A digital output diagnostic method for safety-grade PLC systems in nuclear power plants

Abstract

The present invention discloses a digital output diagnostic method for a nuclear power plant safety-grade PLC system, comprising the following steps: designing a digital output diagnostic circuit using optocoupler isolation, the digital output diagnostic circuit comprising an output channel circuit, a diagnostic recovery circuit, and a processing unit; when no external device is connected to the digital output diagnostic circuit, the circuit enters a dynamic diagnostic mode, wherein the processing unit periodically issues a drive control signal A, performs a logical operation on the drive control signal A and the diagnostic signal A, and outputs a diagnostic result; when an external device is connected to the digital output diagnostic circuit, the circuit enters a real-time diagnostic mode, wherein the processing unit issues a drive control signal A according to a task, performs a logical operation on the drive control signal A and the diagnostic signal A, and outputs a diagnostic result. The present invention can quickly diagnose whether a digital output channel has a fault, ensuring real-time diagnosis and reliable data output.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial control, and in particular to a digital quantity output diagnosis method for a safety-level PLC system of a nuclear power plant. Background Art

[0002] The industrial control field is a field with very high requirements for safety and reliability. Whether it can operate safely and reliably is also an important indicator for evaluating instrumentation and control equipment. However, in the industrial control field, especially in digital instrumentation and control fields such as nuclear power plants, there will be a large number of high and low level signals output to control and drive external devices, participate in shutdown control, and participate in important logical operations, which is related to the safe operation of nuclear power plants.

[0003] In industrial applications, when no faults occur, digital output signals generally maintain an expected output state, providing stable voltage levels for peripheral devices. However, discrepancies between actual output signals and expected outputs due to factors such as device aging and failure can seriously impact the operational safety of nuclear power plants. Currently, however, there is no effective method for determining whether a digital output channel has experienced a fault.

[0004] For example, patent application number CN201710405142.X proposes a self-diagnostic detection circuit, detection device, and detection method for a digital output channel. The circuit includes an electromagnetic relay configured to receive a digital control signal and output an electrical signal converted by an electromagnet to an external circuit. The electromagnetic relay includes two sets of output contacts, one set of contacts serving as dry contacts to form a dry contact output branch, and the other set of contacts connected to the input signal control circuit to form a detection readback branch. Although this application simplifies the self-diagnostic circuit design for the digital output channel, in actual application, its stability is poor and cannot guarantee the safe operation of nuclear power plants. Summary of the Invention

[0005] The purpose of the present invention is to provide a digital output diagnosis method for a safety-level PLC system of a nuclear power plant, so as to solve the technical problem of how to quickly diagnose whether a digital output channel has a fault.

[0006] The object of the present invention is achieved by adopting the following technical solution: a digital output diagnosis method of a nuclear power plant safety-level PLC system, comprising the following steps:

[0007] The digital output diagnostic circuit is designed by adopting the optical coupling isolation method, and the digital output diagnostic circuit includes an output channel circuit, a diagnostic recovery circuit and a processing unit;

[0008] When no external device is connected to the digital output diagnostic circuit, it enters the dynamic diagnostic mode. The processing unit periodically sends the drive control signal A, obtains the diagnostic signal A through the diagnostic recovery circuit, and performs a logical operation on the diagnostic signal A and the drive control signal A to output the diagnostic result.

[0009] When an external device is connected to the digital output diagnostic circuit, it enters the real-time diagnostic mode. The processing unit sends a drive control signal A according to the task, obtains the diagnostic signal A through the diagnostic recovery circuit, and performs a logical operation on the diagnostic signal A and the drive control signal A to output the diagnostic result.

[0010] Furthermore, entering the dynamic diagnosis mode includes the following steps:

[0011] When there is no external device connected to the digital output diagnostic circuit, the high level VCC_EX of the external device connected to the output channel circuit is low, powered by the diagnostic power supply VCC_DIAG, the output contact of the OC3 diagnostic circuit is not conducting, the diagnostic signal B is low, and the dynamic diagnostic mode is entered;

[0012] The processing unit periodically sends a drive control signal A, which is passed through the output channel circuit to obtain an output signal, and the output signal is passed through the OC2 diagnostic circuit to obtain a diagnostic signal A;

[0013] The processing unit receives the diagnostic signal A and performs a logical operation on the diagnostic signal A and the drive control signal A. If the diagnostic signal A is the same as the drive control signal A, no fault occurs and the output diagnostic result channel is normal "0"; if the diagnostic signal A is different from the drive control signal A, a fault occurs and the output diagnostic result channel is faulty "1".

