A constant current input digital input acquisition circuit

Abstract

The application discloses a kind of constant current input digital quantity input acquisition circuit, comprising: constant current circuit, for providing stable current loop for digital quantity input signal, the current of current loop is stabilized at preset value by the negative feedback circuit formed by reference device and adjusting device;And after the stable digital quantity input signal is transmitted to digital quantity input indicating circuit and logic output circuit;Digital quantity input indicating circuit, for by high-low level state conversion as the on-off state of indicator light, the stable digital quantity input signal is shown as the indicator light signal visible on industrial field;Logic output circuit, for outputting the stable digital quantity input signal.The application has high stability, with input protection and constant current capacity, can be applied in complex industrial field environment under digital quantity acquisition module;Reduce the error sampling of digital quantity input module from surrounding environment electromagnetic interference, radio frequency interference and electrostatic interference etc.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of digital quantity input, and particularly relates to a constant-current input digital quantity input acquisition circuit. BACKGROUND

[0002] Modern industrial field digital quantity input is usually integrated in industrial control systems and is widely used in the fields of industrial automation, manufacturing, energy industry, etc. Industrial field digital quantity input is mainly used for collecting and monitoring the state and signals of industrial field devices. In industrial automation control systems, digital quantity input is used to receive digital signals from switches, sensors, relays, etc. These signals can represent the state of the device, the state of the switch, the alarm signal, etc. Through digital quantity input, the state of the industrial field device can be monitored and controlled in real time, so as to realize automation control, fault diagnosis and data acquisition. These signals can be used to monitor the production process, the running state of the device, safety protection, etc., to help industrial enterprises improve production efficiency, reduce cost and improve safety. Due to the complex environment of the industrial field, the digital quantity input module needs to consider various factors when working in a complex environment, including anti-interference ability, reliability, fault tolerance, etc.

[0003] However, the existing digital quantity input acquisition circuit has poor anti-interference ability and cannot well filter abnormal input waveforms. The input current changes with the change of the input source, the input loop current difference is obvious, and the input power consumption changes greatly. It cannot be reliably applied in a variety of industrial environments.

[0004] Therefore, the present application is proposed. SUMMARY

[0005] The technical problem to be solved by the present application is that the existing digital quantity input acquisition circuit has poor anti-interference ability and cannot well filter abnormal input waveforms. The input current changes with the change of the input source, the input loop current difference is obvious, and the input power consumption changes greatly. It cannot be reliably applied in a variety of industrial environments. The present application aims to provide a constant-current input digital quantity input acquisition circuit, which has simple system wiring, high stability, input protection and constant-current capability, and can be applied to digital quantity acquisition modules in complex industrial field environments. It reduces the false sampling and misjudgment of digital quantity input modules caused by electromagnetic interference, radio frequency interference and electrostatic interference from the surrounding environment. It improves the fault tolerance of the digital quantity input module, adapts to diversified digital quantity input sources, and is more likely to meet the relevant standard regulations.

[0006] The present application is realized by the following technical scheme:

[0007] A constant-current input digital quantity input acquisition circuit, comprising:

[0008] The constant current circuit is used for providing a stable current loop for the digital input signal, and a negative feedback circuit formed by a reference device and an adjusting device is combined to stabilize the current loop at a preset value; and the stabilized digital input signal is transmitted to the digital input indication circuit and the logic output circuit.

[0009] The digital input indication circuit is used for converting the high and low level states into the on and off states of the indicator light, displaying the stabilized digital input signal as the indicator light signal visible on the industrial field, so as to realize the intuitive display of the signal and facilitate the monitoring and control of the equipment state by the staff.

[0010] The logic output circuit is used for outputting the stabilized digital input signal.

[0011] Further, the digital input acquisition circuit further comprises an input protection circuit connected before the constant current circuit.

[0012] The input protection circuit is used for filtering the surge, static pulse and short-circuit large current generated by the digital input signal of the previous stage source; when the digital input signal appears the short-circuit large current, the return path of the digital input signal is cut off; when the digital input signal appears the surge and static pulse, the surge and static pulse are clamped to a low voltage.

[0013] Further, the constant current circuit comprises a resistor R2, a triode Q1, a voltage stabilizing source TL431, a resistor R7, a resistor R6 and a resistor R10.

