Current clamps allow you to measure current in a non-contact way - simply by grasping this wire. AC clamps are usually made on the basis of a current transformer, have been produced for a very long time and cost a penny. Pliers for direct current- are based on linear hall sensor(s), and have become available at a price not so long ago. In general, pliers can be divided into pliers for changing and pliers for permanent use, and according to their design - into stand-alone and attachments. Among stand-alone inexpensive AC/DC I can name ut210e, ms2108A, and among consoles - the slightly more expensive appa 32, hantek cc65/cc650, and here is a “new player” in the lower price range - Holdpeak.
In general, the pliers were initially designed to be paired with a multimeter - there is a corresponding position on the selector itself. But in principle they can work with any other tester or even an oscilloscope, because they produce a voltage directly proportional to the measured current - 1mV corresponds to 1A.
The pliers have dimensions of 175x80mm (without the side button that opens the “mouth”), weight about 300g, wire length 70cm. 
The kit includes a piece of paper that I can't even call it an instruction. It says something like this: connect the clamp to the tester, turn it on, select the “clamp” mode on the tester, switch the clamp and tester to the appropriate AC/DC mode, press the REL button on the tester - and measure. No numbers, errors, limits - nothing. However, the instructions from HP890cn promise 2.5%/3% +5 for DC and AC, respectively.
On the front panel there is a power button, an LED indicating the on state and an AC/DC button. Looking ahead, I will say that the difference between AC and DC is in the capacitor connected in series, and the trimmers for AC and DC are different.
Powered by the crown, current consumption 4.4mA 
Output signal - 1mV=1A
The inner world is simple and unpretentious - LDO 7550 at 5V, +5V to -5V converter 7660 and operational amplifier TL062
On the reverse side of the board there are three trimming resistors, buttons and a power LED. 
Additional Information
a couple of photos with sealed microcircuits and a switch: 
Scheme (if I haven't messed something up): 
The names of microcircuits, buttons, connectors are arbitrary (for example, instead of 7550 I drew 78L05, the connectors were taken based on the number of contacts, etc.). I didn’t unsolder or ring the capacitors; for the resistors, the inscriptions on them and their translation into the real value are indicated (because for 0603 with 1% accuracy the designation is not a digit-digit-multiplier, but a whole table)
If I understand correctly (and with a high probability I’m wrong), VR1 sets the initial offset, that is, it adjusts the zero, and VR2 and VR3 calibrate by constant and variable, respectively.
The AC mode differs in addition to a different output circuit and potentiometer - a capacitor connected in series. Why is this needed - as for me, there is a great secret. Apparently, to cut off the constant displacement that is inevitable in the clamps on the hall sensors. How this will differ from switching the tester to AC mode - I don’t even know. As for me, it would be better if they introduced a trimmer for this purpose and quickly set it to 0 permanently.
Now measurements. As I already wrote in the title, clamps are designed for high currents. Therefore, at low currents there will be no accuracy, but nevertheless we will try to check.
Permanent: 
Change: 
As we can see, if during the regular period the accuracy is still pretty good, then during the break it’s not at all good. however, I don’t care much about measuring alternating currents, and I don’t care about such high currents at all, so for me personally this is not a problem, but if I understand correctly, you can, if desired, adjust (?) using VR2 and VR3, which is what I did for direct current, although I didn’t take a photo. But it turned out no more than +-0.1A with the reference tester, at the above currents, which I consider to be quite a good result. Well, they are not designed for such currents. They need tens and hundreds of amperes - there they will show more accurately and “open up to the fullest.”
Now - a small improvement. Since I planned to use these clamps for diagnostics, in particular, measuring the starter current, I decided to replace the wire with a connector. Well, I’ll say right away that I haven’t tried this role yet - there was no opportunity, time or desire. ;)
To do this, I unsoldered the wire, soldered the tulip-male connector to it, and put the corresponding socket in the pliers. To install the socket, I drilled the body with a 10mm drill, after which I took a plastic plate measuring approximately 10x20x1.5mm, drilled a 6mm diameter hole in it, screwed the socket to it and inserted it into the body - between the body and the former wire clamp:
As for me, it became no worse, and besides, it became possible to connect with a “standard” cable. You can, of course, install a BNC connector, or plug an adapter into this connector. There will be no high frequencies here, so there is somehow no need for BNC connectors.
