Interface for use with a process instrumentation system

We claim:

1. Apparatus mountable onto a termination board for use with a plurality of removably mountable intrinsically safe electronic barriers each of which couples a different microprocessor-equipped smart device in a first area to a process controller in a second area, each smart device generating process control information onto a control loop indicative of a condition in said first area and including means for receiving a maintenance command over said control loop for performing a maintenance operation, said apparatus comprising:

selecting means for selecting one of a plurality of outputs each connectable to one of said plurality of intrinsically safe electronic barriers, such that each output when selected electrically connects to one of said control loops used for transmitting process control information between a corresponding smart device and said process controller;

generating means for generating a frequency shift key modulated signal modulated in accordance with a maintenance command to be transmitted to one of said smart devices; and

a microprocessor, coupled to said selecting means and said generating means, for controlling said selecting means to select one of said plurality of outputs and providing said frequency shift key modulated signal to a control loop corresponding to said selected one output, wherein said frequency shift key modulated signal modifies a process control signal on said control loop corresponding to said selected one output without interfering with process control information transmitted over said control loop corresponding to said selected one output; and

means for removably mounting said means for selecting, said means for generating, and said microprocessor onto said termination board in a manner substantially similar to the manner in which said plurality of removably mountable intrinsically safe electronic barriers are removably mounted onto said termination board.

2. The apparatus of claim 1, further comprising a second apparatus adapted to be removably mounted onto a second termination board for use with a second plurality of removably mountable intrinsically safe electronic barriers each of which couples a different smart device located in said first area to said process controller, said second apparatus for generating a second frequency shift keyed signal for one of said second plurality of removably mountable intrinsically safe electronic barriers, wherein said first and second apparatus each comprises an RS-485 interface for receiving maintenance commands from a maintenance processor over an RS-485 link.

3. The apparatus of claim 1, wherein said means for removably mounting comprises a single rectangular housing having a connector on one face, said single rectangular housing disposed to mount said apparatus in parallel with said plurality of intrinsically safe electronic barriers on said termination board.

4. The apparatus of claim 1, further comprising an option select device, coupled to said microprocessor, for selecting a unit address and a baud rate for communicating with a maintenance processor.

5. Apparatus mountable onto a termination board having means for receiving a plurality of removably mountable intrinsically safe electronic barriers each of which couples a different microprocessor-equipped smart device located in a hazardous area to a process controller located in a safe area, each smart device generating process control information onto a control loop indicative of a condition in said hazardous area and including means for receiving a maintenance command over said control loop for performing a maintenance operation, said apparatus comprising:

an assembly adapted to be removably mounted onto said termination board comprising a multiplexer having a plurality of outputs each connectable to one of said plurality of intrinsically safe electronic barriers, such that each output when selected electrically connects within one of said intrinsically safe electronic barriers to one of said control loops used for transmitting process control information between a corresponding smart device and said process controller;

an FSK modem, coupled to said multiplexer, for generating a frequency shift key modulated signal modulated in accordance with a maintenance command to be transmitted to one of said smart devices;

a microprocessor, coupled to said multiplexer, for controlling said multiplexer to select one of said plurality of outputs and providing said frequency shift key modulated signal to a control loop corresponding to said selected one output, wherein said frequency shift key modulated signal modifies a process control signal on said control loop corresponding to said selected one output without interfering with process control information transmitted over said control loop corresponding to said selected one output; and

means for removably mounting said assembly to said termination board in a manner substantially similar to the manner in which said plurality of removably mountable intrinsically safe electronic barriers are mounted onto said termination board.

6. The apparatus of claim 5, wherein said removable mounting means comprises a rectangular housing having a connector on one face, said rectangular housing and connector disposed to mount said assembly in parallel with said plurality of removably mountable intrinsically safe electronic barriers on said termination board.

7. The apparatus of claim 5, wherein each of said multiplexer outputs is coupled to and electrically connects to one of said plurality of intrinsically safe electronic barriers on the safe side of the barrier.