[0014] One end of the resistor R2 is connected to the digital input signal, and the other end of the resistor R2 is connected to the collector of the triode Q1; one end of the triode Q1 is connected to one end of the resistor R7, one end of the triode Q1 is connected to one end of the resistor R10, the other end of the resistor R10 is connected to the ground, and the emitter of the triode Q1 is also connected to the reference electrode of the voltage stabilizing source TL431; the other end of the resistor R7 is connected to the cathode of the voltage stabilizing source TL431, the other end of the resistor R7 is also connected to one end of the resistor R6, the other end of the resistor R6 is connected to the power supply VDD, and the anode of the voltage stabilizing source TL431 is connected to the ground.

[0015] Further, the constant current circuit combines the triode Q1 and the voltage stabilizing source TL431 to form a negative feedback circuit, and the current of the digital input signal flows through the resistor R2 (as a load resistor), the triode Q1 and the resistor R10 (as a feedback resistor) to the ground, thereby constituting a current return circuit of the digital input signal.

[0016] When the current of the digital input signal is within the preset value, the voltage of the resistor R10 is stable, the output voltage of the voltage stabilizer TL431 is stable, the base of the transistor Q1 is stable, the collector current of the transistor Q1 is stable through the negative feedback circuit, and the collector current of the transistor Q1 in the input circuit and the emitter current of the transistor Q1 are constant;

[0017] When the current of the digital input signal is higher than the preset value, the collector current of the transistor Q1 in the return circuit rises, the voltage of the resistor R10 rises, the output voltage of the voltage stabilizer TL431 drops, the base current of the transistor Q1 drops, and the collector current of the transistor Q1 in the input circuit and the emitter current of the transistor Q1 drop;

[0018] When the collector current of the transistor Q1 in the input circuit rises and is adjusted through the negative feedback circuit, the collector current of the transistor Q1 drops; when the collector current of the transistor Q1 in the input circuit drops and is adjusted through the negative feedback circuit, the collector current of the transistor Q1 rises.

[0019] Further, the digital input indication circuit comprises a resistor R5, a resistor R9, a transistor Q3, a light emitting diode D2, a resistor R3 and a resistor R12.

[0020] One end of the resistor R5 is connected to the collector of the transistor Q1, the other end of the resistor R5 is connected to the base of the transistor Q3, and the other end of the resistor R5 is also connected to one end of the resistor R9, and the other end of the resistor R9 is grounded; the collector of the transistor Q3 is connected to the cathode of the light emitting diode D2, the emitter of the transistor Q3 is connected to one end of the resistor R12, and the other end of the resistor R12 is grounded; one end of the anode of the light emitting diode D2 is connected to one end of the resistor R3, and the other end of the resistor R3 is connected to a 24V power supply.

[0021] Further, the working process of the digital input indication circuit is as follows:

[0022] When there is a digital input signal input, the collector and the emitter of the transistor Q3 are both turned on, and the light emitting diode D2 is driven to light up;

[0023] When there is no digital input signal input, the collector and the emitter of the transistor Q3 are both turned off, and the light emitting diode D2 is extinguished.

[0024] Further, the logic output circuit comprises a resistor R4, a resistor R8, a transistor Q2, a resistor R1 and a resistor R11.

[0025] One end of the resistance R4 is connected to the collector of the transistor Q1, the other end of the resistance R4 is also connected to one end of the resistance R8, the other end of the resistance R8 is connected to the ground; the other end of the resistance R4 is also connected to the base of the transistor Q2, the collector of the transistor Q2 is connected to one end of the resistance R1, the other end of the resistance R1 is used as an output terminal; the emitter of the transistor Q2 is connected to one end of the resistance R11, the other end of the resistance R11 is connected to the ground.

[0026] Further, the execution process of the logic output circuit is as follows:

[0027] When the digital input signal is input, the collector and the emitter of the transistor Q2 are both turned on, and the output terminal outputs the signal through the resistance R1;

[0028] When the digital input signal is not input, the collector and the emitter of the transistor Q2 are both turned off, and the output terminal keeps the original signal.

[0029] Further, the input protection circuit comprises a self-resetting fuse F1 and a transient voltage suppressor D3.

[0030] One end of the self-resetting fuse F1 is connected to the digital input signal, the other end of the self-resetting fuse F1 is connected to one end of the transient voltage suppressor D3, and the other end of the transient voltage suppressor D3 is connected to the ground.

