Valve limit switch device and control method thereof

Abstract

The invention provides a valve limit switch device and a control method thereof, the valve limit switch device comprises a signal access circuit, a processor, an APL codec and an interface circuit, an APL is an advanced physical layer, and the signal access circuit is used for receiving an input valve limit switching value signal; the processor is used for converting the valve limit switching value signal into a corresponding digital signal; the APL coder-decoder is used for coding the digital signal to obtain an APL signal containing valve limit switching value information; and the interface circuit is used for transmitting an APL signal containing valve limit switching value information to the central system through the APL field switch. Therefore, digital transmission of valve stroke position mechanical limiting can be achieved, the number of devices from an APL device machine room to a site is reduced, only one twisted pair, one APL power switch and one APL site switch are needed to replace detection signal conversion devices corresponding to the multi-way valve limiting switch, and the device and wiring cost is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of valve control, and in particular to a valve limit switch device and a control method thereof. Background Art

[0002] The control valve is the execution layer of the control loop, so in the process industry, it is necessary to control multiple control valves deployed on site.

[0003] At present, most control valves use valve position limit switches when assembling their valve positioner. When using limit signals for detection and control, the wiring of the overall architecture is very complicated due to the excessive number of detection signal conversion devices in the system. Figure 1 From the transmission process of the limit switch signal shown, it can be seen that at least three cables are required from the machine room to each device on site, and the wiring cost is very high. Summary of the invention

[0004] In view of the defects in the prior art, an object of the present invention is to provide a valve limit switch device and a control method thereof.

[0005] In a first aspect, the present application provides a valve limit switch device, including: a signal access circuit, a processor, an APL codec, and an interface circuit, wherein the APL is an advanced physical layer, wherein:

[0006] The signal access circuit is used to receive the valve limit switch value signal input from the outside and transmit the valve limit switch value signal to the processor;

[0007] The processor is used to convert the valve limit switch signal into a corresponding digital signal and transmit it to the APL codec;

[0008] The APL encoder / decoder is used to encode the digital signal to obtain an APL signal containing valve limit switch quantity information;

[0009] The interface circuit is used to transmit the APL signal containing the valve limit switch quantity information to the APL field switch, so that the APL field switch transmits the APL signal containing the valve limit switch quantity information to the central system.

[0010] Optionally, the above device further comprises: a voltage conversion circuit, the voltage conversion circuit being electrically connected to the processor and the interface circuit respectively, and being used to convert a distribution voltage in an APL control signal from an APL field switch introduced by the interface circuit into an operating voltage of the processor;

[0011] The distribution voltage in the APL control signal is provided by an APL power switch, and the APL power switch superimposes the distribution voltage on the APL control signal sent by the central system.

[0012] Optionally, the input of the valve limit switch signal includes: a single channel, or two channels or more;

[0013] Among them, the valve limit switch signal of each input includes: the switch signal of the valve opening upper limit switch and the switch signal of the valve closing lower limit switch.

[0014] Optionally, the signal access circuit is further provided with an interface protection circuit.

[0015] The interface protection circuit is used to perform overvoltage protection on the signal access circuit.

[0016] Optionally, the interface circuit is communicatively connected to the APL field switch to receive Ethernet messages sent by the central system;

[0017] The APL codec is further used to decode the Ethernet message transmitted by the interface circuit to obtain a corresponding APL control signal, and transmit the decoded APL control signal to the processor;

[0018] The processor is also used to send the decoded APL control signal to the limit switch corresponding to the target valve through the signal access circuit according to the target address indicated by the Ethernet message, so that the limit switch feeds back the valve limit switch quantity signal to the signal access circuit after executing the switching action.

[0019] Optionally, the signal access circuit is further provided with an interface protection circuit, and the interface protection circuit is used to perform overvoltage protection on the signal access circuit;

[0020] The interface circuit includes: a protection circuit, an anti-reverse connection circuit, and a signal / power isolation circuit.

