Schematic diagrams of non-contact current measurement of a round wire. Current converters are the right solution. DC current measurement
To measure high currents, as a rule, a non-contact method is used - with special current clamps. Current clamps - a measuring device that has a sliding ring, which covers the electrical wire and the indicator of the device displays the value of the flowing current.
The superiority of this method is indisputable - in order to measure the current strength, there is no need to break the wire, which is especially important when measuring high currents. This article describes DC current clamp, which is quite possible to do with your own hands.
Description of the design of homemade current clamps
To assemble the device, you will need a sensitive Hall sensor, for example, UGN3503. Figure 1 shows a homemade tongs device. As already mentioned, a Hall sensor is required, as well as a ferrite ring with a diameter of 20 to 25 mm and a large “crocodile”, for example, similar to the wires for starting (lighting) a car.
The ferrite ring must be accurately and accurately sawn or broken into 2 halves. To do this, the ferrite ring must first be filed with a diamond file or an ampoule file. Next, sand the fracture surfaces with fine sandpaper.
On the one hand, on the first half of the ferrite ring, glue a gasket from the drawing paper. On the other hand, stick the Hall sensor on the other half of the ring. It is best to glue with epoxy glue, you just need to make sure that the Hall sensor fits well to the ring break zone.
The next step is to connect both halves of the ring and wrap it around with a “crocodile” and glue it. Now, when you press the crocodile handles, the ferrite ring will diverge.
Clamp electronics
The circuit diagram of the attachment to the multimeter is shown in Figure 2. When current flows through the wire, a magnetic field appears around it, and the Hall sensor captures the lines of force passing through it and generates some constant voltage at the output.
This voltage is amplified (in terms of power) by OU A1 and goes to the terminals of the multimeter. The ratio of the output voltage from the flowing current: 1 Ampere = 1 mV. Trimmer resistors R3 and R6 are multi-turn. To configure, you need a laboratory power supply with a minimum output current of about 3A, and a built-in ammeter.
First, connect this prefix to the multimeter and set it to zero by changing the resistance R3 and the middle position R2. Further, before any measurement, it will be necessary to set zero with the potentiometer R2. Set the power supply to the lowest voltage and connect a large load to it, for example, an electric lamp used in car headlights. Then, on one of the wires connected to this lamp, hook the “pliers” (Figure 1).
Increase the voltage until the power supply ammeter shows 2 amps. Tighten the resistance R6 so that the voltage value of the multimeter (in millivolts) matches the data of the ammeter of the power supply in amperes. Check the readings a few more times by changing the current strength. With this attachment, it is possible to measure current up to 500A.
One of the easiest ways to measure current in an electrical circuit is to measure the voltage drop across a resistor in series with the load. But when current passes through this resistor, useless power is released in the form of heat, so it is chosen as low as possible, which in turn entails subsequent amplification of the signal. It should be noted that the circuits below allow you to control not only direct, but also pulsed current, however, with the corresponding distortions determined by the bandwidth of the amplifying elements.
Measurement of current in the negative pole of the load.
The scheme for measuring the load current in the negative pole is shown in Figure 1.
This diagram and some of the information is taken from the magazine "Components and Technologies" No. 10, 2006 Mikhail Pushkarev [email protected]
Advantages:
low input common mode voltage;
input and output signal have a common "ground";
Ease of implementation with a single power supply.
Disadvantages:
the load has no direct connection with the "ground";
there is no possibility of switching the load with a key in the negative pole;
the possibility of failure of the measuring circuit in the event of a short circuit in the load.
Measuring the current in the negative pole of the load is not difficult. For this purpose, many op amps designed to work with unipolar power supply are suitable. The circuit for measuring current using an operational amplifier is shown in fig. 1. The choice of a specific type of amplifier is determined by the required accuracy, which is mainly affected by the zero offset of the amplifier, its temperature drift and gain setting error, and the required speed of the circuit. At the beginning of the scale, a significant conversion error is inevitable, caused by a non-zero value of the minimum output voltage of the amplifier, which is insignificant for most practical applications. To eliminate this shortcoming, a bipolar power supply to the amplifier is required.
