Low-power-consumption intelligent fault diagnosis valve positioner
By employing a design that integrates zoned power supply and time/zone switching, combined with low-power sensors, the safety issues of the intelligent valve positioner under power outages, gas outages, and signal outages are resolved. This achieves low-power operation and real-time monitoring, ensuring system stability.
Patent Information
- Application Number
- CN202422074416.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-26
- Publication Date
- 2025-12-05
- Estimated Expiration
- 2034-08-26
AI Technical Summary
Intelligent valve positioners lack system safety guarantees in the event of power failure, gas failure, or signal failure, cannot coordinate the safe position of the valve, and have high power consumption.
The design adopts zoned power supply and time/zone switching operation. By adding micro-low power sensors to the auxiliary circuit and combining independent power supply of the main circuit and auxiliary circuit, fault self-diagnosis and real-time monitoring are realized, reducing the power consumption of non-essential functions throughout the process.
It ensures system safety in the event of power outages, gas outages, and signal outages, features a low-power operation mode and complete channel diagnostics, and enables real-time monitoring of valve and pipeline operating status.
Smart Images
Figure CN223635508U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to valve accessory technical field, especially a low -power consumption intelligent fault diagnosis's valve positioner. BACKGROUND
[0002] As the key component of fluid control, pneumatic control valve is the most widely used terminal execution unit in process industry field, and its performance determines the performance and quality of the whole control loop to a large extent. Pneumatic control valve is generally composed of valve positioner, pneumatic actuator and regulating valve, and as the only electronic component, valve positioner undertakes the key role of control coordination and data integration of the whole execution system. Based on the keyness of valve positioner, intelligent valve positioner has completely replaced the application of traditional mechanical valve positioner, and the intelligent degree of intelligent valve positioner determines the advancement, reliability, safety and economy of the system in various aspects.
[0003] The intelligent degree cannot be separated from more signal acquisition, data analysis, control strategy, state estimation and safety decision. However, as a loop power supply instrument, when the collected signals are more and more, the requirement of intelligent valve positioner for power consumption is also rising significantly. At the same time, intelligent valve positioner depends on power supply, gas source and signal to complete the control of valve, so in the case of power failure, gas failure and signal failure, intelligent valve positioner lacks the guarantee of system safety, and cannot coordinate the arrival of safe position of valve in the case of power failure, gas failure and signal failure. UTILITY MODEL CONTENTS
[0004] The utility model discloses a kind of low-power consumption intelligent fault diagnosis's valve positioner and diagnostic method, mainly solve the problems existing in the prior art, by increasing micro low-power consumption pressure sensor in auxiliary circuit, realize valve positioner fault self-diagnosis, execution mechanism and the online detection of multiple faults of valve, early warning and targeted repair, ensure the stable operation of valve system.
[0005] The utility model provides a kind of low-power consumption intelligent fault diagnosis's valve positioner, it is characterized in that, include main signal management unit, auxiliary signal management unit, microprocessor unit, signal feedback unit, isolation communication unit, electrical conversion unit and display control unit;
[0006] The main signal management unit, the microprocessor unit, the electrical conversion unit and the display control unit are arranged in main circuit;The auxiliary signal management unit, the signal feedback unit and the isolation communication unit are arranged in the auxiliary circuit;The main circuit and the auxiliary circuit use independent power supply each other;
[0007] The main signal management unit, the electrical conversion unit and the display control unit are directly electrically connected to the microprocessor unit; the main signal management unit is externally connected to the control system and the valve; the electrical conversion unit is externally connected to the pneumatic actuator; the auxiliary signal management unit and the signal feedback unit are connected to the microprocessor unit through the isolation communication unit; the auxiliary signal management unit is connected to the sensor; the signal feedback unit is externally connected to the control system.
[0008] Further, the main signal management unit comprises a control signal conditioning module, a valve position detection module and a main signal analog-digital conversion module;
[0009] The control signal conditioning module is externally connected to the control system through a control signal loop, and at the same time, a power supply is connected from the control signal loop to the main loop; the valve position detection module is electrically connected to the valve position sensor located on the valve positioner; the control signal conditioning module and the valve position detection module are both internally electrically connected to the main signal analog-digital conversion module; the main signal analog-digital conversion module is electrically connected to the microprocessor unit.