[0021] The protection circuit is used to control the input voltage to be below a preset threshold;

[0022] The anti-reverse connection circuit is used for reverse connection protection;

[0023] The signal / power isolation circuit is used to isolate different signals and to isolate power supplies of different voltages.

[0024] Optionally, the processor is a CPU, and the CPU is a central processing unit;

[0025] The CPU communicates with the APL codec via a serial port.

[0026] Optionally, it also includes: a signal matching circuit, a filtering circuit,

[0027] The signal matching circuit is used to perform matching processing on the Ethernet message transmitted by the interface circuit;

[0028] The filtering circuit is used to filter the Ethernet messages transmitted by the interface circuit.

[0029] In a second aspect, an embodiment of the present application provides a control method for a valve limit switch device, wherein the valve limit switch device described in any one of the first aspects is used to control the valve, and the method includes:

[0030] The Ethernet message sent by the central system is transmitted to the interface circuit through the APL field switch, and the APL is an advanced physical layer;

[0031] Transmit Ethernet messages to the APL codec through the interface circuit;

[0032] The APL codec decodes the Ethernet message to obtain an APL control signal, and transmits the APL control signal to the processor;

[0033] The processor sends the APL control signal to the limit switch corresponding to the target valve according to the target address indicated by the Ethernet message, so that the limit switch performs a switching action.

[0034] Optionally, before transmitting the Ethernet message sent by the central system to the interface circuit through the APL field switch, the method further includes:

[0035] Encapsulate the APL control signal output by the central system into Ethernet messages and transmit them to the APL power switch via a single twisted pair Ethernet cable;

[0036] The APL power switch superimposes the working power distribution on the Ethernet message and transmits it to the APL field switch.

[0037] Optionally, the method further comprises:

[0038] Receiving an externally input valve limit switch quantity signal through a signal access circuit, and transmitting the valve limit switch quantity signal to a processor;

[0039] The valve limit switch signal is converted into a corresponding digital signal by a processor and then transmitted to an APL encoder / decoder;

[0040] The digital signal is encoded and processed by the APL encoder and decoder to obtain an APL signal containing valve limit switch quantity information;

[0041] The APL signal containing the valve limit switch quantity information is transmitted to the APL field switch through the interface circuit, so that the APL field switch transmits the APL signal containing the valve limit switch quantity information to the central system.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention is provided with a valve limit switch device including: a signal access circuit, a processor, an APL encoder / decoder, and an interface circuit, wherein: the signal access circuit is used to receive an externally input valve limit switch quantity signal and transmit the valve limit switch quantity signal to the processor; the processor is used to convert the valve limit switch quantity signal into a corresponding digital signal and transmit it to the APL encoder / decoder; the APL encoder / decoder is used to encode the digital signal to obtain an APL signal containing valve limit switch quantity information; the interface circuit is used to transmit the APL signal containing valve limit switch quantity information to the APL field switch, so that the APL field switch transmits the APL signal containing valve limit switch quantity information to the central system. Thus, the digital transmission of the mechanical limit of the valve stroke position can be realized, and the number of devices from the APL equipment room to the site can be effectively reduced. Only one twisted pair, one APL power switch and an APL field switch are needed to replace the detection signal conversion device corresponding to the multi-way valve limit switch, which greatly reduces the equipment and wiring costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings in the following descriptions are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without creative work. By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more obvious:

[0045] Figure 1 A schematic diagram of the wiring topology for transmitting signals to the existing limit switches;

[0046] Figure 2 A schematic diagram of a wiring topology structure of a valve limit switch device provided in an embodiment of the present application;

[0047] Figure 3 A schematic structural diagram of a valve limit switch device provided in an embodiment of the present application;

[0048] Figure 4A flow chart of a control method of a valve limit switch device provided in an embodiment of the present application;

[0049] In the figure:

[0050] 1-Signal access circuit, 2-CPU, 3-voltage conversion circuit, 4-APL encoder and decoder, 5-interface circuit. DETAILED DESCRIPTION

[0051] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0052] It should be noted that when a component is referred to as being "fixed to" or "disposed on" another component, it can be directly on the other component or indirectly on the other component. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for fixing or for circuit connection.

