Wiring diagram for an electronic ammeter. How to connect an ammeter, what kind of device is it? DSN-VC288 connection diagram

An ammeter is an electrical measuring device designed to fix the strength of a direct or alternating current flowing in a circuit - that is current measuring device... connected in series, with the section of the electrical circuit where the current is supposed to be measured. Since the current that it measures depends on the resistance of the circuit elements, the resistance of the ammeter should be as low as possible (very small). This makes it possible to reduce the influence of the current measuring device on the measured circuit and increase their accuracy.

The instrument scale is calibrated in μA, mA, A and kA, and a suitable instrument is selected depending on the required accuracy and measurement limits. An increase in the measured current strength is achieved by including shunts and magnetic amplifiers in the circuit. This allows you to increase the limit of the measured value of the current.

Ammeter connection diagrams

Figure - Scheme of direct connection of an ammeter

Figure - Scheme of indirect connection of an ammeter through a shunt and a current transformer

Scope of ammeters

Devices for measuring current have found application in various fields. They are actively used at large enterprises related to the generation and distribution of electrical and thermal energy. They are also used in:

- electrical laboratories;

- automotive industry;

- exact sciences;

- construction.

But not only medium and large enterprises use this device: they are in demand among ordinary people. Almost any experienced auto electrician has a similar device in his arsenal, which makes it possible to measure the indicators of power consumption of devices, car assemblies, etc.

Types of ammeters

Based on the type of reading device, they are divided into devices with:

- with a pointer;

- with a light indicator;

- with a writing device;

- electronic devices.

5. Electrodynamic devices are designed to measure the magnitude of the current in circuits / alternating currents of increased frequencies (up to 200 Hz). They are sensitive to overloads and external electromagnetic fields. But due to the high accuracy of measurements, they are used as control devices for checking operating ammeters.

- Measurement error 1%

- Discreteness of indication 0.1 A

- power supply -100 ... -400 V, 50 (+1) Hz Overall dimensions 90x51x64 mm

The performance and durability of household electrical appliances depend on the quality of the electricity received. As a rule, to the failure of electronic equipment, be it refrigerators, televisions or washing machines, results in an increase above acceptable limits. The most dangerous is a prolonged increase above the permissible level. In this case, the power supplies of electronic equipment fail, the windings of the electric motors overheat, and fire often occurs.

2. Laboratory ammeter E537

This device (ammeter E537) is designed to accurately measure the current in AC and DC circuits.

Accuracy class 0.5.

Measurement ranges 0.5 / 1 A;

Weight 1.2 kg.

Specifications ammeter E537:

Measurement range end value 0.5 A / 1 A

Accuracy class 0.5

Normal frequency range (Hz) 45 - 100 Hz

Operating frequency range (Hz) 100 - 1500 Hz

Overall dimensions 140 x 195 x 105 mm

3. Ammeter CA3020

The digital device of the basic model is produced in several standard modifications, depending on the basic value of the parameters of the measured current. When ordering this model of a digital ammeter, you need to declare which basic parameter of the current strength you will have to work with: 1 A, 2 A or 5 A.

Basic parameters of the measured current, In-1 Ampere (CA3020-1), 2 Ampere (CA3020-2) or 5 Ampere (CA3020-5);

Limits of measured currents from 0.01 In to 1.5 In;

The frequency range for the measured currents is from 45 to 850 Hertz;

The boundaries of the basic permissible existing error ± 0.2% to the optimal value of the parameters of the measured current;

Power supply - AC network with voltage (85-260) Volts and frequency (47-65) Hertz or constant (120 - 300) Volts;

The power consumed by the device is not more than 4 VA;

Dimensional dimensions 144x72x190 mm;

Weight is not more than 0.55 kg;

The power consumed by the measuring circuit of the 3020 series does not exceed: for CA3020-1 - 0.12 VA; for CA3020-2 - 0.25 VA; for CA3020-5 - 0.6 VA.