Measurement of current in the positive pole of the load
Advantages:
the load is grounded;
a short circuit in the load is detected.
Disadvantages:
high common-mode input voltage (often very high);
the need to shift the output signal to a level acceptable for further processing in the system (binding to the "ground").
Consider circuits for measuring current in the positive pole of the load using operational amplifiers.
In the diagram in fig. 2, you can use any of the operational amplifiers suitable for the allowable supply voltage, designed to operate with a single supply and a maximum input common-mode voltage that reaches the supply voltage, for example, the AD8603. The maximum supply voltage of the circuit cannot exceed the maximum allowable supply voltage of the amplifier.
But there are op-amps that are capable of operating at an input common-mode voltage that is significantly higher than the supply voltage. In the circuit using the LT1637 op amp shown in fig. 3, the load supply voltage can reach 44 V with an op-amp supply voltage of 3 V. Instrumentation amplifiers such as LTC2053, LTC6800 from Linear Technology, INA337 from Texas Instruments are suitable for measuring the current in the positive pole of the load with a very small error. To measure the current in the positive pole, there are specialized microcircuits, for example, INA138 and INA168.
INA138 and INA168
— high-voltage, unipolar current monitors. A wide range of input voltages, low current consumption and small dimensions - SOT23, allow this chip to be used in many circuits. Power supply voltage 2.7V to 36V for INA138 and 2.7V to 60V for INA168. The input current is no more than 25 μA, which allows measuring the voltage drop across the shunt with a minimum error. Microcircuits are current-voltage converters with a conversion factor from 1 to 100 or more. INA138 and INA168 in SOT23-5 packages have an operating temperature range of -40°C to +125°C.
A typical switching circuit is taken from the documentation for these microcircuits and is shown in Figure 4.
OPA454
— a new low-cost high-voltage operational amplifier from Texas Instruments with an output current of more than 50 mA and a bandwidth of 2.5 MHz. One advantage is the high stability of the OPA454 at unity gain. 
Inside the OS there is protection against overtemperature and overcurrent. The performance of the IC is maintained in a wide range of supply voltages from ±5 to ±50 V or, in the case of a single supply, from 10 to 100 V (maximum 120 V). The OPA454 has an additional “Status Flag” output - an open-drain op-amp status output - which allows you to work with logic of any level. This high voltage op amp has high precision, wide output voltage range, and no phase inversion problems often encountered with simple amplifiers.
Technical features of OPA454:
Wide supply voltage range from ±5 V (10 V) to ±50 V (100 V)
(maximum up to 120 V)
Large maximum output current > ±50 mA
Wide operating temperature range from -40 to 85°C (maximum from -55 to 125°C)
Packaged SOIC or HSOP (PowerPADTM)
The data on the microcircuit is given in "News of Electronics" No. 7 for 2008. Sergey Pichugin
Current shunt signal amplifier on the main power rail.
In amateur radio practice, for circuits whose parameters are not so rigid, cheap dual LM358 op-amps are suitable, which allow operation with input voltages up to 32V. Figure 5 shows one of many typical circuits for using the LM358 chip as a load current monitor. By the way, not all "datasheets" have schemes for its inclusion. In all likelihood, this circuit was the prototype of the circuit given in the Radio magazine by I. Nechaev and which I mentioned in the article “ current limit indicator».
