Industrial standard digital quantity input device

Abstract

The invention relates to an industrial standard digital quantity input device. The device comprises an input circuit, a protection and clamping circuit, a current limiting circuit, a power supply circuit, a hysteresis comparator circuit and a micro-control unit, wherein the input circuit is used for transmitting a digital quantity input (DI) signal to the protection and clamping circuit; the protection and clamping circuit is used for clamping the voltage of the input DI signal within a preset safety range; the current limiting circuit is used for limiting the current of the DI signal passing through the protection and clamping circuit below a preset threshold value; the hysteresis comparator circuit is used for comparing the voltage of the DI signal passing through the current limiting circuit with a reference voltage; the micro-control unit is used for receiving the voltage signal transmitted by the hysteresis comparator circuit and sending the voltage signal to the upper-layer controller; the power supply circuit is used for providing preset voltage for the current limiting circuit, the hysteresis comparator circuit and the micro-control unit. The device has a DI input current control function and a DI signal clamping function, and the stability and the anti-interference performance of the circuit can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronics, in particular to an industrial standard digital input device. BACKGROUND

[0002] One of the most common types of industrial Input / Output (I / O) is digital input module (hereinafter referred to as DI module). DI module is widely used in various fields, such as injection molding industry, textile industry and so on. The application of DI module in industry is mainly used for the acquisition of switch signals of industrial field devices, active or passive digital input signals, such as some sensor signals, various valve switches and other industrial field device signal acquisition.

[0003] The standard industrial DI module is an input of 24V or 48V standard voltage signal, according to the industry standard IEC61131-2, and the input current of the module is also strictly limited. However, the current domestic DI module mostly uses isolator to trigger conduction, which cannot accurately control the size of the input current. SUMMARY

[0004] Therefore, it is necessary to provide an industrial standard digital input device which can meet the industry standard and has DI input current control function and DI signal clamping function, so as to increase the stability and anti-interference of the circuit.

[0005] The present application provides an industrial standard digital input device, comprising: an input circuit, a protection and clamping circuit, a current limiting circuit, a power supply circuit, a hysteresis comparator circuit, and a micro control unit, wherein: The input circuit is used to transmit the digital input DI signal to the protection and clamping circuit; The protection and clamping circuit is used to clamp the voltage of the input DI signal within a preset safety range; The current limiting circuit is used to limit the current of the DI signal passing through the protection and clamping circuit to below a preset threshold; The hysteresis comparator circuit is used to compare the voltage of the DI signal passing through the current limiting circuit with a reference voltage and output a corresponding voltage signal; The micro control unit is used to receive the voltage signal transmitted by the hysteresis comparator circuit and send it to the upper controller; The power supply circuit is used to provide a preset voltage to the current limiting circuit, the hysteresis comparator circuit, and the micro control unit.

[0006] In one embodiment, the protection and clamping circuit comprises a pressure sensitive resistor, a filter capacitor, a first diode and a second diode, wherein: One end of the voltage-dependent resistor, one end of the filter capacitor, and the negative electrode of the first diode are connected to an output end of the input circuit, and the output end of the input circuit is used to output a DI signal; the other end of the voltage-dependent resistor, the other end of the filter capacitor, and the positive electrode of the first diode are grounded; the negative electrode of the first diode is also connected to the positive electrode of the second diode, and the negative electrode of the second diode is connected to a first voltage end.

[0007] In one of the embodiments, when the voltage of the DI signal is within a normal range, the voltage-dependent resistor is in a high-resistance state; When the voltage of the DI signal exceeds a trigger voltage of the voltage-dependent resistor, the voltage-dependent resistor is in a low-resistance state, and is used to shunt the current of the DI signal; The voltage of the DI signal output by the protection and clamping circuit is within a voltage range between a ground voltage and a first voltage.

[0008] In one of the embodiments, the current-limiting circuit comprises a transistor Q1, a resistor R1, a resistor R2, and a resistor R8, wherein: One end of the resistor R8 is connected to an output end of the protection and clamping circuit, and is used to receive the DI signal passing through the protection and clamping circuit; the other end of the resistor R8 is connected to the collector of the transistor Q1, the emitter of the transistor Q1 is connected to one end of the resistor R2, the base of the transistor Q1 is connected to one end of the resistor R1, the other end of the resistor R2 is grounded, and the other end of the resistor R1 is connected to the power supply circuit.