D.C does not change direction in time. An example is a battery in a flashlight or radio, or a battery in a car. We always know where the positive brand of the power supply is, and where is the negative one.

Alternating current- this is a current that changes the direction of movement with a certain frequency. This current flows in our outlet when we connect a load to it. There is no positive and negative pole, but only phase and zero. Zero voltage is close to ground potential. The potential at the phase output changes from positive to negative with a frequency of 50 Hz, that is, the current under load will change its direction 50 times per second.

During one period of oscillation, the current increases from zero to a maximum, then decreases and passes through zero, and then the opposite process takes place, but with a different sign.

Receiving and transmitting alternating current is much easier than direct current: there is less energy loss.With the help of transformers, we can easily change the alternating current voltage.

When transmitting a large voltage, less current is required for the same power. This allows for more subtle reasoning. Welding transformers use the reverse process - they lower the voltage to increase the welding current.

To in electrical circuit, it is necessary to turn on the ammeter or milliammeter in series with the electricity receiver. At the same time, in order to exclude the influence of the measuring device on the consumer's operation, it must have a very low internal resistance, so that in practice it could be taken equal to zero, so that the voltage drop across the device could be simply neglected.

The inclusion of an ammeter in the circuit is always in series with the load. If you connect the ammeter in parallel with the load, parallel to the power source, then the ammeter will simply burn out or the source will burn out, since all the current will flow through the meager resistance of the measuring device.

The measurement limits of ammeters intended for measurements in DC circuits are expandable by connecting the ammeter not directly with a measuring coil in series with the load, but by connecting the measuring coil of the ammeter in parallel with the shunt.

So, only a small part of the measured current will always pass through the coil of the device, the main part of which will flow through the shunt connected in series to the circuit. That is, the device will actually measure the voltage drop across the shunt of a known resistance, and the current will be directly proportional to this voltage.

Almost an ammeter will work as a millivoltmeter. Nevertheless, since the scale of the device is graduated in amperes, the user will receive information about the value of the measured current. The shunting factor is usually chosen as a multiple of 10.

Shunts designed for currents up to 50 amperes are mounted directly into the instrument cases, and shunts for measuring high currents are made remote, and then the device is connected to the shunt with probes. For devices intended for continuous operation with a shunt, the scales are immediately calibrated in specific current values, taking into account the shunting coefficient, and the user no longer needs to calculate anything.

If the shunt is external, then in the case of a calibrated shunt, it indicates the rated current and rated voltage: 45 mV, 75 mV, 100 mV, 150 mV. For current measurements, a shunt is selected so that the arrow deflects a maximum - to the entire scale, that is, the nominal voltages of the shunt and the measuring device should be the same.

If we are talking about an individual shunt for a specific device, then everything is, of course, simpler. According to the accuracy classes, the shunts are divided into: 0.02, 0.05, 0.1, 0.2 and 0.5 - this is the permissible error in fractions of a percent.

Shunts are made of metals with a low temperature coefficient of resistance, and with significant resistivity: constantan, nickelin, manganin, so that when the current flowing through the shunt heats it up, this would not be reflected in the readings of the device. To reduce the temperature factor during measurements, an additional resistor made of the same kind of material is included in series with the ammeter coil.

So that a voltmeter is connected between two points of the circuit, parallel to the circuit, between these two points. The voltmeter always turns on in parallel with the receiver or source. And so that the connected voltmeter does not affect the operation of the circuit, does not cause a decrease in voltage, does not cause losses, it must have a sufficiently high internal resistance so that the current through the voltmeter can be neglected.

And in order to expand the measurement range of the voltmeter, an additional resistor is connected in series with its working winding, so that only a part of the measured voltage would fall directly on the measuring winding of the device, in proportion to its resistance. And with a known value of the resistance of the additional resistor, the total measured voltage acting in this circuit is easily determined from the voltage fixed on it. This is how all classic voltmeters work.

