Apparatus to communicatively couple three-wire field devices to controllers in a process control system

Example apparatus to communicatively couple three-wire field devices to controllers in a process control system are disclosed. An example terminal block is disclosed that includes a first interface having three termination points to terminate each of three wires from a three-wire field device. The example, terminal block further includes a second interface to removably receive a first termination module that is to communicate with the three-wire field device using a first communication protocol and to communicate with a controller via a shared bus of a termination panel using a second communication protocol different than the first communication protocol.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to process control systems and, more particularly, to apparatus to communicatively couple three-wire field devices to controllers in a process control system.

BACKGROUND

Process control systems, like those used in chemical, petroleum, pharmaceutical, pulp and paper, or other manufacturing processes, typically include one or more process controllers communicatively coupled to at least one host including at least one operator workstation and to one or more field devices configured to communicate via analog, digital or combined analog/digital communication protocols. The field devices, which may be, for example, device controllers, valves, valve actuators, valve positioners, switches and transmitters (e.g., temperature, pressure, flow rate, and chemical composition sensors) or combinations thereof, perform functions within the process control system such as opening or closing valves and measuring or inferring process parameters. A process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine, and generates control signals that are sent over the buses or other communication lines to the field devices to control the operation of the process control system.

A process control system can include a plurality of field devices that provide several different functional capabilities and that are often communicatively coupled to process controllers using two-wire interfaces in a point-to-point (e.g., one field device communicatively coupled to a field device bus) or a multi-drop (e.g., a plurality of field devices communicatively coupled to a field device bus) wiring connection arrangements or with wireless communications. Some field devices are configured to operate using relatively simple commands and/or communications (e.g., an ON command and an OFF command). Other field devices are more complex requiring more commands and/or more communication information, which may or may not include simple commands. For example, more complex field devices may communicate analog values with digital communications superimposed on the analog value using, for example, a Highway Addressable Remote Transducer (“HART”) communication protocol. Other field devices can use entirely digital communications (e.g., a FOUNDATION Fieldbus communication protocol).

Some field devices (e.g., photoelectric or capacitive sensors) are implemented using a three-wire architecture to enable communications as well as to provide power to such devices. Typically, such three-wire field devices are coupled to an external power source (and associated external fuse) to power the device in addition to being coupled to one or more I/O cards.

SUMMARY

Example apparatus to communicatively couple three-wire field devices to controllers in a process control system are disclosed. An example terminal block is disclosed that includes a first interface having three termination points to terminate each of three wires from a three-wire field device. The example terminal block further includes a second interface to removably receive a first termination module that is to communicate with the three-wire field device using a first communication protocol and to communicate with a controller via a shared bus of a termination panel using a second communication protocol different than the first communication protocol.

Another example terminal block is disclosed that includes a first interface including three wire termination points. Each of the wire termination points is to terminate corresponding ones of three wires from a three-wire field device. The example terminal block further includes a second interface to be communicatively coupled to a shared bus of a baseplate of a termination panel, the shared bus communicatively coupled to a controller of a process control system to enable communications between the controller and the three-wire field device.

An example apparatus is disclosed that includes a plurality of baseplates on a termination panel including a shared bus. The example apparatus further includes a terminal block communicatively coupled to a first one of the baseplates. The terminal block is to removably receive a first termination module to communicate with a controller via the shared bus. The terminal block includes a first interface to terminate each of three wires from the three-wire field device to communicatively couple the first termination module and the three-wire field device.

DETAILED DESCRIPTION

Although the following describes example apparatus and systems including, among other components, software and/or firmware executed on hardware, it should be noted that such systems are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of these hardware, software, and firmware components could be embodied exclusively in hardware, exclusively in software, or in any combination of hardware and software. Accordingly, while the following describes example apparatus and systems, persons of ordinary skill in the art will readily appreciate that the examples provided are not the only way to implement such apparatus and systems.

An example process control system includes a control room (e.g., a control room108ofFIG. 1), a process controller area (e.g. a process controller area110ofFIG. 1), a termination area (e.g., a termination area140ofFIG. 1), and one or more process areas (e.g., process areas114and118ofFIG. 1). A process area includes a plurality of field devices that perform operations (e.g., controlling valves, controlling motors, controlling boilers, monitoring, measuring parameters, etc.) associated with performing a particular process (e.g., a chemical process, a petroleum process, a pharmaceutical process, a pulp and paper process, etc.). Some process areas are not accessible by humans due to harsh environment conditions (e.g., relatively high temperatures, airborne toxins, unsafe radiation levels, etc.). The control room typically includes one or more workstations within an environment that is safely accessible by humans. The workstations include user applications that users (e.g., engineers, operators, etc.) can access to control operations of the process control system by, for example, changing variable values, process control functions, etc. The process control area includes one or more controllers communicatively coupled to the workstation(s) in the control room. The controllers automate control of the field devices in the process area by executing process control strategies implemented via the workstation. An example process strategy involves measuring a pressure using a pressure sensor field device and automatically sending a command to a valve positioner to open or close a flow valve based on the pressure measurement. The termination area includes a marshalling cabinet that enables the controllers to communicate with the field devices in the process area. In particular, the marshalling cabinet includes a plurality of termination modules used to marshal, organize, or route signals from the field devices to one or more I/O cards communicatively coupled to the controllers. The I/O cards translate information received from the field devices to a format compatible with the controllers and translate information from the controllers to a format compatible with the field devices.

