area under particular fault conditions. 
   An intrinsic safety barrier is a device typically placed in a non-hazardous location or a safe location which permits the electrical interconnection of devices located in a hazardous area. In particular, the intrinsically safe barrier limits the power that can be introduced into the hazardous location to energy levels which are safe for the material being handled (or the process being performed) in such area. This barrier protects against, e.g., fault conditions such as shorting of the wires that are connected to the hazardous area side of the barrier by grounding the wires connected to the hazardous area side of such barrier therefore preventing a misconnection or failure of the power supply which allows an unsafe voltage to be applied to the safe area side of the barrier. 
   In a particular factory within which hazardous conditions exist, a conventional arrangement can be provided that includes intrinsically safe barrier which isolates a portion of the power grid of the factory from an array of sensors located throughout the factory. The sensors are located throughout the hazardous area of the factory. Each of the sensors is connected to the intrinsically safe barrier in order to receive power, and directly coupled to a computer processing system-via a communication link at the safe side of the barrier so as to communicate data and readings of the sensors thereto. In particular, this computer processing system receives the readings from each of the sensors of the sensor array through the associated communications link. While this system can be adequately used for measuring process parameters and variables throughout the factory, certain connections should be made between each of the sensors and the intrinsically safe barrier. 
   Certain publications relate to devices and systems utilizing particular barriers and safety devices. For example, U.S. Pat. No. 5,164,607 describes a fill sensor for a paint gun which provides a light sensor opposing a light source in a housing surrounding a transparent portion of a paint gun overflow line. An electric circuit is connected to an intrinsically safe barrier, and is adapted to operate through the intrinsically safe barrier for use in a manufacturing environment. The electric circuit senses whether there is paint in the overflow line. The electric circuit is electrically energized through the intrinsically safe barrier. The other side of the intrinsically safe barrier is connected to the relay. The relay may be any switch responsive to a predetermined electrical current, and provides an electrical isolation between the activating current carrying elements and the switched elements. The relay is responsive to the electrical circuit, and informs a user when a predetermined condition is sensed by the electrical circuit. 
   Another publication, i.e., U.S. Pat. No. 5,305,639, describes a liquid petroleum gas (LPG) gauge sensor unit that fits between the units of existing magnetically-coupled LPG gauge, and includes a magnetic field sensing switch, a mechanism to variably position the switch and an intermediate magnet. Upon sensing a particular orientation, the LPG gauge sensor transmits an indicative signal to an intrinsically safe barrier unit through cables and a waterproof junction box. The intrinsically safe barrier limits the power supplied to LPG gauge sensor. The indicative signal is sent to a fuel reordering system via another cable, and the fuel reordering system can then transmit a message to the distributor based on the particular orientation sensed by the LPG gauge sensor. 
   Furthermore, U.S. Pat. No. 6,021,162 describes a method and apparatus for decoding an encoded signal. The transmitter, as described in this publication, includes measurement circuitry and sensor circuitry. The measurement circuitry and the sensor circuitry are isolated by isolators. An isolation barrier (described in this publication as the isolators) are used to electrically isolate the sensor from the rest of the circuitry within the transmitter, and to prevent harmful electrical discharges. The sensor circuitry senses a process variable, and provides an output signal. The sensor circuitry frequency modulates process variable related signals to be transmitted across one of the isolators. The transmitter can be configured to communicate over a 4-20 mA current, as in the HART® protocol, or may be fully digital communications as in Fieldbus. 
   Also, U.S. Pat. No. 6,065,332 describes a method and apparatus for sensing and displaying the magnitude of torsional vibrations. As described in this publication, the current sensor senses the current of a motor driving a rotary table. In addition, the current sensor converts the magnetic flux produced by the current passing through the conductors in the power cord into a voltage signal, and delivers this voltage signal to a first intrinsically safe barrier. The signal passes from the first intrinsically safe barrier to a low pass filter, and then to a computer. An A/D converter, which is part of the computer, converts a digital signal that is representative of the voltage signal produced by the current sensor into an analog signal. The analog signal passes through a second barrier before reaching a first display, and then passes through a third intrinsically safe barrier before reaching a second display. The first and second displays provide the operator on a drill floor with information relating to the magnitude of a torsional vibration sensed by the apparatus. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a measuring system in which a sensor array can be located in a hazardous area, with the sensors of the sensor array being isolated from control circuitry and a power source by an intrinsically safe barrier, and with the control circuitry and the intrinsically safe barrier being supplied with power from the same power source, and the power source being directly connected to the control circuitry and the intrinsically safe barrier. 
