Electrical computers and digital processing systems: support – Digital data processing system initialization or configuration
Reexamination Certificate
1999-10-04
2002-09-10
Heckler, Thomas M. (Department: 2185)
Electrical computers and digital processing systems: support
Digital data processing system initialization or configuration
C700S001000
Reexamination Certificate
active
06449715
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to process control systems and, more particularly, to a process control configuration system that integrates the configuration and control of device networks which use a local or specialized input/output interface with the configuration and control of device networks which use a remote input/output interface, such as the Profibus interface.
DESCRIPTION OF THE RELATED ART
Process control systems, like those used in chemical, petroleum or other processes, typically include at least one centralized process controller communicatively coupled to at least one host or operator workstation and to one or more field devices via analog and/or digital buses or other communication lines or channels. The field devices, which may be, for example, valves, valve positioners, switches, transmitters (e.g., temperature, pressure and flow rate sensors), etc. perform functions within the process such as opening or closing valves and measuring process parameters. The process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices via an input/output (I/O) device, uses this information to implement a control routine and then generates control signals which are sent over the buses or other communication channels via the input/output device to the field devices to control the operation of the process. Information from the field devices and the controller is typically made available to one or more applications executed by the operator workstation to enable an operator to perform any desired function with respect to the process, such as viewing the current state of the process, modifying the operation of the process, configuring the process, documenting the process, etc.
In the past, conventional field devices were used to send and receive analog (e.g., 4 to 20 milliamp) signals to and from the process controller via analog lines. These 4 to 20 ma signals were typically indicative of measurements made by the device or of control signals generated by the controller required to control the operation of the device. Each of these conventional field devices was typically individually connected, via a separate line or communication channel, to a local input/output (I/O) device which, in turn, was connected directly to a controller to enable communication between the controller and the devices. These separate lines or communication channels enabled signals measured by the device to be sent individually to the controller at any time or to enable control signals to be sent individually by the controller to the device at any time. This configuration, in which the I/O device multiplexes signals delivered directly from field devices to a controller and vice-versa is called local I/O.
In the past decade or so, smart field devices including a microprocessor and a memory have become prevalent in the process control industry. In addition to performing a primary function within the process, smart field devices may store data pertaining to the device, communicate with the controller and/or other devices in a digital or combined digital and analog format, and perform secondary tasks such as self-calibration, identification, diagnostics, etc. A number of standard and open smart device communication protocols such as the HART®, PROFIBUS®, Actuator Sensor Interface (hereinafter “AS-Interface” or “ASI”), WORLDFIP®, Device-Net®, CAN, and FOUNDATION™ Fieldbus (hereinafter “Fieldbus”) protocols, and have been developed to enable smart field devices made by different manufacturers to be used together within the same process control network.
Generally speaking, for some of these specialized communication protocols such as the Fieldbus protocol, numerous devices are attached to a bus or a network and communicate with an I/O device (which is connected to the controller) over the bus or network. In the case of the Fieldbus protocol, each device is able to send one or more signals separately to the I/O device and, thereby, to the controller. As a result, the Fieldbus protocol uses a bus to perform specialized I/O because each device can communicate individual signals (having individual signal tag names, etc.) at any desired time or at particularly specified times. Similarly, the HART protocol uses a separate line or communication channel extending between each HART device and the I/O device, which enables HART signals to be sent separately to the local I/O device at any time. As a result, the HART protocol provides local I/O operations.
However, others of the smart protocols, such as the Profibus and the AS-Interface protocols, use what is commonly referred to as remote I/O because, generally speaking, the I/O device connected to the field devices is located remotely from the controller and is connected to the controller via a further I/O device. In effect, each Profibus and AS-Interface device (or groups of these devices) has an I/O unit associated therewith. This I/O unit, which is typically located on or near the device with which it is associated, receives the different signals associated with the device and then multiplexes these signals by concatenating these signals into a single data string and placing that data string onto the bus to which other Profibus or AS-Interface devices and, therefore, other Profibus or AS-Interface I/O units, are connected. The data strings from the remote I/O devices are sent over the bus and are received by a master I/O device which is typically located near the controller. The mater I/O device receives the data strings and places these data strings in a memory associated with the master I/O device. Likewise, the master I/O device sends commands and other signals to each of the remote I/O devices by concatenating a set of such signals together (i.e., all of the signals to be sent to a particular device) and then sending this concatenated data string over the remote I/O bus to the I/O units down in the field which, in turn, decode those signals and provide the decoded signals to the appropriate locations or modules of each device.
The master I/O device typically interfaces with a controller, such as a specially designed programmable logic controller (PLC), that performs process control functions. However, the controller or the PLC must know where the individual data associated with any particular signal is stored in the memory of the master I/O device to be able to receive data from a remote I/O field device. Likewise, the controller or the PLC must know where, in the master I/O device memory, to place commands and other data to be delivered to the remote I/O field devices over the remote I/O bus. Because of this requirement, the controller or PLC designer must keep track of what type of data (e.g., string, floating point, integer, etc.) is stored at each memory location within the master I/O device and what the data at each memory location within the master I/O device represents (e.g., to which signal of which remote I/O field device this data belongs). Likewise, when sending data to a remote I/O field device, the controller or PLC must be programmed to place the appropriate type of data at the appropriate memory location within the master I/O device to assure that the correct data string is sent to the designated remote I/O field device.
Most remote I/O communication protocols, such as the Profibus and AS-Interface protocols, specify only the form of the data strings to be placed on the remote I/O bus, e.g., how long the data strings can be, how many signals can be concatenated to form a single data string, the baud rate that the data strings are to be sent, etc., but do not specify or identify the type of data to be sent. Thus, while, the manufacturer of each Profibus device usually provides a GSD (a German acronym) file having some information about the device, such as the number and types of modules that can be placed in a device, the number of bits or bytes of input and output data associated with each device signal that is communicated to the
Fisher-Rosemount Systems Inc.
Heckler Thomas M.
Marshall Gerstein & Borun.
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