Analog signal preprocessing system of power converged terminal

Abstract

The utility model relates to signal preprocessing technical field provides an analog signal preprocessing system of power fusion terminal, including transformer, install voltage transformer on transformer side, the signal preprocessing unit that carries out preprocessing to voltage transformer output electric signal, the analog converter of signal preprocessing unit acquisition, its characterized in that, the signal preprocessing unit includes: switching module, operational amplifier module, voltage division module, DC bias module, suppression module and surge protection module, the utility model overcomes the deficiency of prior art, dynamic path switching, when input voltage is lower than threshold value, triode Q1 conduction activation operational amplifier module U1, linear amplification to attenuation signal, and gain is set by resistance R3 and resistance R4, when input voltage is over limit, triode Q1 cut-off, switch to voltage division module, and voltage division ratio passes through variable resistance POT2 dynamic adaptation overvoltage scene, and diode D1 limiting amplitude output, avoid signal saturation or distortion.

Description

Technical Field

[0001] This utility model relates to the field of signal preprocessing technology, specifically to an analog signal preprocessing system for a power fusion terminal. Background Technology

[0002] In the field of power system monitoring, analog signal preprocessing is a crucial step in ensuring the accurate acquisition of transformer operating parameters (such as voltage and current). Traditional preprocessing systems face three core problems: Insufficient dynamic range: Power signals fluctuate greatly (such as weak signals under normal operating conditions and kilovolt surges during lightning strikes / faults), and a single processing path can easily lead to small signal distortion or overvoltage saturation.

[0003] Severe noise interference: Common-mode interference, high-frequency harmonics and electromagnetic noise exist in the power grid, which directly affect the signal-to-noise ratio and ADC sampling accuracy.

[0004] Weak transient protection: Conventional RC filters or Zener diodes have slow response speeds and are unable to effectively suppress microsecond-level surges, which can easily damage downstream circuits.

[0005] Existing technologies typically employ independent voltage divider or amplifier circuits to process signals of different amplitudes, but lack dynamic switching mechanisms; noise suppression largely relies on simple RC filters, which have limited effectiveness against common-mode interference; surge protection depends on varistors or gas discharge tubes, resulting in large response delays and high residual voltages. These shortcomings lead to signal distortion, ADC bit errors, and reduced system reliability.

[0006] In response to the aforementioned problems, we propose an analog signal preprocessing system for a power fusion terminal. Utility Model Content

[0007] To address the shortcomings of existing technologies, this utility model provides an analog signal preprocessing system for a power fusion terminal. This system is mainly used to preprocess the transformer operating parameter electrical signals collected by the voltage transformer, providing a stable and reliable signal for the analog-to-digital converter, thereby solving the aforementioned problems in the existing technologies.

[0008] To achieve the above objectives, this utility model provides the following technical solution: An analog signal preprocessing system for a power convergence terminal includes a transformer, a voltage transformer installed on the transformer side, a signal preprocessing unit for preprocessing the electrical signal output from the voltage transformer, and an analog-to-digital converter for acquiring the signal preprocessing unit. The signal preprocessing unit includes: The switching module dynamically switches the signal path by turning on / off the transistor Q1. When Q1 is on, it triggers the operational amplifier module to process the attenuated signal. When Q1 is off, it activates the voltage divider module to process the overvoltage signal. The normally closed contact S3 is controlled by relay T1 to open and close. The operational amplifier module, through operational amplifier U1 forming an inverting amplifier, uses resistors R3 and R4 to set the gain, linearly amplifying the attenuated signal. The voltage divider module consists of a voltage divider network composed of resistor R2 and variable resistor POT2, which is suitable for input overvoltage scenarios. The output is limited by diode D1 and then sent to subsequent circuits. The voltage division ratio can be adjusted by POT2. The DC bias module uses transistor Q2, resistors R5 and R6 to form an emitter follower, providing a stable DC bias voltage for the signal. Capacitor C1 filters out high-frequency noise. The suppression module uses a current transformer L1 and capacitors C2 and C3 to form an LC filter network to suppress common-mode interference and high-frequency noise. The surge protection module consists of a fast-response circuit composed of trigger S2 and diode D3. When a transient high voltage is detected, the relay is triggered to cut off the signal path, and resistor R8 absorbs the residual energy.

