Network device and communication method

Abstract

The present application discloses network device and a communication method. The network device comprises: an advanced physical layer (APL) port physical layer (PHY) and a hybrid interface circuit; an APL PHY connection hybrid interface, the hybrid interface being connected to an instrument device, the hybrid interface circuit being connected to the hybrid interface. The hybrid interface circuit is compatible with a power over data line (PoDL) mode, an analog input (AI) mode and an analog output (AO) mode; in the PoDL mode, a power supply supplies power to the instrument equipment; in the AI mode, the power supply supplies power to the hybrid interface; and in the AO mode, voltage is converted into a current corresponding to a control signal of the instrument equipment. The technical solution, based on APL communication, can be compatible with an interface of a conventional instrument equipment.

Description

Network device and communication method

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on September 28, 2023, with application number 202311292731.3 and invention name “A Network Device and Communication Method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of industrial communication technology, and in particular to a network device and a communication method. Background Art

[0003] Currently, most industrial communications rely on low-speed protocols such as analog 4mA-20mA signals and digital signals such as Highway Addressable Remote Transducer (HART), Profibus PA, and Fieldbus Foundation (FF), typically operating at speeds of tens of kilobits per second. The IEEE 802.3cg standard specifies Single Pair Ethernet (SPE), which can provide 10Mbps communication speeds over a single twisted-pair cable and utilizes Power over Data Line (PoDL) to simultaneously power industrial field equipment. Following the approval of the IEEE 802.3cg standard, the Advanced Physical Layer (APL) embedded the standardized solutions of the IEEE 802.3cg series into Ethernet-APL technology, extending the Ethernet physical layer standard and establishing design specifications that meet the field communication requirements of process industries.

[0004] However, the current mainstream instrument equipment in the industry mainly uses 4mA~20mA, and the PoDL pins of the APL switch are incompatible with the interfaces of mainstream instruments, resulting in the inability to directly plug the interfaces of the APL switch and traditional instrument equipment.

[0005] Summary of the Invention

[0006] In order to solve the above technical problems, the present application provides a network device and a communication method, which can be compatible with the interface of traditional instrument equipment based on APL communication.

[0007] In a first aspect, an embodiment of the present application provides a network device, including: an advanced physical layer (APL) port physical layer (PHY) and a hybrid interface circuit; the APL PHY is connected to the hybrid interface; the hybrid interface is used to connect to an instrument device; the hybrid interface circuit is connected to the hybrid interface; the hybrid interface circuit is compatible with single-pair Ethernet power supply (PoDL) mode, analog input (AI) mode, and analog output (AO) mode; in PoDL mode, the power supply supplies power to the instrument device; in AI mode, the power supply supplies power to the hybrid interface; in AO mode, the voltage is converted into a current corresponding to the control signal of the instrument device.

[0008] The hybrid interface circuit in the network device provided in the embodiment of the present application is compatible with the single-pair Ethernet power supply PoDL mode, analog input AI mode and analog output AO mode. In AI mode, the power supply supplies power to the hybrid interface; in AO mode, the output current can be controlled, so that the current conversion circuit can output a current in the range of 4mA to 20mA in AO mode. In PoDL power supply mode, power can be supplied to the instrument equipment. Therefore, the switch integrates the communication and PoDL power supply functions of APL, as well as the 4mA to 20mA AI and AO functions of the instrument equipment, to achieve compatibility between the APL interface and the interface of mainstream instrument equipment.

[0009] In one possible implementation, the instrument device's interface operates in AI mode, while the network device controls the hybrid interface circuit to operate in AO mode. This allows the network device to control the instrument device. For example, the instrument device, such as a switch or valve, can execute commands sent by the network device.

[0010] One possible implementation also includes: a controller, a current conversion circuit, and a detection circuit, both connected to the controller. In PoDL mode, the controller controls the current conversion circuit to shut down, allowing the power supply to directly power the device. In AI mode, the controller controls the current conversion circuit to shut down, providing DC voltage directly to the hybrid interface. The detection circuit detects the current of the hybrid interface and provides it to the controller. In AO mode, the controller controls the current conversion circuit to convert the DC voltage into a current corresponding to the control signal on the device.

[0011] In one possible implementation, the controller is used to control the current conversion circuit to output a DC current, where the DC current is less than a minimum value of a current range in the AI ​​mode.

[0012] Because the effective current range of the AI's 4mA-20mA meter interface is 4mA-20mA, the current value of the detection signal can be set to detect DC currents less than 4mA. This current value will be ignored by the AI's 4mA-20mA meter and will not cause the actuator on the device to erroneously execute an action.

[0013] In one possible implementation, the controller is further configured to control the current conversion circuit to output a current that varies within the PoDL mode range, and to use the voltage range detected by the detection circuit to determine whether the interface of the instrument device is in PoDL mode. If the interface of the instrument device is in PoDL mode, the hybrid interface circuit is controlled to operate in PoDL mode.

[0014] The hybrid interface circuit provided in the embodiment of the present application can automatically identify whether the interface of the instrument device is in PoDL mode, thereby automatically controlling the hybrid interface circuit to operate in PoDL mode to power the instrument device.

[0015] In one possible implementation, the controller is also used to control the current conversion circuit to output a current that changes within the AO mode range, and use the changing voltage detected by the detection circuit to determine whether the interface of the instrument equipment is in AO mode. If the interface of the instrument equipment is in AO mode, the hybrid interface circuit is controlled to operate in AI mode.

[0016] The hybrid interface circuit provided in the embodiment of the present application can automatically identify whether the interface of the instrument equipment is in AO mode. When the interface of the instrument equipment is in AO mode, the hybrid interface circuit is automatically controlled to operate in AI mode to receive signals sent by the instrument equipment.

[0017] In one possible implementation, the current conversion circuit includes: a digital-to-analog converter and a voltage-to-current converter; the input and output ends of the digital-to-analog converter are respectively connected to a controller and a voltage-to-current converter; the voltage-to-current converter is also used to connect to a DC / DC circuit; the controller is used to send a voltage-controlled digital signal to the digital-to-analog converter; the analog-to-digital converter is used to convert the voltage-controlled digital signal into a voltage-controlled analog signal; and the voltage-to-current converter is used to convert the voltage output by the DC / DC circuit into a current according to the voltage-controlled analog signal.

[0018] The current conversion circuit provided in the embodiment of the present application can use a digital-to-analog converter to convert a digital signal into an analog signal, and the voltage-to-current converter can convert a voltage signal into a current signal.

[0019] In one possible implementation, the detection circuit includes: a detection resistor, a current-to-voltage circuit, and an analog-to-digital converter; the first and second ends of the detection resistor are respectively connected to the output end of the current conversion circuit and the hybrid interface; the current-to-voltage circuit is used to connect the two ends of the detection resistor and send the voltage across the two ends of the detection resistor to the analog-to-digital converter; the analog-to-digital converter is used to convert the voltage sent by the current-to-voltage circuit into a digital voltage and send it to the controller.

[0020] The detection circuit provided in the embodiments of the present application can detect current using a relatively small resistance detection resistor, but due to the small resistance, the power consumption is negligible. The current-to-voltage circuit can convert current into voltage, and the analog-to-digital converter can convert analog signals into digital signals, which can be directly processed by the controller.