Known techniques used to communicatively couple field devices within a process control system to controllers involve using a separate bus (e.g., a wire, a cable, or a circuit) between each field device and a respective I/O card communicatively coupled to a controller (e.g., a process controller, a programmable logic controller, etc.). An I/O card enables communicatively coupling a controller to a plurality of field devices associated with different data types or signal types (e.g., analog in (AI) data types, analog out (AO) data types, discrete in (DI) data types, discrete out (DO) data types, digital in data types, and digital out data types)) and different field device communication protocols by translating or converting information communicated between the controller and the field devices. For example, an I/O card may be provided with one or more field device interfaces configured to exchange information with a field device using the field device communication protocol associated with that field device. Different field device interfaces communicate via different channel types (e.g., analog in (AI) channel types, analog out (AO) channel types, discrete in (DI) channel types, discrete out (DO) channel types, digital in channel types, and digital out channel types)). In addition, the I/O card can convert information (e.g., voltage levels) received from the field device into information (e.g., pressure measurement values) that the controller can use to perform operations associated with controlling the field device. The known techniques require a bundle of wires or buses (e.g., a multi-core cable) to communicatively couple a plurality of field devices to I/O cards.

Unlike these known techniques that use a separate bus to communicatively couple each field device to corresponding I/O cards, some known apparatus and methods communicatively couple field devices to an I/O card by terminating a plurality of field devices at a termination panel (e.g., a marshalling cabinet) and using one bus (e.g., a conductive communication medium, an optical communication medium, a wireless communication medium) communicatively coupled between the termination panel and the I/O card to communicatively couple the field devices to the I/O card. Such apparatus and methods are disclosed in U.S. Pat. No. 8,332,567, filed on Sep. 19, 2006; U.S. Pat. No. 8,762,618, filed on Dec. 10, 2012; U.S. patent application Ser. No. 14/170,072, filed on Jan. 31, 2014; and U.S. patent application Ser. No. 14/592,354, filed on Jan. 8, 2015; all of which are hereby incorporated by reference in their entireties. In brief, such techniques involve using an example universal I/O bus (e.g., a common or shared communication bus) that communicatively couples a plurality of termination modules to one or more I/O cards communicatively coupled to a controller. Each termination module is communicatively coupled to one or more respective field devices using a respective field device bus (e.g., an analog bus or a digital bus) from each field device that terminates on a terminal block that is communicatively coupled with a corresponding termination module. In some examples, the termination modules are CHARMs (characterization modules) developed by Emerson Process Management. The termination modules are configured to receive field device information from the field devices via the field device buses and communicate the field device information to the I/O cards via the universal I/O bus by, for example, packetizing the field device information and communicating the packetized information to the I/O cards via the universal I/O bus. The I/O card(s) can extract the field device information received via the universal I/O bus and communicate the field device information to the controller, which can then communicate some or all of the information to one or more workstation terminals for subsequent analysis. Likewise, the I/O cards can packetize the field device information from workstation terminals and communicate the packetized field device information to the plurality of termination modules via the universal I/O bus. Each of the termination modules can then extract or depacketize respective field device information from the packetized communications received from a respective I/O card and communicate the field device information to a respective field device.

Each of the termination modules may be coupled to a different type of field device that communicates using a different communication protocol. As such, in addition to relaying information between the I/O cards and the field devices, the termination modules communicate with the corresponding field devices using a first communication protocol associated with the field device and communication with the I/O cards based on a second protocol associated with the universal I/O bus. Thus, while different termination modules may use different communication protocols to communicate with particular field devices, all of the termination modules use the same communication protocol to communicate with the I/O cards. In this manner, the communications back to the controller are significantly simplified.

Communications with many field devices in a process control system are implemented using a two-wire architecture. For example, in a 2-wire discrete input (DI) field device, one wire is used to feed (e.g., power and/or apply an electrical signal to) a contact input of the field device and cause current to flow when the contact is closed. The second wire in a 2-wire DI field device is used for the output signal of the field device that serves as the input to the process control system (e.g., provides feedback indicating whether the contact is open or closed). Known terminal blocks provide interfaces to directly couple each of the two-wires to a controller in a process control system and/or a termination module as described above which, in turn, communicates with a controller.