[0031] In the second aspect, the application further provides a multi-channel constant-current input digital input acquisition circuit, comprising four-channel optocoupler U2 and four groups of the constant-current input digital input acquisition circuit.

[0032] The output terminals of the four groups of the constant-current input digital input acquisition circuit are connected to pins 2, 4, 6 and 8 of the four-channel optocoupler U2, respectively, as the trigger signals of the four-channel optocoupler U2.

[0033] Pins 10, 12, 14 and 16 of the four-channel optocoupler U2 are connected to the system-side power supply, and pins 9, 11, 13 and 15 of the four-channel optocoupler U2 are used as the system-side output.

[0034] When the four groups of the constant-current input digital input acquisition circuit all acquire the power supply VDD signal, the system-side output outputs the system-side power supply high-level signal.

[0035] Compared with the prior art, the application has the following advantages and beneficial effects:

[0036] The application discloses a constant-current input digital quantity input acquisition circuit, and belongs to the technical field of digital quantity input acquisition. BRIEF DESCRIPTION OF DRAWINGS

[0037] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the embodiments of the application. In the drawings:

[0038] Figure 1 A system block diagram of the constant-current input digital quantity input acquisition circuit is shown in the figure.

[0039] Figure 2 A main circuit principle diagram of the constant-current circuit is shown in the figure.

[0040] Figure 3 A constant-current input digital quantity input acquisition circuit without input protection circuit is shown in the figure.

[0041] Figure 4 A constant-current input digital quantity input acquisition circuit with a single channel and 24V constant current input is shown in the figure.

[0042] Figure 5 A constant-current input digital quantity input acquisition circuit with four channels and 24V constant current input is shown in the figure. DETAILED DESCRIPTION

[0043] Hereinafter, the term "include" or "may include" used in various embodiments of the present application indicates the existence of the invented function, operation, or element, and does not limit one or more functions, operations, or elements from being added. In addition, as used in various embodiments of the present application, the terms "include", "have", and their conjugates merely indicate the presence of specific features, numbers, steps, operations, elements, components, or combinations thereof, and should not be construed as excluding the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof in advance.

[0044] In various embodiments of the present application, the expression "or" or "at least one of A or / and B" includes any combination of the listed terms or all combinations thereof. For example, the expression "A or B" or "at least one of A or / and B" can include A, can include B, or can include both A and B.

[0045] The expressions used in the various embodiments of the present application, such as "first", "second", etc., can modify various constituent elements in the various embodiments, but can not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only for the purpose of distinguishing one element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of the various embodiments of the present application, a first element can be referred to as a second element, and likewise, a second element can be referred to as a first element.

[0046] It should be noted that if a description connects one constituent element to another constituent element, the first constituent element can be directly connected to the second constituent element, and a third constituent element can be "connected" between the first constituent element and the second constituent element. Conversely, when one constituent element is "directly connected" to another constituent element, it can be understood that there is no third constituent element between the first constituent element and the second constituent element.

[0047] The terms used in the various embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the various embodiments of the present application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms used herein, including technical terms and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the present application belong. The terms such as those defined in a generally used dictionary will be interpreted as having the same meaning as the context in the relevant technical field and will not be interpreted as having an idealized or overly formal meaning, unless clearly defined in the various embodiments of the present application.

[0048] In order to make the purposes, technical solutions and advantages of the present application clearer, further detailed description of the present application will be made below in combination with embodiments and drawings, the illustrative embodiments of the present application and their descriptions are only for the purpose of explaining the present application, and do not limit the present application.

[0049] The existing digital input acquisition circuit has poor anti-interference ability and cannot well filter abnormal input waveforms. The input current varies with the change of the input source, the input loop current difference is obvious, and the input power consumption changes greatly. It cannot be reliably applied in diverse industrial environments.

[0050] Based on the above technical problems, the present application designs a constant current input digital quantity input acquisition circuit, the system wiring is simple, the stability is high, has input protection and constant current capacity, can be applied to the digital quantity acquisition module in complex industrial field environment; reduces the error sampling and misjudgment of the digital quantity input module caused by electromagnetic interference, radio frequency interference and electrostatic interference and the like from the surrounding environment; improves the fault tolerance of the digital quantity input module, adapts diversified digital quantity input sources, and is more easy to meet the relevant standard regulations.