   Another object of the present invention is to provide a measuring system in which a sensor array can be located in a hazardous area, the sensors of the sensor array may be isolated from control circuitry and power circuitry by an intrinsically safe barrier, and the control circuitry, the power circuitry and the intrinsically safe barrier are each preferably galvanically isolated from exterior circuit elements. 
   Still another object of the present invention is to provide a measuring system whose sensor array can be located in a hazardous area, such that the sensors of the sensor array are isolated from control circuitry and power circuitry by an intrinsically safe barrier, and the control circuitry, the power circuitry and the intrinsically safe barrier are co-located in an enclosure. 
   Accordingly, a system and method are provided to address at least some, if not all, of these objects is provided. This system includes a control logic arrangement powered by a power source, and an intrinsically safe barrier operatively connected to the control logic arrangement, and also powered by the same power source. The intrinsically safe barrier is adapted to be operatively connected to at least one sensor which is also powered by the same power source. The sensor is configured to communicate data representing a parameter to the control logic arrangement via the intrinsically safe barrier. The power source is directly connected to the control logic arrangement and the intrinsically safe barrier. 
   In an exemplary embodiment of the present invention, the system also includes a control interface powered by a further power source. The control interface is configured to receive data representative of the parameter from the control logic arrangement. The control interface may transmit commands to the sensor via the control logic arrangement and/or via the intrinsically safe barrier. Commands can also be forwarded to the sensor via the intrinsically safe barrier. 
   In another exemplary embodiment of the present invention, the control interface is powered by a further power source. The control interface is configured to receive data representing the parameter from the control logic arrangement, and to transmit commands directly to the sensor. The control logic arrangement can include a transformer having a positive terminal and a negative terminal, a capacitor having a first terminal and a second terminal, and a diode having a cathode and an anode. The anode is electrically connected to the positive terminal of the transformer and the first terminal of the capacitor. The logic arrangement also includes a processor electrically connected to the cathode of the diode, and electrically connected to negative terminal of the transformer and the second terminal of the capacitor. The control logic arrangement can also include a further transformer having a first terminal, a second terminal, a third terminal, and a fourth terminal. Such further transformer can be electrically connected to the processor, and to the processor. 
   In yet another exemplary embodiment of the present invention, the logic arrangement can also include a control interface electrically connected to the further transformer. The control interface may be configured to receive data representing the parameter from the control logic arrangement, and to the sensor via the control logic arrangement. The data may representing the process parameter received by the control logic arrangement from the sensor is digital data. In addition, such data can be transmitted using a communications protocol (e.g., a Fieldbus protocol). 
   In still another exemplary embodiment of the present invention, the intrinsically safe barrier electrically isolates the sensor from the control logic arrangement. Also, the intrinsically safe barrier can limit the voltage differential over the sensor to a particular limit (e.g., approximately 18 V). In addition, the intrinsically safe barrier limits the amount of current provided to the sensor to a particular current amount (e.g., approximately 120 mA). 
   According to a further embodiment of the present invention, the intrinsically safe barrier may include a fuse, a zener diode having a cathode and an anode, and a resistor having a first terminal and a second terminal. The first terminal of the resistor is electrically connected to the cathode of the zener diode and the fuse. The system can include an enclosure, such that the control logic arrangement and the intrinsically safe barrier are located within the enclosure. Also, the control logic arrangement, the intrinsically safe barrier and the sensor may be galvanically isolated from external components. 