By contrast, some field devices are 3-wire field devices that have three wires to enable communications and provide power to the field device to operate. For example, in a 3-wire DI field device, a first wire is used to feed (e.g., power and/or apply an electrical signal to) the field device and the contact input. A second wire of a 3-wire DI field device is used specifically to power the field device. A third wire is used for the output signal of the field device that serves as the input to the process control system. While there are known terminal blocks that can be communicatively coupled directly with a 2-wire field device, there are no terminal blocks that can be communicatively coupled with a 3-wire DI field device without additional components and complexity. For example, a 3-wire field device may be wired to a known termination module for purposes of communications via a known terminal (2-wire) block but the field device must also be wired to an external power source to power the device. Such wiring can involve as many as five external wire terminals in addition to the two used to connect wires to the terminal block. That is, there are two wire terminals associated with the terminal block, an additional two terminals associated with the external power source, and three more terminals to enable the coupling of each of the three wires of the field device with the terminal block and the external power source. Furthermore, adding an external power source in this manner also requires the use of an external fuse between the external power source and the S-wire field device to protect against a short circuit as the power source is not typically energy limited. These additional components and wiring requirements result in increased cost and complexity to implement a 3-wire field device. Some known systems employ specially manufactured terminal blocks to facilitate the wiring of such 3-wire field devices. However, when an engineer or other plant personnel desires to change the signal sensing components attached to such a terminal block (e.g., the DI electronics), the terminal block and all the associated wiring needs to be undone and/or removed. Furthermore, known terminal blocks for 3-wire DI field devices do not include a fuse such that additional components are still required.

The example terminal blocks constructed in accordance with the teachings disclosed herein overcome the above complexities to facilitate the direct coupling of 3-wire field devices to a process control system. In some examples, the terminal blocks disclosed herein include three wire terminals on which each of the three wires of a 3-wire DI field device may be landed to directly couple the field devices to the corresponding termination modules. In some examples, the terminal blocks are communicatively coupled to an external power source to provide power to each of the termination modules to provide the necessary power to the corresponding 3-wire field devices. That is, in some examples, the need to separately couple each S-wire field device to an external power source is avoided because the terminal blocks provide an interface between the power source and the field devices. Further, in some examples, a fuse is built into the terminal blocks disclosed herein to provide surge protection without the need for a separate external fuse. In some such examples, the fuse is replaceable. In some examples, the terminal blocks disclosed herein enable the replacement or changing of termination modules containing the signal sensing components (e.g., the DI electronics contained within the corresponding termination modules) without removing the terminal blocks and/or without unwiring the corresponding field devices to the terminal blocks. As a result, the initial wiring, maintenance, and/or updating of wiring for 3-wire DI field devices is substantially simplified with fewer components to save both time and money and reduce an overall footprint of the system.

Now turning toFIG. 1, an example process control system100is shown implemented according to the teachings of U.S. Pat. No. 8,332,567. The example process control system of100includes a workstation102communicatively coupled to a controller104via a bus or local area network (LAN)106, which is commonly referred to as an application control network (ACN). The LAN106may be implemented using any desired communication medium and protocol. For example, the LAN106may be based on a hardwired or wireless Ethernet communication protocol. However, any other suitable wired or wireless communication medium and protocol could be used. The workstation102may be configured to perform operations associated with one or more information technology applications, user-interactive applications, and/or communication applications. For example, the workstation102may be configured to perform operations associated with process control-related applications and communication applications that enable the workstation102and the controller104to communicate with other devices or systems using any desired communication media (e.g., wireless, hardwired, etc.) and protocols (e.g., HTTP, SOAP, etc.). The controller104may be configured to perform one or more process control routines or functions that have been generated by a system engineer or other system operator using, for example, the workstation102or any other workstation and which have been downloaded to and instantiated in the controller104. In the illustrated example, the workstation102is located in a control room108and the controller104is located in a process controller area110separate from the control room108.

In the illustrated example, the example process control system100includes field devices112a-cin a first process area114and field devices116a-cin a second process control area118. To communicate information between the controller104and the field devices112a-cand116a-c, the example process control system100is provided with field junction boxes (FJB's)120a-band a termination panel or marshalling cabinet122. Each of the field junction boxes120a-broutes signals from respective ones of the field devices112a-cand116a-cto the marshalling cabinet122. The marshalling cabinet122, in turn, marshals (e.g., organizes, groups, etc.) information received from field devices112a-cand116a-cand routes the field device information to respective I/O cards (e.g., I/O cards132a-band134a-b) of the controller104. In the illustrated example, the communications between the controller104and the field devices112a-cand116a-care bidirectional so that the marshalling cabinet122is also used to route information received from I/O cards of the controller104to respective ones of the field devices112a-cand116a-cvia the field junction boxes120a-b.