[0014] Furthermore, entering the real-time diagnostic mode includes the following steps:

[0015] When an external device is connected to the digital output diagnostic circuit, the high level VCC_EX of the external device connected to the output channel circuit is high, powered by VCC_EX, the output contact of the OC3 diagnostic circuit is turned on, the diagnostic signal B is high, and the real-time diagnostic mode is entered;

[0016] The processing unit sends a drive control signal A according to the task, and the drive control signal A is obtained through the output channel circuit to obtain an output signal, and the output signal is obtained through the OC2 diagnostic circuit to obtain a diagnostic signal A;

[0017] The processing unit receives the diagnostic signal A and performs a logical operation on the diagnostic signal A and the drive control signal A. If the diagnostic signal A is the same as the drive control signal A, no fault occurs and the output diagnostic result channel is normal "0"; if the diagnostic signal A is different from the drive control signal A, a fault occurs and the output diagnostic result channel is faulty "1".

[0018] Furthermore, the diagnostic power supply VCC_DIAG is generated by an isolated DC / DC converter.

[0019] Furthermore, the output channel circuit includes an optocoupler isolator OC1, a driving side of the optocoupler isolator OC1 is connected to the processing unit, and an output side of the optocoupler isolator OC1 is connected to the diagnostic recovery circuit through a MOS tube.

[0020] Furthermore, the diagnostic recovery circuit includes an OC2 diagnostic circuit and an OC3 diagnostic circuit. The OC2 diagnostic circuit includes an optocoupler isolator OC2, the driving side of the optocoupler isolator OC2 is connected to the output side of the optocoupler isolator OC1 through a MOS tube, and the output side of the optocoupler isolator OC2 is connected to the processing unit through a logic device NOT gate; the OC3 diagnostic circuit includes an optocoupler isolator OC3, the driving side of the optocoupler isolator OC3 is connected to the output side of the optocoupler isolator OC1 through a MOS tube, and the output side of the optocoupler isolator OC3 is connected to the processing unit through a logic device NOT gate.

[0021] Furthermore, the processing unit adopts a CPU or FPGA processing chip.

[0022] The beneficial effects of the present invention are that it can quickly diagnose whether a digital output channel has a fault. It can not only perform real-time diagnosis when an external device is connected, but also perform periodic dynamic diagnosis when no external device is connected, thereby ensuring the real-time nature of the diagnosis and the reliability of data output, and ensuring that the nuclear power plant can operate safely, reliably and stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0024] Figure 1 Flowchart of the present invention;

[0025] Figure 2 This is a schematic diagram of the digital output diagnostic circuit structure;

[0026] Figure 3 This is a flow chart of the dynamic diagnosis mode;

[0027] Figure 4 This is the flow chart of the real-time diagnosis mode. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0030] Example 1:

[0031] See Figure 1-4 A method for diagnosing digital output of a safety-class PLC system in a nuclear power plant comprises the following steps:

[0032] The digital output diagnostic circuit is designed by adopting the optical coupling isolation method, and the digital output diagnostic circuit includes an output channel circuit, a diagnostic recovery circuit and a processing unit;

[0033] When no external device is connected to the digital output diagnostic circuit, it enters the dynamic diagnostic mode. The processing unit periodically sends the drive control signal A, obtains the diagnostic signal A through the diagnostic recovery circuit, and performs a logical operation on the diagnostic signal A and the drive control signal A to output the diagnostic result.

[0034] When an external device is connected to the digital output diagnostic circuit, it enters the real-time diagnostic mode. The processing unit sends a drive control signal A according to the task, obtains the diagnostic signal A through the diagnostic recovery circuit, and performs a logical operation on the diagnostic signal A and the drive control signal A to output the diagnostic result.

[0035] The present invention addresses the high security and stability of safety-grade PLC systems in nuclear power plants. Specifically, it provides a digital output circuit with novel diagnostic measures. The diagnostic circuit uses an optocoupler to transmit readback values, ensuring the reliability of the output state and isolating external signals from internal signals, ensuring safe system operation. Furthermore, the method monitors the accuracy of digital output pathways in real time and collects current output values ​​to facilitate fault analysis. This diagnostic method effectively determines whether an output channel has failed and is applicable to large-scale projects such as nuclear power plants, ensuring the safety, reliability, and stability of nuclear power plants.

