The Allegro ACS712 is a series of current sensors that use Hall effect technology to measure the current flowing through a conductor. The sensor works by detecting the magnetic field generated by the current and converting it into a proportional voltage output. The ACS712 sensors are available in three different models with different current rating: 5A, 20A, and 30A.
The ACS712 sensors have a number of features that make them useful for a wide range of applications, including:
Overall, the ACS712 sensors are a reliable and accurate solution for measuring current in a wide range of applications, including power supplies, motor control, battery management, and more.
To use the ACS712 current sensor with Arduino, follow these steps:
current = (analogRead(A0) – 512) / sensitivity
where A0 is the analog input pin connected to the sensor, 512 is the midpoint of the analog input range (0-1023), and sensitivity is the sensitivity of the sensor (e.g., 0.185V/A for the 5A model).
According to their purpose, current transformers can be roughly divided into two categories:
Current transformers for measurement (or measuring windings of current transformers) : provide current information of the power grid to measuring and metering devices within the normal working current range.
Current transformer for protection (or protection winding of current transformer) : in the state of power grid fault, to provide the relay protection device with power grid fault current information.
Classified by insulating medium
1. Dry type current transformer: It is made of ordinary insulating materials and treated by dipping paint as insulation.
2. Castable current transformer: current transformer moulded by epoxy resin or other resin mixed materials.
3, oil-immersed current transformer: by insulating paper and insulating oil as insulation, generally outdoor type.
4. Gas insulation current transformer: The main insulation is composed of gas.
Classified by installation mode
1. Penetrant current transformer: current transformer used to pass through the panel or wall.
2, pillar type current transformer: installed on the plane or pillar, as a primary circuit conductor pillar of the current transformer.
3. Bushing current transformer: It is a current transformer directly installed on the insulated bushing without primary conductor and primary insulation.
4: busbar type current transformer: no primary conductor but primary insulation, directly installed on the bus used in a current transformer.
Classification by principle
1. Electromagnetic current transformer: current transformer that realizes current conversion according to the principle of electromagnetic induction.
2. Electronic current transformer:
For example, (1) Optical current transformer refers to the use of optical devices as measured current sensors, optical devices are composed of optical glass, all optical fibers, etc.
(2) hollow coil current transformer. Also known as Rogowski coil current transformer. The hollow coil is usually made of enamelled wire evenly wound on the ring skeleton. The skeleton is made of non-ferromagnetic materials such as plastics and ceramics. The relative permeability of the skeleton is the same as that of the air, which is a significant feature of the hollow coil different from the current transformer with iron core.
(3) Core coil type low power current transformer (LPCT). It is a development of the traditional electromagnetic current transformer. Based on the design of high impedance resistance, the saturation characteristics are improved under very high primary current, the measurement range is expanded, and the power consumption is reduced. It can measure overcurrent and full offset short-circuit current with high accuracy without saturation. The measurement and protection can share a low-power current transformer with core coil, whose output is voltage signal.
According to their purpose, current transformers can be roughly divided into two categories:
Current transformers for measurement (or measuring windings of current transformers) : provide current information of the power grid to measuring and metering devices within the normal working current range. When measuring the high current of alternating current, it is necessary to convert it to a relatively uniform current for the convenience of secondary instrument measurement (China stipulates that the secondary rating of the current transformer is 5A or 1A). In addition, the voltage on the line is relatively high, so direct measurement is very dangerous. The current transformer plays the role of changing current and electrical isolation. It is a sensor used by measuring instruments, relay protection and other secondary devices in power system to obtain the current information of the primary circuit. Current transformer converts high current into low current proportionally. Current transformer is first side connected to the primary system, and second side connected to measuring instruments and relay protection.
Current transformer for protection (or protection winding of current transformer) : in the state of power grid fault, to provide the relay protection device with power grid fault current information. The protection current transformer mainly works with the relay device. When the line fails, such as short circuit and overload, it provides signals to the relay device to cut off the faulty circuit, so as to protect the safety of the power supply system. The working condition of the protection current transformer is completely different from that of the measurement current transformer. The protection current transformer only starts to work effectively when the current is several times and dozens of times larger than the normal current.
