An isolated current alarm device based on low-dropout detection

Abstract

The application relates to an isolated current alarm device based on low-voltage difference detection, belonging to the technical field of electronic measurement, which comprises a sampling detection module connected in series in a measured loop, a signal isolation and comparison module connected with the output end of the sampling detection module, and an audible and light alarm driving module connected with the output end of the signal isolation and comparison module; the sampling detection module adopts a fixed resistance milliohm sampling resistor to convert the loop current into a millivolt voltage signal; the signal isolation and comparison module compares the signal with an adjustable reference voltage through a voltage comparator and outputs the comparison result by using a photoelectric coupler; the audible and light alarm driving module controls the buzzing of a buzzer through a switching transistor; through the combination of low-voltage difference detection and photoelectric isolation technology, the accurate, safe and non-invasive alarm of the milliamperes-level tiny current is realized, and the device has the advantages of simple circuit, low cost and high reliability.

Description

Technical Field

[0001] This utility model relates to the field of electronic measurement and signal isolation technology, and is applicable to circuit continuity testing, status monitoring and safety early warning in fields such as rail transit and industrial control. Specifically, it is a device that can detect milliampere-level microcurrents and drive an audible alarm through opto-isolation. Background Technology

[0002] In scenarios such as electronic equipment testing and industrial control system fault diagnosis, it is often necessary to non-invasively monitor whether a specific amount of current is flowing through a circuit. Current technologies either use expensive dedicated current sensing chips, which are costly, or use simple series indicator lights, which cannot detect minute currents and lack isolation, potentially interfering with the system under test.

[0003] Especially in continuity testing of electrical cabinets in rail transit, operators need to manually test using probes on a functional testing machine. Due to the lack of immediate feedback, operators must frequently look up at the PC screen to confirm current flow, leading to low testing efficiency and a high risk of errors. Currently, there is a lack of a low-cost, high-reliability solution on the market that can be connected in series in the test circuit, is unaffected by small test currents (such as 50mA), and provides immediate isolation alarms. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a plug-and-play, securely isolated, and instantaneous sound feedback portable alarm device, enabling operators to determine test results simply by listening to the sound without needing to view the PC screen during manual probe testing.

[0005] This utility model provides the following technical solution: An isolated current alarm device based on low differential pressure detection is characterized in that it includes: a sampling and detection module connected in series in the circuit under test, a signal isolation and comparison module connected to the output terminal of the sampling and detection module, and an audible and visual alarm drive module connected to the output terminal of the signal isolation and comparison module. The sampling and detection module consists of a sampling resistor with a fixed resistance value. constitute; The signal isolation and comparison module includes a voltage comparator. and optocouplers The voltage comparator The two input terminals are respectively connected to the sampling resistor. Two ends and an adjustable reference voltage source One of its output terminals is connected to a first current-limiting resistor. Connected to the optocoupler The input terminal; The audible and visual alarm driving module includes a switching transistor. and buzzer The buzzer With the switching transistor The collector-emitter circuit is connected in series and then connected to the drive power supply. Between and the earth; The optocoupler One of the output terminals is connected to the switching transistor. Connect and control the switching transistor. The other output terminal is connected to the drive power supply through the second current-limiting resistor R2, which controls the conduction and cutoff of the circuit. The positive pole.

[0006] Furthermore, the sampling resistor The resistance is less than 1Ω.

[0007] Furthermore, the adjustable reference voltage source Includes a potentiometer The potentiometer is composed of... Each end is connected to a power supply. And ground, its sliding terminal outputs reference voltage.

[0008] Furthermore, the optocoupler One of the output terminals is directly connected to the switching transistor. The base.

[0009] Furthermore, the audible and visual alarm driving module also includes a freewheeling diode. The anode and cathode of the freewheeling diode are connected in parallel in opposite directions across the two ends of the buzzer.

[0010] The present invention, by adopting the above technical solution, can achieve the following beneficial effects: 1. High sensitivity and low impact: Using milliohm-level sampling resistors and millivolt-level reference voltages, it can accurately detect tiny currents in the milliampere range, while the voltage drop it introduces is extremely small, and has almost no impact on the operating state of the circuit being tested.

[0011] 2. High safety and reliability: The voltage comparator converts the analog voltage difference into a digital "on / off" signal, which has strong anti-interference ability and clear working status; the optocoupler realizes electrical isolation between the detection side and the alarm side, effectively preventing ground loop interference and switching noise from damaging the precision equipment under test, and ensuring the safe and reliable operation of the system; the current amplification effect of the transistor allows a small optocoupler output current to drive a high-power buzzer load.

