Implementing an adaptive current loop interface circuitry

Abstract

The utility model relates to a kind of current loop interface circuit system achieving self-adaption, including current loop transmitting circuit, interface switching circuit, current loop output port and external power supply port, the input end of current loop transmitting circuit is connected with the IO port of single-chip microcontroller or controller, the output end of current loop transmitting circuit is connected with current loop output port, the negative end of the output end of current loop transmitting circuit is also connected with the input end of interface switching circuit, current loop output port is connected with current loop load, the negative end of the output end of current loop transmitting circuit is connected with the input end of interface switching circuit, the output end of interface switching circuit is connected with power supply ground, the output end of external power supply port is connected with interface switching circuit under three-wire wiring mode.The current loop interface circuit system achieving self-adaption using the utility model, compatible with the transmission of digital signal, not only save the occupancy of interface to physical space, more improve the reliability of sensor's transmission signal transmission.

Description

Technical Field

[0001] This utility model relates to the fields of modern industrial automation, instrumentation, and communication, and particularly to the field of physical quantity detection, specifically referring to an adaptive current loop interface circuit system. Background Technology

[0002] Current loop interface circuits are widely used in modern industrial automation, instrumentation, and communications, and are a key technology for achieving reliable signal transmission and control. According to the wiring method, current loop interface circuits can be divided into two-wire and three-wire systems. In a two-wire system, the current loop device and sensor are located at the field end. Due to difficulties in field power supply, the receiving end typically uses a 4-20mA current loop to supply power to the remote current loop device, and the signal strength is reflected by the current magnitude. For example, in some distributed data acquisition systems, sensors are distributed in different areas; using a two-wire current loop interface circuit can reduce wiring costs while meeting signal transmission and power supply requirements. Three-wire systems are generally used when monitoring systems need to drive field actuators (such as valves) via long lines. In this case, the current loop device is located at the monitoring system end, and the system directly supplies power to the current loop device. The power supply is a third wire in addition to the two current transmission lines. In industrial automated production lines, for actuators requiring precise control, three-wire current loop interface circuits can provide more stable power and signal transmission.

[0003] Generally, different circuit designs are required for the two wiring methods. However, in practical applications, the current loop output interface of the same product may be used for multiple wiring methods. In existing designs, two circuits are usually designed inside the product, corresponding to at least two wiring terminals, or different circuits are switched to the output terminals via jumpers. There is also a utility model patent CN 212785317 U, which describes a 4-20mA current loop circuit that achieves output interface compatibility by adding internal battery modules, signal detection circuits, etc.

[0004] However, this circuit not only requires the addition of multiple circuit modules, but also microcontroller program processing and separate battery power supply, which greatly increases the hardware cost and circuit complexity, making the practical value of this design low. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an adaptive current loop interface circuit system that is highly reliable, simple in structure, and widely applicable.

[0006] To achieve the above objectives, the adaptive current loop interface circuit system of this utility model is as follows:

[0007] The adaptive current loop interface circuit system is characterized by comprising a current loop transmitter circuit, an interface switching circuit, a current loop output port, and an external power supply port. The input of the current loop transmitter circuit is connected to the I / O port of a microcontroller or controller. Both the positive and negative outputs of the current loop transmitter circuit are connected to the current loop output port. The negative output of the current loop transmitter circuit is also connected to the input of the interface switching circuit. The current loop output port is connected to the current loop load. The input of the interface switching circuit is connected to the negative output of the current loop transmitter circuit. The output of the interface switching circuit is connected to the power ground of the external power supply port. In a three-wire connection configuration, the output of the external power supply port is connected to the interface switching circuit.

[0008] Preferably, the current loop transmitter circuit includes a first optocoupler circuit structure, a second optocoupler circuit structure, a third optocoupler circuit structure, a low-power DAC chip, and a current loop driver chip. The input terminals of the first, second, and third optocoupler circuit structures are all connected to the MCU, and the output terminals of the first, second, and third optocoupler circuit structures are all connected to the low-power DAC chip. The output interface of the low-power DAC chip is connected to the input interface of the current loop driver chip, the current loop driver chip is connected to the current loop output interface, the interface switching circuit is connected to the current loop transmitter circuit, and the external power supply port is connected to the interface switching circuit.