   In a still further exemplary embodiment of the present invention, the intrinsically safe barrier can be adapted to be operatively connected to a second sensor,. The second sensor is powered by the power source, and configured to transmit data representing a further parameter via the intrinsically safe barrier to the control logic arrangement. The data representative of the second parameter received by the control logic arrangement from the second sensor is digital data which can be transmitted using a communications protocol (e.g., a Fieldbus protocol). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention, in which: 
       FIG. 1  is a block diagram of a first exemplary embodiment of a measuring system according to the present invention; 
       FIG. 2  is a circuit diagram of an exemplary embodiment of a communication and control logic assembly of the measuring system of  FIG. 1 ; 
       FIG. 3  is a circuit diagram of an exemplary embodiment of an intrinsically safe barrier of the measuring system of  FIG. 1 ; 
       FIG. 4  is a circuit diagram of an exemplary embodiment of a sensor array of the measuring system of  FIG. 1 ; 
       FIG. 5  is a circuit diagram of a second exemplary embodiment of a measuring system according to the present invention; and 
       FIG. 6  is a circuit diagram of a third exemplary embodiment of a measuring system according to the present invention. 
   

   Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the present invention will now be described in detail with reference to the drawings, it is done so in connection with the illustrative embodiments. It is intended that the changes and modifications can be made to the described embodiments without departing from the true scope and spirit of the subject invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a block diagram of a first exemplary embodiment of a measuring system  10  for sensing various process parameters and variables according to the present invention. The measuring system  10  utilizes a communication and control logic arrangement  12 , an intrinsically safe barrier  22  and a sensor array  32  to measure various process parameters. The communication and control logic arrangement  12  preferably provides power for the entire measuring system  10 , issues commands to the sensor array  32 , and receives information regarding various process parameters and variables from the sensor array  32 . The communication and control logic arrangement  12  also includes a first terminal  14  and a second terminal  16  which are connected to a first terminal  18  and a second terminal  20 , respectively, of the intrinsically safe barrier  22 . The intrinsically safe barrier  22  electrically isolates and protects a particular area (e.g., a protected area) in which no electric sparks are desired. In the measuring system  10 , the sensor array  32  is located in the protected area, and the communication and control logic arrangement  12  and the intrinsically safe barrier  22  are located outside the protected area. The intrinsically safe barrier  22  also includes a third terminal  24  and a fourth terminal  26  which are connected to a first terminal  28  and a second terminal  30 , respectively, of the sensor array  32 . The sensors of the sensor array  32  measure various process parameters, for example, temperature, pressure, humidity, etc. The various sensors in the sensor array  32  utilize a communications protocol, such as Fieldbus, to transmit a digital representation of the measured parameters to the communication and control logic arrangement  12  through the intrinsically safe barrier  22 . 
   In particular, the intrinsically safe barrier  22  is preferably an electrical system arrangement which is well known to those having ordinary skill in the art of manufacturing. The intrinsically safe barrier  22  electrically isolates and protects that protected area (e.g., a hazardous area) by preventing electrical power from being introduced into the protected area, by e.g., limiting power, current and voltage to certain levels so as to prevent the electric sparks from being generated therein. The sensor array  32  is located in the protected area, and the communication and control logic arrangement  12  and the intrinsically safe barrier  22  are located outside of the protected area. 
     FIG. 2  shows a circuit diagram of an exemplary embodiment providing certain details of the communication and control logic arrangement  12 , which includes the first terminal  14 , the second terminal  16 , a transformer  102 , a capacitor  104 , a diode  106  and a processor  108 . The transformer  102  of the communication and control logic arrangement  12  is preferably a power transformer that provides power to the measuring system  10 . A power source or network  120  provides power to the transformer  102  at a first power terminal  1020  and a second power terminal  1022 . The transformer  102  also includes a third power terminal  1024  and a fourth power terminal  1026 . The third power terminal  1024  of the transformer  102  and an anode  1060  of the diode  106  are electrically interconnected. Also, a cathode  1062  of the diode  106 , a first terminal  1040  of the capacitor  104 , a first terminal  1080  of the processor  108  and a first terminal  14  of the communication and control logic arrangement  12  are electrically connected to one another. Further, the fourth power terminal  1026  of the transformer  102 , a second terminal  1042  of the capacitor  104 , a second terminal  1082  of the processor  108 , and a second terminal  16  of the communication and control logic arrangement  12  are electrically interconnected. The capacitor  104  preferably acts as a power filtering device for the processor  108  and the intrinsically safe barrier  22  feeding power to the sensor array. In this manner, the capacitor  104  (and the diode  106 ) can be referred to a power arrangement which is preferably directly connected to the processor  108  and to the intrinsically safe barrier  22 . The communication and control logic arrangement  12  is preferably powered by the transformer  102  and the capacitor  104 . In a particular embodiment of the present invention, the transformer  102  provides 18V to the measuring system  10 , and the capacitor  104  is a 1 mF capacitor. 