[0051] Embodiment 1

[0052] As Figure 1 shown, a constant current input digital quantity input acquisition circuit, the embodiment provides a single-channel 24V constant current input digital quantity input acquisition circuit; the digital quantity input acquisition circuit includes an input protection circuit, a constant current circuit, a digital quantity input indication circuit and a logic output circuit;

[0053] The input protection circuit is used for filtering the surge, electrostatic pulse and short-circuit large current generated by the digital quantity input signal of the front-stage source input; when the digital quantity input signal appears short-circuit large current, the return flow path of the digital quantity input signal is cut off; when the digital quantity input signal appears surge and electrostatic pulse, the surge and electrostatic pulse are clamped to a low voltage;

[0054] The constant current circuit is used for providing a stable current loop for the digital quantity input signal passing through the input protection circuit, which is not affected by the load change in the circuit or external interference; the negative feedback circuit formed by the reference device and the adjusting device makes the current of the current loop stable at the preset value; and the stable digital quantity input signal (i.e. the level signal of the effective digital quantity input signal) is transmitted to the digital quantity input indication circuit and the logic output circuit;

[0055] The digital quantity input indication circuit is used for converting the high-low level state into the on-off state of the indicator light, displaying the stable digital quantity input signal as the indicator light signal visible on the industrial field, so as to realize the intuitive display of the signal, and facilitate the staff to monitor and control the equipment state;

[0056] The logic output circuit is used for performing level output conversion, outputting the stable digital quantity input signal, and adapting the input level range of the receiving device.

[0057] The digital quantity input signal is an electric signal from an external sensor or signal source.

[0058] In this embodiment, in order to ensure that the electrical signal from the external sensor or signal source does not cause any damage to the circuit, the application adds an input protection circuit at the input end: (1) can prevent the short-circuiting of the large current of the digital input signal; when the input digital input signal is short-circuited, the input protection circuit can cut off the return path of the signal. (2) The input protection circuit can prevent the large voltage pulse input by the digital input signal; when the input digital input signal appears a pulse such as surge, the input protection circuit can clamp the surge pulse to a lower voltage, thereby protecting the subsequent circuits.

[0059] Specifically, as shown in Figure 4 , the input protection circuit includes a self-resetting fuse F1 and a transient voltage suppressor D3 TVS;

[0060] One end of the self-resetting fuse F1 is connected to the digital input signal, the other end of the self-resetting fuse F1 is connected to one end of the transient voltage suppressor D3 TVS, and the other end of the transient voltage suppressor D3 TVS is grounded.

[0061] The self-resetting fuse F1 can automatically reset and effectively protect the circuit from overcurrent or overvoltage. While the transient voltage suppressor D3 TVS can absorb excessive current when the circuit is subjected to overvoltage impact, thereby protecting the subsequent constant current circuit and other electronic components from damage.

[0062] In this embodiment, the constant current part is the part of the input loop that adjusts the loop current, which is a key part to ensure that the input current always remains at a stable level. The constant current source can effectively eliminate the influence of external environmental factors on the input signal and ensure the accuracy of the acquisition. The constant current circuit is composed of a reference part and an adjustment part to form a negative feedback adjustment circuit, and the main device of the reference part is a voltage regulator TL431, and the main device of the adjustment part is a triode Q1. Figure 2 The main circuit diagram of the constant current circuit of the application.

[0063] Specifically, as shown in Figure 3 and Figure 4 , the constant current circuit includes resistors R2, Q1, TL431, R7, R6 and R10;

[0064] One end of the resistance R2 is connected to the digital input signal, the other end of the resistance R2 is connected to the collector of the transistor Q1, the base of the transistor Q1 is connected to one end of the resistance R7, the emitter of the transistor Q1 is connected to one end of the resistance R10, the other end of the resistance R10 is connected to the ground, the emitter of the transistor Q1 is also connected to the reference electrode of the voltage stabilizer TL431; the other end of the resistance R7 is connected to the cathode of the voltage stabilizer TL431, the other end of the resistance R7 is also connected to one end of the resistance R6, the other end of the resistance R6 is connected to the power supply VDD, and the anode of the voltage stabilizer TL431 is connected to the ground.