Before adding motion sensors to your lights, get these tools ready so you can speed up the process.
1. Motion sensor
2. Screwdriver
3. Optional
(1) Wire cutting machine: cut the wire if necessary
(2) Wire connectors: By default, most motion sensor light switches include wire connectors in the accessory pack
(3) Voltage tester: identify the hot wire and ensure that the voltage is off
(4) Electrical tape: marking hot wire
(5) Junction box: used to fix and install motion sensors
Second, place the motion sensor
Turn off the power to the lamp to which you want to add a motion sensor. Find a spot in your home between the power supply and the lights where you want to install motion sensors. If necessary, install junction boxes and cut live and neutral wires for mounting and securing motion sensors. Now mark the hot lines and load lines.
1. Turn on the power and test each black wire in the junction box with a non-contact voltage tester. The hot line has power, but the load line of the lamp has no power.
2. Turn off the power and confirm with a non-contact voltage tester.
3. Mark hot lines with electrical tape if needed.
Connect the motion sensor to the lamp
This is a standard motion sensor wiring diagram and you can apply almost all of the above wiring. Wiring is very simple, similar to installing a motion sensor light switch. All you need is three wires. L is for wire or hot line, which is the power source in your home. L1 The load line used to power the lamp. N is the zero line, you simply connect them together.
How do I connect a motion sensor to an existing light circuit switch?
1. Connect your home’s hot line to the hot line on your motion sensor.
2. Connect the load cable to the load cable on the lamp and motion sensor.
3. Connect the neutral wire in your home to the neutral wire on the motion sensor.
Four, adjust the motion sensor
Now screw the motion sensor part into the junction box and power it on to test the best Settings. Test several times and adjust the motion sensor Settings to optimal values, such as time delay, motion detection sensitivity, light sensor LUX. Change the motion sensor to ensure that it detects the desired motion detection area. Install and tighten the motion sensor.
According to Faraday’s principle of electromagnetic induction, when a massive metal conductor is placed in a changing magnetic field or when cutting the magnetic field lines (independent of whether the metal is massive or not, and there is no eddy current when cutting the magnetic field that does not change), a vortex-like induced current will be generated in the conductor, which is called eddy current, and the above phenomenon is called eddy current effect. The sensor made according to eddy current effect is called eddy current sensor.
The high frequency oscillating current in the preprocessor flows into the probe coil through the extension cable and generates an alternating magnetic field in the coil at the head of the probe. When the measured metal body is close to this magnetic field, an induced current is generated on the metal surface. Meanwhile, the eddy current field also generates an alternating magnetic field in the direction opposite to that of the head coil. Due to its reaction, the amplitude and phase of the high-frequency current in the head coil are changed (the effective impedance of the coil). This change is related to the permeability of the metal body, electrical conductivity, coil geometry, geometry size, current frequency and the distance between the head coil and the surface of the metal conductor. The physical properties of coil and metal conductor system can be described by the conductivity of metal conductor, permeability ξ, size factor τ, distance D of head coil and metal conductor surface, current intensity I and frequency ω parameters. The characteristic impedance of coil can be expressed by Z=F(τ, ξ, no, D, I, ω) function. Usually we can control the parameters τ, ξ, squirt, I, ω to be constant within a certain range, then the characteristic impedance Z of the coil will be a single value function of distance D, although its whole function is nonlinear, its function characteristic is “S” curve, but it can be selected to be approximately linear. Here, the change of coil impedance Z, that is, the change of the distance D between the coil of the head body and the metal conductor, is converted into the change of voltage or current through the processing of the electronic circuit of the preprocessor. The size of the output signal varies with the distance between the probe and the surface of the measured body. Eddy current sensor can measure the displacement, vibration and other parameters of the metal object according to this principle.
It is characterized by good long-term reliability, high sensitivity, strong anti-interference ability, non-contact measurement, fast response, not affected by oil and water and other media, often used for large-scale rotating machinery axis displacement, shaft vibration, shaft speed and other parameters for long-term real-time monitoring, can analyze the working condition of the equipment and the cause of failure, effectively protect the equipment and pre-maintenance.