[0009] Furthermore, the switching module includes a resistor R1, a variable resistor POT1, a transistor Q1, a normally closed contact S3, a relay T1, and a trigger S1. One end of the resistor R1 is electrically connected to the fixed terminal pin 3 of the variable resistor POT1, the output terminal pin 1 of the voltage transformer, one end of the normally closed contact S3, and the normally open contact pin 1 of the trigger S1. The other end of the resistor R1 is electrically connected to the collector terminal of the transistor Q1. The base terminal of the transistor Q1 is electrically connected to the adjustment terminal pin 1 and the fixed terminal pin 2 of the variable resistor POT1. The emitter terminal of the transistor Q1 is connected to the positive terminal pin 4 of the relay coil of the trigger S1. The negative terminal pin 3 of the relay coil of the trigger S1 is connected to ground GND. The normally open contact pin 2 of the trigger S1 is connected to one end of the relay T1. The relay T1 is connected to ground GND.

[0010] Furthermore, the trigger S1 consists of a normally open contact and a relay. The normally open contact pins 1 and 2 of the trigger S1 are the two ends of the normally open contact, and the positive terminal pin 4 and negative terminal pin 3 of the relay coil of the trigger S1 are the positive and negative terminals of the relay. When the relay T1 is energized, the normally closed contact S3 is opened.

[0011] Furthermore, the operational amplifier module includes an operational amplifier U1, resistors R4 and R3, and diode D2. The inverting input pin 2 of the operational amplifier U1 is connected to one end of resistor R4 and the other end of normally closed contact S3. The non-inverting input pin 3 of the operational amplifier U1 is connected to one end of resistor R3. The other end of resistor R3 is connected to ground GND. The output pin 1 of the operational amplifier U1 is connected to the other end of resistor R4 and the positive terminal of diode D2.

[0012] Furthermore, the voltage divider module includes a resistor R2, a variable resistor POT2, and a diode D1. One end of the resistor R2 is connected to the normally open contact pin 2 of the trigger S1, and the other end of the resistor R2 is connected to the adjustment pin 1 and the fixed pin 2 of the variable resistor POT2. The fixed pin 3 of the variable resistor POT2 is connected to the positive terminal of the diode D1, and the negative terminal of the diode D1 is connected to the negative terminal of the diode D2.

[0013] Furthermore, the DC bias module includes a capacitor C1, a resistor R7, a transistor Q2, a resistor R5, and a resistor R6. One end of each resistor R5 is connected to the input power supply +12V and one end of each resistor R6. The other end of each resistor R6 is connected to the collector terminal of the transistor Q2. The base terminal of each transistor Q2 is connected to the other end of each resistor R5 and the negative terminal of the diode D2. The emitter terminal of each transistor Q2 is connected to one end of each capacitor C1 and one end of each resistor R7. The other end of each resistor R7 is connected to the other end of each capacitor C1 and the ground line GND.

[0014] Furthermore, the suppression module includes capacitor C2, current transformer L1, and capacitor C3. One end of capacitor C2 is connected to the primary coil pin 1 of current transformer L1 and the other end of resistor R6. The other end of capacitor C2 is connected to the primary coil pin 2 of current transformer L1 and the other end of resistor R7. The secondary coil pin 3 of current transformer L1 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to the secondary coil pin 4 of current transformer L1.

[0015] Furthermore, the surge protection module includes a trigger S2, a diode D3, and a resistor R8. The normally closed contact pin 1 and the positive terminal pin 3 of the relay coil of the trigger S2 are connected to one end of the capacitor C3. The normally closed contact pin 2 of the trigger S2 is connected to the input pin 1 of the analog-to-digital converter. The negative terminal pin 4 of the relay coil of the trigger S2 is connected to the negative terminal of the diode D3. The positive terminal of the diode D3 is connected to one end of the resistor R8. The other end of the resistor R8 is connected to the secondary coil pin 4 of the current transformer L1. The grounding pin 2 of the analog-to-digital converter is connected to the ground wire GND.