[0065] The technical scheme, the constant current circuit of the application utilizes the sensitivity of the base current of the transistor in the linear region of the main loop of the digital input signal and the stability of the voltage of the voltage stabilizer TL431, and combines the transistor Q1 and the voltage stabilizer TL431 to form a negative feedback circuit (i.e. a negative feedback adjustment circuit), the collector current of the transistor depends on the base current of the transistor, and the adjustment of the base current is adjusted by the voltage of the feedback resistance of the emitter of the transistor, so that the current of the input loop is stabilized at a preset value. The current of the digital input signal flows through the transistor Q1 and the resistance R10 (as a feedback resistance) to the ground through the resistance R2 (as a load resistance), and a current return circuit of the digital input signal is formed;

[0066] When the current of the digital input signal is within the preset value, the voltage of the resistance R10 is stable, the output voltage of the voltage stabilizer TL431 is stable, the base Ib of the transistor Q1 is stable, the collector current Ic of the transistor Q1 in the input loop and the emitter current Ie of the transistor Q1 are also constant through the negative feedback circuit;

[0067] When the current of the digital input signal is higher than the preset value, the collector current Ic of the transistor Q1 in the return circuit rises, the voltage of the resistance R10 rises, the output voltage of the voltage stabilizer TL431 drops, the base current Ib of the transistor Q1 drops, and the collector current Ic of the transistor Q1 and the emitter current Ie of the transistor Q1 in the input loop also drop;

[0068] When the collector current Ic of the transistor Q1 in the input loop rises and is adjusted through the negative feedback circuit, the collector current Ic of the transistor Q1 drops; similarly, when the collector current Ic of the transistor Q1 in the input loop drops and is adjusted through the negative feedback circuit, the collector current Ic of the transistor Q1 rises. Such a feedback process can keep the input loop Ic current constant within a balanced value.

[0069] It should be noted that: about constant current circuit front stage is connected with a diode D1 as a means of digital input signal anti-reverse, followed by the key part of the entire circuit, the transistor Q1 and U1 (i.e. voltage regulator TL431) for the main constitute constant current circuit. When the input current rises, the collector current of the transistor Q1 rises, the voltage of R10 resistor rises, at this time under the action of voltage regulator TL431, the base current of the transistor Q1 decreases, the collector current of the transistor Q1 also decreases, in this process, the current of the input loop is adjusted to ensure that the current of the input end always remains at a stable level.

[0070] In this way, the application can get a constant current input while considering the detection of digital signal, the logic output transistor Q2, which collects the input signal under the drive of very small base current, almost does not consume current. When there is input, the collector potential of the transistor Q1 rises, the transistor Q2 immediately receives the change of input signal and outputs the corresponding state. When there is input, the transistor Q3 will also trigger the light-emitting diode D2 to emit light, indicating that there is signal input.

[0071] In the embodiment, the digital input indicating circuit is composed of a light-emitting diode driven by a voltage division bias circuit. As shown in Figure 3 and Figure 4 The digital input indicating circuit includes resistor R5, resistor R9, transistor Q3, light-emitting diode D2, resistor R3 and resistor R12.

[0072] One end of the resistor R5 is connected to the collector of the transistor Q1, the other end of the resistor R5 is connected to the base of the transistor Q3, and the other end of the resistor R5 is also connected to one end of the resistor R9, the other end of the resistor R9 is grounded; the collector of the transistor Q3 is connected to the cathode of the light-emitting diode D2, the emitter of the transistor Q3 is connected to one end of the resistor R12, and the other end of the resistor R12 is grounded; one end of the anode of the light-emitting diode D2 is connected to one end of the resistor R3, and the other end of the resistor R3 is connected to a 24V power supply.

[0073] When there is digital input signal input, the collector and emitter of the transistor Q3 are both turned on to drive the light-emitting diode D2 to light up; when there is no digital input signal input, the collector and emitter of the transistor Q3 are both cut off, and the light-emitting diode D2 is extinguished.

[0074] It should be noted that when the input signal (i.e. digital input signal) is high, the transistor Q3 collects the input signal under the drive of very small base current, triggers the light-emitting diode D2 to emit light constantly, indicating that there is signal input. The user is displayed with the high level signal state.