[0010] Further, the auxiliary signal management unit comprises a gas source pressure sensing module, an output pressure sensing module, a temperature sensing module and an auxiliary signal analog-digital conversion module;
[0011] The gas source pressure sensing module is connected to the first pressure sensor located at the gas source input end of the valve positioner; the output pressure sensing module is connected to the second pressure sensor located at the output end of the valve positioner; the temperature sensing module is connected to the temperature sensor in the inner cavity of the container where the valve positioner is located; the gas source pressure sensing module, the output pressure sensing module and the temperature sensing module are electrically connected to the auxiliary signal analog-digital conversion module; the auxiliary signal analog-digital conversion module is connected to the microprocessor unit through the isolation communication unit.
[0012] Further, the signal feedback unit comprises a digital-analog conversion module and a feedback signal output module; the feedback signal output module is externally connected to the control system through a valve position output loop, and at the same time, a power supply is connected from the valve position output loop to the auxiliary loop; the digital-analog conversion module is externally connected to the microprocessor unit through the isolation communication unit, and is internally electrically connected to the feedback signal output module.
[0013] Further, the isolation communication unit comprises a first interface and a second interface; the first interface and the second interface are connected in an electromagnetic isolation or optoelectronic isolation manner; the first interface is connected to the auxiliary signal management unit and the signal feedback unit; the second interface is connected to the microprocessor unit.
[0014] Further, a fault diagnosis unit is further included; the fault diagnosis unit is arranged in the main circuit and connected to the microprocessor unit, the main signal management unit and the electrical conversion unit.
[0015] Further, the fault diagnosis unit includes a power supply diagnosis module and an electrical signal limit value diagnosis module; the power supply diagnosis module and the electrical signal limit value diagnosis module are both electrically connected to the microprocessor unit; the power supply diagnosis module is further electrically connected to the main signal management unit and the electrical conversion unit; the electrical signal limit value diagnosis module is further electrically connected to the main signal management unit.
[0016] Further, the microprocessor unit includes a storage module, an execution module and a built-in analog-to-digital conversion module; the execution module and the built-in analog-to-digital conversion module are connected to the storage module; the built-in analog-to-digital conversion module is externally connected to the fault diagnosis unit.
[0017] Further, the microprocessor unit further includes a built-in switch module; the built-in switch module is arranged between a power supply and the built-in analog-to-digital conversion module; the execution module controls connection to the built-in switch module.
[0018] Further, an external switch unit is further included; the external switch unit is arranged between a power supply and the fault diagnosis unit; the microprocessor unit controls connection to the external switch unit.
[0019] The valve positioner of the low-power intelligent fault diagnosis has the following remarkable features compared with the prior art:
[0020] 1. The valve positioner of the low-power intelligent fault diagnosis has a low-power operation mode, which reduces the power consumption of valve position feedback output, pressure / temperature detection and fault diagnosis and the like non-full-range necessary auxiliary functions through partition power supply and time / zone switching work, and realizes low-power operation of the valve positioner.
[0021] 2. The valve positioner of the low-power intelligent fault diagnosis has complete channel diagnosis function, which realizes diagnosis of the main circuit, power supply diagnosis and electrical signal limit value diagnosis by using a specially designed diagnosis analog-to-digital conversion unit.
[0022] 3. The valve positioner of the low-power intelligent fault diagnosis realizes real-time monitoring of the valve and pipeline operation state and realizes full-system and full-time monitoring of valve position control in combination with an auxiliary signal management unit. BRIEF DESCRIPTION OF DRAWINGS
[0023] Figure 1It is a preferable embodiment system structure schematic view of the low-power consumption intelligent fault diagnosis valve positioner.
[0024] Among them, 100 is a main signal management unit, 200 is a fault diagnosis unit, 300 is a microprocessor unit, 400 is an electrical conversion unit, 500 is a display control unit, 600 is an auxiliary signal management unit, 700 is a signal feedback unit, 800 is an isolation communication unit, 900 is an external switch unit, 1000 is a control system, 1100 is a valve, and 1200 is a pneumatic actuator.
[0025] 101 is a control signal conditioning module, 102 is a valve position detection module, and 103 is a main signal analog-to-digital conversion module.
[0026] 201 is a power supply diagnosis module, and 202 is an electrical signal limit value diagnosis module.