[0016] Furthermore, the trigger S2 is composed of a normally closed contact and a relay. The normally closed contact pins 1 and 2 of the trigger S2 are the two ends of the normally closed contact, and the positive terminal pin 3 and the negative terminal pin 4 of the relay coil are the two ends of the relay.

[0017] This invention provides an analog signal preprocessing system for a power fusion terminal. It offers the following advantages: dynamic path switching (solving the dynamic range problem); when the input voltage is below a threshold, transistor Q1 is activated, turning on the operational amplifier module U1 (inverting amplifier) ​​to linearly amplify the attenuated signal; the gain is set by resistors R3 and R4. When the input voltage exceeds the limit, transistor Q1 is cut off, switching to the voltage divider module (R2+POT2 voltage divider network). The voltage division ratio is dynamically adapted to the overvoltage scenario through the variable resistor POT2. Diode D1 limits the output to avoid signal saturation or distortion, and adaptively covers a wide dynamic range. Comprehensive noise suppression (improving signal-to-noise ratio): The common-mode choke characteristic of L1 is used to suppress common-mode interference from the power grid. Combined with capacitors C2 and C3, a filter is formed to efficiently filter out high-frequency noise (such as switching noise). Surge protection (ensuring circuit safety): When a transient high voltage is detected, the relay coil of normally closed S2 is triggered, the normally closed contact instantly disconnects the signal path, and at the same time, diode D3 conducts to discharge energy, and resistor R8 absorbs residual current. The signal baseline is stabilized (DC drift is eliminated). Transistor Q2 forms an emitter follower. A stable bias voltage is injected through the voltage divider of resistors R5 and R6. Capacitor C1 filters out high-frequency noise from the bias circuit, ensuring zero signal baseline drift and avoiding quantization errors caused by DC offset in ADC sampling. Attached Figure Description

[0018] Figure 1 This is a topological diagram of the present invention.

[0019] Figure 2 This is a circuit diagram of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0021] See attached document Figures 1-2As shown, an analog signal preprocessing system for a power convergence terminal includes a transformer, a voltage transformer installed on the transformer side (for collecting transformer operating parameters), a signal preprocessing unit for preprocessing the electrical signal output from the voltage transformer, and an analog-to-digital converter for acquiring the signal from the signal preprocessing unit. The signal preprocessing unit includes: The switching module dynamically switches the signal path by turning on / off the transistor Q1. When Q1 is on, it triggers the operational amplifier module to process the attenuated signal. When Q1 is off, it activates the voltage divider module to process the overvoltage signal. The normally closed contact S3 is controlled by relay T1 to open and close. The operational amplifier module, through operational amplifier U1 forming an inverting amplifier, uses resistors R3 and R4 to set the gain, linearly amplifying the attenuated signal. The voltage divider module consists of a voltage divider network composed of resistor R2 and variable resistor POT2, which is suitable for input overvoltage scenarios. The output is limited by diode D1 and then sent to subsequent circuits. The voltage division ratio can be adjusted by POT2. The DC bias module, through transistor Q2 and resistors R5 and R6, forms an emitter follower to provide a stable DC bias voltage for signal superposition. Capacitor C1 filters out high-frequency noise and ensures signal baseline stability. The suppression module uses a current transformer L1 and capacitors C2 and C3 to form an LC filter network, which suppresses common-mode interference and high-frequency noise, thereby improving the signal-to-noise ratio. The surge protection module consists of a fast-response circuit composed of trigger S2 and diode D3. When a transient high voltage is detected, the relay is triggered to cut off the signal path, and resistor R8 absorbs the residual energy.

[0022] The switching module includes a resistor R1, a variable resistor POT1, a transistor Q1, a normally closed contact S3, a relay T1, and a trigger S1. One end of the resistor R1 is electrically connected to pin 3 of the variable resistor POT1, pin 1 of the voltage transformer, one end of the normally closed contact S3, and pin 1 of the trigger S1. The other end of the resistor R1 is electrically connected to the collector of the transistor Q1. The base of the transistor Q1 is electrically connected to pins 1 and 2 of the variable resistor POT1. The emitter of the transistor Q1 is connected to pin 4 of the trigger S1. Pin 3 of the trigger S1 is connected to ground GND. Pin 2 of the trigger S1 is connected to one end of the relay T1. The relay T1 is connected to ground GND.

