A digital wattmeter is an improved modification of its analog predecessor. It serves for a network that should not go beyond restrictions. Otherwise, a fire and equipment failure may occur. With constant current, the power indicator is calculated by multiplying the voltage by the current using an ammeter and voltmeter. An alternating current circuit requires special measuring instruments, which include a wattmeter.
Purpose
Digital wattmeters are mainly used in the electrical power industry, mechanical engineering, and in the repair of electrical devices. In everyday life, these devices are used by specialists in electrical engineering, computer equipment, and radio amateurs.
Wattmeter capabilities:
- Testing of electrical circuits or sections thereof.
- Determination of device power.
- Testing of electrical installations by indicator type.
- Monitoring the operation of electrical equipment.
- Accounting for the use of electrical energy.
Kinds
Power is measured based on voltage and current data. According to the method of measuring and issuing final information, the devices in question are divided into analog and digital wattmeters.
The analog type version has a block of recording and display elements. They reveal the active power of a certain section of the circuit. The screen of such a device has a graduated scale and arrow. The dial divisions are divided according to the power indicator in watts.
Digital modifications measure active and information about voltage, current, per unit of time is displayed. The measurement results are displayed on a computer device.
How does it work?
The basic principle of operation of a digital wattmeter, the diagram of which is shown above, is to carry out a preliminary measurement of voltage and current strength. To do this, connect a current sensor in series to the consuming device, and a voltage indicator in parallel circuit. These elements are made of thermistors or their analogues (measuring transformers, thermocouples).
The measured parameters are instantly transmitted through the converter to the internal microprocessor. Power is measured and the results obtained are displayed on the screen and transmitted to external devices.
It is worth noting that electrodynamic devices have a wide spectrum of action, working with both direct and alternating current. Inductive devices are used only for alternating current circuits.
Digital household wattmeter
Most often, Chinese-made devices are presented in the domestic market in this segment. Such a device measures the power of different electricity consumers. To start working, its plug should be inserted into a standard socket, and the plug of the consumer whose power will be measured should be connected to the socket of a household digital wattmeter.
With this device you can measure the power of the consumer and calculate the money spent for the electricity used from a specific device.
This digital wattmeter is equipped with a built-in rechargeable battery, which is used to store the measured power. The front panel has several buttons designed to switch modes, indicate the calculated price, reset information, and switch the upper and lower positions. On the back of the case the maximum operating voltage (230 V), frequency (50 Hz), measured power (from 0 to 3600 W), and current limit (16 A) are indicated.
Testing
Let's consider the operation of a digital wattmeter using the example of a household modification. After plugging into the socket, the display shows the time required to measure the consumer's power. Let's take an LED lamp as an example. When the lamp is turned off, the screen displays an indicator of 0.4 W (the power of the disconnected consumer). When the lamp is turned on, the reading changes to 10.3 W. The price column contains zeros if it is not indicated.
The LED can change the glow power. As brightness increases, power parameters also increase. When the second mode is activated, two fields are also displayed at the top (time and kW/hours). Since the device has been in operation for less than an hour, the time field contains zeros. At the bottom there is a display of information about how many days a specific consumer was measured.
Next mode: the second field displays the network voltage and current frequency. The top part of all modes shows the measurement time. The transition to the next mode is accompanied by current readings in the central part of the screen.
Mode No. 5 displays the minimum power, and mode six displays its maximum. installed manually using buttons. After setting all the parameters, you can measure and calculate the consumption of any household electrical appliance.
CPU model 8506-120
This digital AC wattmeter is designed to measure active and reactive circuit power in a three-phase AC network. The unit demonstrates the current power on the sensor, displaying an analog signal. The digital screen is divided into four digits; the measurements taken are displayed in the form of numbers, taking into account the transformation ratio.
Characteristics:
- Power indicator coefficient - 1.
- Dimensions - 12x12x15 cm.
- Numbers on the screen (height) - 20 mm.
- The maximum reading range is 9999.
- Error - 0.5.
- Conversion speed is no more than 0.5 seconds.
- Operating temperatures - from +5 to +40 degrees Celsius.
- Housing protection category - class IP 40.
- Power consumption - 5 W.
- Operating frequency - 50 Hz.
- Weight - 1200 g.
Multifunctional device CM 3010
This digital wattmeter is designed for measuring direct and alternating current. In addition, it can be used to work with less accurate analogues.