The coefficient that appears as a result of adding an additional resistor will show how many times the measured voltage is greater than the voltage across the measuring coil of the device. That is, the measurement limits of the device depend on the value of the additional resistor.

An additional resistor is built into the device. To reduce the influence of ambient temperature on measurements, an additional resistor is made of a material with a low temperature coefficient of resistance. Since the resistance of the additional resistor is many times greater than the resistance of the device, then the resistance of the measuring mechanism of the device, as a result, does not depend on temperature. Accuracy classes of additional resistors are expressed similarly to the accuracy classes of shunts - in fractions of a percent, they indicate the magnitude of the error.

To further expand the measurement range of voltmeters, voltage dividers are used. This is done so that when measuring, the device has a voltage corresponding to the rating of the device, that is, it would not exceed the limit on its scale. The voltage divider ratio is the ratio of the input voltage of the divider to the output voltage being measured. The division factor is taken equal to 10, 100, 500 and more, depending on the capabilities of the used voltmeter. The divider does not introduce a large error if the resistance of the voltmeter is also high, and the internal resistance of the source is small.

AC current measurement

To accurately measure AC parameters with the instrument, a measuring transformer is required. An instrument transformer used for measuring purposes also provides personnel with safety, since the transformer provides galvanic isolation from the high voltage circuit. In general, safety precautions prohibit connecting electrical instruments without such transformers.

The use of measuring transformers allows you to expand the measurement range of devices, that is, it becomes possible to measure high voltages and currents using low-voltage and low-current devices. Thus, instrument transformers are of two types: voltage transformers and current transformers.

Instrument voltage transformer

To measure AC voltage a voltage transformer is used. This is a step-down transformer with two windings, the primary winding of which is connected to two points in the circuit, between which you need to measure the voltage, and the secondary winding directly to the voltmeter. Instrument transformers in the diagrams are depicted as ordinary transformers.

The transformer without a loaded secondary winding operates in no-load mode, and when a voltmeter is connected, the resistance of which is high, the transformer remains practically in this mode, and therefore the measured voltage can be considered proportional to the voltage applied to the primary winding, taking into account the transformation ratio equal to the ratio of the number of turns in its secondary and primary windings.

In this way, high voltages can be measured and a small, safe voltage is applied to the instrument. It remains to multiply the measured voltage by the transformation ratio of the voltage transformer.

Those voltmeters, which were originally designed to work with voltage transformers, have a scale graduation taking into account the transformation ratio, then the value of the changed voltage is immediately visible on the scale without additional calculations.

In order to increase safety when working with the device, in case of damage to the insulation of the measuring transformer, one of the terminals of the secondary winding of the transformer and its frame are first grounded.

Instrument current transformers

Measuring current transformers are used to connect ammeters to alternating current circuits. These are two-winding step-up transformers. The primary winding is connected in series to the measured circuit, and the secondary to the ammeter. The resistance in the ammeter circuit is small, and it turns out that the current transformer operates practically in a short-circuit mode, while it can be assumed that the currents in the primary and secondary windings relate to each other as the number of turns in the secondary and primary windings.

By choosing a suitable ratio of turns, it is possible to measure significant currents, while currents will always flow through the device sufficiently small. It remains to multiply the current measured in the secondary winding by the transformation ratio. Those ammeters that are designed for continuous operation in conjunction with current transformers have a scale graduation taking into account the transformation ratio, and on the scale of the device without calculations, you can easily read the value of the measured current. In order to increase the safety of personnel, one of the terminals of the secondary winding of the measuring current transformer and its frame are first grounded.

In many applications, bushing current transformers are convenient, in which the magnetic circuit and the secondary winding are insulated and located inside the bushing housing, through the window of which a copper bus with the measured current passes.

The secondary winding of such a transformer is never left open, because a strong increase in the magnetic flux in the magnetic circuit can not only lead to its destruction, but also induce an EMF dangerous for personnel on the secondary winding. To make a safe measurement, the secondary winding is shunted with a resistor of known value, the voltage across which will be proportional to the measured current.