[0036] In this embodiment, entering the dynamic diagnosis mode includes the following steps:

[0037] When there is no external device connected to the digital output diagnostic circuit, the high level VCC_EX of the external device connected to the output channel circuit is low, powered by the diagnostic power supply VCC_DIAG, the output contact of the OC3 diagnostic circuit is not conducting, the diagnostic signal B is low, and the dynamic diagnostic mode is entered;

[0038] The processing unit periodically sends a drive control signal A, which is passed through the output channel circuit to obtain an output signal, and the output signal is passed through the OC2 diagnostic circuit to obtain a diagnostic signal A;

[0039] The processing unit receives the diagnostic signal A and performs a logical operation on the diagnostic signal A and the drive control signal A. If the diagnostic signal A is the same as the drive control signal A, no fault occurs and the output diagnostic result channel is normal "0"; if the diagnostic signal A is different from the drive control signal A, a fault occurs and the output diagnostic result channel is faulty "1".

[0040] In this embodiment, entering the real-time diagnostic mode includes the following steps:

[0041] When an external device is connected to the digital output diagnostic circuit, the high level VCC_EX of the external device connected to the output channel circuit is high, powered by VCC_EX, the output contact of the OC3 diagnostic circuit is turned on, the diagnostic signal B is high, and the real-time diagnostic mode is entered;

[0042] The processing unit sends a drive control signal A according to the task, and the drive control signal A is obtained through the output channel circuit to obtain an output signal, and the output signal is obtained through the OC2 diagnostic circuit to obtain a diagnostic signal A;

[0043] The processing unit receives the diagnostic signal A and performs a logical operation on the diagnostic signal A and the drive control signal A. If the diagnostic signal A is the same as the drive control signal A, no fault has occurred and the output diagnostic result is "0" (normal channel). If the diagnostic signal A is different from the drive control signal A, a fault has occurred and the output diagnostic result is "1" (fault channel). The digital output channel output diagnostic truth table is as follows:

[0044] Table 1 Digital output channel output diagnostic truth table

[0045] Drive control signal A Diagnostic signal A Diagnostic signal B Output Status 1 1 0 0 1 0 0 1 1 1 1 0 1 0 1 1

[0046] Furthermore, the driving control signal A may be a pulse signal.

[0047] In this embodiment, the diagnostic power supply VCC_DIAG is generated by an isolated DC / DC converter. The voltage of VCC_DIAG should be lower than the high level voltage of the external device. Figure 2VCC and GND are the internal high level and ground of the digital output diagnostic circuit, and VCC_EX and GND_EX are the high level and ground of the external device connected to the output channel circuit.

[0048] In this embodiment, the output channel circuit includes an optocoupler isolator OC1, a driving side of the optocoupler isolator OC1 is connected to the processing unit, and an output side of the optocoupler isolator OC1 is connected to the diagnostic recovery circuit through a MOS tube.

[0049] In this embodiment, the diagnostic recovery circuit includes an OC2 diagnostic circuit and an OC3 diagnostic circuit. The OC2 diagnostic circuit includes an optocoupler isolator OC2, the driving side of the optocoupler isolator OC2 is connected to the output side of the optocoupler isolator OC1 through a MOS tube, and the output side of the optocoupler isolator OC2 is connected to the processing unit through a logic device NOT gate; the OC3 diagnostic circuit includes an optocoupler isolator OC3, the driving side of the optocoupler isolator OC3 is connected to the output side of the optocoupler isolator OC1 through a MOS tube, and the output side of the optocoupler isolator OC3 is connected to the processing unit through a logic device NOT gate.

[0050] In the present invention, the output channel circuit and the diagnostic recovery circuit both electrically isolate the digital output diagnostic circuit from the external device through an optocoupler, ensuring that the digital output diagnostic circuit can operate safely and stably, and the processing unit can perform logical operations on the collected signal and the expected signal (drive control signal) and output the diagnostic result, thereby helping the staff to determine whether there is an abnormality in the output channel and issue an alarm when an abnormality occurs. If a fault occurs, the corresponding channel fault indicator light is lit (constant red indication), and the output enters a safe state.

[0051] In this embodiment, the processing unit adopts a CPU or FPGA processing chip.

