JP2000242301A - Fail-safe system for decentralized control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To complete the fail-safe function of a decentralized control system. SOLUTION: For the extension, etc., of this fail-safe system, slave units 2 and 3 are connected to one master unit 1 by a multidrop communication line 10 and also connected to each other by a hard line 20, and the communication by the communication line 10 and a fault detecting function by the hard line 20 (detection by comparing the potential at a point A with a specific value by a comparing circuit 12) are used in combination to implement the fail-safe function more securely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a distributed control system (abbreviated as DCS) and a remote monitoring control system (SCADA) for performing a single control by a master unit and a plurality of slave units, and particularly has a fail-safe function. The present invention relates to a distributed control system.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional example. This shows an example of a relay sequence, for example, 13 is a large capacity relay, 14 is its contact, 23A, 23B, 33A, 33B.
Are small capacity relays, and 24A, 24B, 34A and 34B are their respective contacts. These relays are driven by an instruction from a processing device or the like (not shown). The power supply 40 is turned on by closing the relay contact 14, and the external device (controlled device) 51 is controlled by the relay contacts 24A, 24B, 34A, 34B and the like. To 54 operate. At this time, for example, in order to prevent the small-capacity relay contacts from adhering, insert a small-capacity relay contact, then insert a large-capacity relay contact, apply a large current, cut off the large-capacity relay contact, and cut off the large current. Care has been taken to switch off the small capacity relays afterwards.

On the other hand, small-capacity relays 23A, 23B, 33A and 33B are connected in parallel to the detection line 70, and a current flowing through the line 70 is monitored by a current detection circuit 40 to detect the current. The circuit 40 can detect, for example, the normal or abnormal operation of the small-capacity relay from the current value flowing through the line 70, and when it is determined that the operation is abnormal, fail-safe operation is performed to ensure safety.

[0004]

The structure as shown in FIG.
There is no particular problem when operating as a single closed unit or system, but there are many and many types from small-scale systems to large-scale systems such as controller systems and remote monitoring and control systems. In general, trying to implement failsafe in the event of shrinking or shrinking does not work. Therefore, an object of the present invention is to improve the fail-safe function without impairing scalability (or scalability) and flexibility, that is, regardless of the size.

[0005]

In order to solve the above problems,
According to the first aspect of the present invention, when one unitary control is performed in a distributed manner by the master unit and the plurality of slave units, serial communication is performed by connecting the units with a multidrop signal line, and the multidrop signal is transmitted. A fail-safe signal line for performing fail-safe is provided separately from the line.

In the first aspect of the present invention, the fail-safe signal line is a signal line for notifying a state of each of the slave units to a master unit as a voltage or current signal. An abnormality can be determined from the signal level of the signal, and if it is abnormal, fail-safe can be implemented (the invention of claim 2), or the fail-safe signal line sets the state of each slave unit as an on / off signal. This is a signal line for notifying the master unit. The master unit determines an abnormality based on the on / off signal, and can execute fail-safe when the abnormality is abnormal (claim 3).

[0007]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention. FIG. 1 is an example of the relay sequence similarly to FIG. 3, and shows an example in which units 1, 2, and 3 are provided. Here, the unit 1 is referred to as a master unit, for example, which controls the entire control, and the units 2, 3 and the like are referred to as slave units as being subordinate to the master unit 1. Although two slave units are used here, it goes without saying that the slave units can be provided as appropriate according to the system configuration.

The combination of the unit 1 in FIG. 1 and, for example, the unit 2 corresponds to the one shown in FIG. 3, and therefore FIG. 1 shows a multi-drop serial communication line 10 and a hard line (fail-safe) between the units. It is characterized in that it is connected by a signal line) 20. Reference numerals 11, 21, and 31 denote logic control units, 12 denotes a comparison circuit, T denotes a terminal plate, and the others are the same as those shown in FIG.
3 is, for example, by the logic control unit 11,
The relays 23A, B and 33A, B are driven by, for example, the logic control units 21 and 31, respectively. By configuring as described above, when expanding a unit, the expansion unit is connected to the multi-drop serial communication line 10 and the hard line 2 is connected.
By connecting to 0, it can be easily incorporated into the system and can have a fail-safe function. Further, when the unit is reduced, it can be easily dealt with simply by disconnecting the unit from the serial communication line 10 and the hardware line 20.

That is, the units are connected via a multi-drop serial communication line 10, and serial communication is performed from the master unit 1 to each of the slave units 2 and 3, for example. Since it is possible to collect information on a few normals and abnormalities, it is possible to implement fail-safe on the basis of this information. By comparing the voltage of A with a reference value, it is possible to know whether or not the contacts of the relay are operating normally, so that the fail-safe function can be more reliably performed. Although the number of the comparison circuit 12 is one here,
A plurality can be provided as necessary. Further, instead of monitoring the voltage at the point A, a detection circuit such as the current detection circuit 60 in FIG. 3 for detecting the current flowing through the hard line 20 may be provided.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention. This is because the hard wire 20 shown in FIG.
For example, a switch S is provided on the hard wire 20 to disable the operation when all are normal, and to disable the logic control unit 21 when a failure occurs, while transmitting an analog signal including a voltage or current. For example, the switch S is closed by the output from the switch 31, thereby transmitting an on / off signal. The rest is the same as FIG. 2, so that the drawing is simplified.

Although an example in which the present invention is applied to a relay sequence has been described above, the present invention relates to general distributed control including SCADA, in which one unitary control is performed in a distributed manner between a master unit and a plurality of slave units. It is possible to apply in cases.

[0012]

According to the present invention, a master unit and a plurality of slave units are connected by a multi-drop type serial communication line and by a hard line, thereby impairing expandability and flexibility. This provides an advantage that the fail-safe function can be improved without any problem.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a conventional example.

[Explanation of symbols]

1: Master unit, 2, 3: Slave unit, 10
... Multi-drop serial communication lines 11, 21, 21
31: logic control unit, 12: comparison circuit, 13
... Large-capacity relay, 14 ... Large-capacity relay contact, 20 ... Hard wire (fail-safe signal line), 23A, 23B, 33
A, 33B ... small capacity relay, 24A, 24B, 34A,
34B ... small capacity relay contact, 40 ... power supply, 51-54 ...
External device (controlled device), 60 ... current detection circuit, 70 ...
Detection line, T: terminal board, S: switch.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference)

Claims (3)

[Claims] When performing a united control by a master unit and a plurality of slave units in a distributed manner, serial communication is performed by connecting the units with a multi-drop signal line, and the multi-drop signal line is connected to the units. A fail-safe method in distributed control, wherein a fail-safe signal line for performing fail-safe is separately provided. 2. The fail-safe signal line is a signal line for notifying a state of each of the slave units to a master unit as a voltage or current signal, and the master unit detects an abnormality from the signal level of the voltage or current signal. 2. The fail-safe method in distributed control according to claim 1, wherein the judgment is made and a fail-safe operation is performed when an abnormality occurs. 3. The fail-safe signal line is a signal line for notifying the state of each of the slave units to the master unit as an on / off signal, and the master unit determines an abnormality from the on / off signal, 2. A fail-safe operation is performed when an abnormality occurs.
2. A fail-safe method in the distributed control according to 1.