[0027] 301 is a storage module, 302 is an execution module, 303 is a built-in analog-to-digital conversion module, and 304 is a built-in switch module.
[0028] 601 is a gas source pressure sensing module, 602 is an output pressure sensing module, 603 is a temperature sensing module, and 604 is an auxiliary signal analog-to-digital conversion module.
[0029] 701 is a digital-to-analog conversion module, and 702 is a feedback signal output module. DETAILED DESCRIPTION
[0030] The specific embodiments of the utility model will be described below with reference to the drawings.
[0031] Embodiment
[0032] Please refer to Figure 1 The utility model discloses a kind of low-power consumption intelligent fault diagnosis valve positioner. As shown in the figure, it is a preferable embodiment, including main signal management unit 100, fault diagnosis unit 200, microprocessor unit 300, electrical conversion unit 400, display control unit 500, auxiliary signal management unit 600, signal feedback unit 700, isolation communication unit 800 and external switch unit 900. In complete system, the role of valve positioner is that real-time position feedback of valve 1100 is positioned to control system 1000, and according to the operation request issued by control system 1000, the opening of valve 1100 is adjusted. Every valve 1100 in system, it needs to be equipped with a valve positioner.
[0033] In each low-power intelligent fault diagnosis valve positioner, the units constituting the valve positioner are divided into two groups and arranged in two independent power supply circuits. Specifically, the main signal management unit 100, the fault diagnosis unit 200, the microprocessor unit 300, the electrical conversion unit 400, the display control unit 500 and the external switch unit 900 are arranged in the main circuit, while the auxiliary signal management unit 600, the signal feedback unit 700 and the isolation communication unit 800 are arranged in the auxiliary circuit. The main circuit takes power from the control signal loop through the main signal management unit 100. The control signal loop belongs to a low-power loop, and its current consumption is low. According to the working state of the control signal loop, the devices in the main circuit will further actively enter a low-power mode, thereby saving energy consumption. The auxiliary circuit takes power from the valve position output loop through the signal feedback unit 700. The devices in the auxiliary circuit and the key information controlled by the valve 1100 are related, and they will not enter a low-power mode in work, thereby ensuring the real-time performance of signal processing. The main circuit and the auxiliary circuit realize information transmission in different power supply domains in an isolated communication manner through the isolation communication unit 800.
[0034] In the whole valve positioner, the microprocessor unit 300 is in the control core position, which contains the storage module 301, the execution module 302, the built-in analog-to-digital conversion module 303 and the built-in switch module 304. The execution module 301 and the built-in analog-to-digital conversion module 303 are connected to the storage module 302. The execution module 301 reads instructions from the storage module 302 for execution, and saves the data required in the execution in the storage module 302. The built-in analog-to-digital conversion module 303 is externally connected to the fault diagnosis unit 200, and after converting the obtained analog signal into a digital signal, it is saved to the storage module 302. The built-in switch module 304 is connected and controlled by the execution module 301, and is connected between the built-in analog-to-digital conversion module 303 and the power supply. The execution module 301 can use the built-in switch module 304 to turn off the power supply of the built-in analog-to-digital conversion module 303, thereby reducing the overall power consumption of the microprocessor unit 300. The microprocessor unit 300 obtains various input information from the main signal management unit 100, the fault diagnosis unit 200, the display control unit 500 and the auxiliary signal management unit 600, processes it and controls the valve 1100 to act through the electrical conversion unit 400, and at the same time uses the signal feedback unit 700 to send the valve position feedback information to the control system 1000, providing data support for the control system 1000 to calculate the subsequent control signal. At the same time, the microprocessor unit 300 is also connected to the external switch unit 900. The external switch unit 900 is arranged between the power supply and the fault diagnosis unit 200. The microprocessor unit 300 can use the external switch unit 900 to turn off the power supply of the fault diagnosis unit 200, thereby reducing the power consumption of the main circuit. In this embodiment, the valve position control signal is an analog signal, whose value changes between 4mA and 20mA: 4mA indicates that the valve 1100 is closed, and 20mA indicates that the valve 1100 is fully open. When the microprocessor unit 300 detects that the valve position control signal is less than 4.15mA (close to closed), at this time the power that the control signal loop can provide is already very small, so the microprocessor unit 300 skips the diagnosis process of the valve positioner in its software flow, at the same time uses the external switch unit 900 to turn off the fault diagnosis unit 200, and uses the built-in switch module 304 to turn off the built-in analog-to-digital conversion module 303, to actively reduce the power consumption. Conversely, when the valve position control signal is greater than 4.15mA, the microprocessor unit 300 turns on the fault diagnosis unit 200, and uses the fault diagnosis unit 200 and the built-in analog-to-digital conversion module 303 to jointly provide data, to execute the diagnosis process of the valve positioner.