Instrument transformers are characterized by errors of two types: angular and transformation ratio. The first is associated with the deviation of the phase angle of the primary and secondary windings from 180 °, which leads to inaccurate readings of the wattmeters. As for the error associated with the transformation ratio, this deviation shows the accuracy class: 0.2, 0.5, 1, etc. - as a percentage of the nominal value.

Andrey Povny

If the connected extension cord overheats or the battery is running low quickly, checking the amperage on the appropriate circuit will help identify the source of the problem. To successfully solve these and other tasks, you need a suitable measuring device. This publication describes how to connect the ammeter correctly, perform the necessary operations in safe mode.

What is an ammeter, its types

As shown in the figure, the device is connected in series in a circuit through which an electric current flows. To minimize the impact on real physical processes, it is necessary to reduce the internal resistance of the ammeter. A large scale is useful for taking readings. When choosing the right equipment, the following factors are also taken into account:

• digital indicator simplifies the measurement process;
• working with low and high currents is easier with the use of division into several ranges;
• under unfavorable external conditions (humidity, vibration), the appropriate protection of the device must be taken into account.

Magnetoelectric

The measuring unit for this category consists of two main components. An induction coil is placed between the poles of the permanent magnet. When current passes through the windings, it turns. By attaching an arrow and a scale, these movements are recorded to obtain measurement results. Built-in springs limit the amplitude of deflection, return moving components to their original position. The built-in leash adjusts the tension. The weights are used to compensate for the force of gravity.

In two diagrams, number 1 denotes the source of the field, which turns the coil (3), rigidly fixed on the central axis. The device begins to function when current flows through the circuit. The coil spring (4) adjusts the movements. In the first version, a limiter (2) is installed to prevent damage to the arrow.

The advantages of such engineering solutions are:

• high accuracy;
• good sensitivity;
• absence additional sources food;
• democratic cost.

On a note. The main disadvantage is the mechanical parts. The complexity of the design implies a deterioration in reliability. It should be remembered about the negative impact of impacts and other external influences. Such a device is suitable for measuring direct current.

Electromagnetic

It is unlikely that an ordinary user will have to repair complex devices. Therefore, the selection and connection of an ammeter are further considered in detail. Electromagnetic devices are universal. They are suitable for measuring AC and DC currents. The sensitivity in this case is slightly lower than in the previous example. However, in some situations it is quite enough.

Thermoelectric

Devices in this category perform measurements using an indirect method. A thermocouple or similar device is used to convert alternating current to direct current. Its value is controlled by including a magnetoelectric or other ammeter in an additional circuit. The contact version provides increased sensitivity. To exclude galvanic coupling, the sensor is placed in a layer of neutral material (glass, polymer).

Electrodynamic

In this embodiment, two coils are installed side by side. A current is passed through one connected to the indicator device. The second is fixed motionless. This scheme is characterized by increased sensitivity. Even the weak magnetic fields have strong enough impacts on the moving element. To obtain accurate measurements, the device is removed from sources of interference as much as possible, and shielding is used.

Ferrodynamic

How an ammeter differs from a voltmeter

The main features are clear from the specific names. The first picture shows how the ammeter is connected (in series). This is necessary for the passage of the current and the corresponding measurement of its magnitude. The voltmeter is connected in parallel. In this version, the device will show the potential difference between two points, the voltage across a certain resistor or other element of the electrical circuit.

How to determine the division price of an ammeter

The variety of instruments creates natural difficulties in the measurement process. The following example will help you understand the technique of correctly determining the values ​​on the arrow indicator. In any case, start with the letter designation on the dial:

• "A" is amperes, no recalculation is needed;
• "MA" - milliamps, the total value is calculated by multiplying by 0.001.