In the illustrated example, the field devices112a-care communicatively coupled to the field junction box120aand the field devices116a-care communicatively coupled to the field junction box120bvia electrically conductive, wireless, and/or optical communication media. For example, the field junction boxes120a-bmay be provided with one or more electrical, wireless, and/or optical data transceivers to communicate with electrical, wireless, and/or optical transceivers of the field devices112a-cand116a-c. In the illustrated example, the field junction box120bis communicatively coupled wirelessly to the field device116c. In an alternative example implementation, the marshalling cabinet122may be omitted and signals from the field devices112a-cand116a-ccan be routed from the field junction boxes120a-bdirectly to the I/O cards of the controller104. In yet another example implementation, the field junction boxes120a-bmay be omitted and the field devices112a-cand116a-ccan be directly connected to the marshalling cabinet122.

The field devices112a-cand116a-cmay be Fieldbus compliant valves, actuators, sensors, etc., in which case the field devices112a-cand116a-ccommunicate via a digital data bus using the well-known Fieldbus communication protocol. Of course, other types of field devices and communication protocols could be used instead. For example, the field devices112a-cand116a-ccould instead be Profibus, HART, or AS-i compliant devices that communicate via the data bus using the well-known Profibus and HART communication protocols. In some example implementations, the field devices112a-cand116a-ccan communicate information using analog communications or discrete communications instead of digital communications. In addition, the communication protocols can be used to communicate information associated with different data types. In some examples, one or more of the field devices112a-cand116a-care 2-wire field devices. In some examples, one or more of the field devices112a-cand116a-care 3-wire field devices.

Each of the field devices112a-cand116a-cis configured to store field device identification information. The field device identification information may be a physical device tag (PDT) value, a device tag name, an electronic serial number, etc. that uniquely identifies each of the field devices112a-cand116a-c. In the illustrated example ofFIG. 1, the field devices112a-cstore field device identification information in the form of physical device tag values PDT0-PDT2and the field devices116a-cstore field device identification information in the form of physical device tag values PDT3-PDT5. The field device identification information may be stored or programmed in the field devices112a-cand116a-cby a field device manufacturer and/or by an operator or engineer involved in installation of the field devices112a-cand116a-c.

To route information associated with the field devices112a-cand116a-cin the marshalling cabinet122, the marshalling cabinet122is provided with a plurality of termination modules124a-cand126a-ccommunicatively coupled to corresponding terminal blocks (e.g., the terminal blocks206aofFIG. 2) on the marshalling cabinet122. The terminal blocks provide a first physical interface (e.g., wire termination points) onto which wires from the field devices112a-cand116a-cmay be landed, a second physical interface (e.g., a slot with electrical contacts) to hold and communicatively couple the termination modules124a-cand126a-c, and a third physical interface to communicatively couple the terminal blocks to the marshalling cabinet122and the controller104. In this manner, communications between the controller104, the termination modules124a-cand126a-c, and the field devices112a-cand116a-care enabled. The termination modules124a-care configured to marshal information associated with the field devices112a-cin the first process area114and the termination modules126a-care configured to marshal information associated with the field devices116a-cin the second process area118. As shown, the termination modules124a-cand126a-care communicatively coupled to the field junction boxes120a-bvia respective multi-conductor cables128aand128b(e.g., a multi-bus cable). In an alternative example implementation in which the marshalling cabinet122is omitted, the termination modules124a-cand126a-cand corresponding terminal blocks can be installed in respective ones of the field junction boxes120a-b.

The illustrated example ofFIG. 1depicts a point-to-point configuration in which each conductor (including one or more wires) in the multi-conductor cables128a-bcommunicates information uniquely associated with a respective one of the field devices112a-cand116a-c. For example, the multi-conductor cable128aincludes a first conductor130a, a second conductor130b, and a third conductor130c. Specifically, the first conductor130ais used to form a first data bus configured to communicate information between the termination module124aand the field device112a, the second conductor130bis used to form a second data bus configured to communicate information between the termination module124band the field device112b, and the third conductor130cis used to form a third data bus configured to communicate information between the termination module124cand the field device112c. In an alternative example implementation using a multi-drop wiring configuration, each of the termination modules124a-cand126a-ccan be communicatively coupled with one or more field devices. For example, in a multi-drop configuration, the termination module124acan be communicatively coupled to the field device112aand to another field device (not shown) via the first conductor130a. In some example implementations, a termination module can be configured to communicate wirelessly with a plurality of field devices using a wireless mesh network. In some examples, where the field devices112a-care 3-wire field devices, the multi-conductor cable128aincludes additional conductors to transmit power to the field device112a-c.

