Abstract:
An arrangement operable to communicate with a fieldbus network and operate an attached relay and a method for implementing such arrangement is provided. The arrangement and method provide conventional discrete outputs from a fieldbus device using standard fieldbus function blocks, such as those used for Foundation® and Profibus® fieldbus networks. The arrangement and method may facilitate the integration of traditional discrete relay functions into these more advanced digital fieldbus networks, and also utilize additional functions available to standard Foundation® fieldbus and Profibus® fieldbus network devices.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to a fieldbus relay arrangement. In particular, the invention is directed towards a fieldbus relay arrangement and method for implementing such arrangement which makes discrete outputs available using standard function blocks in Foundation® fieldbus and Profibus® fieldbus networks, and which can further utilize the additional functions available to standard Foundation® fieldbus and Profibus® fieldbus network devices. 
   BACKGROUND OF THE INVENTION 
   The Use of Fieldbus for Process Control Applications 
   Process control systems and methods provide a way for ensuring efficiency, reliability, profitability, quality and safety in a process/product manufacturing environment. Such process control systems and methods can be used for automation, monitoring and control in a wide array of industrial applications for many industry segments, including textiles, glass, pulp and paper, mining, building, power, sugar, food and beverage, oil and gas, steel, water and wastewater, chemicals, etc. 
   The conventional process control systems and methods generally operate with a plurality of field devices positioned at various locations on, e.g., a 4–10 mA analog network. These devices include measurement and control devices (such as temperature sensors, pressure sensors, flow rate sensors, control valves, switches, etc., or combinations thereof). Recently, a number of protocols have been introduced which provide a digital alternative to conventional control systems and methods, and which utilize “smart” field devices. These “smart” field devices can provide the same functionality as the conventional devices listed above, and may additionally include one or more microprocessors, one or more memories, and other components incorporated therein. Such smart field devices can be communicatively coupled to each other and/or to a central processor using an open smart communications protocol. These protocols (e.g. FOUNDATION® Fieldbus protocol) have been widely used in manufacturing and process plants. Many of such protocols were developed for non-process control environments, such as automobile manufacturing or building automation, and were later adapted to be used for process control. Some of the more widely used fieldbus protocols include HART®, PROFIBUS®, FOUNDATION® Fieldbus, Controller Area Network protocols, etc. 
   Fieldbus process control systems and methods may also utilize a controller communicatively coupled to each of the smart field devices using an open, “smart” communications protocol, and a server communicatively coupled to the controller using, for example, an Ethernet connection. Moreover, this controller may include a processor, and can receive data from each of the “smart” field devices. These “smart” field devices preferably include a processor for performing certain functions thereon, without the need to use the central host for such functions. The amount of processing by the centralized host generally depends on the type of a control application and protocol used. 
   A smart fieldbus device, as configured by a software configurator, may be programmed to execute function blocks. A function block provides the fundamental automation functions that are performed by the process control application—function blocks are essentially a software model which defines the behavior of the process control system. More particularly, the function block is a software logic unit which processes input parameters according to a specified algorithm and an internal set of control parameters, and produces resulting output parameters that are available for use within the same function block application or by other function block applications. The input parameters of one function block may be linked to the output parameters of other function blocks on the fieldbus. The execution of each function block can be scheduled. After the function block is executed using the corresponding input values, its outputs are updated and then broadcast on the network, where they can be read by inputs of other function blocks using this information. These linked function blocks may reside either inside the same field device or in different devices on the network. 
   The function blocks replace many of the functions which were traditionally performed by hardware. They provide flexibility in a process control environment, since they may be modified, added or removed, without having to rewire or change the hardware of the system. Different function blocks are defined for use in FOUNDATION® fieldbus and PROFIBUS® fieldbus networks. For example, the Fieldbus Foundation establishes a set of ten standard function blocks for basic control, which are specifically defined in the FF-891 Function Blocks—Part 2 specification. This initial set of 10 function blocks released by the Fieldbus Foundation generally addresses over 80 percent of the basic process control configurations. An additional 19 standard function blocks for advanced control are defined in the FF-892 Function Blocks—Part 3 specification. 
   Three different types of function blocks are used in the fieldbus applications. For example, Resource Blocks define parameters that pertain to the entire application process (e.g., manufacturing ID, device type, etc.). Function Blocks encapsulate control functions (e.g., PID controller, analog input, etc.). Transducer Blocks represent an interface to sensors such as temperature, pressure and flow sensors. 
   Each function block in the system is identified by a unique tag which is assigned by the user. The parameters of each function block are represented by object descriptions that define how the parameters are communicated on the fieldbus network. Thus, many parameters in the system are uniquely identified by their reference to their block tag and parameter name. 