[0075] In the embodiment, the logic output circuit is also composed of a voltage division bias circuit. As shown inFigure 3 and Figure 4 As shown, the logic output circuit includes resistor R4, resistor R8, transistor Q2, resistor R1, and resistor R11;

[0076] One end of resistor R4 is connected to the collector of transistor Q1, and the other end of resistor R4 is also connected to one end of resistor R8, the other end of which is connected to ground; the other end of resistor R4 is also connected to the base of transistor Q2, the collector of transistor Q2 is connected to one end of resistor R1, and the other end of resistor R1 serves as the output terminal; the emitter of transistor Q2 is connected to one end of resistor R11, and the other end of resistor R11 is grounded.

[0077] In the above technical solution, when a digital input signal is input, both the collector and emitter of transistor Q2 are turned on, and the output terminal outputs a signal through resistor R1; when no digital input signal is input, both the collector and emitter of transistor Q2 are turned off, and the output terminal maintains the original signal.

[0078] It should be noted that in the logic output circuit, we designed transistor Q2 as a sinking follower to adapt to other level input modules. A sinking follower can convert the level output into a signal format suitable for other circuits. This design allows for easy connection and communication with other devices, enabling more functionalities.

[0079] This invention can realize power input type 1 to 3 standard input types, can filter out some range of electromagnetic interference, radio frequency interference and electrostatic interference, and has instantaneous high current protection for loop.

[0080] Example 2

[0081] like Figure 5 As shown, this embodiment provides a digital input acquisition circuit with isolated 4-channel 24V constant current input; the digital input acquisition circuit includes a four-channel optocoupler U2 and 4 sets of constant current input digital input acquisition circuits as described in Embodiment 1;

[0082] The input of the isolated branch consists of four single-channel inputs as described in Example 1, and the output level signal of 3.3V can be directly connected to the signal pin of the microcontroller for detection. This clear isolation design in the industrial field ensures the accuracy and reliability of signal transmission, effectively protecting the transmission of input signals.

[0083] Specifically, such as Figure 5 As shown, the output terminals of the constant current input digital input acquisition circuit of the four sets of Embodiment 1 are connected to pins 2, 4, 6 and 8 of the four-channel optocoupler U2 as trigger signals for the four-channel optocoupler U2; the power supply on the isolated field side is always kept at 24V, and the signal level on the system side is 3.3V.

[0084] The pin 10, the pin 12, the pin 14 and the pin 16 of the four-channel optocoupler U2 are connected with the system-side power supply 3.3V, and the pin 9, the pin 11, the pin 13 and the pin 15 of the four-channel optocoupler U2 are used as the system-side output;

[0085] When the digital quantity acquisition circuit CHA(1-4) acquires the 24V signal, the system-side DIOA(1-4) outputs the 3.3V high level signal.

[0086] The above detailed description further explains the purpose, technical scheme and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A constant current input digital input acquisition circuit, characterized in that, The digital input acquisition circuit includes: A constant current circuit is used to provide a stable current loop for digital input signals. Combined with a reference device and an adjustment device, the negative feedback circuit stabilizes the current in the current loop at a preset value. The stabilized digital input signal is then transmitted to the digital input indicator circuit and the logic output circuit. The digital input indicator circuit is used to convert the high and low level states into the on and off states of the indicator lights, and to display the stabilized digital input signal as an indicator light signal that can be seen in the industrial field. The logic output circuit is used to output the stabilized digital input signal. The digital input acquisition circuit also includes an input protection circuit connected before the constant current circuit. The input protection circuit is used to filter surges, electrostatic pulses, and short-circuit currents generated by the digital input signal from the pre-amplifier source; when a short-circuit current occurs in the digital input signal, the return path of the digital input signal is cut off; when a surge or electrostatic pulse occurs in the digital input signal, the surge or electrostatic pulse is clamped to a low voltage. The constant current circuit includes resistor R2, transistor Q1, voltage regulator TL431, resistor R7, resistor R6 and resistor R10; One end of resistor R2 is connected to a digital input signal, and the other end of resistor R2 is connected to the collector of transistor Q1. The base of transistor Q1 is connected to one end of resistor R7, and the emitter of transistor Q1 is connected to one end of resistor R10. The other end of resistor R10 is grounded, and the emitter of transistor Q1 is also connected to the reference terminal of voltage regulator TL431. The other end of resistor R7 is connected to the cathode of voltage regulator TL431, and the other end of resistor R7 is also connected to one end of resistor R6. The other end of resistor R6 is connected to power supply VDD, and the anode of voltage regulator TL431 is connected to ground. In the constant current circuit, transistor Q1 and voltage regulator TL431 are combined to form a negative feedback circuit. The current of the digital input signal flows through resistor R2, transistor Q1 and resistor R10 to ground, forming a current return circuit for the digital input signal. When the current of the digital input signal is within the preset value, the voltage of resistor R10 is stabilized, which stabilizes the output voltage of the voltage regulator TL431, satisfies the base stability of transistor Q1, and stabilizes the collector current of transistor Q1 through the negative feedback circuit. The collector current value and emitter current value of transistor Q1 in the input circuit are constant. When the current of the digital input signal is higher than the preset value, the collector current of transistor Q1 in the return circuit increases, the voltage of resistor R10 increases, the output voltage of the voltage regulator TL431 decreases, the base current of transistor Q1 decreases, and the collector and emitter current values ​​of transistor Q1 in the input circuit both decrease. When the rise in the collector current of transistor Q1 in the input circuit is adjusted by the negative feedback circuit, the collector current of transistor Q1 decreases; when the decrease in the collector current of transistor Q1 in the input circuit is adjusted by the negative feedback circuit, the collector current of transistor Q1 rises.