This device measures current up to 4 amperes inclusive. Translation of values ​​is not needed, because there is an “A” mark. To find out the price of one division, subtract from the larger the smaller value of the adjacent digits. Then it is divided by the number of empty gaps between the risks.

reference... "RISK is a line (stroke) applied ... to the scale of the measuring device." Big Polytechnic Encyclopedia edited by Ryazantsev, no. 2011 r.

In the example given:

The manufacturer's tolerance can be found in the description for the device. This value is usually indicated as a percentage.

How ammeter and voltmeter work

The designs discussed above are suitable for creating one and the other device. The difference is not only in the wiring diagram. The markings and resistance of the induction coil are different. The built-in resistor limits the current / power in the ammeter / voltmeter, respectively.

In the first version, it acts as a shunt. Parallel connection with minimum electrical resistance ensures that most of the current flows through this circuit. This protects the inductive element from damage.

In the second, a resistance is selected that is many times greater than the corresponding indicator of the coil. Another feature is the choice of the resistor material with a minimum change in operating parameters with an increase (decrease) in temperature.

How to connect an ammeter to an electrical circuit

It is not difficult to connect the device to the open circuit. For safety reasons, perform this procedure after disconnecting the power supply. First, you need to make sure that the maximum current does not exceed the capabilities of the ammeter. These scales are duplicated in the accompanying technical documentation.

After the supply voltage is applied, readings are taken. Wait until the arrow stops oscillating. If it moves in the opposite direction, the polarity of the connection is reversed. With an excessively large current, additional shunting is used.

How to choose a shunt for an ammeter

To calculate the parameters of the additional circuit, use the formulaRw =Rext *Ietc/(Iin-Ipr), where:

• Rsh - shunt resistance;
• Rvn - internal resistance of the ammeter (given in the data sheet);
• Ipr - maximum current for which the device is designed;
• Iin is the input current (source) before the branching of the circuit.

Measurement of DC values

To work with such circuits, choose a "classic" magnetoelectric or other suitable device. Check compatibility for maximum currents. If necessary, use a parallel shunt circuit. In circuits with variable electrical parameters, such an ammeter is not useful, since the arrow will oscillate around the zero mark. Strong signal amplitude can cause mechanical damage.

Measurement of AC values

However, if you supplement the magnetoelectric meter with a rectifier, you can get the desired result. This addition will introduce certain errors, so it is better to use a factory product. The connection diagram for an ammeter of this type does not differ from the options discussed above.

Remember! The measurement accuracy is influenced by the shape of the input signal.

Non-contact method of measuring current

It is hardly necessary to violate the integrity of quality cables without special need. Sometimes it is impossible to disconnect the supply voltage. When dealing with powerful lines of force, additional security measures come in handy. In all these situations, the current can be measured using specialized instruments.

The annular part of the tool, after closing, forms an induction coil. A built-in digital instrument registers the induced currents.

Why control the charge current in the battery

The use of a measuring device can be considered on the example of a typical technological operation. Serviced car battery infect by a special technique. The current value is set and maintained at the level of 10% of the capacity indicated in the passport data. This prevents the excessive evolution of explosive gases. The duration of the procedure (24 hours or more) implies the need to supplement the device with automatic shutdown means.

With the help of the information provided, you can independently choose a suitable device, perform measurements, assemble a shunting circuit. At the stage of preliminary preparation, the expected operating range and operating conditions should be clarified. When buying, it is recommended to study official instructions manufacturer.

Video

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

In order to measure the current in some kind of 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 in comparison with the resistance of the energy receiver, in series with which it is switched on, so that its switching on has practically 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 lower, the greater its rated current. For example, at a rated current of 5 A, the resistance of the ammeter is r a = (0.008 - 0.4) ohm. With a low resistance of the ammeter, the power losses in it are also small.

Rice. 1. Scheme for switching on an ammeter and a voltmeter

At a rated current of the ammeter of 5 A, the 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 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 that depends on the current. So in this way, each voltage value at the terminals of a voltmeter boo well defined values ​​of the current and the angle of rotation of the movable part.