[0009] Preferably, the interface switching circuit includes a relay, an NPN transistor, a fourth resistor, and a second diode. One end of the normally open contact of the relay is connected to the negative terminal of the current loop output port, and the other end of the normally open contact is connected to the power ground of the external power supply port. One end of the control coil of the relay is connected to the positive terminal of the external power supply port, and the other end is connected to the collector of the NPN transistor. The second diode is connected in parallel across the control coil of the relay. The anode of the second diode is connected to the collector of the NPN transistor, and the cathode is connected to the positive terminal of the external power supply port. The base of the NPN transistor is connected to the positive terminal of the external power supply port, and the emitter of the NPN transistor is connected to the external power ground.

[0010] Preferably, in a two-wire connection, the current loop output port is connected to the current loop load, the external power supply port is floating, the interface switching circuit is not energized, and the normally open contact of the relay is normally open; in a three-wire connection, the external power supply port is connected to a 24V DC power supply, the normally open contact of the relay is normally closed, and the negative terminal of the current loop output port is connected to the external power supply ground.

[0011] Preferably, the interface switching circuit further includes a relay, a second diode, and an N-channel enhancement-mode MOSFET. One end of the normally open contact of the relay is connected to the negative terminal of the current loop output port, and the other end of the normally open contact is connected to the power ground of the external power supply port. One end of the control coil of the relay is connected to the positive terminal of the external power supply port, and the other end is connected to the source of the N-channel enhancement-mode MOSFET. The second diode is connected in parallel across the control coil of the relay. The anode of the second diode is connected to the source of the N-channel enhancement-mode MOSFET, and the cathode is connected to the positive terminal of the external power supply port. The gate of the N-channel enhancement-mode MOSFET is connected to the positive terminal of the external power supply port, and the drain of the N-channel enhancement-mode MOSFET is connected to the external power ground.

[0012] The adaptive current loop interface circuit system of this invention can be used to transmit digital signals without changing the physical output interface of the sensor's traditional analog voltage signal. This not only saves the physical space occupied by the interface, but also improves the reliability of the sensor's signal transmission. Attached Figure Description

[0013] Figure 1 This is a functional block diagram of the adaptive current loop interface circuit system of this utility model.

[0014] Figure 2 This is a two-wire current loop wiring diagram for the adaptive current loop interface circuit system of this utility model.

[0015] Figure 3 This is a three-wire current loop wiring diagram for the adaptive current loop interface circuit system of this utility model.

[0016] Figure 4 This is a circuit diagram of an embodiment of the adaptive current loop interface circuit system of this utility model.

[0017] Figure 5 This is a circuit diagram of Embodiment 2 of the adaptive current loop interface circuit system of this utility model. Detailed Implementation

[0018] To more clearly describe the technical content of this utility model, the following description is provided in conjunction with specific embodiments.

[0019] This utility model discloses an adaptive current loop interface circuit system, including a current loop transmitter circuit, an interface switching circuit, a current loop output port, and an external power supply port. The input terminal of the current loop transmitter circuit is connected to the I / O port of a microcontroller or controller. Both the positive and negative terminals of the current loop transmitter circuit's output terminal are connected to the current loop output port. The negative terminal of the current loop transmitter circuit's output terminal is also connected to the input terminal of the interface switching circuit. The current loop output port is connected to the current loop load. The input terminal of the interface switching circuit is connected to the negative terminal of the current loop transmitter circuit's output terminal. The output terminal of the interface switching circuit is connected to the power ground of the external power supply port. In a three-wire connection configuration, the output terminal of the external power supply port is connected to the interface switching circuit.

[0020] In a preferred embodiment of this utility model, the current loop transmitter circuit includes a first optocoupler circuit structure, a second optocoupler circuit structure, a third optocoupler circuit structure, a low-power DAC chip, and a current loop driver chip. The input terminals of the first, second, and third optocoupler circuit structures are all connected to the MCU, and the output terminals of the first, second, and third optocoupler circuit structures are all connected to the low-power DAC chip. The output interface of the low-power DAC chip is connected to the input interface of the current loop driver chip, the current loop driver chip is connected to the current loop output interface, the interface switching circuit is connected to the current loop transmitter circuit, and the external power supply port is connected to the interface switching circuit.

