We come across current measurement very often. In order to find out the power of the device, the cross-section of the cable for its power supply, heating of wires and other elements - it all depends on the current strength. In order to directly measure this force, they came up with a device called an ammeter. The ammeter is connected to the measured circuit only in series. Why? Let's look at it a little lower.

As is known, current strength is the ratio of the number of charges ∆Q that passed through a certain surface during time ∆t. In the SI system it is measured in amperes A (1 A = 1 C/s). In order to measure the number of passed charges, an ammeter must be connected in series to the circuit.

To minimize the influence of the ammeter's measuring resistance and, accordingly, reduce power losses during measurement, it is made as small as possible. If an ammeter with such internal resistance is connected in parallel, then the circuit will experience short circuit. Example of a connection diagram:

Direct current is measured with instruments in the range of 10 -3 - 10 2 A, electronic analogue, digital, magneto-electric, electromagnetic, electrodynamic instruments - milliammeters and ammeters. If the current is over 100 A, use a shunt:

Shunts are usually made for different currents. A shunt is a copper plate that has a certain resistance. When current flows through the plate, according to Ohm’s law U=I*R, some voltage drops on it, that is, between points 1 and 2 a voltage arises that will affect the coil of the device.

The shunt resistance is usually selected from the following ratios:

Where R and is the resistance of the measuring winding of the device, is the shunt coefficient, I is the measured one, and I and is the maximum permissible current of the measuring mechanism.

If alternating current is measured, then it is important to know what value is being measured (amplitude, average, effective). This is important, since all scales are usually graduated in actual values.

Variable values ​​above 100 µA are usually measured with rectifier microammeters, and below 100 µA - with digital microammeters. For measurements in the range from 10 mA to 100 A, rectifier, electrodynamic, electromagnetic devices are used, which operate in the frequency range up to several tens of kilohertz, as well as thermoelectric devices, the frequency range of which is up to hundreds of megahertz.

To measure variable quantities from 100 A and above, instruments are used, but using current transformers:

A current transformer is a device in which the primary winding is connected to a current source (or, as can be seen from the figure below, the primary winding is “put on” a bus or cable), and the secondary winding is connected to the measuring winding of some measuring device (the winding of the measuring device or sensor must have low resistance).

Electrical circuits are present in all areas and sectors of life modern man. If the current supply is stopped, its quality will deteriorate significantly, and a lot of serious dangers will arise from different sides. To constantly regulate the proper operation of the electrical network, you need to know how the ammeter is connected. This device measures current strength.

General information about the device

Laws electrical circuit taught in educational institutions. Every teenager knows the nuances about the directional movement of charged particles. It is represented by the movement of electrons through a conductor and is called electricity. If we consider the practical side, any movement of something in nature (air masses, charges, water in a river) can benefit humanity.

You just need to decide on the duration of the force, its direction, and power.

Based on this, they are created various devices, calculating and measuring all kinds of quantities. For example, to have a detailed understanding of the current, it is worth using an ammeter. The device easily determines the number of charged particles that cross the cross section established in the conductor over a certain period (unit) of time, which is the current strength.

Concept and types of ammeter

The device is suitable for determining the current strength in any existing electrical network. The item is easily recognizable by the existing Latin letter “A”. The ammeter connection diagram is extremely simple. You just need to decide on the current value, starting in milliamps.

The devices are also divided into those that are designed for a certain power, and universal ones with a variable measurement limit. It is worth noting that for working with alternating and direct current, different types ammeters. They are also different in design principle:

The connection circuit for a magnetoelectric type ammeter is extremely simple. It makes it possible to find out the current strength in a network powered by constant voltage. It is more appropriate to work with variable indicators using induction and detector devices.

Other devices are usually universal in use. The peculiarity of units in magnetoelectric and electrodynamic design is their maximum accuracy and high sensitivity.

Circuit connection

To understand how to connect an ammeter of any complexity, you need to know that it is connected in series with the load. In this case, a current similar to electricity in the measured network will pass through the device.

The devices are specially manufactured with low input resistance. This prevents a strong influence on the current and provides minimal obstacles to it. It should be remembered that if the connection is incorrect, when the ammeter is connected in parallel with the load, the current will be directed through the described unit, namely, the rule of least resistance will work. In such situations, in practice, current meters simply fail.

Before buying an ammeter, you need to know with what force it will work - constant or variable. Having decided on the choice of device based on the markings on the scale, It is recommended to set it to maximum power, consider the correct connection to the network.

Next, the readings are taken from the meter. When they are smaller in comparison with the set limit, and the arrow is located in the first part of the gradient, it should be moved to the other side of the scale indicating the most accurate values.