   The measuring system  10  is designed so that the communication and control logic arrangement  12 , while being located physically and electrically outside the protected area, is nevertheless in communication with the various sensors of the sensor array  32  which are located on the opposite side of intrinsically safe barrier  22 , and provided within the protected area. The processor  108  transmits commands to these various sensors of the sensor array  32  by utilizing a particular communications protocol and receives commands from the various sensors of the sensor array  32  utilizing a communications protocol which is compliant with the protocol of the sensors. In an exemplary embodiment of the present invention, the communications protocol is Fieldbus. In another certain embodiment, the communications protocol is HART® protocol, PROFIBUS® protocol, etc. 
     FIG. 3  shows a circuit diagram of an exemplary embodiment of the intrinsically safe barrier  22  of the measuring system  10  of FIG.  1 . This exemplary intrinsically safe barrier  22  includes the first terminal  18 , the second terminal  20 , the third terminal  24 , the fourth terminal  26 , a fuse  110 , a zener diode  112  and a resistor  114 . The first terminal  18  of the intrinsically safe barrier  22  and a first terminal  1100  of the fuse  110  are electrically connected. The fuse  110  of the intrinsically safe barrier  22  acts as a current limiter of the voltage across the zener diode  112 . The fuse  110  will preferably “blowout” thus creating an open circuit between the first terminal  1100  and a second terminal  1102  of the fuse  110  if the voltage provided across the fuse  110  and the zener diode  112  exceeds a predetermined amount. The second terminal  1102  of the fuse  110 , a cathode  1120  of the zener diode  112  and a first terminal  1140  of the resistor  114  are electrically connected to one another. A second terminal  1140  of the resistor  114  is electrically connected to the third terminal  24  of the intrinsically safe barrier  22 . In addition, an anode  1122  of the zener diode  112 , the second terminal  20  of the intrinsically safe barrier  22 , and the fourth terminal  26  of the intrinsically safe barrier  22  are electrically connected. With this exemplary configuration, the intrinsically safe barrier  22  allows electrical power to be introduced into the protected area, while limiting power, current and voltage to particular levels so as to prevent the electric sparks. 
   In one exemplary embodiment of the present invention, the predetermined amount of voltage that would likely make the fuse  110  “blowout” is preferably smaller than the zener voltage of the zener diode  112 , thereby protecting the zener diode  112  from experiencing an avalanche breakdown. In another exemplary embodiment of the present invention, the zener diode  22  has a zener voltage of, e.g., 18 V. The zener diode  112  and the resistor  114  operate to limit the voltage drop and current flow between the first terminals and the second terminals of the sensors of the sensor array  32  to a second predetermined amount and a third predetermined amount, respectively. In yet another exemplary embodiment of the present invention, the second predetermined amount for the first terminals of the sensors of the array  32  is, e.g., 18V and the third predetermined amount for the second terminals of the sensors of the sensor array  32  is, e.g., 120 mA. In a certain embodiment, the resistor  114  is a 100 Ω resistor. 