[0023] The trigger S1 consists of a normally open contact and a relay. Pins 1 and 2 of the trigger S1 are the two ends of the normally closed contact, and pins 3 and 4 of the trigger S1 are the positive and negative ends of the relay. When the relay T1 is energized, the normally closed contact S3 is opened.

[0024] The operational amplifier module includes an operational amplifier U1, a resistor R4, a resistor R3, and a diode D2. The pin 2 of the operational amplifier U1 is connected to one end of the resistor R4 and the other end of the normally closed contact S3. The pin 3 of the operational amplifier U1 is connected to one end of the resistor R3, and the other end of the resistor R3 is connected to the ground GND. The pin 1 of the operational amplifier U1 is connected to the other end of the resistor R4 and the positive terminal of the diode D2.

[0025] Specifically, operational amplifier U1 adopts an inverting amplifier topology, and its gain is precisely set by resistors R3 (grounding resistor) and R4 (feedback resistor); diode D2 achieves output limiting (e.g., ±5V) to prevent ADC input overload; The voltage divider module includes a resistor R2, a variable resistor POT2, and a diode D1. One end of the resistor R2 is connected to pin 2 of the trigger S1, and the other end of the resistor R2 is connected to pins 1 and 2 of the variable resistor POT2. Pin 3 of the variable resistor POT2 is connected to the positive terminal of the diode D1, and the negative terminal of the diode D1 is connected to the negative terminal of the diode D2.

[0026] Specifically, resistor R2 and variable resistor POT2 form an adjustable voltage divider network with a voltage division ratio ranging from 1:10 to 1:100, and diode D1 performs secondary limiting (usually a 6.2V Zener diode is selected).

[0027] The DC bias module includes a capacitor C1, a resistor R7, a transistor Q2, a resistor R5, and a resistor R6. One end of each resistor R5 is connected to the input power supply +12V and one end of each resistor R6. The other end of each resistor R6 is connected to the collector terminal of the transistor Q2. The base terminal of each transistor Q2 is connected to the other end of each resistor R5 and the negative terminal of the diode D2. The emitter terminal of each transistor Q2 is connected to one end of each capacitor C1 and one end of each resistor R7. The other end of each resistor R7 is connected to the other end of each capacitor C1 and the ground line GND.

[0028] Specifically, the base voltage is set by the voltage divider between resistors R5 and R6; The suppression module includes capacitor C2, current transformer L1, and capacitor C3. One end of capacitor C2 is connected to pin 1 of current transformer L1 and the other end of resistor R6. The other end of capacitor C2 is connected to pin 2 of current transformer L1 and the other end of resistor R7. Pin 3 of current transformer L1 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to pin 4 of current transformer L1.

[0029] Specifically, current transformer L1 is a common-mode choke; capacitors C2 and C3 form a symmetrical filter network; The surge protection module includes a trigger S2, a diode D3, and a resistor R8. Pins 1 and 3 of the trigger S2 are connected to one end of the capacitor C3. Pin 2 of the trigger S2 is connected to pin 1 of the analog-to-digital converter. Pin 4 of the trigger S2 is connected to the negative terminal of the diode D3. The positive terminal of the diode D3 is connected to one end of the resistor R8. The other end of the resistor R8 is connected to pin 4 of the current transformer L1. Pin 2 of the analog-to-digital converter is connected to ground GND.

[0030] The trigger S2 consists of a normally closed contact and a relay. Pins 1 and 2 of the trigger S2 are the two ends of the normally closed contact, and pins 3 and 4 of the trigger S2 are the positive and negative ends of the relay.