After this modification, you can connect to an oscilloscope. To do this, I assembled a key on some field plant, which I started from an external generator and loaded onto a powerful resistor. It is clear that all this is not serious, but what it is - that is: 
As you can see, the signal is quite noisy, which generally speaking is not surprising - I generally have little understanding of the use of 7660 type converters in circuits with microvolt/millivolt signals. The pole has a complete lack of shielding, so external interference cannot be ruled out in any way.
In terms of frequency, it’s also nothing outstanding.
For comparison, a signal from ut210e in 20A mode: 
The amplitude is higher, the signal is cleaner.
To summarize.
To be honest, my impressions are mixed. I just want to write “for my money...”. That is, yes, this is the cheapest model on the market. “Out of the box” it lies quite strongly, which, however, is most likely the characteristics of a particular instance, and it seems to be adjustable.
I would like to see at least minimal shielding, I would also like to switch the 600/60A limits - but here, in principle, it is clear that this switching is not completely deliberate, it comes as a “set” to the tester, where in the clamp mode the limit is 600A. On the other hand, it was possible to make 60/600A on the tester - but they didn’t. As a result we have low price- but also low precision “trailer”, and also a not very beautiful signal in terms of interference.
I’m thinking about installing a couple of power supply chokes, and I’m also thinking about introducing a 60A mode (more precisely, I won’t reach 60, somewhere around 40 will probably be the maximum), and here I would like to ask advice from more competent circuit designers. because, as for me, the most “uncomplicated” way is to stupidly stick another op-amp at the output with a gain of 10 and not worry about it;) Another option is to change the gain of the existing op-amp, but something didn’t work for me - probably You also need to set zero more accurately in this case. In short, I’ll be happy to hear any advice in the comments other than throwing it out. ;)
I'm planning to buy +8 Add to favorites I liked the review +37 +56To arrange the power supply for a garage, it is very convenient to know the current that is consumed by one or another device connected to this network. The range of these devices is quite wide and is constantly increasing: drill, sharpener, grinder, heaters, welders, charger, industrial hair dryer, and much more….
To measure alternating current, as is known, a current transformer is usually used as the actual current sensor. This transformer is generally similar to a regular step-down transformer, turned on in reverse, i.e. its primary winding is one or several turns (or a bus) passed through a core - a magnetic circuit, and the secondary winding is a coil with a large number of turns of thin wire, located on the same magnetic circuit (Fig. 1).
However, industrial current transformers are quite expensive, bulky and often designed to measure hundreds of amperes. A current transformer designed for the household network range is rarely found on sale. It is for this reason that the idea was born to use an electromagnetic DC/AC relay for this purpose, without any use of the contact group of such a relay. In fact, any relay already contains a coil with a large number of turns of thin wire, and the only thing that is necessary to turn it into a transformer is to ensure that there is a magnetic circuit around the coil with a minimum of air gaps. In addition, of course, such a design requires enough space to pass the primary winding, which represents the input network. The picture shows such a sensor made from a RES22 type relay for 24 V DC. This relay contains a coil with a resistance of approximately 650 ohms. Most likely, many other types of relays, including the remains of faulty magnetic starters, etc., can find similar applications. To ensure the magnetic circuit, the relay armature is mechanically blocked at maximum proximity to the core. The relay seems to be constantly in operation. Next, a turn of the primary winding is made around the coil (in the picture it is a triple blue wire).
Actually, at this point the current sensor is ready, without unnecessary fuss with winding the wire onto the coil. Of course, this device is difficult to consider as a full-fledged transformer due to the small cross-sectional area of the newly obtained magnetic circuit and, possibly, due to the difference in its magnetization characteristics from the ideal one. However, all this turns out to be less important due to the fact that the power of such a “transformer” we need is minimal and is necessary only to ensure a proportional (preferably linear) deviation of the dial indicator of the magnetoelectric system depending on the current in the primary winding.
A possible scheme for pairing a current sensor with such an indicator is shown in the diagram (Fig. 2). It is quite simple and resembles a detector receiver circuit. The rectifier diode (D9B) is germanium and was chosen due to the small voltage drop across it (about 0.3 V). The minimum current threshold that this sensor can detect will depend on this diode parameter. In this regard, it is better to use so-called detector diodes with a low voltage drop, for example GD507 and the like. A pair of KD521V silicon diodes are installed to protect the pointer device from overload, which is possible during significant current surges caused, for example, by a short circuit within the network, or by turning on powerful transformers or a welder. This is a very common technique in such cases. It should be noted that this simplest scheme has the disadvantage that it absolutely may not “see” the load in the form of a current of one polarity, such as a heater or heating element connected through a rectifying diode. In these cases, a somewhat “complicated” circuit is used, for example, in the form of a rectifier with doubling the voltage (Fig. 3).
