Digital communication circuit based on 4-20mA line

Abstract

The invention relates to the technical field of digital communication circuits, in particular to a digital communication circuit based on a 4-20mA line. A comparator COMP, a resistance bridge, a resistance-capacitance circuit and a signal amplification circuit are sequentially arranged in an original 4-20 mA two-wire system circuit, so that receiving, picking, voltage stabilization and amplification of step signals containing digital signals in the 4-20 mA two-wire system circuit are achieved, and the purpose of achieving bidirectional digital communication in the existing 4-20 mA two-wire system circuit is achieved. Compared with the prior art, the number of added circuit elements is relatively small, the increased hardware overhead and power loss are small, and through the resistance bridge and the variable resistor, small-step signals can be filtered, so that digital signals can be extracted more accurately according to the application environment; the problem that a current 4-20mA two-wire system circuit transmits a unidirectional analog current signal and does not support transmission of a bidirectional digital communication signal is solved.

Description

Technical Field

[0001] The invention relates to the technical field of digital communication circuits, and in particular to a digital communication circuit based on a 4-20mA line. Background Art

[0002] The 4-20mA two-wire circuit is widely used in various instruments and equipment in traditional industrial sites to transmit measurement signals of sensors, instruments, meters and other instruments and equipment. The traditional 4-20mA two-wire circuit transmits unidirectional analog current signals and does not support the transmission of two-way digital communication signals. However, with the development of digitalization, more and more customers hope to perform two-way digital communication on the basis of the existing 4-20mA two-wire circuit to realize the digitalization of signal transmission, and can add functions such as setting parameters, calibration and firmware upgrade for sensors through digital communication. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a digital communication circuit based on a 4-20mA line, which solves the problem that the current 4-20mA two-wire circuit transmits a unidirectional analog current signal and does not support the transmission of a bidirectional digital communication signal.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A digital communication circuit based on a 4-20mA line comprises a positive circuit for transmitting a 4-20mA current and a grounded negative circuit, wherein the transmitter end and the main device end of the positive circuit and the negative circuit are both provided with a comparator COMP and a resistance bridge for receiving and sequentially processing a step signal in an electrical signal, a resistance-capacitance circuit for picking up a step signal is provided at the signal output end of the resistance bridge, and a signal amplification circuit for sending a step signal is provided at the output end of the resistance-capacitance circuit.

[0006] Preferably, the resistor bridge comprises resistors R1, R2, R4 and R3 which are connected in series in sequence to form a ring circuit, the low-level output end of the comparator COMP is connected between the resistor R2 and the resistor R4, the high-level output end of the comparator COMP is connected between the resistor R1 and the resistor R3, a power supply VCC is connected between the resistor R1 and the resistor R2, and the resistor R3 and the resistor R4 are grounded.

[0007] Preferably, the RC circuit comprises a resistor R5 connected to the signal output end of the resistor bridge, and a capacitor C1 connected in series with the resistor R5.

[0008] Preferably, the signal amplifying circuit comprises a transistor Q1 connected to the output end of the RC circuit, the emitter of the transistor Q1 is grounded, the base of the transistor Q1 is used to send an electrical signal to the input end of another comparator COMP, and the collector of the transistor Q1 is connected to the positive circuit.

[0009] Preferably, a resistor R7 is connected to the base of the transistor Q1, a resistor R6 is connected to the collector of the transistor Q1, and the emitter of the transistor Q1 is grounded.

[0010] Preferably, the negative pole circuit is provided with a current detection device for detecting a current signal.

[0011] Preferably, at least one of the resistors R1 , R2 , R4 and R3 is a variable resistor.