[0021] In one possible implementation, the detection circuit further includes: a voltage divider circuit and a selection switch; the first and second ends of the voltage divider circuit are respectively connected to the first end of the detection resistor and the ground; the first and second input ends of the selection switch are respectively connected to the output end of the current-to-voltage circuit and the output end of the voltage divider circuit, and the output end of the selection switch is connected to the input end of the analog-to-digital converter; a controller is used to control the output end of the selection switch to be connected to the first input end in PoDL mode and AI mode; in AO mode, it is used to control the output end of the selection switch to be connected to the second input end; the analog-to-digital converter is used to connect the output end of the selection switch to the first input end, collect the current of the detection resistor and send it to the controller; when collecting, the output end of the selection switch is connected to the second input end, detect the voltage of the voltage divider circuit and send it to the controller, and the controller controls the current output of the current conversion circuit according to the voltage detected by the analog-to-digital converter.

[0022] The detection circuit in the hybrid interface circuit provided in the embodiment of the present application can not only detect current, but also detect voltage, and the current detection and voltage detection can be switched by selecting a switch.

[0023] A possible implementation method also includes: an automatic range switching circuit; the input and output ends of the automatic range switching circuit are respectively connected to the output end of the selection switch and the input end of the analog-to-digital converter; the automatic range switching circuit includes at least an amplifier, which is used to change the gain of the amplifier according to the voltage of the output end of the selection switch.

[0024] To expand the range of detected signals, the hybrid interface circuit provided in the embodiments of the present application also includes an automatic range switching circuit that can automatically switch ranges based on the signal magnitude. For example, if the current exceeds a preset current, the automatic range switching circuit can also automatically switch ranges, enabling high current monitoring. If the monitored current exceeds the maximum supply current negotiated by PoDL, the controller disconnects the path switch and stops power supply.

[0025] In one possible implementation, the automatic range switching circuit includes: a hysteresis comparator, an amplifier, a first resistor, a second resistor, and a third resistor; the first input terminal and the second input terminal of the hysteresis comparator are respectively connected to the output terminal of the selection switch and the reference voltage, the first input terminal of the amplifier is connected to the output terminal of the selection switch, the second input terminal of the amplifier is connected to the first end of the first resistor, the second end of the first resistor is connected to the output terminal of the amplifier through the second resistor, the output terminal of the hysteresis comparator is connected to the control terminal of the controllable switch tube, the first end and the second end of the controllable switch tube are respectively connected to the first end of the third resistor and the ground, and the second end of the third resistor is connected to the second end of the first resistor.

[0026] The embodiments of this application do not specifically limit the specific implementation form of the automatic range switching circuit. For example, a variable gain amplifier controlled by a controller program, or an adjustable gain analog front-end circuit integrated into an ADC, etc., can also be a circuit built with analog devices. The embodiments of this application also do not specifically limit the scope of the range. For example, automatic switching from a few mA, tens of mA, to hundreds of mA ranges can be achieved.

[0027] A possible implementation further includes: a path switch; a first end and a second end of the path switch are respectively connected to the output end of the DC / DC circuit and the first end of the detection resistor; a control end of the path switch is connected to a controller; and the controller is further configured to control the path switch to be turned on in PoDL mode or AI mode, and to control the path switch to be turned off in AO mode.

[0028] The path switch can realize the switching of whether the DC / DC circuit provides voltage or current to the line.

[0029] A possible implementation method also includes: a correction switch and a reference current source; the reference current source and the correction switch are connected in series between the second end of the detection resistor and the ground; the control end of the correction switch is connected to the controller; the controller is also used to control the correction switch to be turned on when the current of the detection resistor is greater than the preset current.

[0030] The APL switch provided in the embodiments of the present application also has an automatic calibration function to prevent excessive current from affecting the resistance of the sense resistor, which could cause a deviation in the current detection result. This automatic calibration function is intended to achieve more accurate detection. For example, in current detection, since the resistance of the sense resistor Rsense is typically very small, such as only a few ohms, when a large current flows through it, it is susceptible to thermal effects, causing a change in resistance, which could result in a deviation in the detection current and inaccurate detection.

[0031] A possible implementation also includes: a coupling-decoupling network; the APL PHY is connected to the hybrid interface via a differential capacitor in the coupling-decoupling network; and the hybrid interface circuit is connected to the hybrid interface via a filter inductor in the coupling-decoupling network.

[0032] In one possible implementation, the current signal range of the AI ​​mode and the AO mode is 4 mA-20 mA.

[0033] In one possible implementation, the controller is further configured to, if the AI ​​mode is not met, control the current conversion circuit to output a constant current within the PoDL mode range, and use the voltage detected by the detection circuit to determine whether the PoDL detection mode is met.

[0034] In a second aspect, the embodiment of the present application further provides a communication method for a network device, wherein the network device includes an APL port physical layer PHY and a hybrid interface circuit; an APL The PHY is connected to a hybrid interface; the hybrid interface circuit is compatible with single-pair Ethernet Power over Ethernet (PoDL) mode, analog input AI mode, and analog output AO mode; the hybrid interface is used to connect to an instrument device; the hybrid interface circuit is connected to the hybrid interface; the hybrid interface circuit includes: a current conversion circuit and a detection circuit; the method includes: controlling the current conversion circuit to output a detection current, using a voltage detected by the detection circuit to determine whether the interface of the instrument device is in AI mode; if the interface of the instrument device is in AI mode, controlling the hybrid interface circuit to operate in AO mode; the detection current is a sinusoidal AC current or a DC current less than the minimum value of the current range of the AI ​​mode; if the interface of the instrument device is not in AI mode, controlling the current conversion circuit to output a current that varies within the PoDL mode range, using a voltage range detected by the detection circuit to determine whether the interface of the instrument device is in PoDL mode; if the interface of the instrument device is in PoDL mode, controlling the hybrid interface circuit to operate in PoDL mode; if the interface of the instrument device is not in PoDL mode, controlling the current conversion circuit to output a current that varies within the AO mode range, using a changing voltage detected by the detection circuit to determine whether the interface of the instrument device is in AO mode; if the interface of the instrument device is in AO mode, controlling the hybrid interface circuit to operate in AI mode.

