JPH01137306A - Duplex digital output device - Google Patents

Abstract

PURPOSE:To ensure the easy detection of abnormality as well as the normal continuous operation of a duplex digital output device despite occurrence of abnormality by using 1st-4th comparator circuits. CONSTITUTION:An A-system output command 1 is given to an insulating circuit 2 and the conductive or non-conductive signal is sent to two switch circuits 3 and 4 connected in series to each other. The circuit 2 transmits a signal equal to the command 1 through a terminal 12 and this signal is used by a comparator circuit 11 for detection of abnormality of the circuit 3. While a B-system output command 13 is given to switch circuits 17 and 18 which are connected in series to each other via an insulating circuit 14. Then, a signal equal to the command 13 is led out of the circuit 14 by a terminal 20. A potential comparator 21 which detects the abnormality of the circuit 4 of the system A compares the potentials of terminals 8 and 9 with each other. At the same time, a potential comparator circuit 22 is used for detection of the abnormality of the circuit 18 of the system B. Thus, it is possible to easily detect the abnormality and also to ensure the normal operation of a duplex digital output device despite occurrence of the abnormality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a dual digital output device for a programmable logic controller.

(Prior Art) The output command of the A system of a programmable logic controller (hereinafter referred to as PLO) passes through an insulating circuit that reduces external influences, and issues a conduction/discontinuation command to a switch circuit connected to a positive power supply. Similarly, the output command of the B system is also connected to the switch circuit via an insulating circuit. The counter voltage power supply sides of the two switch circuits are connected to a common load with a connection cable, and are led to the negative power supply that is paired with the positive power supply6.
Even if an abnormality occurs in the insulation circuit or switch circuit in one of the two systems, normal power can be supplied to the load.

Therefore, the timing of the output command being turned on and off is exactly the same, and the timing of the switch circuit is also the same.

In the conventional technology, by comparing the terminals 311 and 312, which are the output commands to the switch circuits 304 and 307, using a comparison circuit, if the output command and the operation of the insulation circuit are the same, the operation is normal, but the operation is determined as if there is a difference in timing, etc. If this occurred, it was determined that there was an abnormality.

(Problems to be Solved by the Invention) In the prior art, it is not easy to prevent or detect abnormalities that occur in switch circuits.

For example, if an abnormality occurs in a switch circuit and it is fixed in a conductive state, the output command will be issued even if an abnormality occurs in one switch circuit during the period in which the switch circuit is in a conductive state to supply current to the load. The normal signal continues from the isolated circuit to the switch circuit. Since the output command that is input to the comparator circuit is normal, no abnormality is detected.

Furthermore, in order to stop power supply to the load, the A system output command and the B system output command are disconnected, and each output command passes through an insulating circuit to disconnect the switch circuit, but in reality, the switch circuit Since it is in a conductive state, power supply to the load continues. Furthermore, even in this state, not only is it impossible to detect an abnormality in the comparator circuit, but also it is impossible to control the load.

An object of the present invention is to provide a PLO duplex digital output device that can easily detect an abnormality and continue normal operation even if an abnormality occurs.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes an isolation circuit for insulating the digital output command of a programmable logic controller from an external control power supply, and for driving a switching circuit at the rear end, and an output of this isolation circuit. The first circuit is composed of two switching circuits that are driven and connected in series to energize the main power supply, and the second circuit has exactly the same configuration. The main circuit has a dual output circuit by connecting the controlled object to the first terminal whose sides are connected in parallel, and the second terminal located between the two switching circuits of the first circuit, and the second terminal located between the two switching circuits of the first circuit. A first comparison circuit that compares the output commands of the circuit and detects an abnormality based on a difference in value, and a second comparison circuit that similarly compares the state of the third terminal between the two switching circuits and the first output command. Second
a comparison circuit, a second terminal similarly located inside the first circuit, a third comparison circuit that detects an abnormality using the first terminal, a third terminal of the second circuit and a second terminal located inside the first circuit. This is a duplex digital output device consisting of a fourth comparison circuit that detects an abnormality using a terminal.

(Function) To facilitate abnormality detection in a duplex digital output device of PLC, and to continue normal operation even if an abnormality occurs.

(Example) An example of the present invention will be described using FIG. The redundant digital output circuit of PLO consists of A system and B system. A system output command 1 from inside the output board is input to an isolation circuit 2 that electrically isolates it from the outside, and 2
A signal indicating conduction or non-conduction is transmitted to the two switch circuits 3 and 4 through the signal line 5. Power is supplied to the load 6 through the switch circuit 3.
, 4 conduct, that is, from the positive electrode 7 to the switch circuit 3,
Terminal 8. A load 6 is connected to a terminal 9 via a switch circuit 4 and guided to a load 10. In addition, the same signal as the A-system output command 1 is extracted from the insulating port wI2 to the outside at a terminal 12 for use in a comparison circuit 11 for detecting an abnormality in the switch circuit 3.