Options:
- The range of measurements taken is 0.002 - 10 A.
- Measurements of direct/alternating current indicators - 1-1000/1-700 V.
- Frequency interval 40-5000 Hz.
- The error in DC/AC current measurements is 0.1%/0.1%.
- The same indicator for measured frequencies in the range 40-5000 Hz is 0.003%.
- Weight - 1 kg.
- Overall dimensions - 22.5x10x20.5 cm.
- Power consumption - 5 W.
D 5085
A universal wattmeter is used to measure power in single-phase DC and AC circuits, as well as control devices with lower accuracy.
Characteristics:
- Dimensions - 20.5x29x13.5 cm.
- Working conditions - temperature from +10 to +35 degrees with humidity not higher than 80%.
- Error - 0.2.
- Rated power factor - 1.0.
- The nominal current of the parallel circuit of the device is 5 mA.
LSENE
This digital wattmeter for batteries, the price of which starts from 500 rubles, is equipped with a liquid crystal display and provides real-time testing of the battery, with readings from 0 to 60 V. The device has low energy consumption and works with batteries of 12, 24, 36, 48 V.
Options:
- Operating voltage - 0-60 V.
- Maximum current - 0.01 A.
- Operating current - 7 A.
- Overall dimensions - 84x50x20 mm.
- The data output sequence is no more than 2 seconds.
A wattmeter is used to directly measure the power of a DC circuit. The fixed series coil or current coil of a wattmeter is connected in series with the electrical energy receivers. A moving parallel coil or voltage coil connected in series with an additional resistance forms a parallel wattmeter circuit, which is connected in parallel to the energy receivers.
Angle of rotation of the moving part of the wattmeter:
α = k2IIu = k2U/Ru
Where I - series coil current; I and is the current of the parallel coil of the wattmeter.
Rice. 1. Diagram of the device and connections of the wattmeter
Since, as a result of the use of additional resistance, the parallel circuit of the wattmeter has an almost constant resistance ru, then α = (k2/Ru)IU = k2IU = k3P
Thus, by the angle of rotation of the moving part of the wattmeter, one can judge the power of the circuit.
The wattmeter scale is uniform. When working with a wattmeter, it must be borne in mind that a change in the direction of the current in one of the coils causes a change in the direction of the torque and the direction of rotation of the moving coil, and since the wattmeter scale is usually made one-sided, i.e., the scale divisions are located from zero to the right, then if the direction of the current in one of the coils, it will be impossible to determine the measured value using a wattmeter.
For these reasons, you should always differentiate between the wattmeter terminals. The series winding terminal connected to the power source is called a generator terminal and is marked on devices and diagrams with an asterisk. The parallel circuit terminal attached to the wire connected to the series coil is also called a generator terminal and is marked with an asterisk.
Thus, with the correct circuit for connecting the wattmeter, the currents in the wattmeter coils are directed from the generator terminals to the non-generator terminals. There can be two schemes for connecting the wattmeter (see Fig. 2 and Fig. 3).
Rice. 2. Correct connection diagram for the wattmeter
Rice. 3. Correct connection diagram for the wattmeter
In the diagram given in Fig. 2, the current of the series winding of the wattmeter is equal to the current of the energy receivers, the power of which is measured, and the parallel circuit of the wattmeter is under a voltage U" greater than the voltage of the receivers, by the amount of the voltage drop in the series coil. Consequently, Рв = IU" = I(U+U1 ) = IU = IU1, i.e. the power measured by the wattmeter is equal to the power of the energy receivers to be measured and the power of the series winding of the wattmeter.
In the diagram given in Fig. 3, the voltage on the parallel circuit of the wattmeter is equal to the voltage on the receivers, and the current in the series winding is greater than the current consumed by the receiver by the amount of the current in the parallel circuit of the wattmeter. Consequently, P in = U(I+Iu) = UI+ UIu, i.e. the power measured by the wattmeter is equal to the power of the energy receivers to be measured and the power of the parallel circuit of the wattmeter.
For measurements in which the power of the wattmeter windings can be neglected, it is preferable to use the circuit shown in Fig. 2, since usually the power of the series winding is less than that of the parallel winding, and therefore the wattmeter readings will be more accurate.
For accurate measurements, it is necessary to introduce corrections into the wattmeter readings, due to the power of its winding, and in such cases we can recommend the circuit in Fig. 3, since the correction is easily calculated using the formula U 2 /Ru, where Ru is usually known, and the correction remains unchanged for different current values if U is constant.