8. The apparatus of claim 5, further comprising means, disposed on said termination board, for connecting said microprocessor to a second microprocessor located on a second termination board, said connection being in parallel with a maintenance workstation which generates said maintenance command.

9. The apparatus of claim 5, further comprising a cross-wiring section, mounted to said termination board, for cross-wiring one of said intrinsically safe electronic barriers to a particular smart device.

10. The apparatus of claim 5, wherein said microprocessor receives said maintenance command from a maintenance processor through the use of an RS-485 protocol.

11. The apparatus of claim 5, further comprising a second apparatus adapted to be removably mounted onto a second termination board having means for receiving a second plurality of removably mountable intrinsically safe electronic barriers each of which couples a different second smart device located in said hazardous area to said process controller located in said safe area, each second smart device generating process control information onto a second control loop indicative of a condition in said hazardous area and including means for receiving a maintenance command over said second control loop for performing a maintenance operation, said second apparatus comprising:

a second assembly adapted to be removably mounted onto said second termination board, comprising

a second multiplexer having a plurality of second outputs each connectable to one of said second plurality of intrinsically safe electronic barriers, such that each second output when selected electrically connects within one of said second intrinsically safe electronic barriers to one of said second control loops used for transmitting process control information between a corresponding second smart device and said process controller;

a second FSK modem, coupled to said second multiplexer, for generating a second frequency shift key modulated signal modulated in accordance with a second maintenance command to be transmitted to one of said second smart devices; and

a second microprocessor, coupled to said second multiplexer, for controlling said second multiplexer to select one of said plurality of second outputs and providing said second frequency shift key modulated signal to a control loop corresponding to said selected one second output, wherein said second frequency shift key modulated signal modifies a process control signal on a control loop corresponding to said selected one second output without interfering with process control information transmitted over said second control loop corresponding to said selected one second output;

means for removably mounting said second assembly to said second termination board in a manner substantially similar to the manner in which said second plurality of removably mountable intrinsically safe electronic barriers are mounted to said second termination board; and

means for electrically connecting to said apparatus of claim 42 and to a maintenance processor over an RS-485 link.

12. The apparatus of claim 5, further comprising a plurality of said removably mountable intrinsically safe electronic barriers mounted on said termination board.

13. Apparatus mountable onto a termination board for use with a plurality of removably mountable intrinsically safe electronic barriers each of which couples a different microprocessor-equipped smart device in a first area to a process controller in a second area, each smart device generating process control information onto a control loop indicative of a condition in said first area and including means for receiving a maintenance command over said control loop for performing a maintenance operation, said apparatus comprising:

an FSK modem for generating a frequency shift key modulated signal modulated in accordance with a maintenance command to be transmitted to one of said smart devices;

a microprocessor, coupled to said FSK modem, for selecting one of said control loops and causing said frequency shift key modulated signal to be superimposed onto said selected one control loop, wherein said frequency shift key modulated signal modifies a process control signal on said selected one control loop without interfering with process control information transmitted over said selected one control loop; and

a rectangular housing having a connector on one face, said rectangular housing for enveloping and removably mounting said microprocessor and said FSK modem onto said termination board in a manner substantially similar to the manner in which said plurality of removably mountable intrinsically safe electronic barriers are removably mounted onto said termination board.

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BACKGROUND OF THE INVENTION

The present invention relates to an interface for a maintenance system used in conjunction with a process instrumentation system. More specifically, the invention relates to an interface used for maintaining and configuring smart devices. Even more specifically, the invention relates to an interface that may safely be used to maintain and configure smart devices where such smart devices are located in hazardous areas.

Modern process control systems often utilize field devices for monitoring and controlling various aspects of a process. These field devices can include level transmitters, mass flow meters, tank gauges, pressure transducers, temperature transducers, or other similar devices. Typically, these field devices output 4-20 mA signals which are operated upon to provide information regarding a process. An example of such a field device is a pressure transducer located in a storage facility filled with gasoline that periodically outputs signals that are operated upon to determine the pressure in the storage facility.