Content:In order to successfully automate various technological processes and effectively manage instruments, devices, machines and mechanisms, it is necessary to constantly measure and control many parameters and physical quantities. Therefore, sensors that provide information about the state of controlled devices have become an integral part of automatic systems.
At its core, each sensor is integral part regulating, signaling, measuring and control devices. With its help, one or another controlled quantity is converted into a certain type of signal, which allows one to measure, process, register, transmit and store the received information. In some cases, the sensor may affect controlled processes. The current sensor used in many devices and microcircuits fully possesses all these qualities. It converts the effects of electric current into signals convenient for further use.
Sensor classification
Sensors used in various devices are classified according to certain characteristics. If it is possible to measure input quantities, they can be: electrical, pneumatic, sensors of speed, mechanical movements, pressure, acceleration, force, temperatures and other parameters. Among them, the measurement of electrical and magnetic quantities takes approximately 4%.
Each sensor converts an input value into some output parameter. Depending on this, control devices can be non-electrical or electrical.
Among the latter, the most common are:
- DC sensors
- AC amplitude sensors
- Resistance sensors and other similar devices.
The main advantage of electrical sensors is the ability to transmit information over certain distances at high speed. The use of a digital code ensures high accuracy, speed and increased sensitivity measuring instruments.
Operating principle
According to the principle of operation, all sensors are divided into two main types. They can be generators - directly converting input quantities into an electrical signal. Parametric sensors include devices that convert input quantities into changed electrical parameters of the sensor itself. In addition, they can be rheostatic, ohmic, photoelectric or optoelectronic, capacitive, inductive, etc.
All sensors have certain requirements for their operation. In each device, the input and output quantities must be directly dependent on each other. All characteristics must be stable over time. As a rule, these devices are characterized by high sensitivity, small size and weight. They can operate in a wide variety of environments and be installed in a variety of ways.
Modern current sensors
Current sensors are devices that are used to determine the strength of direct or alternating current in electrical circuits. Their design includes a magnetic core with a gap and a compensation winding, as well as an electronic board that processes electrical signals. The main sensitive element is a Hall sensor, fixed in the gap of the magnetic circuit and connected to the input of the amplifier.
The principle of operation is generally the same for all such devices. Under the influence of the measured current, a magnetic field arises, then, using a Hall sensor, the corresponding voltage is generated. This voltage is then amplified at the output and applied to the output winding.
Main types of current sensors:
Direct Gain Sensors (O/L). They are small in size and weight, and have low energy consumption. The range of signal conversions has been significantly expanded. Allows you to avoid losses in the primary circuit. The operation of the device is based on a magnetic field that creates a primary current IP. Next comes concentration magnetic field in a magnetic circuit and its further transformation by a Hall element in the air gap. The signal received from the Hall element is amplified and a proportional copy of the primary current is formed at the output.
Current sensors (Eta). They are characterized by a wide frequency range and an extended range of conversions. The advantages of these devices are low power consumption and low latency. The operation of the device is supported by a unipolar power supply from 0 to +5 volts. The operation of the device is based on a combined technology that uses compensation type and direct amplification. This results in significantly improved sensor performance and more balanced operation.
Compensating current sensors (C/L). They are distinguished by a wide frequency range, high accuracy and low latency. Devices of this type have no loss of the primary signal; they have excellent characteristics linearity and low temperature drift. Compensation of the magnetic field created by the primary current IP, occurs due to the same field generated in the secondary winding. The generation of secondary compensating current is carried out by the Hall element and the electronics of the sensor itself. Ultimately, the secondary current is a proportional copy of the primary current.
Compensating current sensors (type C). The undoubted advantages of these devices are a wide frequency range, high accuracy of information, excellent linearity and reduced temperature drift. In addition, these instruments can measure residual currents (CD). They have high isolation levels and reduced interference with the primary signal. The design consists of two toroidal magnetic cores and two secondary windings. The operation of the sensors is based on ampere-turn compensation. Small current from the primary circuit passes through the primary resistor and the primary winding.