[0035] The communication method provided in the embodiment of the present application is compatible with the single-pair Ethernet power supply PoDL mode, analog input AI mode and analog output AO mode; it can automatically identify the interface type of the instrument equipment and automatically adapt to the interface type of the instrument equipment to realize the control of the instrument equipment or receive the signal of the instrument equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a schematic diagram showing the operation of a conventional APL switch;

[0037] FIG2 is a schematic diagram of the operation of an APL switch according to an embodiment of the present application;

[0038] FIG3 is a schematic diagram of an interface of an APL switch provided in an embodiment of the present application;

[0039] FIG4 is a diagram of the internal architecture of an APL switch provided in an embodiment of the present application;

[0040] FIG5 is an internal architecture diagram of another APL switch provided in an embodiment of the present application;

[0041] FIG6 is an internal architecture diagram of another APL switch provided in an embodiment of the present application;

[0042] FIG7 is an internal architecture diagram of another APL switch provided in an embodiment of the present application;

[0043] FIG8 is an internal architecture diagram of another APL switch provided in an embodiment of the present application;

[0044] FIG9 is a schematic diagram of a coupling-decoupling network provided in an embodiment of the present application;

[0045] FIG10 is a schematic diagram of another coupling-decoupling network provided in an embodiment of the present application;

[0046] FIG11 is a flow chart of adaptive detection performed by a hybrid interface module according to an embodiment of the present application;

[0047] FIG12 is a diagram illustrating an internal filter structure of an instrument device according to an embodiment of the present application;

[0048] FIG13 is a schematic diagram of another type of detection interface provided in an embodiment of the present application;

[0049] FIG14 is a flowchart of a communication method of an APL switch provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solutions provided by the embodiments of the present application, the application scenarios are first introduced below.

[0051] The APL switch is applied to the process industry in order to enable all Ethernet access to the field network of the process industry. The embodiments of the present application do not specifically limit the types of instrument equipment or sensors connected to the APL switch. For example, the instrument can detect various physical quantities, such as temperature, pressure, liquid level or flow, etc. In addition, the APL switch can also output signals to the instrument equipment, such as controlling the instrument equipment, such as controlling switches or valves, etc. When the PoDL mode of the APL switch includes detection mode, power supply mode and sleep mode. In detection mode, the APL switch outputs a current in the range of 9mA to 16mA to the instrument equipment. If the detection feedback voltage is within the preset range, it enters the power supply mode. In power supply mode, the APL switch provides voltage to the instrument equipment. The sleep mode is to enter the sleep mode when the current in the detection line is less than the preset current threshold.

[0052] However, APL switches are currently incompatible with traditional data interfaces. For example, in instruments and equipment in industries like petrochemicals, most instruments transmit signals in the 4mA to 20mA range. The ground pins inside these instruments differ from the connection methods of the PoDL ground pins in APL switches, resulting in a mismatch between the PoDL interface on APL switches and the 4mA to 20mA interface on these instruments.

[0053] See FIG1 , which is a schematic diagram of a working scenario of a traditional APL switch.

[0054] The interfaces in the traditional APL switch 100 only include APL PHY and PoDL, which can implement APL data transmission or PoDL power supply. That is, the meter device 200 has APL data transmission requirements and PoDL power supply requirements.

[0055] However, the PoDL power pins are incompatible with the 4mA-20mA pins. The PoDL output pins include a power pin and a GND pin. The power pin provides power voltage output to instrumentation. The 4mA-20mA pins include power pins V+ and V-, with V- connected to a 250Ω resistor to GND. Therefore, direct compatibility between the two interface pins would require a 250Ω resistor to be connected in series, causing most of the PoDL power to be lost in the resistor.

[0056] In order to solve the above technical problems, an embodiment of the present application provides a network device, which can be a switch or a gateway device. The gateway device can be an Internet of Things gateway, and the switch can be, for example, an APL switch. For ease of understanding, the network device APL switch is used as an example in the following embodiments. The network device includes a hybrid interface circuit, which is compatible with the power supply function of PoDL and the analog input (AI, Analog Input) and analog output (AO, Analog Output) functions of 4mA~20mA. The AO function of the interface of the 4mA~20mA signal corresponds to the output signal, that is, outputting the control signal to the instrument, and the AI ​​function corresponds to the input signal, that is, receiving the detection signal of the instrument. AI and AO do not affect each other, so that each functional mode can work independently, and are applied to data communication and power supply in process industry sites. It can not only meet the needs of future Ethernet access, but also be compatible with mainstream 4mA~20mA data transmission.

[0057] See Figure 2, which is a schematic diagram of the working scenario of the APL switch provided in an embodiment of the present application.

[0058] The APL switch 100 provided in this embodiment includes an APL PHY and a hybrid interface circuit. The hybrid interface circuit is compatible with PoDL power supply and 4mA-20mA data transmission. Together with the corresponding instrument device 200, it can implement APL data transmission, PoDL power supply, and 4mA-20mA AI and AO functions. In some embodiments, only one of AI, AO, and PoDL can be implemented simultaneously. The APL switch 100 can be triggered by a host computer to select one of these functions, manually, or automatically, but this is not specifically limited in this embodiment.

[0059] For ease of understanding, refer to FIG3 , which is a schematic diagram of interfaces of an APL switch 100 provided in an embodiment of the present application.

[0060] The APL switch 100 provided in an embodiment of the present application includes a hybrid interface circuit 101 and a hybrid interface 102. The hybrid interface circuit 101 is connected to the hybrid interface 102. The hybrid interface 102 can be connected to a 4mA-20mA AI function meter of an instrument device, or a 4mA-20mA AO function meter of an instrument device, or an APL interface meter of an instrument device. The APL interface meter and the APL switch 100 can realize APL data transmission and PoDL power supply.

[0061] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the embodiments of the present application are further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0062] See FIG. 4 , which is an internal architecture diagram of an APL switch 100 provided in an embodiment of the present application.

[0063] The Ethernet physical layer APL switch 100 provided in the embodiment of the present application includes: an APL port physical layer PHY10 and a hybrid interface circuit;

[0064] APL PHY10 is connected to hybrid interface 102; hybrid interface 102 is used to connect to instrument equipment; hybrid interface circuit is connected to hybrid interface 102;

[0065] The hybrid interface circuit 102 is compatible with single-pair Ethernet power supply PoDL mode, analog input AI mode and analog output AO mode;

[0066] In PoDL mode, the power supply provides power to the instrument equipment;

[0067] In AI mode, the power supply provides power to the hybrid interface 102;

[0068] In AO mode, the voltage is converted into a current corresponding to the control signal of the instrument equipment.

[0069] In one possible implementation, as shown in FIG4 , the hybrid interface circuit includes: a controller 20 , a current conversion circuit 30 , and a detection circuit 40 ; the current conversion circuit 30 and the detection circuit 40 are both connected to the controller 20 ;

[0070] The controller 20 in the hybrid interface circuit provided in the embodiment of the present application can control the hybrid interface circuit to operate in one of the following three modes: PoDL mode, 4mA~20mA AI mode and 4mA~20mA AO mode.

[0071] In the PoDL power supply mode, the controller 20 is used to control the current conversion circuit 30 to convert the DC voltage into the current of the PoDL mode to provide power to the instrument equipment. The power supply current of the PoDL mode is 9mA to 16mA. The embodiment of the present application does not specifically limit the source of the DC voltage. For example, the DC voltage can be provided by the DC / DC (Direct Circuit / Direct Circuit, DC / DC) circuit 50 included in the APL converter 100. The current conversion circuit 30 can convert the voltage provided by the DC / DC circuit 50 into current for output. The current conversion circuit 30 can be implemented using a voltage-to-current circuit or a voltage-to-current chip. In another possible implementation, the control signal sent by the controller 20 is a digital signal, and the current conversion circuit 30 also has a digital-to-analog conversion function, that is, converting the control signal sent by the controller 20 into an analog signal. In another embodiment, the control signal sent by the controller 20 is an analog signal.