Widely used field devices that are commonly referred to as "smart transmitters" (i.e. smart field devices) are often equipped with microprocessors. These microprocessors perform two important functions: (1) process measurement, and (2) calibration, adjustment, and maintenance of the smart transmitter to within desired levels of operation. Collectively, the operations of calibration, adjustment, and maintenance shall be referred to hereinafter as "maintenance." The maintenance function is the focus of the present invention.

The smart transmitters mentioned above are usually connected to what is known in the art as a Distributed Control System (DCS), a Programmable Logic Controller (PLC), a Personal Computer (PC), or other similar control device. Collectively, DCSs, PLCs, PCs, and other similar devices shall be referred to herein as "control systems." It is common in the field of process instrumentation to have the connection of any particular smart transmitter to a control system typically be in the form of a 4-20 mA loop in which power to energize the smart transmitter is supplied from the control system.

Typically, a control system primarily receives and processes the 4-20 mA signals that are transmitted from the smart transmitters over the 4-20 mA loops. In this fashion, data about the process that is being controlled or monitored can be collected and analyzed. Additionally, typical control systems can be equipped with facilities for providing for the maintenance of the smart transmitters (i.e. the calibration, adjustment, and maintenance of smart transmitters). Control systems equipped with facilities for providing for the maintenance of smart transmitters often achieve such operations by incorporating proprietary systems and protocols for the transmission of digital maintenance data to and from the microprocessors found in the smart transmitters. With these types of control systems, only smart transmitters manufactured by the manufacturer of the control system can be used for process control due to the proprietary nature of the systems and protocols involved.

Several problems are associated with using control systems that incorporate proprietary maintenance systems and protocols for the communication of maintenance data, to and from smart transmitters. Initially, communication is commonly not done over the connection forming the 4-20 mA control loop. Instead, separate wiring systems need be installed, thus increasing maintenance cost and complexity.

Another problem is that proprietary protocols can dictate control system and smart transmitter manufacturer uniformity. That is, a plant or process facility that uses a proprietary protocol based control and maintenance system may be restricted in its ability to acquire process control equipment manufactured by differing vendors possibly rendering the plant or process facility vendor or product line dependant. Various tangential problems are associated with being vendor or product line dependant including the possibility of having to pay higher and higher prices for process control equipment due to market monopolies. Even more, being vendor or product line dependant can result in restricting a process facility's operations based on the availability and selection of process control equipment. For example, when a plant or process facility seeks to perform certain tasks, such a facility may have to re-equip to meet changing demands in running and controlling processes. Such re-equipping, in addition to possibly being impracticable, can be quite costly.

Yet another problem can be seen where a process facility, including those involving hazardous areas, may utilize several hundred, or more, smart transmitters to measure and evaluate particular processes. In these situations, wiring of the smart transmitters to both the control system and the maintenance system can become quite complicated, problematic, and costly. The wiring problem is compounded where the control system and the maintenance system each require separate wiring systems. Even in light of these wiring problems, there have been no available centralized wiring harnesses that enable users to simply and easily gain wiring access to the control and maintenance signals communicated to and from the smart transmitters.

Another problem with providing for maintenance of smart transmitters is seen where there is failure of the maintenance system in the context of control systems that incorporate maintenance systems. When the maintenance system in these systems fail, the entire control system may need to be shut down thus requiring any of the processes that are being controlled by the control system to come to a halt as well. Termination of processes can be costly as well as impracticable. Even more, where a process must be halted, it may be necessary to re-start the process once the maintenance system is again operational.

The above-mentioned problems are compounded where there is a requirement of intrinsic safety. In applications requiring intrinsic safety, smart transmitters are used in hazardous areas and the control and maintenance stations reside in a non-hazardous area. Such applications include, for example, gasoline manufacturing facilities and the like. In these applications, it can become quite difficult to adjust, calibrate, and maintain smart transmitters during a process due to the hazards involved. While intrinsically safe circuits (e.g. circuits utilizing opto-isolators, transformers, for examples) are often utilized to protect against the hazards involved in monitoring and measuring processes in hazardous areas, the range of products available for such intrinsic safety applications is quite small. Even more, these intrinsic safety circuits fail to lend themselves to easily and economically allow for maintenance of smart transmitters.