[0009] In one of the embodiments, the resistor R8 is used for voltage division processing to reduce the input voltage of the rear-end hysteresis comparator circuit; the resistor R1 and the resistor R2 are used to provide a static working point for the transistor Q1, and the resistor R1 is also used to limit the base current of the transistor Q1, so that the transistor Q1 works in an amplification zone.

[0010] In one of the embodiments, the current-limiting circuit further comprises a single-ended clamping circuit connected to the input end of the hysteresis comparator circuit, and used to control the input voltage of the hysteresis comparator circuit.

[0011] In one of the embodiments, the single-ended clamping circuit comprises a diode D2, the positive electrode of the diode D2 is connected to the input end of the hysteresis comparator circuit, and the negative electrode of the diode D2 is connected to a second voltage end, so that the input end voltage of the hysteresis comparator circuit is lower than the voltage value of the second voltage end.

[0012] In one embodiment, the hysteresis comparator circuit comprises: a comparator chip U1, a resistor R4, a resistor R5, a resistor R6, a resistor R7, and a light-emitting diode D4, wherein: The positive input end of the comparator chip U1 is connected to the power supply circuit through the resistor R4, the negative input end of the comparator chip U1 is connected to the collector of the transistor Q1 through the resistor R3, the negative output end of the comparator chip U1 is grounded, the positive output end of the comparator chip U1 is connected to the power supply circuit, and the signal output end of the comparator chip U1 is connected to the input end of the micro control unit through the resistor R7; one end of the resistor R5 is connected to the positive input end of the comparator chip U1, and the other end of the resistor R5 is connected to the signal output end of the comparator chip U1; one end of the resistor R6 is connected to the signal output end of the comparator chip U1, and the other end of the resistor R6 is connected to the negative electrode of the light-emitting diode D4; and the positive electrode of the light-emitting diode D4 is connected to the power supply circuit.

[0013] In one embodiment, the comparator chip U1 is provided with two threshold voltages, namely an upper threshold voltage and a lower threshold voltage. When the voltage at the negative input end of the comparator chip changes from low to high, and the voltage at the negative input end of the comparator chip is greater than the lower threshold voltage, the signal output end of the comparator chip U1 outputs a low level. When the voltage at the negative input end of the comparator chip changes from high to low, and the voltage at the negative input end of the comparator chip is less than the upper threshold voltage, the signal output end of the comparator chip U1 outputs a high level. When the voltage at the negative input end of the comparator chip is between the upper threshold voltage and the lower threshold voltage, the signal output end of the comparator chip U1 remains unchanged.

[0014] In one embodiment, the light-emitting diode D4 is used to indicate whether the DI signal is input. When there is a DI signal input, the light-emitting diode D4 is in a lit state. When there is no DI signal input, the light-emitting diode D4 is in an extinguished state.

[0015] The above industrial standard digital input device limits the current of the DI input signal through the current limiting circuit, limits the voltage range through the protection and clamping circuit, thereby meeting the IEC industry standard, while reducing the system power consumption. Optionally, the hysteresis comparator circuit is also used to make the input signal of the DI within a certain range, and when the output signal of the hysteresis comparator circuit does not change, the signal to the micro control unit (MCU) downstream does not change, thereby significantly improving the anti-interference and stability of the circuit. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A circuit block diagram of an industry standard digital input device provided in an embodiment of this application; Figure 2 This is a schematic diagram of the protection and clamping circuit in one embodiment of this application; Figure 3 This is a schematic diagram of the structure of a single-ended clamping circuit in one embodiment of this application; Figure 4 This is a schematic diagram of the current limiting circuit and hysteresis comparator circuit in one embodiment of this application. Detailed Implementation

[0018] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0020] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0021] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0022] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0023] When used herein, the singular forms of “a,” “an,” and “ / the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0024] For example, Figure 1 A circuit block diagram of an industry-standard digital input device provided in an embodiment of this application is shown below. Figure 1 As shown, the device may include: an input circuit (DI input), a protection and clamping circuit, a current limiting circuit, a power supply circuit, a hysteresis comparator circuit, and a microcontroller unit (MCU), wherein: the input circuit is used to transmit the digital input DI signal to the protection and clamping circuit; the protection and clamping circuit is used to clamp the voltage of the input DI signal within a preset safety range; the current limiting circuit is used to limit the current of the DI signal passing through the protection and clamping circuit to below a preset threshold; the hysteresis comparator circuit is used to compare the voltage of the DI signal passing through the current limiting circuit with a reference voltage and output the corresponding voltage signal; the microcontroller unit is used to receive the voltage signal transmitted by the hysteresis comparator circuit and send it to the upper-level controller; the power supply circuit is used to provide a preset voltage to the current limiting circuit, the hysteresis comparator circuit, and the microcontroller unit.