[0072] The embodiments of the present application do not specifically limit the specific implementation form of the controller 20. For example, it can be implemented by a micro control unit (MCU). The controller 20 can send a control signal to the current conversion circuit 30. The control signal indicates the size of the current output by the current conversion circuit. The current conversion circuit 30 can change the output current according to the control signal sent by the controller 20.

[0073] In AI mode, when the APL switch receives signals from instrumentation, the controller 20 bypasses the current conversion circuit 30, for example, shutting it down so that it does not output current. The DC / DC circuit 50 provides a DC voltage to the hybrid interface 102 without passing through the current conversion circuit 30. Specifically, the DC / DC circuit 50 provides an operating voltage to the line via a detection resistor in the detection circuit 40. In one possible implementation, the current conversion circuit 30 is bypassed. The detection circuit 40 detects the current in the hybrid interface 102 and provides it to the controller 20. The instrumentation detection circuit 40 converts the current signal into a voltage signal for detection and transmits the detection result to the controller 20, thereby implementing the 4mA to 20mA AI function.

[0074] In AO mode, the APL switch 100 needs to output a current of 4mA to 20mA to the instrument equipment to control the instrument of the instrument equipment, which may include controlling the on / off switch or valve opening and closing of the instrument equipment. In this case, the controller 20 is used to control the current conversion circuit 30 to convert the DC voltage into the current corresponding to the control signal. For example, the current range corresponding to the control signal of the instrument equipment is 4mA to 20mA. At this time, the detection circuit 40 can be in voltage detection mode, detecting the voltage in the circuit in real time and sending it to the controller 20. The controller 20 controls the output current of the current conversion circuit 30 based on the detection result of the detection circuit 40 to prevent the voltage in the circuit from exceeding the limit and causing overvoltage.

[0075] The APL switch provided in the embodiment of the present application does not specifically limit the method of selecting the working mode, and can be automatically selected or externally triggered.

[0076] The hybrid interface circuit in the APL switch provided in the embodiment of the present application includes a controller, a current conversion circuit, and a detection circuit. In AO mode, the controller can control the magnitude of the output current of the current conversion circuit, thereby enabling the current conversion circuit to output a current in the range of 4mA to 20mA in AO mode. The detection circuit can implement signal detection in the AI ​​mode of 4mA to 20mA, and in the PoDL power supply mode, the APL switch can power the instrument equipment. Therefore, the switch integrates the communication and PoDL power supply functions of APL, as well as the 4mA to 20mA AI and AO functions of the instrument equipment, achieving compatibility between the APL interface and the interface of mainstream instruments.

[0077] See Figure 5, which is an internal architecture diagram of another APL switch provided in an embodiment of the present application.

[0078] The current conversion circuit of the APL switch provided in the embodiment of the present application includes: a digital analog converter (DAC) 31 and a voltage-to-current converter 32;

[0079] The input and output of the DAC 31 are connected to the controller 20 and the voltage-to-current converter 32 respectively;

[0080] The voltage-to-current converter 32 is also used to connect to the DC / DC circuit 50;

[0081] The controller 20 is used to send a voltage control digital signal to the DAC 31;

[0082] DAC 31, for converting the voltage-controlled digital signal into a voltage-controlled analog signal;

[0083] The voltage-to-current converter 32 is configured to convert the voltage output by the DC / DC circuit 50 into a current according to the voltage control analog signal.

[0084] The detection circuit 40 includes a detection resistor Rsense, a current-to-voltage circuit 41 and an analog-to-digital converter (ADC) 42 . The resistance of Rsense is generally small, only a few ohms, so its loss can be ignored.

[0085] The first and second ends of the detection resistor Rsense are respectively connected to the output end of the current conversion circuit and the hybrid interface 102; specifically, the first end of Rsense is connected to the output end of the voltage-current converter 32, that is, the output current of the voltage-current converter 32 passes through the detection resistor Rsense.

[0086] Current-to-voltage circuit 41 is connected to resistor Rsense, detects the voltage across Rsense, and sends the detected voltage value to ADC 42. Current-to-voltage circuit 41 converts the detected current flowing through Rsense into a voltage across Rsense. Current-to-voltage circuit 41 can be implemented using a built-in circuit or a chip, and this embodiment is not specifically limited thereto.

[0087] The ADC 42 is used to convert the analog voltage sent by the current-to-voltage circuit 41 into a digital voltage and send it to the controller 20. Since the controller 20 can only process digital signals, the ADC 42 is required to convert the analog signal into a digital signal.

[0088] As can be seen from the detection circuit shown in Figure 5, the APL switch provided in the embodiments of the present application can detect current on a line, particularly when operating in AI mode, detecting current signals sent by instrumentation. When the APL switch operates in AO mode, ADC 42 can also detect the current on the line and send it to controller 20 to form a closed-loop feedback loop. Controller 20 can then adjust the control signal output to DAC 31 to regulate the current on the line.

[0089] In addition, the APL switch provided in the embodiment of the present application further includes: a path switch 60;

[0090] A first terminal and a second terminal of the path switch 60 are connected to the output terminal of the DC / DC circuit 50 and the first terminal of the detection resistor Rsense respectively;

[0091] The controller 20 is further configured to control the path switch 60 to be turned on in the PoDL mode or the AI ​​mode, and to control the path switch 60 to be turned off in the AO mode.

[0092] The present embodiment does not specifically limit the specific type of path switch 60. For example, it can be a controllable switch tube, such as a metal-oxide-semiconductor (MOS) tube or a diode. The path switch 60 can receive a control signal from the controller 20 to turn on or off the circuit between the DC / DC circuit and Rsense. The controller 20 controls the path switch 60 to control whether the DC / DC circuit 50 provides voltage or current to the line.

[0093] When the pass switch 60 is turned on, the DC / DC circuit 50 is connected to the first end of Rsense, which is equivalent to the turned-on pass switch 60 bypassing the voltage-to-current converter (V / I) 32. That is, V / I 32 no longer outputs current to the first end of Rsense, and the DC / DC circuit 50 provides voltage to the line through Rsense.

[0094] When path switch 60 is off, DC / DC circuit 50 is electrically connected to the first end of Rsense via DAC 31 and V / I 32. V / I 32 converts the voltage provided by DC / DC circuit 50 into a current and provides it to the first end of Rsense. The detection circuit provided in the embodiments of the present application can detect not only the current on the line but also the voltage on the line, which is described in detail below with reference to the accompanying drawings.

[0095] See Figure 6, which is an internal architecture diagram of another APL switch provided in an embodiment of the present application.

[0096] The APL switch provided in the embodiment of the present application, the detection circuit further includes: a voltage divider circuit and a selection switch MUX;

[0097] The selector switch MUX is controlled by the controller 20 and is used to switch between current sampling and voltage sampling by the ADC 42. The voltage divider circuit divides the voltage on the line to make the detected voltage conform to the range of the ADC 42.