[0012] Compared with the prior art, the present invention provides a digital communication circuit based on a 4-20mA line, which has the following beneficial effects:

[0013] 1. By arranging a comparator COMP, a resistor bridge, a resistor-capacitor circuit and a signal amplifying circuit for receiving and sequentially processing step signals in electrical signals in the original 4-20mA two-wire circuit, the step signal containing a digital signal in the 4-20mA two-wire circuit can be received, picked up, stabilized and amplified, thereby achieving the purpose of two-way digital communication in the current 4-20mA two-wire circuit, and the added circuit elements are relatively small, and the added hardware opening cost and power loss are small.

[0014] 2. By setting the resistance bridge and variable resistor, the pickup range of the resistance bridge for the step signal can be controlled, so that the small step signal can be filtered and the electrical signal can be filtered to extract the digital signal more accurately according to the application environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0016] Figure 1 It is a structural block diagram of the digital communication circuit of the present invention;

[0017] Figure 2 It is a circuit diagram of the digital communication circuit of the present invention.

[0018] In the figure: 1. Positive circuit; 2. Negative circuit; 3. Resistor bridge; 4. Resistor-capacitor circuit; 5. Signal amplification circuit. DETAILED DESCRIPTION

[0019] The following will describe the implementation methods of the present application in detail with the help of accompanying drawings and examples, so that the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0020] In order to solve the problem that the current 4-20mA two-wire circuit transmits a unidirectional analog current signal and does not support the transmission of a bidirectional digital communication signal, the present invention provides a digital communication circuit based on a 4-20mA line. The circuit design can be configured in the original 4-20mA two-wire circuit. By configuring limited circuit elements on the host end and the device end, a digital signal communication function can be realized on the basis of current signal transmission, thereby providing an effective information interaction means for the online configuration and operation management of the sensor without increasing excessive hardware overhead and power loss. The digital communication circuit includes a positive circuit 1 for transmitting a 4-20mA current and a grounded negative circuit 2. The transmitter end and the host device end of the positive circuit 1 and the negative circuit 2 are both provided with a comparator COMP and an electric current for receiving and sequentially processing a step signal in the electrical signal. Resistor bridge 3, when there is no digital signal in the circuit, there is no step signal in the circuit, and the signal step amplitude is extremely small. At this time, the small step signal that does not belong to the digital signal is filtered through the comparator COMP and the resistor bridge 3. When there is a digital signal in the circuit, a larger step signal will appear, which is identified by the comparator COMP and the resistor bridge 3. A resistor-capacitor circuit 4 for picking up the step signal is arranged on the signal output end of the resistor bridge 3. The resistor-capacitor circuit 4 is used to further identify the step signal and achieve the effect of DC isolation. A signal amplifier circuit 5 for sending the step signal is arranged on the output end of the resistor-capacitor circuit 4. The signal amplifier circuit 5 amplifies the picked-up step signal, thereby amplifying the digital signal, so that it can be received by the comparator COMP at the other end, thereby realizing the transmission of the digital signal between the transmitter end and the main device end.

[0021] The resistor bridge 3 needs to distinguish the signal output by the comparator COMP, so as to filter the small step signal. The following introduces a simple structure of the resistor bridge 3 to minimize the circuit load. The resistor bridge 3 includes resistors R1, R2, R4 and R3 which are connected in series to form a ring circuit. The low-level output end of the comparator COMP is connected between the resistor R2 and the resistor R4, and the high-level output end of the comparator COMP is connected between the resistor R1 and the resistor R3. A power supply VCC is connected between the resistor R1 and the resistor R2, and the resistor R3 and the resistor R4 are grounded. When there is a digital signal in the circuit, the step signal is more obvious. Therefore, the current input to the comparator COMP between the resistor R1 and the resistor R3 and between the resistor R1 and the resistor R2 is different. At this time, the electrical signal as a digital signal will be output to the resistor-capacitor circuit 4 only when the current difference between the two points is greater than a certain value, thereby realizing the recognition of the step signal current.