Transformer inrush current refers to the transient current caused by the change of magnetic field in the core when the transformer is switched on for the first time. These inrush currents can cause noise and vibration in the transformer and may interfere with other electrical equipment, so they need to be suppressed.
The following are some ways to suppress the transformer inrush current:
Series resistance: A resistor is connected in series at the input end of the transformer to limit the inrush current. However, this method results in energy loss, and appropriate resistance values need to be selected to ensure the safety of the circuit.
Series inductor: Series an inductor at the input end of the transformer can form a low pass filter, which can suppress high frequency noise and interference. However, this method also results in energy loss and requires the selection of appropriate inductance values to ensure the stability of the circuit.
Premagnetization: Before the transformer is powered on, a small power supply can be used to premagnetize the core of the transformer by providing a certain amount of current, thus reducing the size of the inrush current. This method requires an additional power supply and control circuit, but can reduce the size of the inrush current.
Phase shift: The inrush current can be reduced by changing the phase difference between the input voltage and the output voltage of the transformer. This method requires an additional phase shifter, but can effectively reduce the inrush current.
It is necessary to choose the appropriate method to suppress the transformer inrush current according to the specific situation.
1, construction according to the drawing, wiring is correct, the number of both ends of the wire should be clear, label range in line with the requirements of the regulations.
2. The secondary loop conductor or cable should all use copper wire. The cross section of the current transformer loop conductor should not be less than 2.5mm2, and the voltage transformer loop conductor should be cut
The surface should not be less than 1.5mm2.
3. The first terminal block at the exit of the current transformer should use special current terminals. The secondary winding not used by the current transformer should be short-circuited and grounded at the terminal board.
4. There should be no joint in the primary circuit guiding in the disk and cabinet, and there should be no joint in the middle of the control cable or guiding pure. If there must be joint, it should be used appropriately
Terminal box transition connection.
5. The polarity of the current transformer should not be reversed, and the phase sequence and phase difference should meet the requirements of the design and regulations. The transformer connection for differential protection should be put into operation
The two arm current phasor diagram must be measured to verify the correctness of the connection
6, the secondary circuit wire arrangement should be neat and beautiful, wire and electrical components and terminal block connection screws must be free from virtual loosening phenomenon, wire tie card point distance
Separation shall comply with the requirements of the regulations.
7. The secondary circuit should be well insulated to the ground, and there should be no mixed line between the voltage circuit and the current circuit.
8. The current and voltage loop should be grounded at one point at the exit of the transformer secondary side.
If a sensor uses the Hall effect to sense the presence of a magnetic field, the sensor is called a Hall effect sensor. The basic element of a magnetic sensor is the Hall element, and these sensors are usually packaged in a four-terminal housing where two terminals are control terminals and the other two are differential output terminals.
The control current is applied to the control terminal, while the output is observed at the differential output terminal. A basic Hall effect sensor converts magnetic fields into electrical signals. The magnetic system converts physical quantities such as position, velocity, current and temperature into magnetic fields, which in turn can be induced by Hall effect sensors.
Hall effect sensors are most notable for providing solid state reliability. Low power environment isolation package. In addition, Hall sensors will operate over a wide temperature range. Generate consistent activation points at the same time. Hall effect sensor is a kind of semiconductor device. It is manufactured using an integrated process. Hall effect sensors require electrical current to pass through the device. When there is a magnetic field generated by voltage, Hall sensor will realize its switching function. Finally, the relative strength of the magnetic field determines the voltage level in millivolts.
Hall effect sensors are made of silicon material and are mainly divided into two types, namely basic sensor and integrated sensor. Hall coefficient and current density of active element are two important parameters to be considered when making Hall effect sensor to produce high output voltage.
Therefore, high Hall coefficient and low resistance are two important requirements of Hall components. Some of the materials used to manufacture these sensor components include InSb, Ge, InAs, and GaAs.
The battery current sensor is an amp clamp that measures current flow into and out of the battery. The current sensor then translates flow into a variable duty cycle signal. The sensor then sends this variable duty cycle to the BCM to indicate current flow.
Many modern cars have a battery current sensor. It might also be called a battery management or monitor sensor, or simply a battery sensor. Often, it is installed on the negative battery terminal or on the cable. Battery current sensorFord battery monitor sensorIn some cars, it might be installed on the positive terminal. Some cars have two battery sensors, one on each terminal.