[0098] The voltage divider circuit includes a fifth resistor R5 and a sixth resistor R6. The first end of the sixth resistor R6 is connected to the first end of Rsense, and the second end of the sixth resistor R6 is grounded through the fifth resistor R5. The first end of the sixth resistor R6 serves as the first end of the voltage divider circuit, the second end of the fifth resistor R5 serves as the second end of the voltage divider circuit, and the second end of the sixth resistor R6 serves as the output end of the voltage divider circuit, i.e., outputs the divided voltage.

[0099] The first end and the second end of the voltage divider circuit are connected to the first end of the detection resistor Rsense and the ground respectively;

[0100] The selection switch MUX can be implemented by a multi-way selection switch or a selector. In the embodiment of the present application, a multi-way selection switch or a selector with an input terminal greater than or equal to 2 can be selected.

[0101] The first and second input terminals of the selector switch MUX are connected to the output terminal of the current-to-voltage circuit 41 and the output terminal of the voltage divider circuit, i.e., the second terminal of R6, respectively. The output terminal of the selector switch MUX is connected to the input terminal of the ADC 42. In one possible implementation, the current-to-voltage circuit 41 can be implemented using an amplifier.

[0102] The controller 20 is used to control the output end of the selection switch MUX to be connected to the first input end in PoDL mode and AI mode, that is, the current of Rsense can be detected; in AO mode, it is used to control the output end of the selection switch MUX to be connected to the second input end, that is, the voltage on the line can be detected.

[0103] ADC 42 is used to connect the output end of the selection switch MUX to the first input end, collect the current of the detection resistor Rsense and send it to the controller; connect the output end of the collection selection switch MUX to the second input end, detect the voltage of the voltage divider circuit and send it to the controller.

[0104] The controller 20 controls the current output by the V / I 32 according to the voltage detected by the ADC 42 .

[0105] In addition, the APL switch provided in the embodiment of the present application can also realize automatic switching of the detection range of current or voltage, which is described in detail below with reference to the accompanying drawings.

[0106] See Figure 7, which is an internal architecture diagram of another APL switch provided in an embodiment of the present application.

[0107] The APL switch provided in the embodiment of the present application includes: an automatic range switching circuit 43;

[0108] The input and output of the automatic range switching circuit 43 are connected to the output of the selection switch MUX and the input of the ADC 42 respectively;

[0109] The automatic range switching circuit 43 includes at least an amplifier, which is used to change the gain of the amplifier according to the voltage at the output end of the selection switch MUX, thereby realizing automatic switching of the range of the sampled voltage or current.

[0110] The embodiments of the present application do not specifically limit the specific implementation of the automatic range switching circuit 43. For example, it may be a variable gain amplifier controlled by the controller 20, or an adjustable gain analog front-end circuit integrated into the ADC 42. Alternatively, it may be a circuit constructed using analog devices. The embodiments of the present application also do not specifically limit the scope of the range. For example, automatic switching from a few mA, tens of mA, or hundreds of mA can be achieved.

[0111] The following describes three modes of the APL switch provided in the embodiments of the present application operating in PoDL: detection mode, power supply mode, and sleep mode.

[0112] In PoDL detection mode, controller 20 performs PoDL mode detection, controls path switch 60 to open, and sends a voltage-controlled digital signal to DAC 31. DAC 31 converts the voltage-controlled digital signal into a voltage-controlled analog signal. Based on the voltage-controlled analog signal, V / I 32 converts the voltage output of DC / DC circuit 50 into a current, specifically outputting a current between 9mA and 16mA, varying the current value within this range. At this point, selector switch MUX connects to the voltage divider circuit, connecting the common terminals of R5 and R6. ADC 42 detects the feedback voltage and sends it to controller 20, which determines whether the feedback voltage is between 4.05V and 4.7V. If the feedback voltage of the instrument device is within this range, PoDL power supply mode is initiated (according to the standard PoDL process). If the interaction is successful, power supply mode is entered.

[0113] In PoDL power supply mode, controller 20 opens the access switch, and DC / DC circuit 50 supplies power to the instrument equipment. At this point, the operating current in power supply mode needs to be limited and monitored. The detection circuit is in current detection mode. Specifically, controller 20 sets the detection circuit to current detection mode, connecting the MUX and current-to-voltage circuit 41. ADC 42 monitors the supply current in real time. If the current exceeds a first preset current value, the automatic range switching circuit 43 automatically switches the range to enable high-current monitoring. If the monitored current exceeds the maximum supply current negotiated by PoDL, and the power supply is not over-limited, the controller disconnects the access switch and stops power supply.

[0114] In PoDL sleep mode, the controller 20 monitors the low current (between 1.25 mA and 1.85 mA) in the line. The controller 20 controls the path switch 60 to close, and the DC / DC circuit 50 first provides voltage to the line through the path switch 60. At this time, the controller 20 controls the MUX and the current-to-voltage circuit 41 to be connected. The detection circuit is in current detection mode, that is, the ADC 42 detects the current of Rsense and sends it to the controller 20. The controller 20 determines that the current is lower than the second preset current value. The automatic range switching circuit 43 can also automatically switch the range to achieve low current monitoring.

[0115] In order to facilitate those skilled in the art to understand the automatic range switching circuit provided in the embodiment of the present application, a specific implementation method of the automatic range switching circuit is introduced below with reference to the accompanying drawings.

[0116] See Figure 8, which is an internal architecture diagram of another APL switch provided in an embodiment of the present application.

[0117] The APL switch provided in the embodiment of the present application includes an automatic range switching circuit comprising: a hysteresis comparator U3, an amplifier U2, a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4;

[0118] The first and second input terminals of the hysteresis comparator U3 are connected to the output terminal of the selection switch MUX and a reference voltage, respectively. The first input terminal of the amplifier U2 is connected to the output terminal of the selection switch MUX. The second input terminal of the amplifier U2 is connected to the first terminal of the first resistor R1. The second terminal of the first resistor R1 is connected to the output terminal of the amplifier U2 via the second resistor R2. The output terminal of the hysteresis comparator U3 is connected to the control terminal of the controllable switch U6. The first and second terminals of the controllable switch U6 are connected to the first terminal of the third resistor R3 and ground, respectively. The second terminal of the third resistor R3 is connected to the second terminal of the first resistor R1. The second input terminal of the amplifier U2 is grounded via the fourth resistor R4.

[0119] In the embodiment of the present application, the controllable switch tube U6 is described as a MOS tube as an example, but it can also be implemented by other controllable semiconductor devices.

[0120] The reference voltage may be provided by a voltage source. For example, as shown in FIG8 , the second input terminal of the hysteresis comparator U3 is grounded via the voltage source.

[0121] The function of the automatic range switching circuit provided in Figure 8 is to adapt to a larger voltage or current detection range. The working principle is that when the voltage output by the selection switch MUX exceeds the hysteresis voltage of the hysteresis comparator U3, the hysteresis comparator U3 outputs a drive signal to drive the MOS tube U6 to turn on, so that the third resistor R3 is connected to the circuit, thereby changing the feedback coefficient of the amplifier U2, and then realizing the adjustment of the gain of the amplifier U2.