[0035] From the perspective of analog signals, the main signal management unit 100 is a one-way receiving information unit, including a control signal conditioning module 101, a valve position detection module 102 and a main signal analog-to-digital conversion module 103. The control signal conditioning module 101 is externally connected to the control system 1000 to receive valve position control signals from the control system 1000. After receiving the valve position control signals, the control signal conditioning module 101 performs signal conditioning in the analog domain to optimize signal quality. At the same time, the control signal conditioning module 101 is also connected to the control signal loop to take power from the control signal loop to provide power for all units on the main loop. The valve position detection module 102 collects the valve position in the valve 1100 through the valve position sensor to generate a valve position state signal. The valve position sensor is located in the valve positioner. Both the valve position control signal and the valve position state signal are analog signals, so they need to be converted into digital signals by the main signal analog-to-digital conversion module 103 before being transmitted to the microprocessor unit 300. Therefore, the control signal conditioning module 101 and the valve position detection module 102 are both internally connected to the input end of the main signal analog-to-digital conversion module 103, and the conditioned valve position control signal and valve position state signal are converted into digital signals by the main signal analog-to-digital conversion module 103. The output of the main signal analog-to-digital conversion module 103 is connected to the microprocessor unit 300 to transmit the converted digital signals to the microprocessor unit 300. From the perspective of digital signals, the main signal management unit 100 also accesses a two-way HART port debugging and diagnostic signal. The debugging and diagnostic signal is modulated on the valve position control signal and is used to bidirectionally transmit debugging and alarm information between the control system 1000 and the microprocessor unit 300.
[0036] The electrical conversion unit 400 is an execution unit, which is electrically connected to the pneumatic actuator externally and to the microprocessor unit 300 internally. The microprocessor unit 300 processes the valve position control signal and generates control instructions to send to the electrical conversion unit 400, which further manipulates the actuator in the external pneumatic actuator to adjust the position of the valve 1100. Similarly, when the microprocessor unit 300 detects an abnormality in the valve positioner, it also manipulates the actuator through the electrical conversion unit 400 to complete the fault handling operation, ensuring the safety of the entire system. On the other hand, in order to deal with the abnormal situation of power failure, gas failure and signal failure of the system, the initial default position of the reversing valve and the actuator in the pneumatic actuator corresponds to the valve hold position or full discharge position. The specific action can be different according to the design requirements of the system. When the system is in the situation of power failure, gas failure and signal failure, the microprocessor unit 300 no longer sends control instructions to the electrical conversion unit 400, and even the electrical conversion unit 400 itself is powered off. At this time, the mechanical structure inside the electrical conversion unit 400 still sends instructions to the reversing valve and the actuator to return to the initial default position, thereby switching the entire system to the fault handling mode defined according to the design requirements of the system, such as valve hold or full discharge, thereby ensuring the safety of the system.
[0037] The display control unit 500 is electrically connected to the microprocessor unit 300 and serves as the user interface of the microprocessor unit 300, which facilitates manual configuration of the working mode and parameters (such as various threshold values) of the valve positioner, and also prompts the user about the running status of the valve positioner, especially when the microprocessor unit 300 diagnoses an abnormality, which alarms the staff.
[0038] The auxiliary signal management unit 600 collects the gas source pressure signal, output pressure signal and cavity temperature signal in analog signal form, and then converts them into digital signals before sending them to the microprocessor unit 300. The auxiliary signal management unit 600 includes a gas source pressure sensing module 601, an output pressure sensing module 602, a temperature sensing module 603 and an auxiliary signal analog-digital conversion module 604.