Definition of DC current

This type of electricity passes through various electronic circuits. A striking example will be all kinds of chargers and power supplies. To repair such devices, the technician must know and understand how the ammeter is connected to the circuit.

In everyday life, such knowledge will not be superfluous. They will help a person who is not very interested in radio electronics to independently determine, for example, the time it will take to charge the battery from a camera.

To carry out the experiment, you will need a fully charged battery with a nominal voltage of, for example, 3.5 volts. Also It’s worth stocking up on a light bulb of the same value to create a sequential circuit:

• battery;
• ammeter;
• lamp.

The entry marked on the measuring device is recorded. For example, a lighting product consumes 150 milliampere of electricity, and the battery has a capacity of 1,500 milliamp-hours. Means, the latter should function for 10 hours, delivering a current of 150 mA.

AC Electricity Measurement

Any household appliances powered from the mains show the load with which they consume alternating current. When considering issues of energy use, it is worth remembering the concept of power, for which the final payment is made in kilowatts. In this case, the ammeter acts as a device for performing indirect measurements. In this way the current strength is determined through standard formula according to Ohm's law:

P=I*U, where:

There are cases when information recorded by the electrical panel is lost. To restore the necessary parameters you will need an ammeter. Sometimes, when servicing a large building, it is not possible to control all the devices that record electricity. The problem is solved by connecting an amplified ammeter to the output of the panel and taking the required measurements. Such tasks should only be performed by specially trained people.

Non-contact measurement option

It happens that breaking the electrical circuit without turning on the measuring unit is impossible for technical reasons. It is necessary to find out the current values; this applies to working with high-voltage and conventional networks. The connection diagram for a voltmeter and ammeter in such cases involves the use of special current clamps, which allow non-contact measurements to be taken.

The principle of operation of such a device is based on the fact that current flows to the conductor, thereby creating a certain magnetic field. The magnitudes of these values ​​are interdependent. The intensity in the existing field is measured, converted according to the formula, and the output is a real indicator of the force, expressed in amperes.

This method is often used in practice because of its simplicity, convenience and safety, and the absence of the need to use an ammeter, thinking about how to insert it into the circuit. For example, clamps are fixed on an insulated wire of any circuit and charger, after which the necessary indicators are simply taken. A significant drawback is their high cost.

An ammeter is a popular device when working with electrical networks. At home, it brings no less benefits. The use of such a unit is extremely simple and straightforward.

A miniature Chinese voltmeter can simplify the process of measuring voltage and the amount of current consumed on a power supply or homemade charger. Its cost rarely exceeds 200 rubles, and if you order it from China through partnership programs, you can also get a significant discount.

To charger

Those who like to design their own chargers will appreciate the ability to monitor the volts and amperes of the network, without the help of bulky portable devices. This will also appeal to those who work on expensive equipment, the operation of which can be adversely affected by regular drops in network voltage.

Using a Chinese ampere-voltmeter, which is no larger than a box of matches, you can easily monitor the condition electrical network. One of the tangible problems that new electricians encounter may be the language barrier and wire markings different from standard. Not everyone will immediately understand which wire needs to be connected where, and the instructions are usually only in Chinese.

100 V/10 A devices are very popular among independent designers. It is also desirable that the device have a shunt to finalize the connection process. A tangible advantage of this device is that it can be connected to the charger's power supply or to a self-powered battery.

*The power supply voltage of the ammeter and voltmeter must be in the range from 4.5 to 30 V.

The connection diagram is as follows:

• The black wire is negative. It also needs to be connected to minus.
• The red wire, which should be thicker than the black one, is a plus, and accordingly must be connected to the power source.
• The blue wire connects the load to the network.

If everything has been connected correctly, two scales should light up on the display.

To power supply

Power supplies play an important role in leveling the network readings to the desired state. If not operated correctly, they can cause serious damage to expensive equipment by causing overheating. In order to avoid problems during their operation, and especially in cases where the power supply is made manually, it is advisable to use an inexpensive ammeter and voltmeter.

From China you can order the most different models, but for standard devices, working from home network those that measure current from zero to 20 A and voltage up to 220 V are suitable. Almost all of them are small-sized and can be installed in small power supply cases.

Most devices can be adjusted using built-in resistors. In addition, they have high accuracy, almost 99%. The display displays six positions, three each for voltage and current. They can be powered either from a separate or built-in source.

To connect a voltmeter you need to understand the wires, there are five of them:

• Three thin ones. Black minus, red plus, yellow to measure the difference.
• Two fat ones. Red plus, black minus.