[0122] In one possible implementation, the APL switch provided in an embodiment of the present application also has an automatic calibration function. This function is intended to prevent excessive current from causing changes in the resistance of the sense resistor, which could offset the current detection result. Specifically, the automatic calibration function is intended to achieve more accurate detection. For example, in current detection, since the resistance of the sense resistor Rsense is typically very small, such as only a few ohms, when a large current flows through it, it is susceptible to thermal effects, causing a change in resistance, which could result in a current offset and inaccurate detection.

[0123] Continuing to refer to FIG8 , the APL switch provided in the embodiment of the present application further includes: a calibration switch and a reference current source U5 ;

[0124] The reference current source U5 and the correction switch are connected in series and connected between the second end of the detection resistor Rsense and the ground; the control end of the correction switch is connected to the controller 20.

[0125] Controller 20 is further configured to control the calibration switch to conduct when the current in sense resistor Rsense exceeds a preset current. Because reference current source U5 is a bypass current source and is unaffected by the power current, it can mitigate the thermal effects of high current. Reference current source U5 is only connected during calibration. When calibration is not required, controller 20 controls the calibration switch to be disconnected.

[0126] The following formula introduces the calculation method of the correction coefficient K: I=K*U ADC1 I+ΔI=K*U ADC2 K=ΔI / (U ADC2 -U ADC1 )

[0127] in:

[0128] I is the current flowing through Rsense when the reference current source U5 is not connected;

[0129] U ADC1 The voltage sampled by the ADC when the reference current source U5 is not connected;

[0130] ΔI is the reference current output by the reference current source U5;

[0131] U ADC2 It is the current flowing through Rsense when the reference current source U5 is connected.

[0132] In a specific implementation, the APL switch provided in the embodiment of the present application further includes: a coupling-decoupling network;

[0133] The APL PHY connects to the hybrid interface through differential capacitors C1 and C2 in the coupling-decoupling network;

[0134] The hybrid interface circuit is connected to the hybrid interface via a filter inductor L in a coupling-decoupling network.

[0135] Capacitors C1 and C2 form a differential channel, isolating DC signals from low-frequency signals. They form a high-speed signal path with the APL PHY, providing APL data transmission and reception. Inductor L filters high-speed APL data and provides a low-speed signal path for connecting to the low-speed PoDL and 4mA-20mA hybrid interface circuits.

[0136] The coupling-decoupling network provided in the embodiment of the present application is not limited to the architecture shown in FIG9 , and can also be implemented through other coupling-decoupling networks. As shown in FIG10 , it is a schematic diagram of another coupling-decoupling network provided in the embodiment of the present application.

[0137] In addition to the differential capacitors C1 and C2 and filter inductor L shown in Figure 9, Figure 10 also includes a first isolation transformer T1 and a second isolation transformer T2. The APL PHY is connected to both ends of the first winding of the first isolation transformer T1, the first end of the second winding of the first isolation transformer T1 is connected to the first differential capacitor C1, and the second end of the second winding of the first isolation transformer T1 is connected to the second differential capacitor C2. The PoDL and 4mA-20mA hybrid interface circuit are connected to the first end of the first winding and the first end of the second winding of the second isolation transformer T2. The second end of the first winding and the second end of the second winding of the second isolation transformer T2 are connected to the first end of the first winding and the first end of the second winding of the filter inductor, respectively. The second end of the first winding and the second end of the second winding of the filter inductor L are connected to the first end and the second end of the hybrid interface, respectively. It should be understood that the first end of the hybrid interface is a data or power interface, and the first end of the hybrid interface is generally grounded.

[0138] The hybrid interface circuit in the APL switch provided in the embodiment of the present application can also implement interface adaptation, that is, automatically identify the interface type of the instrument equipment and adjust the working mode to adapt to the operation of the instrument equipment. The specific implementation method is described in detail below.

[0139] The hybrid interface circuit sends a detection signal and senses the signal fed back from the instrument interface, thereby determining the physical layer differences between different interface types and identifying the instrument interface type of the instrument. In the hybrid interface module provided by the present application embodiment, since the controller can control the magnitude of the detection signal, the detection signal will not cause malfunction of 4mA-20mA actuators with an AI interface type, such as switches or valves.

[0140] See FIG11 , which is a flow chart of adaptive detection performed by the hybrid interface module provided in an embodiment of the present application.

[0141] The hybrid interface module detects instrument device interface types including AI 4mA~20mA, AO 4mA~20mA, and PoDL interfaces.

[0142] S1101: The controller controls the current conversion circuit to output a sinusoidal AC current, and uses the voltage detected by the detection circuit to determine whether the interface of the instrument equipment is in AI mode.

[0143] When the interface of the instrument equipment is in AI mode, the hybrid interface circuit is controlled to work in AO mode.

[0144] The embodiment of the present application first performs AI mode detection in order to exclude the possibility that the instrument device is in AI mode. Otherwise, subsequent detection may cause the detection signal to be mistakenly regarded by the AI ​​device as a real signal.

[0145] When operating in AO mode, an APL switch must output current to the line, providing the specified current to instruments and equipment, thereby controlling the instruments (valves, switches, etc.) on the other end. In this mode, the controller controls the current conversion circuit to supply current to the cable. At this time, the detection circuit is in voltage detection mode, monitoring the voltage feedback from the instrument equipment in the line in real time.

[0146] For example, the hybrid interface circuit generates a sinusoidal AC signal Is of ±0.5 mA and a frequency of 1.2 kHz or 2.2 kHz through a current conversion circuit as a detection signal. The above current and frequency values ​​are merely examples; other sinusoidal AC current values ​​or frequencies may also be used. A detection circuit then detects the peak-to-peak voltage Vsense fed back to the hybrid interface circuit by the instrument. By calculating whether the impedance of the instrument interface connected to the instrument is approximately 250 ohms (taking into account detection errors and errors such as cable impedance), it can be determined whether the instrument interface type is an AI 4 mA to 20 mA. The impedance calculation formula is: R = Vsense / Is.

[0147] The instrument device supports a 4mA-20mA interface circuit compatible with Highway Addressable Remote Transducer (HART) signals. HART includes 1.2kHz and 2.2kHz sine waves with a signal amplitude of plus or minus 0.5mA or plus or minus 500mV, superimposed on a two-wire 4mA-20mA current loop. As shown in FIG12 , the internal architecture diagram of the instrument device 200 is shown. To address the interference of HART signals on 4mA-20mA detection, the instrument device is typically provided with a filter before the internal ADC sampling to filter out the HART signal. The instrument device includes a filter 21 and an ADC. The ADC is used to sample signals sent by the APL switch received by the instrument device, such as the detection signal in the embodiment of the present application. Due to the presence of filter 21, the detection signal sent by the APL switch will not be sampled by the ADC to control the actuator action. Therefore, the detection signal provided in the embodiment of the present application can use a detection signal similar to HART, which will be filtered out by the filter in the 4-20mA circuit of the instrument equipment AI. Therefore, the detection signal provided in the embodiment of the present application will not cause the actuator of the instrument equipment to malfunction.

[0148] The embodiment of the present application does not specifically limit the internal architecture of the filter 21. FIG. 12 is only an example, including two inductors and two capacitors. For example, it may also include one inductor and one capacitor.