In order to determine the voltage at the terminals of the energy receiver or generator according to the voltmeter reading, it is necessary to connect its terminals to the voltmeter terminals 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 in comparison with 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 the circuit with two series-connected receivers (Fig. 2), having resistancer1 = 2000 ohms and r2 = 1000ohm, voltage appliedU = 120 V.

Rice. 2. Scheme for switching on a voltmeter

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

If you turn on a voltmeter with a resistance in parallel with 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 voltage change at the first receiver withU1 = 80 V to U "1 = 60V, that is, the error in measuring the voltage due to the inclusion of a voltmeter is equal to ((60V - 80V) / 80V) x 100% = -25%

Thus, the resistance of the voltmeter should be greater and the greater, the greater its nominal voltage. At a rated voltage of 100 V, the resistance of the voltmeter rv = (2000 - 50,000) ohm. Due to the large resistance of the voltmeter, the power losses in it are low.

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

From the foregoing it follows that the ammeter and 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.

When designing chargers for rechargeable batteries, and various power supplies, many radio amateurs use ready-made voltmeters-ammeters made in China, which can be easily bought on the Internet, for example, on the Aliexpress website. Moreover, the cost of such ready-made devices is very attractive, and many suppliers, in addition to everything, carry out free delivery of goods to the buyer. Having found the most advantageous offer, we ordered a pair of WR-005 devices for testing, designed to measure voltage up to 100 Volts, and current up to 10 Amperes. The order came, everything is in order with the blocks, there is no mechanical damage, but there was no passport or instructions describing how to connect the device. This was the reason for writing this article, because, most likely, we are not alone who are faced with the issues of connecting the WR-005 to the measurement circuits.

Such measuring devices can be designed for other measurement parameters, but in any case, you will have two connectors on the board:

● The first connector has two thin wires, usually red and black. They serve to supply the supply voltage to the measuring circuit. The supply voltage has a very wide range, you can supply from 4 to 30 Volts, the red wire is positive, the black wire is negative. After applying power to the circuit, the indicator will light up.
● The second connector is three-wire, the wires are thick, intended for connecting the device to the measuring circuits. But let's deal with the colors of the wires.

It seems that indicators were produced earlier in which thick wires were black, red and yellow, so you can find this picture on the Internet:

In our case, this connector has blue, black and red wires, and the black wire is in the middle of the connector, so we decided to double-check them.

As it turned out, nothing has changed globally:

● The black wire, as in the previous version, is the common wire (COM);
● Red wire - voltage measurement;
● Blue wire - current measurement.

For those who do not quite understand: the black thick wire is connected to the minus of the source, the red to the plus (the voltmeter will start showing), the blue thick wire is connected to the load, and from the second end of the load goes to the plus of the source (the ammeter shows).

About the shunt. In devices up to 10 Amperes, the shunt is built-in (soldered directly to the board), over 10 Amperes, as a rule, there must be an external shunt in the kit, see the pictures below:

Our version of the device with a built-in shunt:

An external shunt looks like this:

Even after the correct connection, there is no guarantee that the readings of the voltmeter and ammeter will be correct, so it is worth checking them using, for example, an external multimeter. If necessary, you can correct the readings using the trimming resistors located on the board of the WR-005 device.

The microcircuit on which the device is assembled does not have any identification marks, but the schematic diagram is like this:

In conclusion, I would like to say that after connecting and testing the device, it showed itself on the positive side, the build quality is not bad, the error in the readings corresponds to the declared supplier, that is, the voltage error is 0.1 Volts, the current is 0.01 Ampere, the current consumption of the measuring circuit does not exceed 20 mA. Any electronics are prone to fail over time, so how long this voltmeter-ammeter will serve us - time will tell. But, in principle, for that kind of money, we believe that the WR-005 is a worthy purchase with quick installation and connection in devices that need to display digital indication of current and voltage parameters.

If anyone knows the brand of the microcircuit used in the circuit of the device, please write in the comments.