[0021] In a preferred embodiment of this utility model, the interface switching circuit includes a relay K1, an NPN transistor Q2, a fourth resistor R4, and a second diode D2. One end of the normally open contact of the relay K1 is connected to the negative terminal of the current loop output port, and the other end of the normally open contact is connected to the power ground of the external power port. One end of the control coil of the relay K1 is connected to the positive terminal of the external power port, and the other end is connected to the collector of the NPN transistor Q2. The second diode D2 is connected in parallel across the control coil of the relay K1. The anode of the second diode D2 is connected to the collector of the NPN transistor Q2, and the cathode is connected to the positive terminal of the external power port. The base of the NPN transistor Q2 is connected to the positive terminal of the external power port, and the emitter of the NPN transistor Q2 is connected to the external power ground.

[0022] In a preferred embodiment of this utility model, in a two-wire connection, the current loop output port J1 is connected to the current loop load, the external power supply port is floating, the interface switching circuit is not energized, and the normally open contact of relay K1 is normally open; in a three-wire connection, the external power supply port is connected to a 24V DC power supply, the normally open contact of relay K1 is normally closed, and the negative terminal of the current loop output port is connected to the external power supply ground.

[0023] In a preferred embodiment of this utility model, the interface switching circuit further includes a relay K1, a second diode D2, and an N-channel enhancement-mode MOSFET. One end of the normally open contact of the relay K1 is connected to the negative terminal of the current loop output port, and the other end of the normally open contact is connected to the power ground of the external power supply port. One end of the control coil of the relay K1 is connected to the positive terminal of the external power supply port, and the other end is connected to the source of the N-channel enhancement-mode MOSFET. The second diode D2 is connected in parallel across the control coil of the relay K1. The positive terminal of the second diode D2 is connected to the source of the N-channel enhancement-mode MOSFET, and the negative terminal is connected to the positive terminal of the external power supply port. The gate of the N-channel enhancement-mode MOSFET is connected to the positive terminal of the external power supply port, and the drain of the N-channel enhancement-mode MOSFET is connected to the external power ground.

[0024] In the specific embodiments of this utility model, in view of the application requirements for the same product to be compatible with two-wire and three-wire current loop interfaces, and the shortcomings of existing technical solutions, this utility model proposes a 4-20mA current loop interface circuit based on hardware control principle. By using different wiring combinations for the output interface, it can more simply and reliably adapt to the use of two-wire or three-wire wiring methods automatically.

[0025] This invention provides an adaptive current loop interface circuit, such as... Figure 1 As shown, it includes a current loop transmitter circuit, an interface switching circuit, a current loop output port, and an external power supply port.

[0026] The aforementioned current loop transmitter circuit is used to generate a current loop signal that is isolated from other circuits within the product. Its output and output signals are isolated by isolation modules such as optocouplers. Its input is generally the I / O port of the microcontroller or controller inside the product, and the interface type may be an SPI interface. The positive and negative terminals of the current loop signal at its output are both connected to the current loop output port. In addition, the negative terminal of the current loop signal is also connected to the input of the interface switching circuit.

[0027] The current loop output port is connected to the positive and negative terminals of the current loop signal output by the current loop transmitter circuit, and is used to connect to the current loop load. By combining it with the external power supply port in different ways, it can realize different applications of two-wire or three-wire wiring.

[0028] The interface switching circuit has its input terminal connected to the negative terminal of the current loop signal output by the current loop transmitter circuit, and its output terminal connected to the power ground of the external power port. When a 24V DC power supply is connected to the external power port, the negative terminal of the current loop signal is controlled to conduct with the externally connected 24V power ground.

[0029] The external power port is connected to the interface switching circuit and is used to provide power input and control the switching circuit when the three-wire wiring method is applied, so as to realize the automatic switching from two-wire to three-wire sink current or source current wiring method.