   Each fieldbus device likely has a Resource Block and at least one Function Block with input and/or output parameters that link to other function blocks, either in the same device or in separate devices by using the bus. Each input/output parameter includes a particular value portion and a particular status portion. The status portion of each parameter includes information regarding the reliability of the data contained in the input/output parameter, and instructs the receiving function block as to whether the reliability of contained data is acceptable, uncertain or unacceptable. In addition, a Function Block Application Process (“FBAP”) can specify the handling of control modes, alarms, events, trend reports and views. These features comply with the FOUNDATION® Fieldbus specification in order for the device to be considered interoperable at a User Layer. 
   Distribution of control to the field devices can be performed by synchronizing the execution of the function block and transmitting the function block parameters on the fieldbus network. Such function, along with the publication of the time of day to the devices, an automatic switch over to a redundant time publisher, an automatic assignment of device addresses, and a search for parameter names or “tags” on the fieldbus, are generally handled by System Management and Network Management. 
   A control strategy may be created through the interconnection of various function blocks contained by the field devices. The control strategy may also be modified without any hardware changes, thus providing another level of flexibility. The creation of the function blocks and control strategies further includes the automatic assignment of device addresses and parameter indexes. The function blocks and control strategies are described in the FOUNDATION® fieldbus and PROFIBUS® fieldbus specifications, both of which are incorporated herein by reference. 
   Relays 
   Relays are used in process control and other applications to control a load in response to a control line input as well as to control various conventional devices, such as alarm generators, limit switches and motors. Many types of relays are unintelligent devices that merely conduct a load current when an input voltage is above or below a particular threshold input value. An early conventional relay is generally an electromechanical device in which a solenoid is used to connect two switch contacts. Recently, solid state relays have become more widely used. However, these conventional relay devices are not compatible with the advanced technologies that have recently been developed for intelligent process automation and control. 
   Some relays may contain microprocessors and memory, and can perform logic functions: such relays are described in U.S. Pat. No. 6,360,277 the entire disclosure of which is incorporated herein by reference. The relays described in this publication are addressable, can store various protocols internally, and may therefore be inter-operable with various different process control networks. These relays can provide standard discrete outputs for the fieldbus network. 
   However, no fieldbus relay exists which can be easily integrated into a fieldbus control scheme by executing fieldbus function blocks, receiving power from the fieldbus network, and performing various other functions which are generally performed by FOUNDATION® or PROFIBUS® fieldbus devices. Such relay may allow the system to be homogenous, and can simplify a control strategy configuration by enabling a seamless integration of traditional discrete-controlled components into an advanced FOUNDATION® fieldbus or PROFIBUS® fieldbus process control scheme. 
   SUMMARY OF THE INVENTION 
   Therefore, a need has arisen to provide a relay arrangement and method which overcomes the above-described and other shortcomings of the conventional systems and processes. According to an exemplary embodiment of the present invention, a fieldbus relay arrangement is provided. The arrangement provides conventional discrete outputs using standard fieldbus function blocks. In one exemplary embodiment of the present invention, the fieldbus relay arrangement includes a central processing unit, a storage arrangement and a relay. The arrangement can execute standard function blocks, and may control outputs of the relay based on this execution. In one exemplary variation, the arrangement may include multiple processors which can be dedicated to various tasks, such as for a communications with the fieldbus network or for processing the function blocks. Additionally, the arrangement may include various types of storage arrangements, e.g., flash memory, RAM, ROM, and EEPROM. The exemplary embodiment of the fieldbus relay arrangement according to the present invention can operate in a manner similar to that of other Foundation® or Profibus® fieldbus devices, e.g., the arrangement may obtain power from the fieldbus, transmit status information via standard status variables defined in the FOUNDATION® and PROFIBUS® fieldbus specifications, etc. 
   The exemplary embodiment of the fieldbus relay arrangement according to the present invention may execute a plurality of fieldbus function blocks. These function blocks may include resource blocks, edge trigger and flip-flop blocks, analog alarm blocks, timer blocks, discrete output blocks, arithmetic blocks, input selector blocks, Proportional-Integral-Derivative (PID) control blocks and step-output PID control blocks, etc. 
   In another exemplary embodiment according to the present invention, the arrangement may include one or more optically-isolated solid-state relays. The relays may be operated automatically based on the operation of the function block, and/or manually using a tool which can magnetically activate the relays of the arrangement. The arrangement may further include a liquid-crystal display (LCD) for displaying certain information (e.g., device status, etc.). 