The above schemes are very convenient to use in self-made power supplies for monitoring, telemetry and measuring the load current, for building short circuit protection circuits. The current sensor in these circuits can have a very small resistance and there is no need to adjust this resistor, as is done in the case of a conventional ammeter. For example, the voltage across the resistor R3, in the circuit in Figure 5 is: Vo = R3∙R1∙IL / R2 i.e. Vo = 1000∙0.1∙1A / 100 = 1V. One ampere of current flowing through the sensor corresponds to one volt of voltage drop across resistor R3. The value of this ratio depends on the value of all resistors included in the converter circuit. It follows that by making the resistor R2 trimmer, you can safely compensate for the spread in the resistance of the resistor R1. This also applies to the circuits shown in figures 2 and 3. In the circuit shown in fig. 4, you can change the resistance of the load resistor RL. To reduce the dip in the output voltage of the power supply, the resistance of the current sensor - the resistor R1 in the circuit in Fig. 5 is generally better to take equal to 0.01 Ohm, while changing the value of the resistor R2 to 10 Ohm or increasing the value of the resistor R3 to 10 kOhm.
Measure the current of a high voltage power supply? Or the current drawn by the car's starter? Or current from a wind generator? All this can be done contactlessly with a single chip.
Melexis is taking the next step in sustainable solutions by opening up new possibilities for non-contact current measurement in renewable energy, hybrid electric vehicles (HEV) and electric vehicles (EV) applications. The MLX91206 is a programmable monolithic sensor based on Triaxis™ Hall technology. The MLX91206 allows the user to build small cost-effective sensor solutions with fast response times. The chip directly controls the current flowing in an external conductor, such as a busbar or PCB track.
The MLX91206 non-contact current sensor consists of a CMOS Hall IC with a thin layer of ferromagnetic structure on its surface. An integrated ferromagnetic layer (IMC) is used as a magnetic flux concentrator, providing high flux 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 isolation, characterized by very low insertion loss, fast response time, small package size and easy assembly.
The MLX91206 satisfies the demand for the widespread use of electronics in the automotive industry, renewable energy conversion (solar and wind), power supplies, motor control and overload protection.
Areas of use:
- measurement of consumed current in battery supply;
- solar energy converters;
- automotive inverters in hybrid vehicles, etc.
The MLX91206 has surge protection and reverse voltage protection and can be used as a standalone 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 measured current level 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 polarity reversal;
- lead-free components for lead-free soldering, MSL3;
- fast analog output (DAC resolution 12 bits);
- programmable switch;
- thermometer output;
- PWM output (ADC resolution 12 bits);
- 17-bit ID number;
- diagnostics of a faulty track;
- fast response time;
- huge DC bandwidth - 90 kHz.
How the sensor works:
MLX91206 is a monolithic sensor based on the technology Triais® Hall. Traditional planar Hall technology is sensitive to flux density applied perpendicular to the IC surface. The IMC-Hall ® current sensor is sensitive to the flux density applied parallel to the IC surface. This is achieved by an integrated magnetic concentrator (IMC-Hall ®) that is applied to the CMOS chip. 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 horizontal flux density and is therefore suitable for current measurement. It is ideal as an open loop current sensor for PCB mounting. The transfer characteristic of the MLX91206 is programmable (offset, gain, clamp 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.
Measurement of small currents up to ±2 A
Small currents can be measured with the MLX91206 by increasing the magnetic field through the coil around the sensor. The sensitivity (output voltage versus coil current) of the measurement will depend on the size of the coil and the number of turns. Additional sensitivity and desensitization to external fields can be obtained by adding a shield around the coil. The bobbin provides very high dielectric isolation, 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 measurement accuracy and resolution.
Fig.1. Solution for low current.
Average currents up to ±30 A
Currents up to 30 A can be measured with a single conductor located on the PCB. When tracing the PCB, the allowable current and the total power dissipation of the trace must be taken into account. The tracks on the PCB must be thick enough and wide enough to handle the average current continuously. The differential output voltage for this configuration can be approximated by the following equation:
Vout = 35mV/ * I
For a current of 30 A, the output will be approximately 1050 mV.
Fig.2. Solution for average current values.