[0052] Furthermore, the specific operation of the digital output diagnostic method is as follows: the digital output diagnostic circuit drives the optocoupler isolator OC1 through the IO port of the processing unit to conduct or disconnect. Pins 1 and 2 of the optocoupler isolator OC1 are the driving side. When the current flowing from pin 1 to pin 2 is 3mA to 5mA, pins 4 and 3 on the output side are conductive. When the current flowing from pin 1 to pin 2 is close to 0, pins 4 and 3 on the output side are disconnected. To improve the output drive capability, the output side of the optocoupler isolator OC1 is generally not directly connected to the output channel circuit, but instead drives a MOS transistor, which ultimately outputs the expected level signal. The diagnostic recovery circuit connects the final signal output by the MOS tube to the driving side of another optocoupler isolator (including optocoupler isolator OC2 and optocoupler isolator OC3), and uses the output signal to drive whether the optocoupler isolator of the diagnostic recovery circuit is turned on. The output side of the optocoupler isolator of the diagnostic recovery circuit is connected to the NOT gate. Because the state of the level signal will be reversed once after passing directly through the optocoupler isolator, a NOT gate is added to reverse the level signal again, thereby obtaining a recovery signal consistent with the actual output signal. The high level inside the output channel circuit is a high level voltage within the recognition range of the processing unit, and the high level signal ultimately output to the external device can be any voltage value, which can be applied to external devices with different level requirements. When the processing unit IO sends a high level drive signal, the output channel circuit optocoupler isolator OC1 is turned on, and a conduction voltage difference is generated at both ends of the MOS tube G and S of the output channel circuit. The MOS tube is turned on, and the output channel circuit outputs a high level signal. At the same time, this high-level signal drives the optocoupler isolator in the diagnostic recovery circuit, turning it on. The output of the optocoupler isolator then outputs a low-level signal, which is converted through a logic NOT gate and then fed into the processing unit. The processing unit then performs a logical operation on the collected diagnostic signal and the expected value, ultimately outputting the diagnostic results: "0" for a normal channel and "1" for a faulty channel. The processing unit reads the channel diagnostic information and reports the channel output and diagnostic fault information. Both the output channel circuit and the diagnostic recovery circuit utilize optocoupler isolation, ensuring that output-side faults do not propagate throughout the entire nuclear power plant PLC system, thus ensuring plant safety in the event of a serious fault.

[0053] The above description describes the static diagnostic portion of the digital output signal. Static diagnostics are real-time. Once a digital signal is output, the digital output diagnostic circuit continuously monitors the switch output status. However, static diagnostics cannot periodically diagnose the output channels when no digital signal is output. This is why dynamic diagnostics for digital output signals are introduced. In actual industrial applications, a digital output module has many digital output channels. While static diagnostics can determine whether active channels are faulty, it is impossible to determine whether unused channels are functioning properly. Therefore, dynamic diagnostics can be used to determine in advance whether unused digital output channels are functioning as expected. If not, the channel fault is reported, allowing the nuclear power plant PLC system to enter a safe state earlier, improving system safety and reliability.

[0054] The present invention can diagnose the disconnection, adhesion and output readback link failures of any components, and is applicable to the output diagnostic control mode of optocouplers, relays and field effect transistors, and the diagnostic method can also be used for high-speed pulse signals; the diagnostic time is better than 1ms, and the dynamic diagnostic cycle can be flexibly configured; the digital output diagnostic method of the present invention is novel, and adopts a combination of static diagnosis (real-time diagnosis) and dynamic diagnosis. It can not only monitor the status of digital output signals in real time, but also perform periodic self-tests when there is no output signal; the design of the present invention meets the isolation requirements, and the isolation withstand voltage requirement is 1500VAC@1min<5mA; the processing unit adopts a parallel processing mode, with a fast processing speed, which meets the response time requirements; it can be applied to the safety-level digital instrumentation and control system of nuclear power plants or other industrial control industries to achieve high-reliability output control of switch output signals; the reliability of the present invention is mainly reflected in strong stability, fast diagnostic speed and high diagnostic coverage.

[0055] It should be noted that for the aforementioned embodiments, for simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions involved are not necessarily required by this application.

[0056] Furthermore, the terms "connected" and "set" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. Thus, a feature defined as "connected" or "set" may explicitly or implicitly include one or more of such features. Furthermore, the terms "connected," "set," and the like are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential sequence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the invention described herein can be implemented in sequences other than those illustrated or described herein.