On the other hand, the B system also has a similar configuration. B system output command 13
is connected to the terminal 16 by the signal line 15 via the insulated circuit 14.
are connected to switch circuits 17 and 18 connected in series between them. The same signal as the B-system output command 13 is extracted from the insulation circuit 14 through a terminal 20 in order to be input to the B-system comparison circuit 19.

Potential comparison circuit 2 for detecting abnormality in switch circuit 4 of system A
1 has a function of comparing the potentials of terminals 8 and 9 at the timing of terminal 20. Similarly, terminals 12, 16, .
Enter 9.

In Figure 1, we will explain how each device works.

The switch circuit 3.4.17.18 has the function of supplying power for driving the load 6, but when an abnormality occurs, it is in a conductive state (the switch circuit is short-circuited and current cannot be cut off) or - non-conductive state (the switch The circuit becomes open and cannot be energized), making it impossible to control the switch circuit using output commands. In the case of an abnormality in which the switch circuit is in a non-conducting state, no power is supplied from the abnormal system, and operation can be continued with conduction and non-conduction using the healthy switch circuit on the side of the other system.

Also, if we consider the case where two switch circuits are used for each system, there will be no problem if a continuity command is received when the switch circuit is in a conductive state and there is an abnormality, but if the switch circuit is in a conductive state and an abnormality is received, there will be no problem, but if a non-conductive command is received, Even though one switch circuit does not become non-conductive, the other switch circuit becomes non-conductive, so power supply is also stopped.

That is, the switch circuits 3, 4 and 17, 18 are designed to provide backup protection to each other.

Next, consider a case where the switch circuits 3 and 4 of the A system are abnormal.

When the switch circuit 3 is abnormally in a conductive state, an output is generated at the terminal 8 regardless of whether the output command 5 is in a non-conductive state. Further, in an abnormal state of non-conduction, the output command 5 is contrary to the continuity state, and no output is generated at the terminal 8. That is, the command 5 and the terminal 8 are constantly compared, and if they are different, an abnormality is detected.

The A system output command 1 and the B system output command 13 are always the same signal, but considering the case where an internal abnormality occurs and synchronization of both signals becomes impossible, A,! i? The output command 15 of the B system is compared with the terminal 8 instead of the output command 5 of the B system, and an abnormality is determined if they are different.

Similarly, in the switch circuit 17 of the B system, an abnormality in the switch circuit I7 and a mismatch between the output commands of the A system and the B system are detected using the output command 5 of the A system and the comparison circuit I9.

To detect an abnormality in the switch circuit 4, a circuit 21 compares the potentials of the input terminal 8 and the output terminal 9 in accordance with the timing of the output command 5.

That is, when the content of the output command 5 is conduction, if the switch circuit 4 is normal, it becomes conductive, and the terminals 8 and 9 are at the same potential. However, when the switch circuit 4 is in an abnormal state of non-conduction, the terminals 8 and 9 have different potentials, and an abnormality is detected. Conversely, if the switch circuit 4 is in an abnormal state, the abnormality can be detected since the terminals 8 and 9 are at the same potential when the output command is non-conducting. Similar to the comparison circuit 11 described above, the timing follows the output terminal 15 of the B system. Furthermore, the comparison circuit 22 compares the potentials to detect an abnormality in the switch circuit of the B system.

In FIG. 2, in the A system, a terminal 101 is connected to a photocoupler 102 for driving the main circuit, and transistors 101 and 105 are connected in series by a terminal 105 via resistors 103 and 104.
6. Connects to the base of 107. Similarly, in the B system circuit, the terminal 108 is connected to the photocoupler 109, and the resistor 110.
111 is connected to transistors 113 and 114 connected in series at a terminal 112. The collectors of the A-system transistor 106 and the B-system transistor 113 are connected to a positive electrode 115. Furthermore, the emitters of the transistor 107 and the transistor 114 are connected to the terminal 1.
16 and connected to the load 117, and the negative electrode 11
Continues to 8.

The diode circuit of the photocoupler 119 is the photocoupler 102
It is located in series with the diode circuit of
A value passing through 0 is input to the base.

Collector of transistor 121 and transistor 12
The collector of the transistor 122 is connected to the terminal 112 and the resistor 1, thereby forming a first comparison circuit.
23, and the emitter side of the transistor 121 and the terminal 124 are common.

B system side photocoupler 125, NOT circuit 126, 12
7. Transistor 128.129. The terminal 130 also has the same configuration as the above-mentioned A system and serves as a second comparison circuit.

The B system output terminal 108 functions to make the diodes of the photocouplers 201 and 202 conductive. These photocouplers 2
The collector sides of 01 and 202 are connected to terminals 112 and 116, respectively, and the emitter side is a comparison circuit 2 for detecting abnormality.
03.