How the battery sensor works: it measures the current to and from the battery. The sensor may also monitor the voltage, state of charge and state of health of the battery (aging). In some cars, it even measures the temperature of the battery.
The vehicle computer (BCM or PCM) uses these inputs to precisely adjust charging system voltage, idle speed and other parameters for better fuel efficiency and longer battery life. This system is called Power or Battery Management System or BMS. If the system detects that the battery is getting weak, it may turn off some electrical accessories (load shedding), such as the navigation, heated steering, heated seats, etc., to save the battery power. In this case, the computer will display a warning message on the instrument panel.
The function of the battery sensor is particularly important in vehicles with Stop-Start feature, as the battery management system must verify that the battery has enough charge to re-start the vehicle. If the battery is low on charge, the Stop-Start feature is disabled. The charging system current is also often higher in vehicles with Stop-Start feature. For this reason, in some vehicles, if the sensor has been disconnected or the battery has been replaced, the Stop-Start feature might not work for some time, until the computer (BCM or PCM) re-learns the parameters of the battery.
Hold the transformer winding with the right hand, four fingers for the direction of the applied current, thumb for the direction in the flux.
The induced electromotive force always resizes the increase of the value of the current, so turn the hand (just up, this time down) four fingers is the direction of the induced electromotive force. (that is, in the opposite direction of the applied current)
Extend the right hand, so that the thumb is perpendicular to the other four fingers, and they are in a plane with the palm, so that the magnetic wire enters from the palm, and the thumb points to the direction of the wire movement, then the direction of the four fingers is the direction of the induced current. When the magnet is inserted into the coil, the direction of the original magnetic flux is downward, and the magnetic flux tends to increase. According to Lenz’s law, the direction of the magnetic flux established by the induced potential is opposite to that of the original magnetic flux. That is, when the new flux direction is up, use the right hand screw rule to determine the direction of the induced electromotive force, and when the magnet is pulled out of the coil, the original magnetic field direction in the coil is down. Induced electromotive force is in the phenomenon of electromagnetic induction. Since there is induced current in the closed circuit, there must also be electromotive force in the circuit. The electromotive force generated in the phenomenon of electromagnetic induction is called induced electromotive force.
Method for determining the direction of induced electromotive force in transformers
1. The reference direction of the voltage in the primary winding is consistent with that of the current.
2. The reference direction of the flux and the reference direction of the current conform to the right hair screw rule,
3. The reference direction of the induced electromotive force of the winding is consistent with that of the current.
4. The reference direction of the electromotive force in the secondary winding is consistent with that of the current.
5. The reference direction of the voltage in the secondary winding is consistent with that of the current.
Demagnetization is through primary or secondary winding with alternating excitation current, to the core with alternating magnetic field. Gradually increase the alternating magnetic field (excitation current) from 0 to saturate the core, and then slowly reduce the excitation current to zero to eliminate remanence.
According to the electrical theory, the use of power transformer degaussing instrument from positive and negative through DC current, and gradually reduce, reduce the hysteresis loop of the core, to eliminate the purpose of remanence. Direct current, such as 5A, is fed into the high-voltage winding of the current transformer under test (it is sufficient for the three-phase current transformer to degausse only B-0 or A-C), whose degaussing current is no less than the test current of the high-voltage winding. Dc demagnetization ends when the current value is reduced by 5%-10% each time until the current is 0.5mA.
Or apply 50Hz ac voltage (such as generator) respectively to the low-voltage side of the current transformer (between ac,ab and bc), and ground the high-voltage neutral point. Depending on the capacity of the power supply, adjust the compensating capacitor C to reduce the current of the power supply. The test changed the low-voltage side to reflect the Va reading of the average voltmeter, and gradually increased the voltage to 50% of the rated voltage, and stayed for about 5 min. The voltage slowly dropped to “zero” and then slowly increased the voltage to 100% of the rated voltage until complete demagnetization.
