|Title of Invention||
AN APPARATUS FOR PROVIDING REDUNDANCY TO A PROCESSOR MODULE IN A DISTRIBUTED CONTROL SYSTEM.
|Abstract||This invention relates to an apparatus for providing redundancy to a processor module in a distributed control system comprising plurality of operator stations (1,2,3,4) and plurality of processing stations (6,7,8,9,10) and all communications between said operator and processing stations takes place over a set of lines through an electronic switch wherein each of said processor unit comprises of a processor block (21) input modules and output modules, said process block has an I/O bus (20) and said input and output modules are connected to said I/O bus as well as to I/O bus (28) of a stand by processor so as to affect switching between processors with the same input and ouput modules.|
|Full Text||This invention relates to an apparatus for providing redundancy to a processor module in distributed control systems which utilize a microprocessor, microcomputer and a stored software programme for monitoring, data acquisition and control of industrical processes. More particularly, this invention relates to an apparatus for achieving a bumpless transfer from a failed processor to a backup processor without using extra switching hardware to transfer the process signals from failed processor to backup processor. PRIOR ART
Distributed Control Systems used to monitor the process parameters and control various euqipments of an industrial plant or electric power generating equipment are required to operate continuously without interruption in service to the customer. They must be always available for use.Such distributed control systems comprise of a network of processing stations that are in turn connected to a large number of electronic modules (Input/ Output or I/O modules) which interact with the equipment and sensors of the plant. The connections between several I/O modules and processor is through a set of common signal lines called a I/O bus. To achieve high availability for the system, a backup
processor is normally employed to perform the functions of primary processor that fails. However,since functions are related to the process parameters, the interactions with whom is through the Input/Output modules, the backup processor must establish connections with these modules in order to perform its functions. This change in connection of Input/Output modules from primary processor to backup and vice versa necessitates use of external hardware circuits, that switched the bus from one processor to another or hardware circuits built into processor modules that connected/disconnected from the I/O. bus.
There are disadvantages associated with the present system distributed control systems.
One of the main disadvantages of the present system is that the success of the takeover by backup processor critically depended upon the proper functioning of these hardware circuits as well as the bus to which they are connected. SUMMARY OF THE INVENTION
Therefore the main object of the present invention is to propose an apparatus for providing redundancy to a processor module in a distributed control system in order to improve the availability by using backup processor and to achieve the changeover to backup processor without the use of such hardware circuits, to switch the processing functions between primary and backup processor.
Another object of the present invention is to avoid bus switchings and to achieve the changeover of processing functions from a failed processor to a backup processor by use of combination fault detection and recovery methods in the processors and new electronic circuit in the I/O modules.
Yet another object of the present invention is to propose a new electronic circuit in the I/O module for the changeover to a backup processor in which the Input /Output module is provided with two identical I/O buses over which the process parameters can be monitored and controlled.
Still another object of the present invention is to provide an electronics circuit in the I/O modules in such a manner that facilitates connecting primary processor to one bus and back processor to another bus. Both processors continuously interact with process parameters and keep the results ready to be exchanged with other nodes in the network and changeover of functions to backup processor which is communicating with I/O modules over the second I/O bus of the I/O modules.
Accordingly to this invention there is provided an apparatus for providing redundancy to a processor module in a distributed control system comprising plurality of operator stations (1,2,3,4) and plurality of processing stations (6,7,8,9,10) and all communications between said operator and processing stations take place over
a set of lines (11 to 19) through an electronic switch (5) wherein each of said processor unit (6 to 10) comprises of a processor block (21), input moudles (34,35) and output modules (34,35,36,37), said processor block has an I/O bus(26) and said input and output modules are connected to said I/O bus (26)through lines (38 to 41) characterized in that said switch (5) is connected between processors (21,27) through line (19,20) in hot standby mode and input modules (22,23) and output modules (24,25) are connected to the I/O bus (26,28) of the processor (21,27) through lines represented by (31,32). The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings.
Fig.l shows atypical distributed control system of the prior art,
Fig. 2 shows atypical processing station block diagram of the prior art,
Fig. 3 block diagram of input module of the invention.
Fig.4 block diagram of output module of the invention,
Fig. 5 hot stand by connection of processors of the invention.
DETAIL DESCRIPTION OF THE INVENTION
According to this invention the bus switching is avoided and the changeover of processing functions from a failed processor to a backup processor is achieved by use of combination fault detection and recovery methods in the processors and a new electronic circuit in the I/O modules.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Typical configuration of a Distributed Control System used for monitoring and controlling a process is shown in Fig 1. This system consists of a set of computers termed as operator stations (1 to 4 in Fig.l) located in plant control room. Operator stations 1 to 4 are used as interfaces between the plant operators and the plant process. They are used to display the process parameters in a way that is easy and convenient for the operators to monitor the process conditions, including alarm conditions, trends in the variation of parameters etc. Operators will also be able to access the informations about different parts of the process at different operator stations simultaneously. For performing these functions, operator
stations (1 to 4)collect the necessary information on the process parameters, from a set of processing stations (6 to 10)
by sending message telegrams over the network and receiving replies from processing stations.
Each operator station ( 1 to 4) works independently from others and sends the message telegrams asynchronously . Replies from processing stations ( 6 to 10) also are asynchronous ly sent to operator stations ( 1 to 4) . An electronic switch 5 establishes proper connection and routing of these message telegrames between any two stations ( 1 to 4). Any operator stations (1 to 4) can also acquire _.nece.ssary data from other operator stations ( 1 to 4 ) by sending an appropriate message telegram. Similarly, data exchange from one processing stations ( 6 to 10 ) to another can take place asynchronously using appropriate message telegrams. Plant operators can also perform functions such as opening/closing of valves, starting/stopping of plant equipment changing of control loop set points and other operating conditions from operator stations. For performing thse tasks, operator sations (1 to 4) send out control commands to processing stations by means of appropriate message telegrams. All the communication between operator/processing stations takes place over a set of lines 11 to 19 of Fig 1 which can be twisted pair wires, coaxial cables, fiber optic cables etc.