PRIME current sensors. A wide dynamic range is used to convert AC current. The device is characterized by good linearity, insignificant temperature losses and the absence of magnetic saturation. The advantage of the design is its small dimensions and weight, high resistance to various types overloads The accuracy of the readings does not depend on how the cable is positioned in the hole and is not influenced by external fields. This sensor does not use a traditional open-loop coil, but rather a sensor head with sensor printed circuit boards. Each board consists of two separate coils with air cores. All of them are mounted on a single base printed circuit board. Two concentric circuits are formed from the sensor boards, at the outputs of which the induced voltage is summed. As a result, information is obtained about the parameters of the amplitude and phase of the measured current.
Current sensors (type IT). Features high accuracy, wide frequency range, low output noise, high temperature stability and low crosstalk. The design of these sensors does not contain Hall elements. The primary current creates a magnetic field, which is subsequently compensated by the secondary current. At the output, the secondary current is a proportional copy of the primary current.
Advantages of current sensors in modern circuits
Current sensor chips play a big role in energy conservation. This is facilitated by low power and energy consumption. Integrated circuits combine all the necessary electronic components. The characteristics of the devices are significantly improved due to the joint operation of magnetic field sensors and all other active electronics.
Modern current sensors enable further reduction in size because all electronics are integrated into a single common chip. This has led to new innovative compact design solutions, including the primary busbar. Each new current sensor has increased insulation and successfully interacts with other types of electronic components.
The latest sensor designs allow them to be installed in existing installations without disconnecting the primary conductor. They consist of two parts and are detachable, allowing these parts to be easily installed on the primary conductor without any disconnection.
Each sensor has technical documentation, which reflects all the necessary information that allows preliminary calculations to be made and the location of the most optimal use to be determined.
To control current consumption, record motor blocking or emergency de-energization of the system.
Working with high voltage is hazardous to health!
Touching the terminal block screws and terminals may result in electric shock. Do not touch the board if it is connected to a household network. For the finished device, use an insulated housing.
If you don’t know how to connect the sensor to an electrical appliance operating from a common 220 V network or you have doubts, stop: you could start a fire or kill yourself.
You must clearly understand the operating principle of the device and the dangers of working with high voltage.
Video review
Connection and setup
The sensor communicates with the control electronics via three wires. The output of the sensor is an analog signal. When connecting to Arduino or Iskra JS, it is convenient to use Troyka Shield, and for those who want to get rid of wires, Troyka Slot Shield is suitable. For example, let's connect a cable from the module to a group of Troyka Shield contacts related to analog pin A0. You can use any analog pins in your project. 
Examples of work
To make working with the sensor easier, we wrote the TroykaCurrent library, which converts the values of the analog output of the sensor into milliamps. Download and install it to repeat the experiments described below.
DC current measurement
To measure direct current, connect the sensor to the open circuit between LED strip and food. Let's output the current value of direct current in milliamps to the Serial port. 
AC current measurement
To measure alternating current, we connect the sensor to the open circuit between the alternating voltage source and the load. Let's output the current value of alternating current in milliamps to the Serial port. 
Board elements
Sensor ACS712ELCTR-05B
The ACS712ELCTR-05B current sensor is based on the Hall effect, the essence of which is as follows: if a conductor with current is placed in a magnetic field, an EMF appears at its edges, directed perpendicular to the direction of the current and the direction of the magnetic field. 
The microcircuit is structurally composed of a Hall sensor and a copper conductor. The current flowing through the copper conductor creates a magnetic field, which is perceived by the Hall element. The magnetic field depends linearly on the current strength.
The output voltage level of the sensor is proportional to the measured current. Measurement range from −5 A to 5 A. Sensitivity - 185 mV/A. In the absence of current, the output voltage will be equal to half the supply voltage. 
The current sensor is connected to the load in the open circuit through screw blocks. To measure direct current, connect the sensor, taking into account the directions of the current, otherwise you will get values with the opposite sign. For alternating current, polarity does not matter.
Contacts for connecting a three-wire loop
The module is connected to the control electronics via three wires. Purpose of three-wire loop contacts:
Power (V) - red wire. Based on the documentation, the sensor power supply is 5 volts. As a result of the test, the module operates on 3.3 volts.
Ground (G) - black wire. Must be connected to microcontroller ground;
Signal (S) - yellow wire. Connects to the analog input of the microcontroller. Through it, the control board reads the signal from the sensor.
Measure the current of a high voltage power supply? Or the current consumed by the car's starter? Or current from a wind generator? All this can be done contactlessly using a single chip.