   One of the advantages of the present invention is that the fieldbus relay can be considered as any other device on the FOUNDATION® or PROFIBUS® fieldbus, and may be operated with the same advanced level of control as any other fieldbus device. Fieldbus control strategies can thereby be configured with uniformity. Further, a conversion of existing control systems to FOUNDATION® or PROFIBUS® fieldbus systems can be simplified since a modification of existing output field elements is likely minimized. The use of the fieldbus relay arrangement according to the present invention makes the use of conventional discrete-controlled devices completely transparent at the fieldbus control configuration level. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, the objects satisfied thereby, and further objects, features, and advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
       FIG. 1  is a block diagram of a first exemplary embodiment of a fieldbus relay arrangement according to the present invention. 
       FIG. 2  is a block diagram of a second exemplary embodiment of the fieldbus relay arrangement according to the present invention. 
       FIG. 3  is a front view of a third exemplary embodiment of the fieldbus relay arrangement according to the present invention showing the physical connectors of the arrangement. 
       FIG. 4  is a block diagram of an exemplary embodiment of a portion of the fieldbus relay arrangement according to the present invention coupled to a fieldbus network. 
       FIG. 5  is an exemplary fieldbus installation that includes an exemplary embodiment of the fieldbus relay arrangement of  FIGS. 1–3 . 
       FIG. 6  is a block diagram of a fourth exemplary embodiment of the fieldbus relay arrangement according to the present invention that can be used for switching to a conventional output device. 
       FIG. 7  is a block diagram of a fifth exemplary embodiment of the fieldbus relay arrangement according to the present invention that can be used for switching to a conventional output device in an alarm-type application. 
       FIG. 8  is a block diagram of a sixth exemplary embodiment of the fieldbus relay arrangement according to the present invention that can be used for PID-step applications. 
   

   DETAILED DESCRIPTION 
   Preferred embodiments of the present invention and their advantages may be understood by referring to  FIGS. 1–8 , like numerals being used for like corresponding parts in the various drawings. 
     FIG. 1  shows a first exemplary embodiment of a fieldbus relay arrangement  10  according to the present invention. This exemplary fieldbus relay arrangement  10  includes a main circuit board  20  which has coupled thereto or contains therein certain components such as power supply and signal shaper  30 , a firmware download interface  40 , a flash memory  50 , a random access memory (RAM)  60 , a modem  70 , a factory reset module  80 , as well as a central processing unit (CPU) with electrically erasable programmable read-only memory (EEPROM)  90 . In addition to the main circuit board  20 , the relay arrangement  10  may include a relay apparatus  100  that has an optical isolation circuit  120  and a fuse  130 . Output connectors  160  are provided for connecting a load  140  and a power supply  150  in parallel with the relay arrangement  10  of the present invention for switching purposes in a FOUNDATION® or PROFIBUS® fieldbus network. 
   In particular, the control components of the main circuit board  20  are operable to perform various control and communications functions, including storing and modifying certain status variables, executing fieldbus function blocks, communicating with other field devices on the H1 fieldbus network, etc. For example, an executing function block can instruct the CPU  90  to control the switching operation in the relay apparatus  100 , thus affecting the outputs  160  and the load  140  in an output circuit. 
     FIG. 2  shows a block diagram of a second exemplary embodiment of the fieldbus relay arrangement  200  according to the present invention. In this exemplary embodiment, the output circuit can include two separate relay outputs. For example, the fieldbus interface  210  can connect the fieldbus relay arrangement  200  to the fieldbus network. The output circuit may include two or more optical isolation circuits  120  and two or more fuses  130 , each connected in parallel with the respective loads  140  and power supplies  150  via the respective output connectors  160  of the relay arrangement of the present invention for executing the switching operations. It should be understood by those skilled in the art that power supply  150  can be either an A.C. or D.C. power supply. 
     FIG. 3  shows a front view of a third exemplary embodiment of the fieldbus relay arrangement  300  according to the present invention which may include a plurality of exterior electrical connectors. An external power supply may be connected to power supply terminals  310  so as to provide power for the exemplary relay arrangement  300 . Communication terminals  330  may be used for coupling the relay arrangement  300  to the fieldbus networks to, e.g., communicate with other field devices on the FOUNDATION® or PROFIBUS® fieldbus network. Relay output terminals  340  and  350  can be provided as discrete outputs, and may facilitate a switching functionality from the respective relays of the relay arrangement  300 . 
     FIG. 4  illustrates an exemplary portion of any one of the fieldbus relay arrangements of  FIGS. 1–3  as integrated into an exemplary fieldbus network  420  (e.g., the FOUNDATION® or PROFIBUS® fieldbus networks). A computer  410  may be coupled to the fieldbus network  420  for configuring and controlling fieldbus field devices  430  attached thereto. The exemplary fieldbus relay arrangement  100 ,  200 , or  300  can be coupled to the fieldbus network  420 . An output circuit  440  of Fieldbus relay arrangement  200  may include two or more loads connected to a power supply. The fieldbus relay arrangement of  FIG. 4  may communicate with the fieldbus network  420  in the same manner as any other field device  430 . Also, in accordance with the execution results of the function blocks, this fieldbus relay arrangement can switch the relays  200  connected at the output circuit  440 . 