[0012] 3. Low cost and high practicality: The circuit structure is simple, the manufacturing cost is low, the performance is stable, and it is easy to popularize and promote. Its plug-and-play feature allows it to be seamlessly integrated into existing testing processes, significantly improving testing efficiency. Attached Figure Description

[0013] Figure 1 This is the circuit schematic diagram of this utility model; Figure 2 This is a schematic diagram of the test system device connections. Detailed Implementation

[0014] like Figure 1 and Figure 2 As shown, an isolated current alarm device based on low differential pressure detection includes: a sampling and detection module connected in series in the circuit under test, a signal isolation and comparison module connected to the output terminal of the sampling and detection module, and an audible and visual alarm drive module connected to the output terminal of the signal isolation and comparison module. The sampling and detection module consists of a sampling resistor with a fixed resistance value. The configuration can be reasonably selected based on the actual situation of the circuit under test. The resistance value is generally selected to be below 1Ω; The signal isolation and comparison module includes a voltage comparator. and optocouplers The voltage comparator The two input terminals are respectively connected to the sampling resistor. Two ends and an adjustable reference voltage source Its output terminal is connected to the first current-limiting resistor. Connected to the optocoupler The input terminal of the adjustable reference voltage source; From a potentiometer The potentiometer is composed of... Each end is connected to a power supply. And ground, its sliding terminal outputs a reference voltage; The audible and visual alarm driving module includes a switching transistor. and buzzer The buzzer With the switching transistor The collector-emitter circuit is connected in series and then connected to the drive power supply. Between and the earth; The optocoupler One of the output terminals is connected to the switching transistor. Connect and control the switching transistor. The other output terminal is connected to the drive power supply through the second current-limiting resistor R2, which controls the conduction and cutoff of the circuit. The positive electrode; It should be noted that the audible and visual alarm drive module also includes a freewheeling diode. The anode and cathode of the freewheeling diode are connected in parallel in reverse to the buzzer. The two ends.

[0015] Example 1: Component selection and rationality analysis: 1. Sampling and Detection Module: Low Differential Pressure Sampling A 0.33Ω precision resistor is used as the sampling resistor. Using a test clip or banana plug, quickly connect it in series to the circuit under test; according to Ohm's law, when the current of the circuit under test flows through the sampling resistor... At this time, a slight voltage drop will be generated across its terminals. This voltage signal is the target of detection in subsequent circuits; Component selection and rationality analysis: sampling resistor A precision resistor of 0.33Ω was selected, whose resistance value is much smaller than the maximum on-resistance error of 2.2Ω in existing functional testing machines. Under a target detection current of 50mA, the resulting voltage drop... The voltage is 16.5mV; this voltage value is sufficient to be recognized by the subsequent comparator, while being small enough to ensure that when it is connected in series with the circuit under test, it will not affect the normal operation of the original equipment, thus achieving "non-invasive" detection.

[0016] External terminals: Test clips or banana plugs are used for easy and quick connection in series to the circuit under test.

[0017] 2. Signal Isolation and Comparison Module: Comparison and Isolation Voltage Comparison: Voltage Comparator Continuously compare the sampled voltage at its non-inverting input. Reference voltage at the inverting input terminal .when When this occurs, it indicates that the measured current has exceeded the set threshold. The output terminal transitions to a high level (close to) Conversely, it outputs a low level (close to 0V).

[0018] Opto-isolation: Voltage comparator The high-level output is passed through a current-limiting resistor. Drive optocoupler Internal LEDs The light emitted shines onto the internal phototransistor, causing it to switch from a cutoff state to a conduction state. This "electrical-optical-electrical" conversion process achieves complete electrical isolation between the input and output, cutting off the ground loop.

[0019] Component selection and rationality analysis: Voltage comparator The general-purpose operational amplifier LM358 is selected, which can detect DC or slow-changing current signals. It contains two independent op-amps. In this embodiment, only one is used. The other can be used as a backup or to add hysteresis function to enhance anti-interference capability, which provides design margin. At the same time, the LM358 general-purpose operational amplifier is easy to purchase, which meets the low cost goal of this utility model. optocoupler The PC817 is selected because it is one of the most commonly used linear optocouplers in the industry. It is inexpensive, has stable performance, and its typical current transfer ratio can meet the requirements of driving subsequent phototransistors.

[0020] Adjustable reference voltage source Includes a 10KΩ adjustable potentiometer And a 9V DC battery as a power source. By adjusting the potentiometer The alarm current threshold can be set flexibly and continuously. For example, if the alarm current is 30mA, then... Set to 10mV; if the alarm current is 50mA, then The voltage is set to 16.5mV. This design broadens the device's application range and enhances its adaptability.

[0021] First current-limiting resistor The resistance value is chosen to be 500Ω, located between pin 1 of the LM358 and pin 1 of the PC817. When the output high level is approximately 8V, If the forward voltage drop is approximately 1.2V, then the current-limiting resistor... The voltage across the terminals is 6.8V. Flow through... The current is approximately 13.6mA. This current value is within the optimal operating range of 5-20mA recommended by the PC817, ensuring reliable conduction without overdriving and causing damage. .