[0030] In two-wire wiring scenarios, such as Figure 2 Wiring as shown: connect the external 24V power supply in series with the current loop load and connect it to the current loop output port in the positive and negative directions. No wiring is required at the external power supply port. The current loop signal is directly output through the current loop output interface.

[0031] In three-wire wiring scenarios, such as Figure 3 The wiring method shown is as follows: the current loop load is connected between the current loop output ports, and the external power supply port is connected to a 24V DC power supply. Under the control of the external 24V power supply, the negative terminal of the current loop is connected to the ground wire of the external 24V power supply, realizing the three-wire wiring operation.

[0032] Based on the above technical solution, by adjusting whether an external power supply is connected to the external power port and the load wiring method of the current loop output interface, the two-wire or three-wire wiring method can be automatically switched, achieving compatibility between the two interfaces.

[0033] Appendix in conjunction with the embodiments Figure 4 This utility model will be described in detail.

[0034] Figure 4 This is a specific circuit diagram of Example 1 of an interface circuit that achieves compatibility between adaptive two-wire and three-wire current loops.

[0035] In this embodiment, the isolated current loop transmitter circuit includes three optocouplers, a low-power DAC chip with an SPI interface, and a dedicated current loop driver chip. The MCU sends digital signals through the IO port according to the SPI signal timing, which are then driven by the low-power DAC chip at the other end of the optocoupler through the optocoupler isolation. The output interface of the low-power DAC chip is connected to the input interface of the current loop driver chip. At the same time, the current loop driver chip draws power from the current loop output interface and outputs a power supply signal to the DAC chip through its internal LDO. In this way, the digital signal output by the MCU's IO passes through the optocoupler, the DAC chip, and the dedicated two-wire current loop driver chip, and then outputs a 4-20mA current signal at the output interface.

[0036] The interface switching circuit consists of a single-pole single-throw relay K1, an NPN transistor Q2, a fourth resistor R4, and a second diode D2. One end of the normally open contact of relay K1 is connected to the negative terminal of the current loop output port, and the other end is connected to the power ground of the external power supply port. One end of the control coil of relay K1 is connected to the positive terminal of the external power supply port, and the other end is connected to the collector of NPN transistor Q2. The second diode D2 is connected in parallel across the control coil of relay K1 to eliminate the reverse electromotive force when the coil is working. The anode of the second diode D2 is connected to the collector of NPN transistor Q2, and the cathode is connected to the positive terminal of the external power supply port. The base of NPN transistor Q2 is connected to the positive terminal of the external power supply port through the second resistor R2, and the emitter of NPN transistor Q2 is connected to the external power ground.

[0037] In this embodiment, under the two-wire wiring mode, according to Figure 2 As shown, the load is connected to the current loop output port J1, the external power supply port is floating, the above interface switching circuit is not powered, the contacts of relay K1 remain in the normally open state, so the current loop signal is normally output from the current loop output port J1.

[0038] In a three-wire wiring configuration, according to Figure 3 With the wiring as shown, the external power supply port is connected to a 24V DC power supply. Due to the power supply, the base of the NPN transistor Q2 is saturated and conducts, controlling the collector and emitter of the NPN transistor Q2. Therefore, the control coil of relay K1 flows through the current, causing the normally open contact of relay K1 to switch to the normally closed state. This results in the negative terminal of the current loop signal being connected to the external power supply ground, thus enabling the current loop signal powered by the external power supply to work normally in a three-wire mode.

[0039] In this embodiment, the three optocouplers are PC457L, the low-power DAC chip is TPC112S1, the dedicated current loop driver chip is LTS115, the relay K1 has a rated DC voltage of 24V, includes at least one single-pole single-throw relay, and the NPN transistor controlling the relay is S8050.

[0040] Based on the above principle, the NPN transistor can also be replaced with an N-channel enhancement-mode MOSFET, and resistor R4 can be omitted. The specific circuit diagram is shown below. Figure 5 As shown.