Current sensor is a kind of detection device, can feel the measured current information, and can detect the perceived information, according to a certain law into a certain standard of electrical signal or other required form of information output, in order to meet the information transmission, processing, storage, display, record and control requirements. Is a kind of sensor classification, its main signal source is the size of the current acquisition signal! The main parameter is its current size! The detection method is generally used to detect current characteristics of devices, generally ammeter and so on.
The working principle of current transmitter is mainly Hall effect principle. Take the principle of zero-flux closed-loop product as an example:
1. When the original side wire passes through the current sensor, the original side current IP will generate magnetic force lines. The original side magnetic force lines are concentrated around the air gap of the magnetic core. This tiny signal can be converted into secondary side current IS by subsequent electronic circuit, and the following relationship exists: IS* NS= IP*NP, where IS – secondary side current; IP – primary side current; NP — number of turns of primary side coil; NS — number of turns of secondary side coil; NP/NS – turns ratio, generally take NP=1. The output signal of the current sensor IS the side current IS, it is proportional to the input signal (original side current IP), IS generally small, only 10~400mA. If the output current passes through the measured resistance RM, a voltage output signal of several volts proportional to the original side current is obtained.
2, sensor power supply voltage VA VA refers to the power supply voltage of the current sensor, it must be in the range specified by the sensor. Beyond this range, the sensor cannot work normally or its reliability decreases. In addition, the supply voltage VA of the sensor is divided into positive ji supply voltage VA+ and negative ji supply voltage VA-. Note that the power supply voltage VAmin of the single-phase power supply sensor is twice that of the two-phase power supply voltage VAmin. Therefore, the measurement range of the two-phase power supply sensor should be higher than that of the two-phase power supply sensor.
3, measurement range Ipmax Measurement range refers to the maximum current value that can be measured by the current sensor, the measurement range is generally higher than the standard rating IPN.
In fact, there are many classifications of current sensors, and different classifications are different in use. We first need to choose the appropriate current sensor according to the use requirements, and then use according to the product instructions.
Conventional current sensors have four pins: positive (+), negative (-), measuring (M), and ground (0), but line current sensors do not have these four pins, but red, black, yellow, and green leads correspond to the positive electrode, negative electrode, measuring end, and ground. At the same time, most sensors have an internal hole through which a wire passes when measuring primary current. The size of the aperture has a certain relationship with the product type and the size of the measured current.
Regardless of the type of current sensor, the wiring of the pins during installation shall be carried out according to the conditions specified in the instruction manual.
1. When measuring AC power supply, it must be forced to use bipolar power supply. That is, the positive (+) terminal of the sensor is connected to the “+ VA” terminal of the power supply, and the negative terminal is connected to the “-VA” terminal of the power supply. This connection is called a bipolar power supply. At the same time, the measuring terminal (M) is connected to the “0V” terminal of the power supply via a resistor (single-finger zero magnetic formula).
2. When measuring DC current, you can use single-pole or single-phase power supply, that is, short connect the positive or negative terminal with the “0V” terminal, so that only one electrode is connected. In addition, the use, model, range and installation environment of the product must be fully considered during the installation process. For example, current sensors should be installed whenever possible to dissipate heat. In addition to installing wiring, immediate calibration and calibration, and paying attention to the working environment of the current sensor, the following should be noted to ensure the accuracy of the test:
1) The primary side conductor should be placed in the center of the inner hole of the current sensor, and should not be biased as far as possible;
2) The primary side line should be completely filled with the inner hole of the current sensor as far as possible, leaving no gap; 3) The current to be measured should be close to the standard rating IPN of the current sensor, not too large. If the conditions are limited, only one current sensor has a high rating, and the current to be measured is much lower than the rating. To improve measurement accuracy, the primary side line may be wound several times to bring it close to the rating.
The connection mode of a current transformer used for single-phase circuit is suitable for measuring single-phase current and single-phase power and protecting single-phase grounding short circuit.
The incomplete star connection mode of two current transformers is suitable for measuring three-phase current and three-phase power and protecting short-circuit faults between phases.
The connection mode of two-phase current difference between two current transformers is suitable for measuring one-phase current and protecting short-circuit fault between phases.
The star connection mode of three current transformers is suitable for measuring current and power in three-phase four-wire system, which can protect any form of fault.
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