[0025] For example, the above-mentioned input circuit is typically a connector device with a DI signal input.

[0026] For example, the protection circuit in the protection and clamping circuit is mainly used for overvoltage protection and filtering of the DI input signal, and the clamping circuit in the protection and clamping circuit is mainly used to clamp the input voltage range within a safe range, thereby effectively protecting the back-end circuit.

[0027] For example, the current limiting circuit is mainly used to limit the range of input current. On the one hand, it is also a protection circuit, and on the other hand, it is to make the circuit comply with the IEC61131-2 standard, which strictly limits the input current of DI.

[0028] For example, the power supply circuit may include modules such as voltage input, voltage conditioning, and overcurrent and overvoltage protection to provide operating voltage to other circuits.

[0029] Exemplarily, the hysteresis comparator circuit utilizes the hysteresis comparator principle, such that when the input voltage is within a certain range, the signal output to the MCU remains unchanged, improving the stability and anti-interference ability of the circuit.

[0030] Among them, the MCU communicates with the upper-layer controller and is used to transmit the collected DI signal to the upper-layer controller.

[0031] Exemplarily, Figure 2 is a schematic structural diagram of the protection and clamping circuit in an embodiment of the present application. As Figure 2 shown, the protection and clamping circuit includes: a varistor, a filter capacitor, a first diode, and a second diode. Among them: one end of the varistor, one end of the filter capacitor, and the negative electrode of the first diode are all connected to the output end of the input circuit, and the output end of the input circuit is used to output the DI signal; the other end of the varistor, the other end of the filter capacitor, and the positive electrode of the first diode are all grounded; the negative electrode of the first diode is also connected to the positive electrode of the second diode, and the negative electrode of the second diode is connected to the first voltage terminal.

[0032] In this embodiment, when the voltage of the DI signal is within the normal range, the varistor is in a high-resistance state; when the voltage of the DI signal exceeds the trigger voltage of the varistor, the varistor is in a low-resistance state and is used to shunt the current of the DI signal; among them, the voltage value of the DI signal output by the protection and clamping circuit is within the voltage range between the ground terminal voltage and the first voltage terminal.

[0033] Specifically, as shown in Figure 2 , when the DI signal is input, it first passes through a varistor R1, which plays a role in overvoltage protection. When the input DI signal is within the normal range, this resistor is equivalent to an open circuit and does not affect the operation of the circuit. When the voltage of the input DI signal suddenly increases and exceeds the trigger voltage of the varistor, its resistance will suddenly decrease, and the large current generated by the overvoltage is discharged through the varistor itself, thereby protecting the subsequent circuit. Among them, C1 is a filter capacitor, and D1 is a pair of series-connected diodes (but belongs to one component, with a small package size). The function of connecting in this way here is to clamp the input DI signal to the voltage value between U1_CLAMP and GND, and prevent the DI signal from exceeding this range: GND < DI_IN < U1_CLAMP. Once it exceeds, protection is triggered and the current is discharged. D2 is a switching diode, and the single-ended clamping circuit formed is connected to the input end of the hysteresis comparator, and its function is to control the input voltage of the comparator and clamp it to a voltage value not exceeding U2_CLAMP to protect the comparator.

[0034] Optionally, the above device may further include: a single-ended clamping circuit, and the single-ended clamping circuit is connected to the input end of the hysteresis comparator circuit and is used to control the input voltage of the hysteresis comparator circuit.

[0035] For example, Figure 3 This is a schematic diagram of a single-ended clamping circuit in one embodiment of this application, as shown below. Figure 3 As shown, the single-ended clamping circuit includes diode D2, which is connected to the input terminal of the hysteresis comparator circuit to control the input voltage of the hysteresis comparator circuit. Specifically, the anode of diode D2 is connected to the input terminal of the hysteresis comparator circuit, and the cathode of diode D2 is connected to the second voltage terminal, so that the input voltage of the hysteresis comparator circuit is lower than the voltage value of the second voltage terminal.

[0036] In this embodiment, the voltage can be clamped to a safe range through two clamping circuits, effectively protecting the components of the back-end circuit.