Each of the termination modules124a-cand126a-cmay be configured to communicate with a respective one of the field devices112a-cand116a-cusing a different data type. For example, the termination module124amay include a digital field device interface to communicate with the field device112ausing digital data while the termination module124bmay include an analog field device interface to communicate with the field device112busing analog data.

To control I/O communications between the controller104(and/or the workstation102) and the field devices112a-cand116a-c, the controller104is provided with the plurality of I/O cards132a-band134a-b. In the illustrated example, the I/O cards132a-bare configured to control I/O communications between the controller104(and/or the workstation102) and the field devices112a-cin the first process area114, and the I/O cards134a-bare configured to control I/O communications between the controller104(and/or the workstation102) and the field devices116a-cin the second process area118.

In the illustrated example ofFIG. 1, the I/O cards132a-band134a-breside in the controller104. To communicate information from the field devices112a-cand116a-cto the workstation102, the I/O cards132a-band134a-bcommunicate the information to the controller104and the controller104communicates the information to the workstation102. Similarly, to communicate information from the workstation102to the field devices112a-cand116a-c, the workstation102communicates the information to the controller104, the controller104then communicates the information to the I/O cards132a-band134a-b, and the I/O cards132a-band134a-bcommunicate the information to the field devices112a-cand116a-cvia the termination modules124a-cand126a-c. In an alternative example implementation, the I/O cards132a-band134a-bcan be communicatively coupled to the LAN106internal to the controller104so that the I/O cards132a-band134a-bcan communicate directly with the workstation102and/or the controller104.

To provide fault tolerant operations in the event that either of the I/O cards132aand134afails, the I/O cards132band134bare configured as redundant I/O cards. That is, if the I/O card132afails, the redundant I/O card132bassumes control and performs the same operations as the I/O card132awould otherwise perform. Similarly, the redundant I/O card134bassumes control when the I/O card134afails.

To enable communications between the termination modules124a-cand the I/O cards132a-band between the termination modules126a-cand the I/O cards134a-b, the termination modules124a-care communicatively coupled to the I/O cards132a-bvia a first universal I/O bus136aand the termination modules126a-care communicatively coupled to the I/O cards134a-bvia a second universal I/O bus136b. Unlike the multi-conductor cables128aand128b, which use separate conductors or communication mediums for each one of the field devices112a-cand116a-c, each of the universal I/O buses136a-bis configured to communicate information corresponding to a plurality of field devices (e.g., the field devices112a-cand116a-c) using the same communication medium. For example, the communication medium may be a serial bus, a two-wire communication medium (e.g., twisted-pair), an optical fiber, a parallel bus, etc. via which information associated with two or more field devices can be communicated using, for example, packet-based communication techniques, multiplexed communication techniques, etc.

The universal I/O buses136aand136bare used to communicate information in substantially the same manner. In the illustrated example, the I/O bus136ais configured to communicate information between the I/O cards132a-band the termination modules124a-c. The I/O cards132a-band the termination modules124a-cuse an addressing scheme to enable the I/O cards132a-bto identify which information corresponds to which one of the termination modules124a-cand to enable each of the termination modules124a-cto determine which information corresponds to which of the field devices112a-c. When a termination module (e.g., one of the termination modules124a-cand126a-c) is connected to one of the I/O cards132a-band134a-b, that I/O card automatically obtains an address of the termination module (from, for example, the termination module) to exchange information with the termination module. In this manner, the termination modules124a-cand126a-ccan be communicatively coupled anywhere on the respective buses136a-bwithout having to manually supply termination module addresses to the I/O cards132a-band134a-band without having to individually wire each of the termination modules124a-cand126a-cto the I/O cards132a-band134a-b.

By providing the termination modules124a-cand the termination modules126a-cthat can be configured to use different data type interfaces (e.g., different channel types) to communicate with the field devices112a-cand116a-cand that are configured to use respective common I/O buses136aand136bto communicate with the I/O cards132a-band134a-b, the illustrated example ofFIG. 1enables routing data associated with different field device data types (e.g., the data types or channel types and corresponding communication protocols used by the field devices112a-cand116a-c) to the I/O cards132a-band134a-bwithout having to implement a plurality of different field device interface types on the I/O cards132a-band134a-b. Therefore, an I/O card having one interface type (e.g., an I/O bus interface type for communicating via the I/O bus136aand/or the I/O bus136b) can communicate with a plurality of field devices having different field device interface types.