The first three cords are most often combined for convenience. The connection can be made through a special socket connector, or using soldering.

*A connection by soldering is more reliable; with minor vibrations, the socket mount of the device may become loose.

Step-by-step connection:

1. It is necessary to decide from which power source the device will operate, separate or built-in.
2. The black wires are connected and soldered to the minus of the power supply. Thus, a general minus is created.
3. In the same way, you need to connect the thin red and yellow contacts. They are connected to the power contact.
4. The remaining red pin will connect to the electrical load.

If the connection is incorrect, the device display will show zero values. In order for the measurements to be as close as possible to the actual ones, it is necessary to correctly observe the polarity of the supply contacts. Only connecting a thick red wire to the load will give an acceptable result.

Note! Receive exact values voltage can only be regulated source nutrition. In other cases, the display will only show the voltage drop.

A popular voltmeter model that is often used by radio amateurs. Has the following characteristics:

• Operating voltage DC from 4.5 to 30 V.
• Power consumption less than 20 mA.
• The display is two-color red and blue. Resolution 0.28 inches.
• Performs measurements in the range 0 – 100 V, 0 – 10 A.
• The lower limit is 0.1 V and 0.01 A.
• Error 1%.
• Temperature operating conditions from -15 to 75 degrees Celsius.

Connection

Using a voltmeter, you can measure the current voltage in the power supply network. To do this, you need the following:

• Connect the thick black wire to the negative of the power supply.
• Red connects to the load, and then to the power.

This connection diagram does not provide for the use of a thin black contact.

If a third-party power source is used, the connection will be as follows:

• Thick cords are connected in the same way as in the previous example.
• Thin red connects to the plus of a third-party source.
• Black with a minus.
• Yellow with source plus.

This voltmeter and ammeter is also convenient because it is sold in an already calibrated state. But even if inaccuracies in its operation were noticed, they can be corrected using two tuning resistors on the rear panel of the device.

Which digital voltmeters are the most reliable?

The electrical equipment market is crowded with manufacturers who provide a wide variety of choices. However, not every device brings positive emotions from use. With a large number of products, it is not always possible to find a reliable and inexpensive copy.

Tested and reliable voltmeters include:

• TK 1382. Inexpensive Chinese, the average price of which rarely rises above 300 rubles. Equipped with tuning resistors. Performs measurements in the ranges 0-100 Volts, 0-10 Amps.
• YB27VA. Almost a twin of the previous voltmeter, it differs in the marking of the wires and at a reduced price.
• BY42A. Costs more previous models, but also has an increased upper measurement limit of 200 V.

These are the most popular representatives of this type voltmeters, which can be freely purchased for conversion on the radio market or ordered via the Internet.

Calibration of Chinese voltmeter ammeter

Over time, any equipment wears out. Since the operation of measuring instruments is affected not only by their own faults, but also by faults in the connected devices, sometimes it is necessary to make adjustments.

Most models have special resistors on their housing. By rotating them, you can change the zero values.

All measuring instruments have a measurement error, which is indicated in the documentation.

Conclusion

Including inexpensive voltmeters in the circuit avoids problems with inappropriate network voltage. For a small fee, you can find out whether the equipment works in suitable conditions. To connect them, you need to know the markings of all wires and the location of the plus and minus of the energy source.

In ammeters, the current passing through the device creates a torque, causing its moving part to deflect by an angle depending on this current. This deflection angle is used to determine the current value of the ammeter.

In order to measure the current in some energy receiver with an ammeter, it is necessary to connect the ammeter in series with the receiver so that the current of the receiver and the ammeter is the same.The resistance of the ammeter should be small compared to the resistance of the energy receiver, in series with which it is connected, so that its inclusion has virtually no effect on the magnitude of the receiver current (on the operating mode of the circuit).Thus, the resistance of the ammeter should be small and the smaller, the greater its rated current. For example, with a rated current of 5 A, the resistance of the ammeter is r a = (0.008 - 0.4) ohm. If the resistance of the ammeter is low, the power loss in it is also low.

Rice. 1. Connection diagram for ammeter and voltmeter

With a rated current of the ammeter of 5 A, power loss P a = I a 2 r = (0.2 - 10) Va. The voltage applied to the terminals of the voltmeter causes a current in its circuit. At constant current depends only on the voltage, i.e. Iv = F(Uv).This current, passing through the voltmeter, as well as in the ammeter, causes a deflection of its moving part by an angle depending on the current. So Thus, for each voltage value at the terminals, a voltmeter boo will correspond to well-defined values ​​of current and angle of rotation of the moving part.