[0031] Specifically, operational amplifier U1 is model OPA2188AIDR, current transformer L1 is model DLW21HN121SQ2L; transistors Q1 and Q2 are both NPN. Working principle: First, the voltage transformer acquires the electrical signals of the transformer's operating parameters and transmits the signals to the signal preprocessing unit. Based on the input signal, the signal preprocessing unit selects different processing paths through a switching module. After processing by the operational amplification module, voltage divider module, DC bias module, suppression module, and surge protection module, the processed signal is finally transmitted to the analog-to-digital converter. The variable resistor POT1 is used to adjust the voltage at the base of transistor Q1, thereby controlling the conduction and cutoff of transistor Q1. When the input signal is an overvoltage signal, the variable resistor POT1 is adjusted to turn on transistor Q1. At this time, the conduction state triggers the voltage divider module to work. After transistor Q1 is turned on, the current passes through pin 4 of trigger S1, causing the relay in trigger S1 to operate. Relay T1 is energized, and normally closed contact S3 is opened. When the input signal is an attenuating signal, transistor Q1 is cut off, trigger S1 is cut off, and the operational amplifier module processes the overvoltage signal. At this time, the normally closed contact S3 remains closed, and the signal enters the operational amplifier module.

[0032] When the switching module enables the operational amplifier module to work, the attenuated signal enters pin 2 of the operational amplifier U1, is amplified by inversion, and is output from pin 1. Diode D2 is used to prevent the signal from being reversed, thus providing protection. When the switching module enables the voltage divider module to work, the voltage division ratio is changed by adjusting the resistance value of the variable resistor POT2, and the overvoltage signal is divided to a suitable range. The output signal is then limited by diode D1 and sent to the subsequent circuit to prevent the signal amplitude from being too large and damaging the subsequent components. Transistor Q2, along with resistors R5 and R6, forms an emitter follower. Its emitter output voltage follows the base voltage, providing a stable DC bias voltage to stabilize the signal baseline. Capacitor C1 filters out high-frequency noise, ensuring signal purity. When the signal passes through the suppression module, the LC filter network suppresses common-mode interference and high-frequency noise, improving the signal-to-noise ratio and making the signal more stable and reliable. When a transient high voltage is detected, the relay in trigger S2 activates, the normally closed contact opens, and the signal path is cut off to prevent the transient high voltage from damaging the analog-to-digital converter. Diode D3 and resistor R8 are used to absorb residual energy and protect the circuit. The signal processed by the signal preprocessing unit is finally input to the analog-to-digital converter, which converts the analog signal into a digital signal for subsequent processing and analysis.

[0033] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0034] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. An analog signal preprocessing system for a power convergence terminal, comprising: a transformer; a voltage transformer installed on the transformer side; a signal preprocessing unit for preprocessing the electrical signal output from the voltage transformer; and an analog-to-digital converter for acquiring the signal preprocessing unit, characterized in that: The signal preprocessing unit includes: The switching module dynamically switches the signal path by turning on / off the transistor Q1. When Q1 is on, it triggers the operational amplifier module to process the attenuated signal. When Q1 is off, it activates the voltage divider module to process the overvoltage signal. The normally closed contact S3 is controlled by relay T1 to open and close. The operational amplifier module, through operational amplifier U1 forming an inverting amplifier, uses resistors R3 and R4 to set the gain, linearly amplifying the attenuated signal. The voltage divider module consists of a voltage divider network composed of resistor R2 and variable resistor POT2, which is suitable for input overvoltage scenarios. The output is limited by diode D1 and then sent to subsequent circuits. The voltage division ratio can be adjusted by POT2. The DC bias module uses transistor Q2, resistors R5 and R6 to form an emitter follower, providing a stable DC bias voltage for the signal. Capacitor C1 filters out high-frequency noise. The suppression module uses a current transformer L1 and capacitors C2 and C3 to form an LC filter network to suppress common-mode interference and high-frequency noise. The surge protection module consists of a fast-response circuit composed of trigger S2 and diode D3. When a transient high voltage is detected, the relay is triggered to cut off the signal path, and resistor R8 absorbs the residual energy.