[0053] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0054] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0055] Figure 1 A schematic diagram of the wiring topology for transmitting signals to existing limit switches, such as Figure 1 As shown in the figure, after the traditional valve limit switch signal arrives at the machine room, it needs to be converted into a digital signal through each AI module + A / D module and then transmitted to the central system. Each valve limit switch requires one detection signal conversion device (AI module + A / D module), and the equipment and wiring costs are very high.

[0056] Figure 2 A schematic diagram of the wiring topology structure of a valve limit switch device provided in an embodiment of the present application is shown in FIG. Figure 2 As shown in the figure, the central system can be connected to the APL (Advanced Physical Layer) field switch through a single-pair Ethernet twisted pair cable. The APL field switch connects various APL valve limit switches, and the APL field switch transmits the Ethernet message of the central system to the limit switch corresponding to the target valve. Only one twisted pair is needed from the APL equipment room to the site. One APL power switch and APL field switch can replace the detection signal conversion equipment (AI module + A / D module) corresponding to the multi-way valve limit switch, greatly reducing the construction cost.

[0057] Exemplarily, the APL control signal of the central system is obtained, and the APL control signal is encapsulated into an Ethernet message and transmitted to the APL power switch through a single twisted pair Ethernet. The APL power switch is connected to the APL field switch after superimposing the working power distribution. The APL field switch controls each APL valve limit switch through a single twisted pair, and provides the working power distribution to each APL valve limit switch. Among them, the Ethernet message is distributed to the limit switch corresponding to the target valve according to the target address indicated by it, so that the limit switch performs the switching action.

[0058] For example, after the limit switch performs the switching action, the valve limit switch quantity signal can also be fed back to the central system along the original path.

[0059] Exemplarily, an embodiment of the present application provides a valve limit switch device, which may include: a signal access circuit, a processor, an APL encoder / decoder, and an interface circuit, wherein the APL is an advanced physical layer, wherein: the signal access circuit is used to receive an externally input valve limit switch quantity signal and transmit the valve limit switch quantity signal to the processor; the processor is used to convert the valve limit switch quantity signal into a corresponding digital signal and transmit it to the APL encoder / decoder; the APL encoder / decoder is used to encode the digital signal to obtain an APL signal containing valve limit switch quantity information; the interface circuit is used to transmit the APL signal containing valve limit switch quantity information to the APL field switch, so that the APL field switch transmits the APL signal containing valve limit switch quantity information to the central system.

[0060] In this embodiment, the central system can be connected to the APL field switch via a single-pair Ethernet twisted pair cable, and the APL field switch is used to connect each valve limit switch device, thereby greatly reducing the wiring cost of the valve limit switch device and simplifying the system architecture of the valve limit switch device.

[0061] For example, it can be combined with Figure 2 As shown, a two-wire APL bus is used for communication between the machine room and the site (only one twisted pair is required). After arriving at the site, the APL field switch is used to communicate with each APL valve limit switch.

[0062] Exemplarily, the above-mentioned valve limit switch device may also include: a voltage conversion circuit, which is electrically connected to the processor and the interface circuit respectively, and is used to convert the distribution voltage in the APL control signal from the APL field switch introduced by the interface circuit into the working voltage of the processor; wherein the distribution voltage in the APL control signal is provided by the APL power switch, and the APL power switch superimposes the distribution voltage on the APL control signal sent by the central system.

[0063] In this embodiment, when the power distribution voltage (9 to 32V) in the APL signal is converted to 3.3V, it can provide working power for the processor.

[0064] Exemplarily, the input of the valve limit switch signal includes: a single channel, or two channels or more; wherein, the valve limit switch signal of each input channel includes: a switch signal of the valve opening upper limit switch, and a switch signal of the valve closing lower limit switch.

