Hitachi, Ltd.

Makoto Kogure

Hiroyuki Tanaka

Takeiki Aizono

Dai Fujii

Masahiro Ohashi

Masao Fukunaga

Akira Sase

Toshimitsu Tsuchihashi

Koji Tomaoki

In a distributed control system in which a plurality of nodes are connected to a transmission line, each node controlling components connected to this node and transmitting a message to other nodes, a message sent by each node includes at least two message-sending condition-identifying portions, one of the condition-identifying portions including data indicating a message-receiving node or non-designation of a message-receiving node; and a comparison-selection circuit provided in each node includes registration parts for registering data of message-receiving conditions, at least two registration parts for comparing contents of the condition-identifying portion in the taken-in message with the data of message-receiving conditions registered in the registration parts, a received-message storing part for storing a message to be received in this node, a control part for determining whether or not the taken-in message is to be received in this node based on a result of comparison-processing performed in the comparison and selection means and for transferring the taken-in message to the received-message storing part if it is determined that the taken-in message is received in this node, otherwise, abandoning the taken-in message.

Distributed control system and filtering method used in the distributed control system

In a distributed control system with a plurality of nodes connected to a transmission line, each node controlling components and transmitting a message to other nodes, a message includes at least two message-sending condition-identifying portions, one of the portions including data indicating a message-receiving node or non-designation of a message-receiving node. A comparison-selection circuit in each node includes at least two registration parts for comparing contents of the condition-identifying portion in the taken-in message with the data of message-receiving conditions registered in the registration parts, a received-message storing part for storing a message to be received, a control part for determining whether or not the taken-in message is to be received based on a result of comparison-processing performed in the comparison and a selector transferring the taken-in message to the received-message storing part if it is determined that the taken-in message is to be received, otherwise, abandoning the taken-in message.

A communicator for field instruments connected to a transmission line for transmitting electric signals from the field instruments to a host instrument. The communicator operates on electric power fed from an external power supply over the transmission line. The external power supply is arranged in the transmission line. Electric current consumed by the transmission line is set to a constant value.

Communicator for field instruments and method of supplying power to this communicator

In a decentralized control system configuring a network between plural field devices for measuring and controlling the controlled objects and plural upper-level apparatus for communicating data to the field devices and controlling the field devices, and forming a control loop among the devices, in which the field device has a normal communication means for communicating with other devices in a normal operation mode, and an emergency communication means for communicating with other devices in an emergent operation mode, in which the normal communication means and the emergency communication means use their own communication signals and the emergency communication means operates in an asynchronous communication mode. In addition, on the network, a shutdown control means is formed for transmitting a shutdown command signal to the shutdown target control device if necessary by detecting the abnormal state of the individual devices.

Decentralized control system and shutdown control apparatus

Communicator for field instruments and method for supplying power to

In a field bus system for performing communication between at least one field device and at least one higher-rank apparatus which are connected on a field bus transmission line constituted by a pair of transmission lines, an intrinsically safe barrier disposed between a hazardous area and a safe area on the transmission line in order to limit energy to be used in the hazardous area, the intrinsically safe barrier comprising impedance converting circuits provided in the barrier for reducing impedance in a frequency band of communication data.

Intrinsically safe barrier and field bus system

A field bus system may be used in which transmission ability of the system can be maintained even if communication error occurs due to noises or failure of a transmission line. The system can be easily shifted at a lower cost from a conventional system to the field bus system without degrading the high reliability thereof. The transmission line is constituted by a multiple-cable transmission line having at least three transmission cables. An external power supply supplies power to field devices through a pair of transmission cables of the multiple-cable transmission line. The field devices are connected to the transmission cables through a transmission line switching unit constituted by a plurality of rectifier elements, so that the field devices are supplied with current flowing in one predetermined direction when any of the pairs of transmission cables is selected. The external power supply monitors a failure of a currently used pair of transmission cables and, upon detection of failure of the currently used pair of transmission cables, the failed pair is replaced by a normal pair of transmission cables such that the field devices are continuously supplied with power.

Multiple-cable field bus system

In a system for performing signal transmission, through a field bus, between field devices and higher-rank apparatuses connected on a transmission line, the field devices are of the analog signal type. A substitution device is provided between the analog type field devices and the field bus. The substitution device acts to perform communication on the field bus as a substitute for the field devices. By the substitution device, the field devices can be gradually changed to those adapted to the field bus as occasion demands, so that an existing system can be transformed step by step into a field bus system.

Field bus system and virtual field apparatus

A Manchester code signal is used as a communication signal to be superimposed onto an operating current. The amplitude value in the plus direction with respect to an average current value is made larger than that in the minus direction, and the time width of an 'H' level in one bit time is made smaller than that of an 'L' level so as to establish the average current value into a low level. Accordingly, it is possible to make the average current value at the time of not-communication equal to that at the time of communication, and it is also possible to establish the average current value to a low level.

Communication apparatus and method in a field bus system

A field sensor communication system is arranged in such a manner that, when an electric current, the level of which can be changed to a predetermined level, is, transmitted to a signal transmission line having at least one load resistor connected in series and the voltage change across the load resistor due to the change in the electric current is detected as a reception signal, the predetermined level is cyclically changed to a plurality of levels so that the level at which a good signal reception condition can be realized is determined to perform a communication at the thus determined level. As a result, even if the value of the load resistor in the signal transmission line is changed, the communication can be performed normally, since an undesirable change of the level of the reception signal can be prevented.

Field sensor communication system

A duplex field bus system in which a transmission is provided by first and second transmission lines. At least one of field device, an upper-rank apparatus and an external power supply is connected to both of the first and second transmission lines so that power supply and communication can be performed by using either one of or both of the transmission lines selectively. When failure is detected in the currently used one of the first and second transmission lines, not only is the failed transmission line switched over into the other one transmission line, but also information related to the occurrence of failure is transmitted to other devices before the communication is restarted. Accordingly, even in the case where fatal failure related to the transmission line occurs in the field bus system, communication can be continued by automatically switching the transmission line used by the devices.

Duplex field bus system

In a communication system in which a plurality of communication units are connected to a common two-wire transmission line and signal transmission/reception is made between the communication unit and a field sensor connected to one end of the transmission line, the communication unit transmits a signal to the field sensor under the condition that no signal is present on the transmission line during a period of time not shorter than a predetermined time while the field sensor transmits a signal indicative of in-use of the transmission line at an interval of time shorter than the predetermined time during a period of time until the field sensor sends back a signal in response to the signal from the communication unit, whereby signal collision between the plurality of communication units is prevented with no provision of any specific means.

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Hitachinaka, Japan

Makoto Kogure