2. The analog signal preprocessing system for a power fusion terminal according to claim 1, characterized in that: The switching module includes a resistor R1, a variable resistor POT1, a transistor Q1, a normally closed contact S3, a relay T1, and a trigger S1. One end of the resistor R1 is electrically connected to the fixed pin 3 of the variable resistor POT1, the output pin 1 of the voltage transformer, one end of the normally closed contact S3, and the normally open contact pin 1 of the trigger S1. The other end of the resistor R1 is electrically connected to the collector terminal of the transistor Q1. The base terminal of the transistor Q1 is electrically connected to the adjustment pin 1 and the fixed pin 2 of the variable resistor POT1. The emitter terminal of the transistor Q1 is connected to the positive terminal pin 4 of the relay coil of the trigger S1. The negative terminal pin 3 of the relay coil of the trigger S1 is connected to ground GND. The normally open contact pin 2 of the trigger S1 is connected to one end of the relay T1, and the relay T1 is connected to ground GND. The trigger S1 consists of a normally open contact and a relay. The normally open contact pins 1 and 2 of the trigger S1 are the two ends of the normally open contact. The positive terminal pin 4 and the negative terminal pin 3 of the relay coil of the trigger S1 are the positive and negative terminals of the relay. When the relay T1 is energized, the normally closed contact S3 is opened.

3. The analog signal preprocessing system for a power convergence terminal according to claim 1, characterized in that: The operational amplifier module includes an operational amplifier U1, resistors R4 and R3, and diode D2. The inverting input pin 2 of the operational amplifier U1 is connected to one end of resistor R4 and the other end of normally closed contact S3. The non-inverting input pin 3 of the operational amplifier U1 is connected to one end of resistor R3. The other end of resistor R3 is connected to ground GND. The output pin 1 of the operational amplifier U1 is connected to the other end of resistor R4 and the positive terminal of diode D2.

4. The analog signal preprocessing system for a power convergence terminal according to claim 1, characterized in that: The voltage divider module includes a resistor R2, a variable resistor POT2, and a diode D1. One end of the resistor R2 is connected to the normally open contact pin 2 of the trigger S1. The other end of the resistor R2 is connected to the adjustment pin 1 and the fixed pin 2 of the variable resistor POT2. The fixed pin 3 of the variable resistor POT2 is connected to the positive terminal of the diode D1, and the negative terminal of the diode D1 is connected to the negative terminal of the diode D2.

5. The analog signal preprocessing system for a power convergence terminal according to claim 1, characterized in that: The DC bias module includes a capacitor C1, a resistor R7, a transistor Q2, a resistor R5, and a resistor R6. One end of each resistor R5 is connected to the input power supply +12V and one end of each resistor R6. The other end of each resistor R6 is connected to the collector terminal of the transistor Q2. The base terminal of each transistor Q2 is connected to the other end of each resistor R5 and the negative terminal of the diode D2. The emitter terminal of each transistor Q2 is connected to one end of each capacitor C1 and one end of each resistor R7. The other end of each resistor R7 is connected to the other end of each capacitor C1 and the ground line GND.

6. The analog signal preprocessing system for a power convergence terminal according to claim 1, characterized in that: The suppression module includes capacitor C2, current transformer L1, and capacitor C3. One end of capacitor C2 is connected to the primary coil pin 1 of current transformer L1 and the other end of resistor R6. The other end of capacitor C2 is connected to the primary coil pin 2 of current transformer L1 and the other end of resistor R7. The secondary coil pin 3 of current transformer L1 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to the secondary coil pin 4 of current transformer L1.

7. The analog signal preprocessing system for a power convergence terminal according to claim 1, characterized in that: The surge protection module includes a trigger S2, a diode D3, and a resistor R8. The normally closed contact pin 1 and the positive terminal pin 3 of the relay coil of the trigger S2 are connected to one end of the capacitor C3. The normally closed contact pin 2 of the trigger S2 is connected to the input pin 1 of the analog-to-digital converter. The negative terminal pin 4 of the relay coil of the trigger S2 is connected to the negative terminal of the diode D3. The positive terminal of the diode D3 is connected to one end of the resistor R8. The other end of the resistor R8 is connected to the secondary coil pin 4 of the current transformer L1. The grounding pin 2 of the analog-to-digital converter is connected to the ground wire GND. The trigger S2 consists of a normally closed contact and a relay. The normally closed contact pins 1 and 2 of the trigger S2 are the two ends of the normally closed contact, and the positive terminal pin 3 and the negative terminal pin 4 of the relay coil are the two ends of the relay.

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