[0065] In this embodiment, the external valve limit switch quantity can be input in a single channel or in multiple channels, and each channel has two sets of valve limit switches (valve opening upper limit switch and valve closing lower limit switch). For example, if the valve is opened to the set limit position, the upper limit switch is closed and the lower limit switch is disconnected; if the valve is closed to the set limit position, the lower limit switch is closed and the upper limit switch is disconnected.

[0066] Exemplarily, the interface circuit is communicatively connected to the APL field switch for receiving Ethernet messages sent by the central system; the APL encoder and decoder is further used to decode the Ethernet messages transmitted by the interface circuit to obtain corresponding APL control signals, and transmit the decoded APL control signals to the processor; the processor is further used to send the decoded APL control signal to the limit switch corresponding to the target valve through the signal access circuit according to the target address indicated by the Ethernet message, so that the limit switch feeds back the valve limit switch quantity signal to the signal access circuit after executing the switching action.

[0067] In this embodiment, multiple limit switches on site can be remotely controlled through Ethernet messages sent by the central system, and after the limit switches execute the switching action, the valve limit switch quantity signal is fed back to the central system in real time.

[0068] Exemplarily, the signal access circuit is further provided with an interface protection circuit, and the interface protection circuit is used to perform overvoltage protection on the signal access circuit.

[0069] Exemplarily, the interface circuit includes: a protection circuit, an anti-reverse connection circuit, and a signal / power isolation circuit. The protection circuit is used to control the input voltage below a preset threshold; the anti-reverse connection circuit is used to perform reverse protection; the signal / power isolation circuit is used to isolate different signals and isolate power supplies of different voltages.

[0070] In this embodiment, a signal matching circuit, a filtering circuit, a protection circuit, etc. may also be provided on the periphery of the APL codec, so as to ensure the reliability and integrity of the signal.

[0071] In this embodiment, by setting a protection circuit, an anti-reverse connection circuit, and a signal / power isolation circuit in the signal access circuit, overvoltage and reverse protection can be achieved, meeting EMC-related standards and 1000V withstand voltage requirements.

[0072] Exemplarily, the processor is a central processing unit (CPU); the CPU is communicatively connected to the APL codec via a serial port.

[0073] In this embodiment, in addition to the CPU, other low-power processors can also be used to implement the following functions: parsing the Ethernet message transmitted from the APL encoder / decoder, and converting the valve limit switch signal into a corresponding digital signal.

[0074] Exemplarily, the valve controller may further include: a signal matching circuit and a filtering circuit, wherein the signal matching circuit is used to perform matching processing on the Ethernet message transmitted by the signal access circuit; and the filtering circuit is used to perform filtering processing on the Ethernet message transmitted by the signal access circuit.

[0075] Figure 3 A schematic diagram of the structure of a valve limit switch device provided in an embodiment of the present application is shown in FIG. Figure 3 As shown, it may include: signal access circuit 1, CPU2, APL encoder / decoder 3, voltage conversion circuit 4, interface circuit 5. Exemplarily, the external valve limit switch inputs the switch quantity signal, which is transmitted to CPU2 through the signal access circuit 1, and CPU2 outputs the corresponding digital signal, and communicates with APL encoder / decoder 3 through the serial port, which is encoded by APL encoder / decoder 3 and transmitted to APL field switch and APL power switch through interface circuit 5, and finally delivered to the central system.

[0076] In this embodiment, the external valve limit switch quantity can be input in a single channel or multiple channels, and each channel has two sets of valve limit switches, including: valve open upper limit switch and valve close lower limit switch. Figure 3 As shown in the figure, when the valve is opened to the set limit position, the upper limit switch is closed and the lower limit switch is opened. When the valve is closed to the set limit position, the lower limit switch is closed and the upper limit switch is opened.

[0077] In this embodiment, APL technology (Advanced Physical Layer Ethernet, whose greatest features are long cable distance, intrinsic safety and application-level protocol support to achieve maximum productivity and output) is used to realize the switch control of the on-site valves by the system center, which effectively solves the problem of the large number of system detection signal conversion devices and high wiring costs when the control valves and valve positioners are currently assembled and use valve limit switches and use limit signals for detection and control.