2. The constant current input digital input acquisition circuit according to claim 1, characterized in that, The digital input indicator circuit includes resistor R5, resistor R9, transistor Q3, light-emitting diode D2, resistor R3, and resistor R12; One end of resistor R5 is connected to the collector of transistor Q1, and the other end of resistor R5 is connected to the base of transistor Q3. The other end of resistor R5 is also connected to one end of resistor R9, and the other end of resistor R9 is grounded. The collector of transistor Q3 is connected to the cathode of light-emitting diode D2, and the emitter of transistor Q3 is connected to one end of resistor R12, and the other end of resistor R12 is grounded. The anode of light-emitting diode D2 is connected to one end of resistor R3, and the other end of resistor R3 is connected to the power supply.

3. The constant current input digital input acquisition circuit according to claim 2, characterized in that, The operation of the digital input indicator circuit is as follows: When a digital input signal is input, both the collector and emitter of transistor Q3 are turned on, driving LED D2 to light up; when no digital input signal is input, both the collector and emitter of transistor Q3 are turned off, and LED D2 is turned off.

4. The constant current input digital input acquisition circuit according to claim 1, characterized in that, The logic output circuit includes resistor R4, resistor R8, transistor Q2, resistor R1, and resistor R11; One end of resistor R4 is connected to the collector of transistor Q1, and the other end of resistor R4 is also connected to one end of resistor R8, the other end of which is connected to ground; the other end of resistor R4 is also connected to the base of transistor Q2, the collector of transistor Q2 is connected to one end of resistor R1, and the other end of resistor R1 serves as the output terminal; the emitter of transistor Q2 is connected to one end of resistor R11, and the other end of resistor R11 is grounded.

5. The constant current input digital input acquisition circuit according to claim 4, characterized in that, The execution process of the logic output circuit is as follows: When a digital input signal is input, both the collector and emitter of transistor Q2 are turned on, and the output terminal outputs a signal through resistor R1; when no digital input signal is input, both the collector and emitter of transistor Q2 are turned off, and the output terminal retains the original signal.

6. The constant current input digital input acquisition circuit according to claim 1, characterized in that, The input protection circuit includes a resettable fuse F1 and a transient voltage suppressor D3; One end of the self-resetting fuse F1 is connected to a digital input signal, and the other end of the self-resetting fuse F1 is connected to one end of the transient voltage suppressor D3, with the other end of the transient voltage suppressor D3 grounded.

7. A multi-channel constant current input digital input acquisition circuit, characterized in that, Includes a four-channel optocoupler U2 and four sets of constant current input digital input acquisition circuits as described in any one of claims 1 to 6; The output terminals of the four sets of constant current input digital input acquisition circuits as described in any one of claims 1 to 6 are respectively connected to pins 2, 4, 6 and 8 of the four-channel optocoupler U2, as trigger signals for the four-channel optocoupler U2; Pins 10, 12, 14, and 16 of the four-channel optocoupler U2 are all connected to the system-side power supply, while pins 9, 11, 13, and 15 of the four-channel optocoupler U2 serve as system-side outputs. When all four sets of constant current input digital input acquisition circuits as described in any one of claims 1 to 6 acquire the power supply VDD signal, the system side outputs the system side power supply signal.

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