[0041] In this invention, MCU refers to Microprogrammed Control Unit, SPI refers to Serial Peripheral Interface, and DAC refers to Digital-to-Analog Converter.

[0042] For the specific implementation scheme of this embodiment, please refer to the relevant descriptions in the above embodiments, which will not be repeated here.

[0043] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0044] It should be noted that in the description of this utility model, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this utility model, unless otherwise stated, "a plurality of" means at least two.

[0045] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] The adaptive current loop interface circuit system of this invention can be used to transmit digital signals without changing the physical output interface of the sensor's traditional analog voltage signal. This not only saves the physical space occupied by the interface, but also improves the reliability of the sensor's signal transmission.

[0047] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

Claims

1. A current loop interface circuit system for achieving adaptive operation, characterized in that, The system includes a current loop transmitter circuit, an interface switching circuit, a current loop output port, and an external power supply port. The input terminal of the current loop transmitter circuit is connected to the I / O port of a microcontroller or controller. Both the positive and negative terminals of the current loop transmitter circuit's output terminal are connected to the current loop output port. The negative terminal of the current loop transmitter circuit's output terminal is also connected to the input terminal of the interface switching circuit. The current loop output port is connected to the current loop load. The input terminal of the interface switching circuit is connected to the negative terminal of the current loop transmitter circuit's output terminal. The output terminal of the interface switching circuit is connected to the power ground of the external power supply port. In a three-wire wiring configuration, the output terminal of the external power supply port is connected to the interface switching circuit.

2. The adaptive current loop interface circuit system according to claim 1, characterized in that, The current loop transmitter circuit includes a first optocoupler circuit structure, a second optocoupler circuit structure, a third optocoupler circuit structure, a low-power DAC chip, and a current loop driver chip. The input terminals of the first, second, and third optocoupler circuit structures are all connected to the MCU. The output terminals of the first, second, and third optocoupler circuit structures are all connected to the low-power DAC chip. The output interface of the low-power DAC chip is connected to the input interface of the current loop driver chip. The current loop driver chip is connected to the current loop output interface. The interface switching circuit is connected to the current loop transmitter circuit. The external power supply port is connected to the interface switching circuit.

3. The adaptive current loop interface circuit system according to claim 2, characterized in that, The interface switching circuit includes a relay, an NPN transistor, a fourth resistor, and a second diode. One end of the normally open contact of the relay is connected to the negative terminal of the current loop output port, and the other end of the normally open contact is connected to the power ground of the external power supply port. One end of the relay's control coil is connected to the positive terminal of the external power supply port, and the other end is connected to the collector of the NPN transistor. The second diode is connected in parallel across the control coil of the relay. The anode of the second diode is connected to the collector of the NPN transistor, and the cathode is connected to the positive terminal of the external power supply port. The base of the NPN transistor is connected to the positive terminal of the external power supply port, and the emitter of the NPN transistor is connected to the external power ground.

4. The adaptive current loop interface circuit system according to claim 3, characterized in that, In a two-wire connection, the current loop output port is connected to the current loop load, the external power supply port is floating, the interface switching circuit is not energized, and the normally open contact of the relay is normally open. In a three-wire connection, the external power supply port is connected to a 24V DC power supply, the normally open contact of the relay is normally closed, and the negative terminal of the current loop output port is connected to the external power ground.

5. The adaptive current loop interface circuit system according to claim 2, characterized in that, The interface switching circuit further includes a relay, a second diode, and an N-channel enhancement-mode MOSFET. One end of the normally open contact of the relay is connected to the negative terminal of the current loop output port, and the other end of the normally open contact is connected to the power ground of the external power supply port. One end of the control coil of the relay is connected to the positive terminal of the external power supply port, and the other end is connected to the source of the N-channel enhancement-mode MOSFET. The second diode is connected in parallel across the control coil of the relay. The anode of the second diode is connected to the source of the N-channel enhancement-mode MOSFET, and the cathode is connected to the positive terminal of the external power supply port. The gate of the N-channel enhancement-mode MOSFET is connected to the positive terminal of the external power supply port, and the drain of the N-channel enhancement-mode MOSFET is connected to the external power ground.

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