[0039] The gas source pressure sensing module 601 is connected to the first pressure sensor located at the input end of the valve positioner gas source to collect the gas source pressure signal at the gas source outlet. The output pressure sensing module 602 is connected to the second pressure sensor located at the output end of the valve positioner to collect the output pressure signal of the pneumatic actuator 1200. The temperature sensing module 603 is connected to the temperature sensor inside the valve positioner to collect the cavity temperature signal of the container cavity where the valve positioner is located.
[0040] The gas source pressure signal, the output pressure signal and the chamber temperature signal are analog signals, and therefore need to be converted into digital signals by the auxiliary signal analog-digital conversion module 604 before being transmitted to the microprocessor unit 300 for reception and processing. When these digital signals from the auxiliary circuit are transmitted to the microprocessor unit 300 in the main circuit, the digital isolation communication unit 800 is used for digital isolation communication.
[0041] The signal feedback unit 700 includes a digital-analog conversion module 701 and a feedback signal output module 702, which are electrically connected to the control system 1000 and are responsible for converting the valve position feedback information from the microprocessor unit 300 into analog signals and then sending them to the control system 1000. The feedback signal output module 702 is connected to the control system 1000. The digital-analog conversion module 701 is connected to the microprocessor unit 300 through the isolation communication unit 800, converts the digital signals from the microprocessor unit 300 into analog signals, and then outputs them from the feedback signal output module 702. In this embodiment, the microprocessor unit 300 uses the digital-analog conversion module 701 and the feedback signal output module 702 to send valve position feedback information to the control system 1000, informing the control system 1000 of the real-time position of the valve 1100. At the same time, the feedback signal output module 702 is also connected to the valve position output loop, which provides power for the auxiliary signal management unit 600, the signal feedback unit 700 and the isolation communication unit 800 in the auxiliary circuit.
[0042] The isolation communication unit 800 is used to provide isolated digital communication between the main circuit and the auxiliary circuit, and has a first interface and a second interface.
[0043] The first interface is used to simultaneously connect multiple devices in the auxiliary circuit. In this embodiment, the first interface is connected to the auxiliary signal management unit 600 and the signal feedback unit 700. The second interface is used to connect the microprocessor unit 300 in the main circuit. Inside the isolation communication unit 800, the first interface and the second interface are connected in an electromagnetic isolation or optoelectronic isolation manner to bidirectionally transmit digital signals.
[0044] The fault diagnosis unit 200 adds additional enhanced reliability to the system. On the one hand, it collects various analog signals from the main signal management unit 100 to form the first type of fault diagnosis information. On the other hand, it also collects analog signals related to its own working state from the main signal management unit 100 and the electrical conversion unit 400 to form the second type of fault diagnosis information. Finally, the fault diagnosis unit 200 sends both types of fault diagnosis information to the microprocessor unit 300, which converts them into digital signals by the built-in analog-digital conversion module 303, and then evaluates the working state of the valve positioner by the diagnosis logic.
[0045] The fault diagnosis unit 200 comprises a power supply diagnosis module 201 and an electrical signal limit value diagnosis module 202. The power supply diagnosis module 201 collects working voltage signals, reference voltage signals and excitation voltage signals of the main signal management unit 100, the electrical conversion unit 400 and the microprocessor unit 300, for generating the second type of fault diagnosis information. The electrical signal limit value diagnosis module 202 generates the first type of fault diagnosis information in combination with the main signal management unit 100. Specifically, the electrical signal limit value diagnosis module 202 is connected to the main signal management unit 100 and reads the valve position control signal and the valve position state signal. Under the scheduling of the diagnosis logic of the microprocessor unit 300, the built-in analog-to-digital conversion module 303 is connected to the power supply diagnosis module 201 and the electrical signal limit value diagnosis module 202 in sequence, converts the working voltage signals, the reference voltage signals, the excitation voltage signals, the valve position control signal and the valve position state signal into digital signals one by one, and then sends them to the microprocessor unit 300 for further processing by using the diagnosis flow.
[0046] The above merely describes preferred embodiments of the present application, but is not intended to limit the scope of the present application. Any equivalent changes and modifications made within the scope of the present application should be within the technical scope of the present application.