     FIG. 4  shows a circuit diagram of an exemplary embodiment of the sensor array  32  of the present invention. The exemplary sensor array  32  includes the first terminal  28 , the second terminal  30 , a first sensor  116  and a second sensor  118 . The first terminal  28  of the sensor array  32 , a first terminal  1160  of the first sensor  116  and a first terminal  1180  of the second sensor  118  are electrically connected to one another. In addition, the second terminal  30  of the sensor array  32 , a second terminal  1162  of the sensor  116  and a second terminal  1182  of the sensor  118  are electrically connected to one another. The first and second sensors  116 ,  118  of the sensor array  32  communicate with the processor  108  of the communication and control logic assembly  12  by utilizing a particular communications protocol which is compatible for each such device. Although the first and second sensors  116 ,  118  of the sensor array  32  are located in the unprotected or hazardous area, and the processor  108  is provided in the protected or safe area, the first and second sensors  116 ,  118  can communicate with the processor  108  using such particular communications protocol via the intrinsically safe barrier  22 . 
   The measuring system  10  can be galvanically isolated, such that no ground is needed or provided at any portion thereof. By omitting the ground from the measuring system  10 , the processor  108  can draw power from the transformer  102 , and communicate with the first and second sensors  116 ,  118  of the sensor array  32 . Additionally, the transformer  102 , the capacitor  104 , the diode  106 , the processor  108 , the fuse  110 , the zener diode  112  and the resistor  114  can all be situated in a single enclosure to minimize the size of the entire measuring system  10 . 
     FIG. 5  illustrates a circuit diagram of a second exemplary embodiment of the measuring system  10  according to the present invention. For example, this measuring system  10  can be a circuit diagram version of the measuring system  10  of FIG.  1 . The differences between the measuring system illustrated in FIG.  5  and the measuring system  10  as shown in  FIG. 1  are that the terminals  14 ,  16 ,  18 ,  20 ,  24 ,  26 ,  28  and  30  are omitted from the measuring system  10  as shown in  FIG. 5  for the sake of simplicity. However, it is within the scope of the present invention for this second exemplary embodiment of the measuring system  10  to include additional components (e.g., fuses) so as to reduce the possibility of overloading the barrier  22  and/or the sensors. As described above, the capacitor  104  (and the diode  106 ) can be thought of as forming a power arrangement which is directly connected to the processor  108  and to the intrinsically safe barrier  22 . 
     FIG. 6  illustrates a third exemplary embodiment of a measuring system  600  according to the present invention which is substantially similar to the second embodiment of the measuring system  10  shown in FIG.  5 . The differences between the measuring system  600  shown in FIG.  6  and the measuring system  10  shown in  FIG. 5  is that the exemplary measuring system  600  includes a transformer  602  and a control interface  604 . One side of the transformer  602  is connected in parallel with the processor  108  and the intrinsically safe barrier  22 . The other side of the transformer  602  is connected in parallel to the control interface  604 . In this exemplary system  600 , the transformer  602  electrically isolates the control interface  604  from the rest of the measuring system  600 , and the control interface  604  allows the user thereof to control the sensors  116 ,  118  located in the sensor array  32  from an electrically isolated location. Preferably, the control interface  604  receives the readings from the sensors  116 ,  118  of the sensor array  32  after the readings from the sensors  116 ,  118  of the sensor array  32  have been aggregated by the processor  108 . 
   The control interface  604  of the exemplary measuring system  600  shown in  FIG. 6  also transmits commands to the sensors  116 ,  118  of the sensor array  32 . This control interface  604  can utilize a particular communications protocol (which is known to those having ordinary skill in the art) to transmit commands for the sensors  116 ,  118  to the processor  108 , which in turn sends the commands to the sensors  116 ,  118  of the sensor array  32 . In another embodiment of the measuring device  600  of the present invention, the communications protocol is Fieldbus protocol. In yet another embodiment of the present invention, the communications protocol is HART® protocol. In still another certain embodiment, the communications protocol is PROFIBUS® protocol. In a further embodiment of the measuring device  600 , the control interface  604  transmits commands directly to the sensors  116 ,  118 , thus circumventing the processor  108 . 
   While the invention has been described in connecting with preferred embodiments, it will be understood by those of ordinary skill in the art that other variations and modifications of the preferred embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those of ordinary skill in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are considered as exemplary only, with the true scope and spirit of the invention indicated by the following claims.