[0149] The above describes an APL switch that sends an AC sinusoidal signal to an instrument to detect its interface type. This function requires the DAC and ADC in the hybrid interface module to support a 1.2kHz or 2.2kHz operating rate, placing high demands on the DAC and ADC, and increasing overall cost. To achieve lower costs using lower-rate DACs and ADCs, the following describes an alternative implementation in which the APL switch sends a DC signal to the instrument to detect its interface type.

[0150] See FIG. 13 , which is a schematic diagram of another type of detection interface provided in an embodiment of the present application.

[0151] The controller controls the current conversion circuit to output a direct current, and the direct current is less than the minimum value of the current range of the AI ​​mode; and the voltage detected by the detection circuit is used to determine whether the resistance of the instrument equipment complies with the AI ​​mode.

[0152] Since the effective current range of the AI's 4mA-20mA instrument interface is 4mA-20mA, the current value of the detection signal can be set to detect a DC current less than 4mA. This current value will be ignored by the AI's 4mA-20mA instrument and will not cause the instrument device's actuator to erroneously execute an action. One possible implementation method, for example, is to select a 2mA DC current as the detection signal. The controller controls the current conversion circuit to output 2mA to the line and sets the detection circuit to voltage detection mode to detect whether the voltage fed back from the instrument device's instrument interface is approximately 0.5V, thereby determining whether the impedance of the instrument device's instrument interface is 250 ohms. Furthermore, the voltage detection mode is used to monitor the voltage in the line to prevent excessive voltage from being output to the line and damaging the instrument device's instrument interface.

[0153] If it does not meet the AI ​​mode, continue to execute S1102;

[0154] S1102: The controller controls the current conversion circuit to output a current that varies within the PoDL mode range, and uses the voltage range detected by the detection circuit to determine whether the interface of the instrument device is in the PoDL mode.

[0155] The interface of the instrument equipment is in PoDL mode, and the hybrid interface circuit is controlled to work in PoDL mode.

[0156] The reason why the embodiment of the present application detects the PoDL mode first and then detects the AO mode is that the voltage in the PoDL mode is higher than the voltage in the AO mode.

[0157] S1103: The controller controls the current conversion circuit to output a current that varies within the AO mode range. The detection circuit detects the changing voltage and determines whether the instrument device's interface is in AO mode. If the voltage changes accordingly as the current changes, the instrument device can be determined to be a constant current source.

[0158] When the interface of the instrument equipment is in AO mode, the hybrid interface circuit is controlled to operate in AI mode.

[0159] It should be understood that when the APL switch needs to operate in AI mode, the instrumentation equipment is in AO mode. When operating in AI mode, the APL switch needs to detect the current in the line. In this mode, the DC / DC circuit provides the appropriate power supply, and the controller opens the path switch to provide the supply voltage to the line. At this time, the instrumentation equipment has an AO interface, which can convert various physical quantities (temperature, pressure, liquid level, flow rate, etc.) into current output to the line. Therefore, the detection circuit is set to current detection mode. Rsense converts the current in the line into voltage through the current-to-voltage circuit to detect the current in the line, thus realizing the AI ​​function.

[0160] Based on the APL switch provided in the above embodiment, an embodiment of the present application further provides a communication method for the APL switch, which is described in detail below with reference to the accompanying drawings.

[0161] See Figure 14, which is a flowchart of a communication method of an APL switch provided in an embodiment of the present application.

[0162] The communication method of an APL switch provided in an embodiment of the present application, wherein the APL switch includes an APL port physical layer PHY and a hybrid interface circuit; the APL PHY is connected to the hybrid interface; the hybrid interface is used to connect to an instrument device; the hybrid interface circuit is connected to the hybrid interface; the hybrid interface circuit includes: a current conversion circuit and a detection circuit;

[0163] The method includes:

[0164] S1401: Control the current conversion circuit to output a detection current. The voltage detected by the detection circuit determines whether the instrument device's interface is in AI mode. If the detection current is a sinusoidal AC current or a DC current less than the minimum current range in AI mode, proceed to S1402. If not, indicating that the instrument device's interface is not in AI mode, proceed to S1403.

[0165] S1402: The interface of the instrument equipment is in AI mode, and the control hybrid interface circuit operates in AO mode.

[0166] S1403: Control the current conversion circuit to output a current that varies within the PoDL mode range, and use the voltage range detected by the detection circuit to determine whether the interface of the instrument device is in PoDL mode; if so, execute S1404. If not, that is, the interface of the instrument device is not in PoDL mode, execute S1405.

[0167] S1404: The interface of the instrument device is in PoDL mode, and the hybrid interface circuit is controlled to operate in PoDL mode;

[0168] S1405: Adjust the output voltage, detect whether the current in the cable changes with the adjustment of the output voltage, and detect whether the cable current is a constant current. If so, execute S1406.

[0169] S1406: The interface of the instrument equipment is in AO mode, and the hybrid interface circuit is controlled to operate in AI mode.

[0170] The specific implementation of the automatic identification interface of S1401, S1403 and S1405 can be found in the description of the corresponding part of Figure 11, which will not be repeated here.

[0171] It should be understood that in order to avoid malfunction of the instrument equipment, the above steps have a sequential order. That is, the APL switch first identifies the AI ​​mode of the instrument equipment. If it is not in AI mode, since the voltage in the PoDL mode is greater than that in the AO mode, it is necessary to identify the PoDL mode first. If it is not in PoDL mode, then identify the AO mode.

[0172] The APL switch provided in the embodiment of the present application can automatically identify the interface of the instrument device through the above steps. After identifying the interface of the instrument device, it then cooperates with the instrument device to set the operating mode of the internal hybrid interface circuit, thereby communicating data or providing power to the instrument device. The communication method provided in the embodiment of the present application can realize automatic recognition of the AI, AO, and PoDL modes of the instrument device, thereby being compatible with the instrument devices of the above three modes and achieving compatibility between APL communication and the interfaces of traditional instrument devices.

[0173] Since the specific manners of the APL switch operating in the AI, AO or PoDL mode have been introduced in the above embodiments, they will not be repeated here.

[0174] The above description is only a preferred embodiment of the present application and does not constitute any formal limitation to the present application. Although the present application has been disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the art can use the above-disclosed methods and technical contents to make many possible changes and modifications to the technical solution of the present application without departing from the scope of the technical solution of the present application, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application still falls within the scope of protection of the technical solution of the present application.

Claims

1. A network device, characterized in that: include: Advanced physical layer APL port physical layer PHY and hybrid interface circuit; The APL PHY is connected to a hybrid interface; the hybrid interface is used to connect to an instrument device; the hybrid interface circuit is connected to the hybrid interface; The hybrid interface circuit is compatible with single-pair Ethernet power supply PoDL mode, analog input AI mode and analog output AO mode; In the PoDL mode, a power supply supplies power to the instrument device; In the AI ​​mode, the power supply supplies power to the hybrid interface; In the AO mode, the voltage is converted into a current corresponding to the control signal of the instrument device.

2. The network device according to claim 1, characterized in that: Instrument equipment: The interface of the instrument equipment is in the AI ​​mode, and the hybrid interface circuit is controlled to work in the AO mode.