In the illustrated example, the I/O card132aincludes a data structure133and the I/O card134aincludes a data structure135. The data structure133stores the field device identification numbers (e.g., field device identification information) corresponding to field devices (e.g., the field devices112a-c) that are assigned to communicate with the I/O card132avia the universal I/O bus136a. The termination modules124a-ccan use the field device identification numbers stored in the data structure133to determine whether a field device is incorrectly connected to one of the termination modules124a-c. The data structure135stores the field device identification numbers (e.g., field device identification information) corresponding to field devices (e.g., the field devices116a-c) that are assigned to communicate with the I/O card134avia the universal I/O bus136b. The data structures133and135can be populated by engineers, operators, and/or users via the workstation102during a configuration time or during operation of the example process control system100. Although not shown, the redundant I/O card132bstores a data structure identical to the data structure133and the redundant I/O card134bstores a data structure identical to the data structure135. Additionally or alternatively, the data structures133and135can be stored in the workstation102.

In the illustrated example, the marshalling cabinet122is shown located in a termination area140separate from the process control area110. By using the I/O buses136a-binstead of substantially more communication media (e.g., a plurality of communication buses, each uniquely associated with one of the field devices112a-cand116a-cor a limited group of them along a multi-drop segment) to communicatively couple the termination modules124a-cand126a-cto the controller104facilitates locating the controller104relatively farther from the marshalling cabinet122than in known configurations without substantially decreasing the reliability of communications. In some example implementations, the process control area110and the termination area140can be combined so that the marshalling cabinet122and the controller104are located in the same area. In any case, placing the marshalling cabinet122and the controller104in areas separate from the process areas114and118enables isolating the I/O cards132a-band134a-b, the termination modules124a-cand126a-cand the universal I/O buses136a-bfrom harsh environmental conditions (e.g., heat, humidity, electromagnetic noise, etc.) that may be associated with the process areas114and118. In this manner, the cost and complexity of designing and manufacturing the termination modules124a-cand126a-cand the I/O cards132a-band134a-bcan be substantially reduced relative to the cost of manufacturing communications and control circuitry for the field devices112a-cand116a-cbecause the termination modules124a-cand126a-cand the I/O cards132a-band134a-bdo not require operating specification features (e.g., shielding, more robust circuitry, more complex error checking, etc.) required to guarantee reliable operation (e.g., reliable data communications) as would otherwise be necessary to operate in the environmental conditions of the process areas114and118.

Additional details and alternative example implementations that may be used to communicatively couple workstations, controllers, and I/O cards, as well as additional details and alternative example implementations of the example marshalling cabinet122and termination modules124a-cand126a-care disclosed in U.S. Pat. No. 8,332,567; U.S. Pat. No. 8,762,618; U.S. patent application Ser. No. 14/170,072; and U.S. patent application Ser. No. 14/592,354; all of which were incorporated above.

FIG. 2is a detailed diagram of the example termination panel or marshalling cabinet122ofFIG. 1. In the illustrated example, the marshalling cabinet122includes a baseplate202that is provided with a socket rail204. The socket rail204of the illustrated example is structured to receive terminal blocks206a-cto which the termination modules124a-cmay be communicatively coupled. In addition, the marshalling cabinet122is provided with an I/O bus transceiver208that communicatively couples the termination modules124a-cto the universal I/O bus136adescribed above in connection withFIG. 1. The I/O bus transceiver208may be implemented using a transmitter amplifier and a receiver amplifier that conditions signals exchanged between the termination modules124a-cand the I/O cards132a-b. The marshalling cabinet122is provided with another universal I/O bus210communicatively coupling the terminal modules124a-c(via the terminal blocks206a-c) to the I/O bus transceiver208. In some examples, multiple baseplates202may be communicatively coupled to enable additional termination modules to be communicatively coupled to the I/O transceiver208. In some such examples, the baseplates are provided with connectors212to interconnect the I/O bus210across each baseplate202as successive baseplates202are attached to an underlying support frame214(e.g., a DIN rail).

Using a common communication interface (e.g., the I/O bus210and the I/O bus136a) to exchange information between the I/O cards132a-band the termination modules124a-cenables defining field device-to-I/O card connection routing late in a design or installation process. For example, the termination modules124a-ccan be communicatively coupled to the I/O bus210at various locations (e.g., various terminal blocks206a-cin different sockets of the socket rail204) within the marshalling cabinet122. In addition, the common communication interface (e.g., the I/O bus210and the I/O bus136a) between the I/O cards132a-band the termination modules124a-creduces the number of communication media (e.g., the number of communication buses and/or wires) between the I/O cards132a-band the termination modules124a-c, thus enabling installation of relatively more of the termination modules124a-c(and/or the termination modules126a-c) in the marshalling cabinet122than the number of known termination modules that can be installed in known marshalling cabinet configurations.