[0022] 3. Audible and visual alarm drive module: power drive and protection optocoupler When the internal phototransistor is turned on, its emitter current flows out, which acts as a switching transistor. Provide base current , After obtaining enough After entering a saturated conduction state, the collector and emitter are equivalent to a small resistor, thus turning the buzzer on. When the negative terminal is grounded, a complete circuit is formed, and the buzzer is energized and sounds. Component selection and rationality analysis: Switching transistors The NPN transistor SS8050 is selected because it has sufficient current amplification capability. Taking driving a 30mA buzzer as an example, only a base current of 0.3mA is required for saturation, while an optocoupler... It can provide more than 2mA of current, with sufficient drive margin to ensure the switching transistor... It can be fully conductive, reducing its own power consumption.

[0023] Second current-limiting resistor The resistance value is selected as 1kΩ, located at pin 4 of the PC817 and connected to a 3V DC drive power supply. Between the positive terminals. Second current-limiting resistor. The output characteristics of the optocoupler together determine the current supplied to the base of the transistor. The optocoupler's saturation voltage drop is approximately 0.2V, and the transistor's base-emitter junction voltage drop is 0.7V. With a voltage drop of 2.1V, the base current is 2.1mA. This current is much greater than the base current required to drive a common buzzer, ensuring reliable saturation conduction of the transistor.

[0024] buzzer The selected buzzer is the TMB12A03, which contains an oscillation circuit and operates at 1.5-4V, along with the drive power supply. The device can be powered by two 1.5V dry batteries, making it portable.

[0025] freewheeling diode The selected diode is the 1N4148 switching diode, which has a fast switching speed and fully meets the protection requirements. (Due to the buzzer...) It is an inductive load, which generates a very high reverse induced electromotive force at the moment of power failure. The freewheeling diode... Connected in reverse parallel across the buzzer, this provides a discharge path for the induced electromotive force, preventing it from being superimposed on the power supply voltage and damaging the switching transistor. .

[0026] Brief introduction to working principle: When the current in the circuit under test reaches approximately 50mA A voltage drop of approximately 16.5mV is generated, which is higher than the set reference voltage of 10mV. (Voltage comparator) Output high level to drive optocoupler Turning on, thus enabling the switching transistor to conduct. Saturation conduction, buzzer A beep sounds upon receiving power. Throughout the process, the power supply on the detection side (power supply) is activated. ) and alarm-side power supply (drive power supply) via optocoupler Complete electrical isolation has been achieved.

[0027] Brief introduction to the operation process: During operation, the sampling resistor of this utility model device is... Connect external terminals at both ends, and connect them in series with the probe circuit of the functional testing machine via test leads. Turn on the power supply. When the operator taps the correct contact with the probe and forms a complete circuit, the test current (e.g., 50mA) output by the functional testing machine flows through the sampling resistor. This generates a voltage drop. This voltage is compared with a preset reference voltage, triggering subsequent circuitry, including the optocoupler. Turning on the transistor drives it to switch. Saturation, buzzer The circuit is activated and a beep sounds. Once the operator hears the sound, it confirms that the circuit is active and the test is successful, and the next point can be tested immediately.

[0028] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any equivalent substitutions and modifications made by those skilled in the art without departing from the guidance of the present utility model shall be deemed to fall within the protection scope of the present utility model.

Claims

1. An isolated current alarm device based on low differential pressure detection, characterized in that, include: A sampling and detection module connected in series in the circuit under test, a signal isolation and comparison module connected to the output terminal of the sampling and detection module, and an audible and visual alarm drive module connected to the output terminal of the signal isolation and comparison module; The sampling and detection module consists of a sampling resistor with a fixed resistance value. constitute; The signal isolation and comparison module includes a voltage comparator. and optocouplers The voltage comparator The two input terminals are respectively connected to the sampling resistor. Two ends and an adjustable reference voltage source One of its output terminals is connected to a first current-limiting resistor. Connected to the optocoupler The input terminal; The audible and visual alarm driving module includes a switching transistor. and buzzer The buzzer With the switching transistor The collector-emitter circuit is connected in series and then connected to the drive power supply. Between and the earth; The optocoupler One of the output terminals is connected to the switching transistor. Connect and control the switching transistor. The other output terminal is connected to the second current-limiting resistor, which controls the conduction and cutoff of the circuit. Connect to drive power supply The positive pole.

2. The isolated current alarm device based on low differential pressure detection according to claim 1, characterized in that, The sampling resistor The resistance is less than 1Ω.

3. The isolated current alarm device based on low differential pressure detection according to claim 1, characterized in that, The adjustable reference voltage source Includes a potentiometer The potentiometer is composed of... Each end is connected to a power supply. And ground, its sliding terminal outputs reference voltage.

4. The isolated current alarm device based on low differential pressure detection according to claim 1, characterized in that, The optocoupler One of the output terminals is directly connected to the switching transistor. The base.

5. The isolated current alarm device based on low differential pressure detection according to claim 1, characterized in that, The audible and visual alarm driving module also includes a freewheeling diode. The anode and cathode of the freewheeling diode are connected in parallel in opposite directions across the two ends of the buzzer.

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