Melexis is taking the next step in creating green solutions by opening up new possibilities for non-contact current sensing in renewable energy, hybrid electric vehicle (HEV) and electric vehicle (EV) applications. The MLX91206 is a programmable monolithic sensor based on Triaxis™ Hall technology. The MLX91206 allows the user to build small, cost-effective touch solutions with fast response times. The chip directly controls the current flowing in an external conductor, such as a bus or trace on a printed circuit board.
The MLX91206 non-contact current sensor consists of CMOS integrated circuit Hall effect with a thin layer of ferromagnetic structure on its surface. An integrated ferromagnetic layer (IMC) is used as a magnetic flux concentrator, providing high gain and a higher signal-to-noise ratio of the sensor. The sensor is particularly suitable for measuring DC and/or AC current up to 90 kHz with ohmic insulation, characterized by very low insertion loss, fast response time, small housing size and ease of assembly.
The MLX91206 meets the demand for widespread electronics applications in the automotive industry, renewable energy conversion (solar and wind), power supplies, motor control and overload protection.
Areas of use:
- measurement of current consumption in battery power supply;
- solar energy converters;
- automotive inverters in hybrid vehicles, etc.
The MLX91206 has overvoltage protection and reverse voltage protection and can be used as a stand-alone current sensor connected directly to the cable.
The MLX91206 measures current by converting the magnetic field created by currents flowing through a conductor into a voltage that is proportional to the field. The MLX91206 has no upper limit on the current level it can measure because the output level depends on the conductor size and distance from the sensor.
Distinctive features:
- programmable high-speed current sensor;
- magnetic field concentrator providing a high signal-to-noise ratio;
- protection against overvoltage and reverse polarity;
- lead-free components for lead-free soldering, MSL3;
- fast analog output (DAC resolution 12 bit);
- programmable switch;
- thermometer output;
- PWM output (ADC resolution 12 bits);
- 17-bit ID number;
- faulty track diagnostics;
- fast response time;
- huge DC bandwidth - 90 kHz.
How the sensor works:
MLX91206 is a monolithic sensor made on the basis of technology Triais® Hall. Traditional planar Hall technology is sensitive to the flux density applied perpendicular to the IC surface. The IMC-Hall ® current sensor is sensitive to the flux density applied parallel to the surface of the IC. This is achieved through an integrated magnetic concentrator (IMC-Hall®), which is applied to the CMOS crystal. The IMC-Hall ® current sensor can be used in the automotive industry. It is a Hall effect sensor that provides an output signal proportional to the flux density applied horizontally and is therefore suitable for current measurement. It is ideal as an open loop current sensor for mounting on printed circuit board. The transfer characteristic of the MLX91206 is programmable (bias, gain, clamping levels, diagnostic functions...). The output is selectable between analog and PWM. Linear analog output is used for applications requiring fast response (<10 мкс.), в то время как выход ШИМ используется для применения там, где требуется низкая скорость при высокой надежности выходного сигнала.
Measures small currents up to ±2 A
Small currents can be measured with the MLX91206 by increasing the magnetic field through a coil around the sensor. The sensitivity (output voltage compared to coil current) of the measurement will depend on the size of the coil and the number of turns. Additional sensitivity and reduced sensitivity to external fields can be obtained by adding a shield around the coil. The bobbin provides very high dielectric insulation, making the MLX91206 a suitable solution for high voltage power supplies with relatively low currents. The output must be extended to obtain the maximum voltage for high currents in order to obtain maximum accuracy and resolution in measurements.
Fig.1. Low current solution.
Average currents up to ±30 A
Currents in the range of up to 30 A can be measured using a single trace on a PCB. When routing a PCB, the current allowance and total power dissipation of the trace must be taken into account. The traces on the PCB must be thick enough and wide enough to continuously handle the average current. The differential output voltage for this configuration can be approximated by the following equation:
Vout = 35 mV/ * I
For a current of 30 A, the output will be approximately 1050 mV.
Fig.2. Solution for average current values.
High current measurement up to ±600 A
Another method for measuring large currents on PCBs is to use thick copper traces that can carry current on the opposite side of the PCB. MLX91206 should be located close to the center of the conductor, however, since the conductor is very wide, the output is less sensitive to placement on the board. This configuration also has less sensitivity depending on distance and conductor width.
Fig.3. Solution for large current values.
About melexis
Established for over ten years, Melexis designs and manufactures products for the automotive industry, offering a variety of integrated sensors, ASSPs and VLSI products. Melexis solutions are extremely reliable and meet the high quality standards required in automotive applications.