[0078] For example, Figure 4 As shown, the embodiment of the present application also provides a control method of a valve limit switch device, which can be used to control the valve using the above-mentioned valve limit switch device, and the method includes the following steps:

[0079] Step S401: The Ethernet message sent by the central system is transmitted to the interface circuit through the APL field switch.

[0080] Exemplarily, the APL control signal output by the central system can be encapsulated into an Ethernet message and transmitted to the APL power switch via a single twisted pair Ethernet cable. The APL power switch then superimposes the working power distribution on the Ethernet message and transmits it to the APL field switch.

[0081] Step S402: Transmit the Ethernet message to the APL codec through the interface circuit.

[0082] In this embodiment, the APL codec decodes the Ethernet message transmitted by the interface circuit to obtain an APL control signal that can be recognized by the processor.

[0083] Step S403: The Ethernet message is decoded by the APL codec to obtain an APL control signal, and the APL control signal is transmitted to the processor.

[0084] In this embodiment, the processor parses the decoded APL control signal to obtain a control instruction that can be recognized by the limit switch, wherein the control instruction is used to control the switch opening of the limit switch.

[0085] In step S404, the processor sends the APL control signal to the limit switch corresponding to the target valve according to the target address indicated by the Ethernet message, so that the limit switch performs a switching action.

[0086] In this embodiment, the target address sent by the Ethernet message corresponds to the target limit switch, and the processor transmits the control instruction for the target limit switch to the corresponding target limit switch through the signal access circuit to control the limit switch to perform the switching action.

[0087] Exemplarily, the above method may further include the following steps:

[0088] An external valve limit switch quantity signal is received through a signal access circuit, and the valve limit switch quantity signal is transmitted to a processor; the valve limit switch quantity signal is converted into a corresponding digital signal by the processor, and then transmitted to an APL encoder / decoder; the digital signal is encoded and processed by the APL encoder / decoder to obtain an APL signal containing valve limit switch quantity information; the APL signal containing valve limit switch quantity information is transmitted to an APL field switch through an interface circuit, so that the APL field switch transmits the APL signal containing valve limit switch quantity information to a central system.

[0089] The steps in this embodiment provide a process for the valve limit switch to feed back the limit switch value signal to the central system. After the central system sends the APL control signal for each limit switch on site through an Ethernet message, the valve limit switch value of each limit switch on site can also be obtained in real time through the original route, so that the central system can obtain the control result of the valve in real time.

[0090] In this embodiment, the APL technology is used to realize the control of the limit switch of the on-site valve by the system center. It can be connected to the APL on-site switch through a single-pair Ethernet twisted-pair cable, and the APL on-site switch is used to connect each valve limit switch. Among them, only one twisted pair is needed from the machine room to the site. After arriving at the site, it is connected to each APL valve position mechanical limit switch through the APL on-site switch to realize the digital transmission of the valve stroke position mechanical limit. In addition, by adopting a two-wire APL bus, only an APL power switch and an APL on-site switch are needed to directly transmit the limit switch signal to the central system. This greatly reduces the wiring cost of the valve limit switch, and well solves the problem of the large number of system detection signal conversion devices and high wiring costs when the control valve and valve positioner are assembled and use the valve position mechanical limit switch to detect and control with the limit signal.

[0091] The above is the core idea of ​​the present invention. In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the drawings in 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0092] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other. The above description of the disclosed embodiments enables professionals and technicians in this field to implement or use the present invention. Various modifications to these embodiments will be obvious to professionals and technicians in this field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown in this article, but will comply with the widest range consistent with the principles and novel features disclosed herein.

[0093] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A valve limit switch device, characterized in that: include: Signal access circuit, processor, APL codec, interface circuit, the APL is an advanced physical layer, wherein: The signal access circuit is used to receive the valve limit switch value signal input from the outside and transmit the valve limit switch value signal to the processor; The processor is used to convert the valve limit switch signal into a corresponding digital signal and transmit it to the APL codec; The APL encoder / decoder is used to encode the digital signal to obtain an APL signal containing valve limit switch quantity information; The interface circuit is used to transmit the APL signal containing the valve limit switch quantity information to the APL field switch, so that the APL field switch transmits the APL signal containing the valve limit switch quantity information to the central system.