Another problem associated with currently used process instrumentation devices is seen where the control system protocols, whether proprietary or not, are incompatible with commercially available smart transmitters. Control systems within these process instrumentation systems often cannot interface with the smart transmitters and thus require the use of an additional maintenance system. These problems are compounded when intrinsic safety is required.

The above-listed problems have led the Inventors to invent solutions that are practical and economical and which are defined in the appended claims.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above-mentioned problems by providing an interface for a maintenance system that is used in a process instrumentation system.

It is another object of the present invention to provide an interface for a maintenance system to be used in applications requiring intrinsic safety, the interface having a control section for controlling the operations of the interface, a permanent storage section for permanently storing information, a temporary storage means for temporarily storing information, a first communication section for communicating with a maintenance system that is used in a process instrumentation system, a second communication section for communicating with a maintenance information bus, an option selection section for selecting various interface operation modes, a channel selection section for selecting a channel on which is connected a smart transmitter, and a wave shaping section for changing the shape of signals output from the control section.

It is a further object of the present invention to provide for a termination board for use in a process instrumentation system which is used in applications requiring intrinsic safety wherein at least one transmitter is connected to a first side of at least one intrinsically safe barrier and relays data about a process to a control system connected to a second side of said intrinsically safe barrier and wherein the termination board has a connector for connecting together the termination board and an interface device that is used to interface smart transmitters with a maintenance work station.

It is a further object to provide a system for maintaining smart transmitters that includes a wiring harness for use in applications requiring intrinsic safety wherein smart transmitters communicate signals through intrinsically safe barriers to a control system and wherein the signals that are communicated by the smart transmitters are frequency shift keyed to bi-directionally communicate digital maintenance information with a maintenance work station.

It is another object of the present invention to provide a method of maintaining a smart transmitter located in a hazardous area.

It is another object of the present invention to provide a method of bi-directionally communicating maintenance information between a smart transmitter located in a hazardous area and a maintenance work station located in a non-hazardous area.

It is a final object of the present invention to provide a method for selecting a particular channel on which a smart transmitter located in a hazardous area may be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-listed objects have been achieved and will be explained in detail below with reference to FIGS. 1-4. Here, FIGS. 1-4 are briefly described.

FIG. 1 is a schematic block diagram that shows a system according to the present invention comprising an interface between a plurality of transmitters and a maintenance system.

FIG. 2 is block diagram that shows a preferred embodiment of an interface of the present invention according to FIG. 1.

FIG. 2A is a schematic diagram of the clock pulse generation device shown in FIG. 2.

FIG. 2B is a table that shows the logical truth assignments for selecting a channel on which a smart transmitter may be maintained.

FIG. 3 is a block diagram that shows a preferred embodiment of a termination board of the present invention which includes an interface according to FIG. 2 which allows for the maintenance of smart transmitters.

FIG. 4 is a graph that shows a frequency shift keyed signal used to carry both digital data and analog data in a system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

What follows is a detailed description of the invention with particular regard to FIGS. 1 through 4. It should be understood that the embodiments shown in FIGS. 1 through 4 are merely exemplary of the preferences selected by the Inventors.

Referring now to FIG. 1, therein depicted is a block diagram that shows an exemplary system according to the present invention. More specifically, FIG. 1 shows, for example, a system used in a plant that monitors processes that require intrinsic safety. Smart transmitters 10 are located to the left of a dotted line that represents the separation between the hazardous area of a plant (i.e. that portion of FIG. 1 that is to the left of the dotted line) and the non-hazardous area of that plant (i.e. that portion of FIG. 1 that is to the right of the dotted line). Several different types of smart transmitters are often used within process instrumentation systems. These smart transmitters can include, for example, level transmitters, mass flow meters, tank gauges, pressure transducers, temperature transducers, or other similar devices. These smart transmitters are equipped with microprocessors or similar control devices that enable them to be calibrated, adjusted, and maintained to operate within desired levels of process control performance.