In order to determine the voltage at the terminals of the energy receiver or generator using the readings of a voltmeter, it is necessary to connect its terminals to the terminals of the voltmeter so that the voltage at the receiver (generator) is equal to the voltage at the voltmeter (Fig. 1).

The resistance of the voltmeter must be large compared to the resistance of the energy receiver (or generator) so that its inclusion does not affect the measured voltage (the operating mode of the circuit).

Example. To the terminals of a circuit with two series connecting receivers (Fig. 2) having resistancer1 = 2000 ohms and r2 = 1000ohm, voltage appliedU =120 V.

Rice. 2. Voltmeter connection diagram

In this case, at the first receiver the voltageU1 = 80 V, and on the second U 2 = 40 V.

If you connect a voltmeter with resistance in parallel to the first receiver rv= 2000 ohms to measure the voltage at its terminals, then the voltage at both the first and second receivers will have a valueU " 1 = U " 2 =60 V.

Thus, turning on the voltmeter caused a change in voltage at the first receiver withU1= 80 V to U " 1 = 60V, i.e. the error in voltage measurement caused by turning on the voltmeter is equal to ((60V - 80V)/80V) x 100% = -25%

Thus, the resistance of the voltmeter should be large, and the greater the higher its rated voltage. At rated voltage 100 V, the voltmeter resistance rv = (2000 - 50000) ohm. Due to the high resistance of the voltmeter, the power loss in it is low.

At a rated voltage of the voltmeter of 100 V, the loss power Pv = (Uv 2 /rv) Va.

From the above it follows that an ammeter and a voltmeter can have measuring mechanisms of the same device, differing only in their parameters. But the ammeter and voltmeter are included in the measured circuit in different ways and have different internal (measuring) circuits.

If you have a regular analog ammeter and you don’t know how to connect it, then this is very easy to do. In addition to the ammeter, you need a SHUNT, since the ammeter measures the voltage drop across the shunt. The connection diagram for an ammeter with a shunt looks like this (figure below). If you don’t have a shunt, you can make one yourself, and more on that later in the article.

If you have an ammeter and there is no shunt for it, you can make one yourself. As a shunt, you can take a segment copper wire, the thickness of this wire depends on the current that will be measured. For example, for currents up to 10A, you can take a wire with a cross-section of 1.5 kW, if the current is up to 30A, then it is better to take a wire of 2.5 kW.

A length of approximately 30 cm is needed; it must be completely stripped of insulation. Next, we connect this wire instead of the shunt; in the picture below, I think everything is clear.

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Such a shunt is no worse than the factory one, except of course appearance. And calibrating an ammeter is quite simple. We need a second ammeter, which is connected in series with our shunt. It can be before our homemade shunt, or it can be after. We connect the energy consumer to the power source and see how much the second ammeter shows. Next, we look at our ammeter and use a homemade shunt to move the contacts of the ammeter, bringing them closer or further away from each other so that the readings on both ammeters are the same. That's all, when the ammeter readings are the same, all that remains is to solder the contacts from the ammeter to the shunt so that they do not move and the ammeter does not go astray.

After this, the ammeter is ready for use, and the homemade shunt can be placed in some kind of housing or hidden from view if you don’t like it. In addition, the shunt can be made not only from copper wire. A metal plate will do, even a simple bolt where you can use nuts to clamp the wires from the ammeter and adjust the distance between the wires to calibrate the device.

Below is the photo of my ammeter with a homemade shunt.

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I did not measure the length of the active zone of the shunt, so I cannot say at what distance to solder the wires from the ammeter. Well, the cross-section of the copper wire may be different and the ammeter itself may also be different, so you still have to calibrate it. I did this using a multimeter. A few more photos of an ammeter with a homemade shunt.

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This is what it looks like from the reverse side, you can see how the wires come out of the ammeter and how they connect to this copper shunt

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I think it’s clear how the ammeter works and how to connect the shunt. The shunt is connected in series, that is, into a break in one of the wires going to the energy consumer. You can place the shunt either on the plus side or on the minus side. If the ammeter needle deviates in the wrong direction, then you just need to turn the shunt over. And so the ammeter measures the voltage drop across the shunt, the voltage drop there in millivolts.

In my opinion, almost all factory shunts have a voltage drop of up to 75 mV, and the shunt must be selected according to the characteristics of the ammeter. If the ammeter is 50A and 75mV, then you need to buy the same shunt, otherwise the ammeter will show incorrectly." I hope this information helped you, thank you for reading and leave comments.