2. The valve limit switch device according to claim 1, characterized in that: Also includes: Voltage conversion circuit, The voltage conversion circuit is electrically connected to the processor and the interface circuit respectively, and is used to convert the distribution voltage in the APL control signal from the APL field switch introduced by the interface circuit into the working voltage of the processor; The distribution voltage in the APL control signal is provided by an APL power switch, and the APL power switch superimposes the distribution voltage on the APL control signal sent by the central system.

3. The valve limit switch device according to claim 1, characterized in that: The input of the valve limit switch signal includes: single channel, or two channels or more; Among them, the valve limit switch signal of each input includes: the switch signal of the valve opening upper limit switch and the switch signal of the valve closing lower limit switch.

4. The valve limit switch device according to any one of claims 1 to 3, characterized in that: The interface circuit is connected to the APL field switch for receiving Ethernet messages sent by the central system; The APL codec is further used to decode the Ethernet message transmitted by the interface circuit to obtain a corresponding APL control signal, and transmit the decoded APL control signal to the processor; The processor is also used to send the decoded APL control signal to the limit switch corresponding to the target valve through the signal access circuit according to the target address indicated by the Ethernet message, so that the limit switch feeds back the valve limit switch quantity signal to the signal access circuit after executing the switching action.

5. The valve limit switch device according to any one of claims 1 to 3, characterized in that: The signal access circuit is also provided with an interface protection circuit, and the interface protection circuit is used to perform overvoltage protection on the signal access circuit; The interface circuit includes: a protection circuit, an anti-reverse connection circuit, and a signal / power isolation circuit. The protection circuit is used to control the input voltage to be below a preset threshold; The anti-reverse connection circuit is used for reverse connection protection; The signal / power isolation circuit is used to isolate different signals and to isolate power supplies of different voltages.

6. The valve limit switch device according to any one of claims 1 to 3, characterized in that: The processor is a CPU, which is a central processing unit; The CPU communicates with the APL codec via a serial port.

7. The valve limit switch device according to any one of claims 1 to 3, characterized in that: Also includes: Signal matching circuit, filtering circuit, The signal matching circuit is used to perform matching processing on the Ethernet message transmitted by the interface circuit; The filtering circuit is used to filter the Ethernet messages transmitted by the interface circuit.

8. A control method for a valve limit switch device, characterized in that: The valve limit switch device according to any one of claims 1 to 7 is used to control the valve, and the method comprises: The Ethernet message sent by the central system is transmitted to the interface circuit through the APL field switch, and the APL is an advanced physical layer; Transmit Ethernet messages to the APL codec through the interface circuit; The APL codec decodes the Ethernet message to obtain an APL control signal, and transmits the APL control signal to the processor; The processor sends the APL control signal to the limit switch corresponding to the target valve according to the target address indicated by the Ethernet message, so that the limit switch performs a switching action.

9. The method according to claim 8, characterized in that Before transmitting the Ethernet message sent by the central system to the interface circuit through the APL field switch, the method further includes: Encapsulate the APL control signal output by the central system into Ethernet messages and transmit them to the APL power switch via a single twisted pair Ethernet cable; The APL power switch superimposes the working power distribution on the Ethernet message and transmits it to the APL field switch.

10. The method according to claim 8 or 9, characterized in that: The method further comprises: Receiving an externally input valve limit switch quantity signal through a signal access circuit, and transmitting the valve limit switch quantity signal to a processor; The valve limit switch signal is converted into a corresponding digital signal by a processor and then transmitted to an APL encoder / decoder; The digital signal is encoded and processed by the APL encoder and decoder to obtain an APL signal containing valve limit switch quantity information; The APL signal containing the valve limit switch quantity information is transmitted to the APL field switch through the interface circuit, so that the APL field switch transmits the APL signal containing the valve limit switch quantity information to the central system.

Images