Similarly, the A-system output terminal 101 has its collector connected to the terminals 105 and 116, respectively, and its emitter connected to the diode side of the photocoupler 205 and 206, which are input to the comparator circuit 204.

Power can be supplied to the load 117 when both transistors 106 and 107, which form the switch circuit on the A system side, conduct, or when both transistors 113 and 114, which form the switch circuit on the B system side, conduct, so the transistor is abnormal. Even if the transistor does not become conductive, power can be supplied from the system that does not include that transistor.

- For example, if the transistor 106 becomes abnormal and becomes non-conductive, power can be supplied to the load 117 by directly connecting the positive electrode 115 to the load through the transistor 113, the terminal 112, and the transistor 114.

Abnormal conditions in each device are typified by abnormalities in transistors,
Since the system and B system are similar, the following case can be assumed.

First case: The transistor 106 is in a conductive state and is abnormal.

Second case: The transistor 106 is in a non-conducting state and is abnormal.

Third case: Transistor 107 is in a conductive state and abnormal.

Fourth case: Transistor 107 is non-conducting and abnormal.

For each case, a method of abnormality detection will be described.

In the first case, even though the output command is off, transistor 106 becomes conductive due to an abnormality, and terminal 10
Since there is no output command under the condition that the potential of the terminal 5 is the same as that of the positive electrode 115, the photocoupler 125 becomes non-conductive, and therefore the transistor led to the NOT circuit 127 is conductive. As a result, a conductive signal appears at terminal 130.

This abnormality detection cannot be detected when the output command is conductive, but becomes detectable as soon as the output command becomes non-conductive.

Next, in the second case, even though the output command is conductive, the transistor 107 becomes abnormal and does not become conductive, so if the output of the A system cannot be obtained, the photocoupler 1
25 becomes conductive, and the NOT circuit 126 causes the transistor 128 to become conductive, so that an abnormal state appears at the terminal 130.

In this case as well, no abnormality is detected during the period in which the output command is non-conductive, and the abnormality is detected when the terminal 130 becomes conductive during the period in which the output command is conductive.

In the third case, when the transistor 107 on the terminal 116 side of the A system continues to be conductive due to an abnormality, the comparison circuit 201 compares the potentials of the terminals 105 and 116. This comparison circuit 201 compares when the terminal 101 is conductive, when the potentials of the terminals 105 and 116 are different, and when the terminal 1
If terminals 105 and 116 have the same potential when 01 is non-conductive, an abnormality is detected.

In the fourth case, if the transistor 107 on the terminal 116 side of the A system is abnormal and the conduction state continues, the above-mentioned comparison circuit 201 detects that the transistor 107 on the terminal 116 side is abnormal when the potentials of the terminals 105 and 116 are the same. Perform detection.

In these first and second cases, the A-system transistor 10
The output command to conduct the photocoupler 125 in the circuit for detecting the abnormality of transistor 1 is in the B system.
Even if 06.107.113.114 are operating normally, if the states of output command terminals 101 and 108 of system A and system B are different, different states will occur at terminals 124 and 130 to prevent abnormality. This is to facilitate detection.

The following effects can be obtained in the embodiment described above.

(a) By duplicating the PLC digital circuit,
Even if one system becomes abnormal, operation can continue using the other system.

(b) Even if one transistor in one system becomes conductive and malfunctions, the remaining transistors can sufficiently perform the switching action.

(c) Since the output command of the B system is used to detect an abnormality in the transistor of the A system, an abnormality in the output command itself can also be detected.

〔Effect of the invention〕

According to the present invention, it is possible to easily detect an abnormality in a dual PLO digital output device, and to continue normal operation even if an abnormality occurs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an output device showing one embodiment of the present invention, and FIG. 2 shows another embodiment. 106, 107...Transistor 102, 109...Photocoupler 119...Photocoupler 120...NOT circuit 121.122...Transistor 123...NOT circuit 125...
Photocoupler 126, 127...N07 circuit 128.
...Transistor agent Patent attorney Nori Chika Ken Yudo Sanno - Figure 1

Claims (1)

[Claims] The digital output command of the programmable logic controller is isolated from the external control power supply, and the isolation circuit that drives the switching circuit at the rear end is driven by the output of this isolation circuit and connected in series, thereby energizing the main power supply. a first terminal in which the output side of each main power-carrying part is connected in parallel, a main circuit in which the output circuit is duplicated by connecting the controlled object, and the first a first comparison circuit that compares a second terminal provided between two switching circuits of the circuit and an output command of the second circuit and detects an abnormality based on a difference in value; A second comparison circuit that compares the state of a third terminal provided between the switching circuits and the first output command, and a second terminal located inside the first circuit and the first terminal detect an abnormality. A duplex digital output device comprising: a third comparison circuit that performs detection; and a fourth comparison circuit that performs abnormality detection using the third terminal and the first terminal.