[0037] For example, Figure 4 This is a schematic diagram of the current limiting circuit and hysteresis comparator circuit in one embodiment of this application, as shown below. Figure 4 As shown, the dashed box on the left represents the current limiting circuit, which includes: transistor Q1, resistors R1 and R2, and resistor R8. One end of resistor R8 is connected to the output of the protection and clamping circuit to receive the DI signal passing through the protection and clamping circuit; the other end of resistor R8 is connected to the collector of transistor Q1; the emitter of transistor Q1 is connected to one end of resistor R2; the base of transistor Q1 is connected to one end of resistor R1; the other end of resistor R2 is grounded; and the other end of resistor R1 is connected to the power supply circuit.

[0038] V1 is the voltage supplied to the current limiting circuit and hysteresis comparator circuit through the power supply circuit, typically 3.3V. V2 can be understood as the DI input signal after passing through the front-end protection and clamping circuit.

[0039] In this embodiment, resistor R8 is used for voltage division to reduce the input voltage of the back-end hysteresis comparator circuit; resistors R1 and R2 are used to provide the static operating point of transistor Q1, and resistor R1 is also used to limit the base current of transistor Q1 so that transistor Q1 operates in the amplification region.

[0040] It should be understood that the function of transistor Q1 is to operate in the amplification region. At this time, the collector current is controlled by the base current and satisfies the relationship Ic≈β⋅Ib (β is an important parameter of the transistor, representing the current amplification factor when operating in the amplification region). Thus, by limiting the base current, the collector current can be limited.

[0041] It should be noted that the collector current is also the current flowing through R8, and is also the input current of the DI signal, thus limiting the current of the DI input signal.

[0042] It should be understood that the current-limiting circuit in this implementation cleverly utilizes the characteristic that the base current controls the collector current when the transistor is operating in the amplification region, achieving three functions: voltage division and reduction, current limiting, and power consumption reduction. This ensures strict compliance with the input current limits in IEC 61132-2, while also reducing system power consumption by limiting the current.

[0043] See also Figure 4 , Figure 4 The dashed box on the right shows the hysteresis comparator circuit, which includes: comparator chip U1, resistors R4, R5, R6, and R7, and LED D4. Specifically: the positive input of comparator chip U1 is connected to the power supply circuit through resistor R4; the negative input of comparator chip U1 is connected to the collector of transistor Q1 through resistor R3; the negative output of comparator chip U1 is grounded; the positive output of comparator chip U1 is connected to the power supply circuit; and the signal output of comparator chip U1 is connected to the input of the microcontroller unit through resistor R7. One end of resistor R5 is connected to the positive input of comparator chip U1, and the other end of resistor R5 is connected to the signal output of comparator chip U1. One end of resistor R6 is connected to the signal output of comparator chip U1, and the other end of resistor R6 is connected to the negative terminal of LED D4; the positive terminal of LED D4 is connected to the power supply circuit.

[0044] Optionally, comparator chip U1 has two threshold voltages, namely an upper threshold voltage and a lower threshold voltage. When the voltage at the negative input terminal of the comparator chip changes from low to high, and the voltage at the negative input terminal of the comparator chip is greater than the lower threshold voltage, the signal output terminal of comparator chip U1 outputs a low level. When the voltage at the negative input terminal of the comparator chip changes from high to low, and the voltage at the negative input terminal of the comparator chip is less than the upper threshold voltage, the signal output terminal of comparator chip U1 outputs a high level. When the voltage at the negative input terminal of the comparator chip is between the upper threshold voltage and the lower threshold voltage, the signal output terminal of comparator chip U1 remains unchanged.

[0045] Combination Figure 4As shown, resistors R4 and R5 are used to set the threshold voltage of the hysteresis comparator. Based on the virtual short and virtual open principle of U1, the voltage formula at the + terminal of U1 can be derived as follows. The voltage at the + terminal of U1 is also the reference voltage of the comparator, i.e., the threshold voltage. Due to its special feedback principle, the hysteresis comparator has two threshold voltages (let's assume they are Vt), namely the upper threshold voltage (Vut) and the lower threshold voltage (Vlt). The voltage at the - terminal of U1 is compared with the threshold voltage each time. If the voltage at the - terminal of U1 changes from low to high and is higher than the lower threshold voltage Vlt at the + terminal, then U1 outputs a low level. If the voltage at the - terminal of U1 changes from high to low and is lower than the upper threshold voltage Vut at the + terminal, then U1 outputs a high level. When the voltage at the - terminal of U1 is within the upper and lower thresholds, the voltage Vo output by the comparator remains unchanged.