To provide electrical power to the termination modules124a-cand the I/O bus transceiver208, the marshalling cabinet122is provided with a power supply218. In some examples, the termination modules124a-cuse the electrical power from the power supply218to power communication channels or communication interfaces used to communicate with field devices (e.g., the field devices112a-cofFIG. 1) and/or to provide the field devices electrical power for operation. Additionally or alternatively, in some examples as shown in theFIG. 2, each baseplate202is provided with a local power bus216that may be connected to an external power source220. The external power source220may be any suitable power source such as 24 volts direct current (VDC) or 120/230 volts alternating current (VAC). In some examples, the termination modules124a-cuse the electrical power from the external power source220to power communication channels or communication interfaces and/or to provide power to the field devices for operation. Providing power through the local power bus216in this manner eliminates the need to separately wire each S-wire field devices requiring such power to an external power source. The cost of implementing the control system is reduced as a result of less time being needed to wire and maintain the system in addition to the costs saved from fewer components. In the illustrated example, although the termination modules124a-cmay use power from either the internal power supply218or the external power source220, in either case, communications with the I/O cards132a-bare still achieved via the I/O bus transceiver208over the I/O bus210. Whether the termination modules124a-cuse power from the internal power supply218or the external power source220depends upon the type or configuration of the terminal block used to interface the termination modules124a-cwith the baseplate202. That is, in some examples, the terminal block206ais provided with a plurality of connectors (e.g., the baseplate connectors310ofFIG. 3B) to electrically couple the terminal block206ato the baseplate202. In some examples, at least one of the connectors directly couples the termination module124ato the local power bus216of the baseplate202(to provide power) while at least one other connector directly couples the termination module124ato the universal I/O bus210of the baseplate202(to enable communications).

FIGS. 3A-3Cdepict a top view, a side view, and an end view, respectively, of the example terminal block300, which may be similar or identical to the terminal blocks206a-cofFIG. 2.FIG. 4depicts a side view of the example terminal block300ofFIGS. 3A-3Cwith the example termination module124aofFIGS. 1 and 2partially inserted into a slot301of the terminal block300. As shown in the illustrated example ofFIG. 4, the termination module124ais removably coupled to the terminal block300via the slot301. More particularly, the example termination module124aincludes a plurality of contacts302that communicatively couple and/or electrically couple the termination module124ato corresponding contacts304of the terminal block300when the termination module124ais inserted into the slot301of the terminal block300. In this manner, the termination module124acan be selectively removed and/or coupled to the termination block300while the termination block300is in place and coupled to the baseplate202(FIG. 2) and/or communicatively coupled with a field device. In some examples, the terminal block300includes a moveable latch305that either releases the termination module124aor secures the termination module124ain an installed position when the contacts304of terminal bock300are electrically coupled to the contacts302of the termination module124a. Additionally or alternatively, in some examples, the latch305selectively secures the termination module124ain a partially installed position. In the partially installed position, the termination module124ais held in place within the slot301while preventing electrical contact between contacts302,304of the termination module124aand the terminal block300(similar to what is shown inFIG. 4). In this manner, wiring to a field device may be decoupled from the control system to facilitate maintenance or to remove power to the field device (e.g., provided from the external power source220ofFIG. 2).

In some examples, to communicatively couple the termination module124ato the universal I/O bus210ofFIG. 2, the terminal block300is provided with a plurality of baseplate connectors310. As described above, in some examples, at least one of the baseplate connectors310couples the termination module124ato the universal I/O bus210while at least one other baseplate connector310couples the termination module124ato the local power bus216to provide power to the termination module124aand the associated field device from the external power source220. That is, unlike some known terminal blocks where all connectors to the baseplate202directly couple the universal I/O bus210with a termination module, the terminal block300of the illustrated example provides separate connections to each of the universal I/O bus210and the local power bus216. The baseplate connectors310may be implemented using any suitable interface including, for example, an insulation piercing connector, a knife connector, etc. In this manner, the termination module124acan enable both communications to the I/O bus210and power delivery to a corresponding field device. More particularly, to enable communicating information between the termination module124aand the I/O bus210, the baseplate connectors310coupled to the I/O bus210are also internally connected to one or more of the contacts302of the termination module124a. Likewise, to enable power transmission between the termination module124aand the field device, the baseplate connectors310coupled to the local power bus216are also internally connected to one or more different ones of the contacts302of the termination module124a.

In some examples, the terminal block300is provided with a field device interface such as wire termination points306to secure (e.g., via moveable cage clamps actuated by screws308) conductive communication media (e.g., a bus wire) from a field device (e.g., the field device112aofFIG. 1). More particularly, in some examples, the field device112ais a 3-wire DI field device. In some such examples, each of the three wire termination points306of the terminal block300is to receive one of the three wires from the 3-wire field device. When the termination module124ais removably coupled to the terminal block300, the termination points306are communicatively coupled to one or more of the contacts302of the termination module124ato enable communicating information between the termination module124aand the field device112a. Additionally, in some examples, the termination points306are communicatively coupled to one or more of the contacts302to enable power transmission between the termination module124aand the field device112abased on power from the external power source220.