Processing stations (6 to 10) perform the task of acquiring parameters values and status of binary logic elements/sensors by continuous and sequential scanning of signals from a number of transducers connected to them. It is possible to use different scan rates for selected set of transducers as well as alter the scan sequence and/or scan interval by appropriate commands from operator stations. Processing stations also perform the task of equipment control either on receiving such a command from an operator station or as a result of a calculation performed by it. In addition to acquiring parameter values by scanning the transducers and controlling the plant equipment processor stations (6 to 10) perform signal conditioning, signal validation, logic control and modulating control calculations. The logic and other control programmes required to perform the binary random/sequential logic calculations and modulating control calculations at the processing stations (6 to 10) are transmitted from operator stations and stored in the memory of processing stations. A more detailed block diagram of a typical processing station used in the past is shown in Fig.2. It consists of a processor represented by block 21, input modules represented by blocks 34 and 35, output modules represented by blocks 36 and 37. Processor 21 has an I/O bus 26.Input and output modules are all connected to this 1/0 bus using lines
38 to 41. Input modules (34,35) receive signals from the plant sensors and perform tasks such as conditioning, validations filtering,. Output modules (36,37) control output lines that are connected to final control elements of the plant. The output values sent out by output module are received from the processor I/O bus. These values are a result of the calculations performed by processor (21) using input values received from input modules (34,35) and the control program that is stored in its memory. The input and outputs are made up of simple electronic hardware circuits whose reliability is very high. Each of these input/output modules is connected to only a small number of plant signals. If any such module fails, only a small number of plant signals are affected. Also, it is possible that the processor can take remedial measures to minimise the effect due to failure of the module. Compared to this situations, a processing station is connected to a large number of plant signals through a number of I/O modules. As such, failure of processor will result in loss of all functions performed by the processing stations. Moreover, the functions are performed by complex software programs which are inherently less reliable. In order to achieve high availability for the system, it is necessary to use a backup processor as well as a proper method of switchover incase of failure of primary processor.
The availability of such a system with a backup processor working in a standby mode can be expressed as:
A = MTBE
= 1 - MTTR MTBF
MTBF = Meantime Between Failure of Processor
Meantime to Repair the Processor
For the standby configuration, MTTR represents the 'downtime or the time for which the processing functions are unavailable.
According to the present invention, the backup processor is in hot stand by mode and takes over the processing functions in the next cycle of operations following the failure of primary processor. Since no extra bus switching hardware is used, there is no single point failure and additional switching delays associated with such external hardware, according to this invention. Such switchover of functions by back up processor is possible because of the new circuit in the I/O modules whose block diagrams are shown in Fig.3 and Fig.4
Fig.3 is the block diagram of an input module Block 29 represents the electronic circuits used for signal conditioning. Logic circuit #1 and logic circuit #2 are identical in function and represent electronic circuits used to convert the outputs of signal conditioning block to I/O bus signals. Fig.5 is a block diagram showing the connection between processors and I/O modules .
According to this invention, the outputs of logic ciruit #1 in all input modules are connected together to form I/O bus (26) going to processor #1 (21). In a similar way, the outputs of logic circuit #2 in all input modules are connected together to form I/O bus #2 (28) going to processor #2 (27). The connection between output modules and processors #1 is #2 similar. The invention described hereinabove is in relation to a non-
I limiting embodiment and as defined by the accompanying claims.
1. An apparatus for providing redundancy to a processor module
in a distributed control system comprising plurality of operator
Stations (1,2,3,4) and plurality of processing stations
(6,7,8,9,10) and all communications between said operator and
processing stations takes place over a set of lines (11 to 19)
through an electronic switch (5) wherein each of said processor
unit (6 to 10) comprises of a processor block (21), input
modules (34,35) and output modules (36,37), said processor
block (21) has an I/O bus (26)and said input and output modules
(34,35,36,37) are connected to said i/0 bus ,(26) through lines -
(38 to 41) characterized in that said switch (5) is connected
between processors (21,27)through line (19,20) in hot standby
mode and input modules (22,23) and output modules (24,25) are
connected to the I/O bus (26,28) of the processor (21,27) through
lines represented by (31,32)
2. The apparatus as claimed in claim 1 wherein the input
module (22) comprises a signal conditioning circuits (29)
connected to receive inputs from the plants and outputs to two
identical logic circuits (30,31) which convert the outputs
of the signal conditioning block (29) to I/O bus signals (28,26).
3. The apparatus as claimed in claim 1 wherein the output
module (24) comprises an output signal conditioning circuit
(42) for providing output to plants and connected to two
identical logic circuits (43,44) and said logic circuit (43,44)
are connected to I/O bus (28,26).
4. An apparatus for providing redundancy to a processor module in a distributed control system as herein described and illustrated in the accompanying drawings.
|Indian Patent Application Number||522/DEL/2001|
|PG Journal Number||06/2012|
|Date of Filing||25-Apr-2001|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LTD,|
|Applicant Address||BHEL HOUSE, SIRI FORT, NEW DELHI-1100 049|
|PCT International Classification Number||G06F 15/16|
|PCT International Application Number||N/A|
|PCT International Filing date|