[0046] Among them, the threshold voltage V t The formula is as follows: Among them, V t It is the threshold voltage, V ref This is the power supply voltage; in this circuit, it is 3.3V. Vo is the output voltage of the comparator.

[0047] For example, the upper threshold voltage V ut The formula is as follows: Among them, V oH V is the high-side voltage output of the comparator. ref This is the power supply voltage; in this circuit, it is 3.3V.

[0048] For example, the formula for the lower threshold voltage Vlt is as follows: Among them, V oL This is the low-side voltage output of the comparator; in this circuit, it is 0V.

[0049] Optionally, LED D4 is used to indicate whether a DI signal is input; when a DI signal is input, LED D4 is lit; when no DI signal is input, LED D4 is off.

[0050] In this embodiment, the current of the DI input signal is limited by a current-limiting circuit, and the voltage range is limited by a protection and clamping circuit, thereby meeting IEC industry standards and reducing system power consumption. Optionally, a hysteresis comparator circuit is also used to ensure that within a certain range, when the output signal of the hysteresis comparator circuit remains unchanged, the signal downstream to the microcontroller unit remains unchanged, thereby significantly improving the circuit's anti-interference and stability.

[0051] This embodiment effectively limits not only the input voltage range but also the input current, thereby protecting the circuit and reducing power consumption. Furthermore, the voltage holding range is expanded using a hysteresis comparator, ensuring the detected voltage remains constant within a certain range, effectively improving the system's anti-interference and stability.

[0052] This embodiment utilizes a diode pair to set the voltage range of the DI signal input, clamping the input voltage within a fixed range and effectively protecting the circuit. Simultaneously, a clamping diode is also added to the comparator input terminal to effectively control the voltage input to the comparator and protect the comparator.

[0053] This embodiment cleverly sets the transistor to operate in the amplification region, so that the base current of the transistor can effectively control the collector current of the transistor, that is, the input current of the DI signal. On the one hand, it makes it conform to the input current range specified by the IEC standard, and on the other hand, it controls the system power consumption by controlling the current.

[0054] In this embodiment, a common comparator chip is combined with peripheral circuitry to convert it into a hysteresis comparator circuit. The upper and lower threshold voltages of the hysteresis comparator define a voltage range. When the input voltage is within this range, the output voltage of the comparator remains unchanged, that is, the voltage to the MCU remains unchanged. This greatly improves the anti-interference capability and avoids the defect of traditional isolation devices that only have one threshold voltage.

[0055] The device in this embodiment has a simple structure, concise circuitry, and low cost. It possesses sufficient and comprehensive protection and safeguards, and strictly complies with IEC61131-2's limitations on the voltage and current of DI signals, thus avoiding the current limitation deficiency that most domestic DI devices lack.

[0056] This embodiment also cleverly adds a light-emitting diode (LED) to indicate the input DI signal. When a DI signal is input, the LED lights up, and when no DI signal is input, the LED turns off.

[0057] It should be understood that the circuit in this embodiment only takes the DI signal input of one channel as an example. Within the system's carrying capacity (voltage load capacity and MCU processing capacity), the number of channels can be expanded to a limited extent. Moreover, each channel is isolated from each other, does not interfere with each other, and operates independently.

[0058] In the description of this specification, references to terms such as "some embodiments," "other embodiments," 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 this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. An industrial standard digital input device, characterized in that, include: The circuitry includes input circuitry, protection and clamping circuitry, current limiting circuitry, power supply circuitry, hysteresis comparator circuitry, and a microcontroller unit, among which: The input circuit is used to transmit the digital input (DI) signal to the protection and clamping circuit. The protection and clamping circuit is used to clamp the voltage of the input DI signal within a preset safety range. The current limiting circuit is used to limit the current of the DI signal passing through the protection and clamping circuit to below a preset threshold. The hysteresis comparator circuit is used to compare the voltage of the DI signal after passing through the current limiting circuit with the reference voltage and output the corresponding voltage signal. The microcontroller unit is used to receive the voltage signal transmitted by the hysteresis comparator circuit and send it to the upper-level controller. The power supply circuit is used to provide a preset voltage to the current limiting circuit, the hysteresis comparator circuit, and the microcontroller unit.