In other example implementations, the terminal block300may be provided with any other suitable type of field device interface (e.g., a socket) instead of the termination screws308. In addition, although one field device interface (e.g., the termination points306with the screws308) is shown, the terminal block300may be provided with more field device interfaces configured to enable communicatively coupling a plurality of field devices to the termination module124a.

With the example termination block300electrically coupled to the local power bus216, there is the possibility that a short circuit associated with the corresponding termination module124aand corresponding field device may occur and draw away power from other termination modules in other terminal blocks on the baseplate202. Accordingly, in the illustrated example, the termination block300is provided with a fuse312to protect other termination modules (in other terminal blocks) from losing power. In some examples, the fuse is replaceable. In this manner, the cost of acquiring and wiring a separate external fuse is eliminated. Furthermore, incorporating the fuse312into the terminal block300reduces the overall footprint of the system.

FIG. 5is a schematic illustration of an example implementation of the example terminal block300ofFIGS. 3 and 4wired to a 3-wire field device502(e.g., corresponding to the field device112aofFIG. 1). In some examples, the field device502is a discrete input (DI) field device, such as, for example, photoelectric or capacitive sensors, switches, or other such DI devices that need power to operate. In the illustrated example, the terminal block300is communicatively coupled to the baseplate202that provides power504from the external power source220. Further, in the illustrated example ofFIG. 5, the terminal block300is communicatively coupled to the termination module124athat provides isolation and control circuitry506to enable communications between the field device502and the controller104(FIG. 1) as described more fully in U.S. Pat. No. 8,332,567; U.S. Pat. No. 8,762,618; U.S. patent application Ser. No. 14/170,072; and U.S. patent application Ser. No. 14/592,354; all of which were incorporated above.

As shown in the illustrated example ofFIG. 5, each of the three wires of the field device502is landed directly onto one of the three termination points306of the terminal block300. Signaling and electrical power delivery are accomplished through the internal wiring and design of the terminal block300(including the baseplate connectors310) in relation to the termination module124aand the baseplate202(that may be coupled to the external power source220). Furthermore, in some examples, the terminal block300includes the fuse312built into the terminal block300between the termination points306and the baseplate202(through which power is provided) to provide short circuit protection.

For purposes of comparison,FIG. 6illustrates a schematic implementation of the 3-wire DI field device502wired to the termination module124ausing a known terminal block602constructed to handle common 2-wire architectures. As described above, to implement a 3-wire field device, there is the need for an external power source. Unlike the illustrated example ofFIG. 5, the terminal block602ofFIG. 6is not equipped to provide power through the baseplate202. As a result, an external power source604must be separately coupled to the S-wire field device502. In such scenarios, interfacing the 3-wire field device502with both the external power source604and the terminal block602may require three intermediate terminals606. Furthermore, additional wires608may be required to land on the terminal block602and to electrically couple to the external power source604via two additional terminals610. Further still, with the external power source604wired in, there is also a need for an external fuse612to protect against short circuits. Each of the terminals606,610, the wires608, and the fuse612shown inFIG. 6are additional and separate components adding to the cost and complexity to a control system that may be avoided using the example terminal block300shown inFIG. 5. Furthermore, the example implementation shown inFIG. 5has a much smaller footprint than what is shown inFIG. 6because the additional components are either excluded or incorporated within the terminal block300.

Although the external power source220still needs to be wired to the baseplate202to provide power in the illustrated example ofFIG. 5, in some examples, this wiring only needs to be performed once for all field devices communicatively coupled to the baseplate202. In some examples, the baseplate202holds up to twelve terminal blocks and corresponding termination modules. By contrast, using known techniques, as shown inFIG. 6, each additional 3-wire field device would need to be separately coupled to the external power source604, thereby further increasing the cost and complexity of setting up and maintaining the control system.

FIG. 7is a schematic illustration of an example implementation of the example terminal block300ofFIGS. 3 and 4wired to a 2-wire field device702(e.g., which may be similar or identical to the field device112aofFIG. 1). While the terminal block300may be advantageously employed to communicatively couple a S-wire field device as shown inFIG. 5, in some examples, the terminal block300may also be used to communicatively couple with a common 2-wire field device as illustrated inFIG. 7. In some examples, the 2-wire field device702is powered via the external power source220. As a result, the example terminal block300disclosed herein may be used to communicatively coupled either a 2-wire field device or a S-wire field device to a process control system.