     FIG. 5  shows another exemplary embodiment of one or more fieldbus relay arrangements  560  according to the present invention, which is illustrated as being integrated into an exemplary fieldbus process control scheme  500 . In this scheme  500 , a power supply  510  can be utilized to provide power to the fieldbus network. Interface devices or cards  530  may be installed into or connected to a computer (e.g., personal computer, server, etc.), and facilitate the control and configuration of the fieldbus network and devices situated thereon using a software configuration program (e.g., Smar Research&#39;s Syscon software). Trunks  540  and spurs  550  may be used to interconnect segments of the fieldbus network and a plurality of devices, and junction boxes  520  can provide junctions for the branches in the fieldbus network. The exemplary fieldbus relay arrangements  560  are coupled to the fieldbus network via the spurs  550 , which may provide power to the relay arrangements and communications with the other field devices attached to the fieldbus network. In addition, these fieldbus relay arrangements  560  may execute the function blocks in accordance with the configuration set forth in the FOUNDATION® or PROFIBUS® fieldbus specification. Also, the function blocks can direct the fieldbus relay arrangements  560  to switch their outputs to control the conventional discrete process control devices  570 . In one example, the process control devices  570  may be used to monitor and control the flow of a liquid through a conduit  580  attached thereto. 
     FIG. 6  shows a block digram of an exemplary embodiments of a fieldbus control system  600  according to the present invention. This control system includes the computer  410  which is used to monitor, control a configure a fieldbus network  660  (e.g, the fieldbus network). As provided in this exemplary embodiment, a fieldbus relay arrangement  610  includes a discrete output (DO) function blocks  650 . This fieldbus relay arrangement  610  may execute the instructions of the function block  650 , and communicate data such as an output value and status variable (corresponding with such execution) to a relay apparatus  630 , which may, in turn, switch the relay output to, e.g., enable or disable an alarm signal lamp  620  in response to a particular condition. 
     FIG. 7  illustrates another exemplary embodiments of a fieldbus relay arrangement  700  for an alarm detection according to the present invention which is connected to a fieldbus network  770  and to a pressure sensor fieldbus device  780 . In particular, the pressure sensing fieldbus device  780  may include a transducer (“TRD”) function block  785  and an analog input (“AI”) function block  790 . This pressure sensing fieldbus device  780  may be used to monitor a pressure level  795 , and may transmit a signal  760  to the fieldbus relay arrangement  700  when a particular predetermined alarm condition occurs. The signal  760  can be received by an alarm function block  750  which can send an output signal to a discrete output (DO) function block  740 . The DO function block  740  can transmit a signal to a transducer block  730  which is coupled to an output  720  of the fieldbus relay arrangement  700 . An alarm signal lamp  710  can be connected to the output  720  of the fieldbus relay arrangement  700 , and may be illuminated due to the occurrence of the predefined alarm condition. Numerous other discrete devices may be used instead of or in addition to the alarm signal lamp  710 , as would be understood by those skilled in the art. 
   Referring to a block diagram of  FIG. 8 , another exemplary embodiment of the fieldbus relay arrangement of the present invention is illustrated, which may be used when, e.g., a final control element has an actuator that can be driven by an electric motor with an actual position feedback. The final control element may be positioned by rotating the motor clockwise or counter-clockwise. This positioning may be accomplished by activating a discrete signal of the motor for each direction. For example, a control valve may use one control signal to open and another control signal to close itself. Also, when no signal is applied, the valve may be configured to maintain its current position. The exemplary embodiment of the fieldbus relay arrangement  800  of  FIG. 8  includes two discrete relay outputs  850 , and thus can be utilized to implement such exemplary operation. A proportional/Integral/Derivative (PID) Step control block  810  may provide an output  820  to a transducer block (TRD)  830 . This transducer block  830  may be used to convert the control signal into a form suitable for controlling the motor which is connected to relay outputs  850  of a relay module  840  of the fieldbus relay arrangement  800 . 
   The exemplary embodiments of the fieldbus relay arrangements of the present invention can be used in a variety of process control applications which are not necessarily related to manufacturing processes. For example, the relay arrangement may be utilized for a building automation process and operation. In particular, such arrangement may be used to control the opening and closing of solenoid valves for water and gas control in an apartment building, in a manner similar to that described above with reference to the relay arrangement of  FIG. 5  for controlling a flow of a liquid. A variety of other building automation applications could be used as is apparent to those with ordinary skill in the art.