Also shown in FIG. 1, are a plurality of termination boards 15 which are connected to each other through interconnection of interfaces 20 as well as other forms of interconnection such as power for example. The termination boards 15 provide terminal points for connecting signal wires to the smart transmitters 10. The termination boards 15 also provide terminal points for connecting process signals 25 to a control system 30. Additionally, the termination boards 15 also house a plurality of mountable/removable cartridges that contain intrinsically safe barriers 45 which provide electronic barriers between the control system 30 and the smart transmitters 10 as well as between the maintenance system 35 and the smart transmitters 10.

The interfaces 20 are shown to be mounted on the termination boards 15, but are in fact, removable when such is desired. The fact that the interfaces 20 are mountable and removable from the termination boards 15 results in several advantages. For example, the interfaces 20, can fail while the control system remains in operation thus not requiring the termination of either control system or the processes that it is controlling and/or monitoring. Additionally, the interfaces 20, and the rest of the maintenance system may be put into operation any time after initial implementation of smart transmitters in conjunction with termination boards 15, even during the monitoring or controlling of a process as the interfaces are electrically, and otherwise, isolated from the smart transmitters 10 and ultimately from the hazardous area, as are the control system and the maintenance system. Subsequent installation of the interfaces 20 is achieved by merely acquiring a maintenance work station 35 and by mounting interfaces 20 to the termination boards 15 and connecting them as is exemplified in typical configurations of the kind shown in FIG. 1.

Where there are to be a plurality of interfaces 20 in a particular application, the interfaces 20 can be connected to each other to form a multi-drop network 24 that is used to interface the smart transmitters to the maintenance work station 35. This multi-drop network is achieved by connecting together the termination boards in parallel fashion via maintenance terminal block 130.

The maintenance work station 35 can be a personal computer or the like and can run a software package tailored for maintenance of process instrumentation equipment. Even more, the maintenance work station can be a dedicated, custom processor designed specifically for overseeing maintenance operations in a process instrumentation system. Such dedicated architecture can be achieved, for example, by way of permanently storing maintenance software in a ROM or EPROM and retro-fitting existing micro-computers or by way of particular circuitry.

The maintenance system 35 is used to maintain the smart transmitters 10 by communicating instructions and queries to and reading outputs from the smart transmitters 10 which are communicated through the interfaces 20. Generally, communication of instructions and queries to the smart transmitters is achieved by first selecting an instruction or query at the maintenance work station, communicating that instruction or query to the maintenance terminal block 130 directly or via the multi-drop network, altering the 4-20 mA signals communicated from the smart transmitter to the control system, and communicating the altered 4-20 mA signal to the smart transmitter. Also generally, communication from the smart transmitter to the maintenance work station occurs in the same way.

More specifically and in regard to the generalized discussions of the immediately preceding paragraphs, bi-directional communications between the maintenance work station 35 and the interface 20 is achieved through utilization of the RS-485 standard protocol. However, other forms of communications protocols, both parallel and serial (e.g. RS-232) could also be used for this purpose. Of course, the maintenance terminal block need be adequate in terms of the appropriate number of electrical leads in order to support whatever protocol is chosen.

Bi-directional communication between the smart transmitters 10 and the interface 20 is achieved, for example, by first Frequency Shift Keying (FSK) the 4-20 mA process signals 25 that are communicated between the control system 30 and the smart transmitters 10, and then communicating the frequency shift keyed process signals. In this fashion, traditional analog 4-20 mA signals are superimposed with a digital sequence to convey maintenance data. The FSK aspect of the present invention will be addressed in greater detail below in regard to a discussion of FIG. 4. While FSK can be used for data transmission, other forms of data transmission can be used. Such other forms of