[0057] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, modifications and variations made by those skilled in the art without departing from the spirit and scope of the present invention should be within the scope of protection of the appended claims.

Claims

1. A digital output diagnostic method for a safety-grade PLC system in a nuclear power plant, characterized in that: The steps include: The digital output diagnostic circuit is designed by adopting the optical coupling isolation method, and the digital output diagnostic circuit includes an output channel circuit, a diagnostic recovery circuit and a processing unit; When no external device is connected to the digital output diagnostic circuit, the system enters the dynamic diagnostic mode. The processing unit periodically sends the drive control signal A, obtains the diagnostic signal A through the diagnostic recovery circuit, and performs a logical operation on the diagnostic signal A and the drive control signal A to output the diagnostic result. Entering the dynamic diagnostic mode includes the following steps: When there is no external device connected to the digital output diagnostic circuit, the high level VCC_EX of the external device connected to the output channel circuit is low, powered by the diagnostic power supply VCC_DIAG, the output contact of the OC3 diagnostic circuit is not conducting, the diagnostic signal B is low, and the dynamic diagnostic mode is entered; The processing unit periodically sends a drive control signal A, which is passed through the output channel circuit to obtain an output signal, and the output signal is passed through the OC2 diagnostic circuit to obtain a diagnostic signal A; The processing unit receives the diagnostic signal A and performs a logical operation on the diagnostic signal A and the drive control signal A. If the diagnostic signal A is the same as the drive control signal A, no fault has occurred and the output diagnostic result is "0" indicating normal channel. If the diagnostic signal A is different from the drive control signal A, a fault has occurred and the output diagnostic result is "1" indicating fault channel. When an external device is connected to the digital output diagnostic circuit, the real-time diagnostic mode is entered. The processing unit sends a drive control signal A according to the task, obtains the diagnostic signal A through the diagnostic recovery circuit, and performs a logical operation on the diagnostic signal A and the drive control signal A to output the diagnostic result. Entering the real-time diagnostic mode includes the following steps: When an external device is connected to the digital output diagnostic circuit, the high level VCC_EX of the external device connected to the output channel circuit is high, powered by VCC_EX, the output contact of the OC3 diagnostic circuit is turned on, the diagnostic signal B is high, and the real-time diagnostic mode is entered; The processing unit sends a drive control signal A according to the task, and the drive control signal A is obtained through the output channel circuit to obtain an output signal, and the output signal is obtained through the OC2 diagnostic circuit to obtain a diagnostic signal A; The processing unit receives the diagnostic signal A and performs a logical operation on the diagnostic signal A and the drive control signal A. If the diagnostic signal A is the same as the drive control signal A, no fault has occurred and the output diagnostic result is "0" indicating normal channel. If the diagnostic signal A is different from the drive control signal A, a fault has occurred and the output diagnostic result is "1" indicating fault channel.

2. A digital output diagnostic method for a safety-class PLC system in a nuclear power plant according to claim 1, characterized in that: The diagnostic power supply VCC_DIAG is generated by an isolated DC / DC converter.

3. The digital output diagnostic method for a safety-class PLC system of a nuclear power plant according to claim 1, characterized in that: The output channel circuit includes an optocoupler isolator OC1, a driving side of the optocoupler isolator OC1 is connected to the processing unit, and an output side of the optocoupler isolator OC1 is connected to the diagnostic recovery circuit through a MOS tube.

4. A digital output diagnostic method for a safety-class PLC system in a nuclear power plant according to claim 3, characterized in that: The diagnostic recovery circuit includes an OC2 diagnostic circuit and an OC3 diagnostic circuit. The OC2 diagnostic circuit includes an optocoupler isolator OC2, the driving side of the optocoupler isolator OC2 is connected to the output side of the optocoupler isolator OC1 through a MOS tube, and the output side of the optocoupler isolator OC2 is connected to the processing unit through a logic device NOT gate; the OC3 diagnostic circuit includes an optocoupler isolator OC3, the driving side of the optocoupler isolator OC3 is connected to the output side of the optocoupler isolator OC1 through a MOS tube, and the output side of the optocoupler isolator OC3 is connected to the processing unit through a logic device NOT gate.

5. The digital output diagnostic method for a safety-class PLC system of a nuclear power plant according to claim 1, characterized in that: The processing unit adopts a CPU or FPGA processing chip.

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