2. The industrial standard digital input device according to claim 1, characterized in that, The protection and clamping circuit includes: a varistor, a filter capacitor, a first diode, and a second diode, wherein: One end of the varistor, one end of the filter capacitor, and the cathode of the first diode are all connected to the output terminal of the input circuit, which is used to output the DI signal; the other end of the varistor, the other end of the filter capacitor, and the anode of the first diode are all grounded; the cathode of the first diode is also connected to the anode of the second diode, and the cathode of the second diode is connected to the first voltage terminal.

3. The industrial standard digital input device according to claim 2, characterized in that, When the voltage of the DI signal is within the normal range, the varistor is in a high resistance state; When the voltage of the DI signal exceeds the trigger voltage of the varistor, the varistor is in a low resistance state to shunt the current of the DI signal. The voltage value of the DI signal output by the protection and clamping circuit is within the voltage range between the ground terminal voltage and the first voltage terminal.

4. The industrial standard digital input device according to claim 1, characterized in that, The current limiting circuit includes: transistor Q1, resistor R1, resistor R2, and resistor R8, wherein: One end of the resistor R8 is connected to the output terminal of the protection and clamping circuit to receive the DI signal passing through the protection and clamping circuit; the other end of the resistor R8 is connected to the collector of the transistor Q1, the emitter of the transistor Q1 is connected to one end of the resistor R2, the base of the transistor Q1 is connected to one end of the resistor R1, the other end of the resistor R2 is grounded, and the other end of the resistor R1 is connected to the power supply circuit.

5. The industrial standard digital input device according to claim 4, characterized in that, The resistor R8 is used for voltage division to reduce the input voltage of the downstream hysteresis comparator circuit; the resistors R1 and R2 are used to provide the static operating point of the transistor Q1, and the resistor R1 is also used to limit the base current of the transistor Q1 so that the transistor Q1 operates in the amplification region.

6. The industrial standard digital input device according to any one of claims 1 to 5, characterized in that, Also includes: A single-ended clamping circuit is connected to the input terminal of the hysteresis comparator circuit and is used to control the input voltage of the hysteresis comparator circuit.

7. The industrial standard digital input device according to claim 6, characterized in that, The single-ended clamping circuit includes a diode D2, the anode of which is connected to the input terminal of the hysteresis comparator circuit, and the cathode of which is connected to a second voltage terminal, so that the input voltage of the hysteresis comparator circuit is lower than the voltage value of the second voltage terminal.

8. The industrial standard digital input device according to claim 4, characterized in that, The hysteresis comparator circuit includes: comparator chip U1, resistors R4, R5, R6, and R7, and light-emitting diode D4, wherein: The positive input terminal of comparator chip U1 is connected to the power supply circuit through resistor R4, the negative input terminal of comparator chip U1 is connected to the collector of transistor Q1 through resistor R3, the negative output terminal of comparator chip U1 is grounded, the positive output terminal of comparator chip U1 is connected to the power supply circuit, and the signal output terminal of comparator chip U1 is connected to the input terminal of microcontroller unit through resistor R7; one end of resistor R5 is connected to the positive input terminal of comparator chip U1, and the other end of resistor R5 is connected to the signal output terminal of comparator chip U1; one end of resistor R6 is connected to the signal output terminal of comparator chip U1, and the other end of resistor R6 is connected to the negative terminal of light-emitting diode D4; the positive terminal of light-emitting diode D4 is connected to the power supply circuit.

9. The industrial standard digital input device according to claim 8, characterized in that, The comparator chip U1 has two threshold voltages, namely the upper threshold voltage and the lower threshold voltage; When the voltage at the negative input terminal of the comparator chip changes from low to high, and the voltage at the negative input terminal of the comparator chip is greater than the lower threshold voltage, the signal output terminal of the comparator chip U1 outputs a low level. When the voltage at the negative input terminal of the comparator chip changes from high to low, and the voltage at the negative input terminal of the comparator chip is less than the upper threshold voltage, the signal output terminal of the comparator chip U1 outputs a high level. When the voltage at the negative input terminal of the comparator chip is between the upper threshold voltage and the lower threshold voltage, the signal output terminal of the comparator chip U1 remains unchanged.

10. The industrial standard digital input device according to claim 8, characterized in that, The light-emitting diode D4 is used to indicate whether a DI signal is input; When a DI signal is input, the light-emitting diode D4 is lit. When there is no DI signal input, the light-emitting diode D4 is in the off state.

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