Measurement of high currents up to ±600 A
Another method for measuring high currents on PCBs is to use thick copper traces capable of carrying current on the opposite side of the PCB. The MLX91206 should be placed close to the center of the trace, however, since the trace is very wide, the output is less sensitive to board placement. This configuration also has less sensitivity depending on the distance and width of the conductor.
Fig.3. Solution for high currents.
About melexis
Established over a decade, Melexis designs and manufactures products for the automotive industry, offering a variety of integrated sensors, ASSPs and VLSIs. Melexis solutions are extremely reliable and meet the high quality standards required in automotive applications.
To control the current consumption, fix the blocking of the motors or the emergency de-energization of the system.
Working with high voltage is hazardous to health!
Touching the terminal block screws and their 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 do not know how to connect the sensor to an electrical appliance powered by a common 220 V network or if you have doubts, stop: you can start a fire or kill yourself.
You must clearly understand the principle of operation 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 connected 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 the group of Troyka Shield contacts related to the analog pin A0. You can use any analog pins in your project. 
Work examples
To make it easier to work with the sensor, we have written the TroykaCurrent library, which converts the sensor's analog output values to 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 the LED strip and the power supply. Let's output the current value of the DC 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 the 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 current-carrying conductor 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 structurally consists 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 strength of the current.
The sensor output voltage level 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 an open circuit through the pads under the screw. 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. The purpose of the contacts of the three-wire loop:
Power (V) - red wire. Based on the documentation, the sensor is powered by 5 volts. As a result of the test, the module also works from 3.3 volts.
Ground (G) - black wire. Must be connected to the ground of the microcontroller;
Signal (S) - yellow wire. Connected to the analog input of the microcontroller. Through it, the control board reads the signal from the sensor.
There is a need to track the presence of current flowing in the circuit in two states: either there or not. Example: you are charging a battery with a built-in charge controller, connected to a power source, but how to control the process? You can, of course, include an ammeter in the circuit, you say, and you will be right. But you won't do it all the time. It’s easier to build a charge flow indicator into the power supply once, which will show whether current is flowing into the battery or not.
Another example. Let's say there is some kind of incandescent lamp in the car that you do not see and do not know if it is on or burned out. In the circuit to this lamp, you can also turn on the current indicator and control the flow. If the lamp burns out, it will be immediately visible.
Or is there a sensor with a filament. Tapa gas or oxygen sensor. And you need to know for sure that the filament is not broken and everything is working properly. This is where the indicator will come to the rescue, the scheme of which I will give below.
There can be a lot of applications, of course the main idea is the same - control of the presence of current.
Current indicator circuit
The scheme is very simple. The resistor with an asterisk is selected depending on the controlled current, it can be from 0.4 to 10 ohms. To charge a lithium-ion battery, I took 4.7 ohms. A current flows through this resistor (if it flows), according to Ohm's law, a voltage is released on it, which opens the transistor. As a result, the LED lights up, indicating that charging is in progress. As soon as the battery is charged, the internal controller will turn off the battery, the current in the circuit will disappear. The transistor will close and the LED will turn off, indicating that charging is complete.Diode VD1 limits the voltage to 0.6 V. You can take any, for a current of 1 A. Again, it all depends on your load. But you can’t take a Schottky diode, since it has a too small drop - the transistor simply may not open from 0.4 V. Through such a circuit, you can even charge car batteries, the main thing is to choose a diode with a current higher than the desired charging current.
In this example, the LED turns on during the passage of current, but if you want to show when there is no current? In this case, there is a scheme with the reverse logic of work.
Everything is the same, only an inverting key is added on one transistor of the same brand. By the way, a transistor of any of the same structure. Domestic analogues are suitable - KT315, KT3102.
In parallel with the resistor with the LED, you can turn on the buzzer, and when there is no current when controlling, say, a light bulb, there will be an audible signal. What will be very convenient, and do not attach to the output of the LED is not the control panel.
In general, there can be many ideas on where to use this indicator.