[0022] In order to perform DC isolation and prevent DC current from passing through the RC circuit 4 and affecting the normal operation of other circuits, and to obtain the step signal at the same time, the RC circuit 4 includes a resistor R5 connected to the signal output end of the resistor bridge 3, and a capacitor C1 connected in series with the resistor R5. When the step signal is input to the RC circuit 4, the capacitor will first charge and store energy, and then discharge. This process simulates the natural response of the circuit in the absence of external excitation, thereby realizing the pickup and voltage stabilization of the step signal.

[0023] The picked-up digital signal needs to be amplified and then output, so that when the transmitter end or the main device end receives the comparator COMP which is a step signal of the digital signal, the digital signal is clearer. The signal amplification circuit 5 includes a transistor Q1 connected to the output end of the resistor-capacitor circuit 4, the emitter of the transistor Q1 is grounded, the base of the transistor Q1 is used to send an electrical signal to the input end of another comparator COMP, and the collector of the transistor Q1 is connected to the positive circuit 1.

[0024] In order to ensure the normal operation of transistor Q1, the current in the control circuit needs to be controlled through a resistor to prevent damage to transistor Q1. Therefore, a resistor R7 is connected to the base of transistor Q1, a resistor R6 is connected to the collector of transistor Q1, and the emitter of transistor Q1 is grounded.

[0025] In order to conveniently detect whether there is current in the negative pole circuit 2 and monitor whether the circuit is running, a current detection device for detecting a current signal is provided on the negative pole circuit 2 .

[0026] At least one of the resistors R1, R2, R4 and R3 is a variable resistor, so that by changing the resistance value of at least one of the four resistors, the current difference threshold between the comparator COMP input to the resistors R1 and R3 and between the resistors R1 and R2 can be controlled, thereby controlling the step threshold of the picked-up step signal, thereby achieving control of the step signal pickup range.

[0027] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0028] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A digital communication circuit based on a 4-20mA line, comprising a positive circuit (1) for transmitting a 4-20mA current and a grounded negative circuit (2), characterized in that: The transmitter end and the main device end of the positive circuit (1) and the negative circuit (2) are both provided with a comparator COMP and a resistance bridge (3) for receiving and sequentially processing a step signal in the electrical signal; a resistance-capacitance circuit (4) for picking up the step signal is provided at the signal output end of the resistance bridge (3); and a signal amplification circuit (5) for sending the step signal is provided at the output end of the resistance-capacitance circuit (4).

2. The digital communication circuit according to claim 1, characterized in that: The resistor bridge (3) comprises a resistor R1, a resistor R2, a resistor R4 and a resistor R3 which are connected in series in sequence to form a ring circuit, a low-level output end of the comparator COMP is connected between the resistor R2 and the resistor R4, a high-level output end of the comparator COMP is connected between the resistor R1 and the resistor R3, a power supply VCC is connected between the resistor R1 and the resistor R2, and a ground is connected between the resistor R3 and the resistor R4.

3. The digital communication circuit according to claim 1, characterized in that: The resistor-capacitor circuit (4) comprises a resistor R5 connected to the signal output end of the resistor bridge (3), and a capacitor C1 connected in series with the resistor R5.

4. The digital communication circuit according to claim 1, characterized in that: The signal amplifying circuit (5) comprises a transistor Q1 connected to the output end of the resistor-capacitor circuit (4), the emitter of the transistor Q1 being grounded, the base of the transistor Q1 being used to send an electrical signal to the input end of another comparator COMP, and the collector of the transistor Q1 being connected to the positive circuit (1).

5. The digital communication circuit according to claim 4, characterized in that: The base of the transistor Q1 is connected to a resistor R7 , the collector of the transistor Q1 is connected to a resistor R6 , and the emitter of the transistor Q1 is grounded.

6. The digital communication circuit according to claim 1, characterized in that: The negative pole circuit (2) is provided with a current detection device for detecting a current signal.

7. The digital communication circuit according to claim 2, characterized in that: At least one of the resistors R1 , R2 , R4 and R3 is a variable resistor.

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