Claims
1. A low power consumption intelligent fault diagnostic valve positioner, characterized by, The device comprises a main signal management unit, an auxiliary signal management unit, a microprocessor unit, a signal feedback unit, an isolated communication unit, an electrical conversion unit and a display control unit. The main signal management unit, the microprocessor unit, the electrical conversion unit and the display control unit are arranged in a main circuit; the auxiliary signal management unit, the signal feedback unit and the isolated communication unit are arranged in an auxiliary circuit; the main circuit and the auxiliary circuit are powered by independent power sources; The main signal management unit, the electrical conversion unit and the display control unit are directly electrically connected to the microprocessor unit; the main signal management unit is externally connected to a control system and a valve; the electrical conversion unit is externally connected to a pneumatic actuator; the auxiliary signal management unit and the signal feedback unit are connected to the microprocessor unit through the isolated communication unit; the auxiliary signal management unit is connected to a sensor; the signal feedback unit is externally connected to the control system.
2. The low power consumption smart fault diagnostic valve positioner of claim 1, wherein, The main signal management unit comprises a control signal conditioning module, a valve position detection module and a main signal analog-to-digital conversion module; The control signal conditioning module is externally connected to the control system through a control signal loop, and at the same time, a power source is connected from the control signal loop to the main circuit; the valve position detection module is electrically connected to a valve position sensor located on a valve positioner; the control signal conditioning module and the valve position detection module are both internally electrically connected to the main signal analog-to-digital conversion module; the main signal analog-to-digital conversion module is electrically connected to the microprocessor unit.
3. The low power consumption smart fault diagnostic valve positioner of claim 1, wherein, The auxiliary signal management unit comprises a gas source pressure sensing module, an output pressure sensing module, a temperature sensing module and an auxiliary signal analog-to-digital conversion module; The gas source pressure sensing module is connected to a first pressure sensor located at a gas source input end of a valve positioner; the output pressure sensing module is connected to a second pressure sensor located at an output end of the valve positioner; the temperature sensing module is connected to a temperature sensor located in the valve positioner; the gas source pressure sensing module, the output pressure sensing module and the temperature sensing module are electrically connected to the auxiliary signal analog-to-digital conversion module; the auxiliary signal analog-to-digital conversion module is connected to the microprocessor unit through the isolated communication unit.
4. The low power consumption smart fault diagnostic valve positioner of claim 1, wherein, The signal feedback unit comprises a digital-to-analog conversion module and a feedback signal output module; the feedback signal output module is externally connected to the control system through a valve position output loop, and at the same time, a power source is connected from the valve position output loop to the auxiliary circuit; the digital-to-analog conversion module is externally connected to the microprocessor unit through the isolated communication unit, and is internally electrically connected to the feedback signal output module.
5. The low power consumption smart fault diagnostic valve positioner of claim 1, wherein, The isolated communication unit comprises a first interface and a second interface; the first interface and the second interface are connected in an electromagnetic isolation or optoelectronic isolation manner; the first interface is connected to the auxiliary signal management unit and the signal feedback unit at the same time; The second interface is connected to the microprocessor unit.
6. The low power consumption smart fault diagnostic valve positioner of claim 1, wherein, The fault diagnosis unit is arranged in the main circuit and connected to the microprocessor unit, the main signal management unit and the electrical conversion unit.
7. The low power consumption smart fault diagnostic valve positioner of claim 6, wherein, The fault diagnosis unit comprises a power supply diagnosis module and an electrical signal limit value diagnosis module, both of which are electrically connected to the microprocessor unit; the power supply diagnosis module is further electrically connected to the main signal management unit and the electrical conversion unit; the electrical signal limit value diagnosis module is further electrically connected to the main signal management unit.
8. The low power consumption smart fault diagnostic valve positioner of claim 6, wherein, The microprocessor unit comprises a storage module, an execution module and a built-in analog-to-digital conversion module; the execution module and the built-in analog-to-digital conversion module are connected to the storage module; the built-in analog-to-digital conversion module is externally connected to the fault diagnosis unit.
9. The low power consumption smart fault diagnostic valve positioner of claim 8, wherein, The microprocessor unit further comprises a built-in switch module; the built-in switch module is arranged between a power supply and the built-in analog-to-digital conversion module; the execution module controls connection to the built-in switch module.
10. The low power consumption smart fault diagnostic valve positioner of claim 6, wherein, The microprocessor unit further comprises an external switch unit; the external switch unit is arranged between a power supply and the fault diagnosis unit; the microprocessor unit controls connection to the external switch unit.