3. The network device according to claim 1 or 2, characterized in that: Also includes: A controller, a current conversion circuit and a detection circuit, wherein the current conversion circuit and the detection circuit are both connected to the controller.

4. The network device according to claim 3, characterized in that: The controller is used to control the current conversion circuit to output a direct current, and the direct current is less than a minimum value of a current interval of the AI ​​mode.

5. The network device according to claim 3 or 4, characterized in that: The controller is also used to control the current conversion circuit to output a current that varies within the PoDL mode range, and use the voltage range detected by the detection circuit to determine whether the interface of the instrument device is in the PoDL mode. If the interface of the instrument device is in the PoDL mode, the hybrid interface circuit is controlled to operate in the PoDL mode.

6. The network device according to any one of claims 3 to 5, characterized in that: The controller is also used to control the current conversion circuit to output a current that changes within the AO mode range, and use the changing voltage detected by the detection circuit to determine whether the interface of the instrument equipment is in the AO mode. If the interface of the instrument equipment is in the AO mode, the hybrid interface circuit is controlled to operate in the AI ​​mode.

7. The network device according to any one of claims 3 to 6, characterized in that: The current conversion circuit includes: a digital-to-analog converter and a voltage-to-current converter; The input end and the output end of the digital-to-analog converter are connected to the controller and the voltage-to-current converter respectively; The voltage-to-current converter is also used to connect a DC / DC circuit; The controller is used to send a voltage control digital signal to the digital-to-analog converter; The analog-to-digital converter is used to convert the voltage-controlled digital signal into a voltage-controlled analog signal; The voltage-to-current converter is used to convert the voltage output by the DC / DC circuit into a current according to the voltage control analog signal.

8. The network device according to any one of claims 3 to 6, characterized in that: The detection circuit includes: a detection resistor, a current-to-voltage circuit and an analog-to-digital converter; The first end and the second end of the detection resistor are connected to the output end of the current conversion circuit and the hybrid interface respectively; The current-to-voltage circuit is used to connect the two ends of the detection resistor to convert the current at the two ends of the detection resistor The voltage is sent to the analog-to-digital converter; The analog-to-digital converter is used to convert the voltage sent by the current-to-voltage circuit into a digital voltage and send it to the controller.

9. The network device according to claim 8, characterized in that: The detection circuit also includes: a voltage divider circuit and a selection switch; The first end and the second end of the voltage divider circuit are connected to the first end of the detection resistor and the ground respectively; The first input terminal and the second input terminal of the selection switch are respectively connected to the output terminal of the current-to-voltage conversion circuit and the output terminal of the voltage divider circuit, and the output terminal of the selection switch is connected to the input terminal of the analog-to-digital converter; The controller is used to control the output end of the selection switch to be connected to the first input end in the PoDL mode and the AI ​​mode; and to control the output end of the selection switch to be connected to the second input end in the AO mode; The analog-to-digital converter is used to conduct the output end of the selection switch with the first input end, collect the current of the detection resistor and send it to the controller; when the output end of the selection switch is conducted with the second input end, detect the voltage of the voltage divider circuit and send it to the controller, and the controller controls the current output by the current conversion circuit according to the voltage detected by the analog-to-digital converter.

10. The network device according to claim 9, characterized in that: Also includes: Automatic range switching circuit; The input end and the output end of the automatic range switching circuit are connected to the output end of the selection switch and the input end of the analog-to-digital converter respectively; The automatic range switching circuit at least includes an amplifier, which is used to change the gain of the amplifier according to the voltage at the output end of the selection switch.

11. The network device according to claim 10, characterized in that: The automatic range switching circuit comprises: a hysteresis comparator, an amplifier, a first resistor, a second resistor and a third resistor; The first input terminal and the second input terminal of the hysteresis comparator are respectively connected to the output terminal of the selection switch and the reference voltage, the first input terminal of the amplifier is connected to the output terminal of the selection switch, the second input terminal of the amplifier is connected to the first end of the first resistor, the second end of the first resistor is connected to the output terminal of the amplifier through the second resistor, the output terminal of the hysteresis comparator is connected to the control terminal of the controllable switch tube, the first end and the second end of the controllable switch tube are respectively connected to the first end of the third resistor and the ground, and the second end of the third resistor is connected to the second end of the first resistor.

12. The network device according to claim 10, characterized in that: Also includes: Access switch; The first end and the second end of the path switch are respectively connected to the output end of the DC / DC circuit and the first end of the detection resistor; the control end of the path switch is connected to the controller; The controller is further configured to control the path switch to be turned on in the PoDL mode or the AI ​​mode, and to control the path switch to be turned off in the AO mode.

13. The network device according to any one of claims 8 to 12, characterized in that: Also includes: Calibration switch and reference current source; The reference current source and the correction switch are connected in series between the second end of the detection resistor and the ground; the control end of the correction switch is connected to the controller; The controller is further used to control the correction switch to be turned on when the current of the detection resistor is greater than a preset current.

14. The network device according to any one of claims 1 to 13, characterized in that: Also includes: Coupling and decoupling networks; The APL PHY is connected to the hybrid interface via a differential capacitor in the coupling-decoupling network; The hybrid interface circuit is connected to the hybrid interface via a filter inductor in the coupling-decoupling network.

15. The network device according to any one of claims 1 to 14, characterized in that: The current signal range of the AI ​​mode and the AO mode is 4mA-20mA.

16. The network device according to any one of claims 3 to 15, characterized in that: The controller is further configured to, if the AI ​​mode is not met, control the current conversion circuit to output a constant current within the PoDL mode range, and use the voltage detected by the detection circuit to determine whether the PoDL detection mode is met.

17. A communication method for a network device, characterized in that: The network device includes an APL port physical layer PHY and a hybrid interface circuit; the APL PHY is connected to the hybrid interface; the hybrid interface circuit is compatible with a single-pair Ethernet power supply PoDL mode, an analog input AI mode and an analog output AO mode; the hybrid interface is used to connect instrument equipment; The hybrid interface circuit is connected to the hybrid interface; The hybrid interface circuit comprises: a current conversion circuit and a detection circuit; The method includes: Control the current conversion circuit to output a detection current, and use the voltage detected by the detection circuit to determine whether the interface of the instrument device is in the AI ​​mode. If the interface of the instrument device is in the AI ​​mode, control the hybrid interface circuit to work in the AO mode; the detection current is a sinusoidal alternating current or a direct current that is less than the minimum value of the current interval of the AI ​​mode; The interface of the instrument device is not in the AI ​​mode, controlling the current conversion circuit to output a current that varies within the PoDL mode range, using the voltage range detected by the detection circuit to determine whether the interface of the instrument device is in the PoDL mode, and if the interface of the instrument device is in the PoDL mode, controlling the hybrid interface circuit to operate in the PoDL mode; The interface of the instrument device is not the PoDL mode, the current conversion circuit is controlled to output a current that changes within the AO mode range, and the changing voltage detected by the detection circuit is used to determine whether the interface of the instrument device is the AO mode. If the interface of the instrument device is the AO mode, the hybrid interface circuit is controlled to operate in the AI ​​mode.

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