When the wattmeter is turned on according to the diagram in Fig. 2, the potentials of the ends of the coils differ only by the amount of voltage drop in the moving coil, since the generator terminals of the coils are connected together. The voltage drop in the moving coil is negligible compared to the voltage across the parallel circuit because the resistance of this coil is negligible compared to the resistance of the parallel circuit.
Rice. 4. Incorrect wattmeter connection circuit
In Fig. 4 shows an incorrect diagram for connecting a parallel circuit of a wattmeter. Here, the generator terminals of the coils are connected through an additional resistance, as a result of which the potential difference between the ends of the coils is equal to the circuit voltage (sometimes very significant 240 - 600 V), and since the fixed and moving coils are in close proximity to one another, conditions are created that are favorable for breakdown of coil insulation. In addition, there will be electrostatic interaction between coils that have very different potentials, which can cause additional error when measuring power in an electrical circuit.
WATTMETER, a device for measuring electrical power consumed in some part of an electrical circuit. In technology and in laboratory practice, two types of wattmeter are used: electrodynamic and induction.
Based on the interaction of currents and consists of two windings (Fig. 1): stationary A, carrying the entire circuit current I, and mobile b, carrying current i, proportional to the circuit voltage. The moving winding is connected in series with a large non-inductive resistance and is connected in parallel to the receiver. Current is supplied to the moving winding through two spiral springs c, which at the same time create a torque that counteracts the rotation of the winding.
For sinusoidal currents, if E is the effective voltage, I is the effective current of a single-phase circuit and ϕ is the phase angle between current and voltage, the power P consumed in the circuit is expressed by the product:
In electrodynamic wattmeters, the interaction of two magnetic fluxes Ф 1 and Ф 2, created by the currents I and i in the windings, forms a torque:
Here α is the lag angle of the current i in the moving winding of the wattmeter, which has an inductance L. Due to the presence of the angle α, the moment M is not entirely proportional to the power P; Therefore, the calculation of the device must be carried out so that the error of the wattmeter created by the angle α does not exceed the limits of the reading accuracy. Because
then the angle α can be reduced by introducing a large additional resistance into the moving winding circuit. This resistance is made of a material with a negligible temperature coefficient and makes the device insensitive to changes in ambient temperature. From the transformation of formula (2)
it follows that this same additional resistance makes the device insensitive to changes in current frequency, since with a small value of the fraction it can be taken 
An electrodynamic wattmeter is a precision instrument and is used in Chap. arr. in laboratory practice. Its advantages: high accuracy (up to 0.25%), suitability for direct and alternating current, independence of readings from current frequency, voltage curve shape and temperature. Disadvantages: lightweight design, weak magnetic fields, low torque and, as a result, a strong influence of the external field on the wattmeter readings. To reduce this influence and adapt the electrodynamic wattmeter to the operating conditions on switchboards, use an iron casing that protects the wattmeter mechanism from the action of an external field, or arrange the entire magnetic circuit of iron, thus enhancing the field and torque. The mechanism of an electrodynamic wattmeter is shown in Fig. 2.
It differs from the electrodynamic one in that the current into the moving system is not supplied from the outside, but is induced by currents in the stationary windings (Fig. 3).
The induction wattmeter consists of a ring-shaped core A with two pairs of inwardly projecting poles b, enclosing a central cylindrical core c; both cores are made of sheet iron. In the gap between the poles and the cylinder, a thin-walled aluminum drum d rotates on supports. A winding is located on each pole of the ring-shaped core; windings of diametrically opposite poles are connected in series. One pair of windings carries the entire current of the circuit, the other carries a current proportional to the voltage of the circuit, and in this winding a 90° lag of the current from the voltage is artificially created. When such a wattmeter is connected to an alternating current circuit, the pulsation of two fields, shifted by 1/4 of a period in time and 90° in space, creates a rotating field that induces a current in the drum and causes it to rotate. The counteracting moment is developed by spiral or cylindrical springs. The torque of an induction wattmeter is expressed by the formula:
where c is the frequency of the current and ϱ is the resistivity of the drum material. An induction wattmeter cannot be used. classified as precision instruments, since its readings depend on the shape of the voltage curve, on the frequency of the current and on the temperature of the medium. An induction wattmeter is only suitable for alternating current and is calibrated to a specific frequency. Its advantages: durable and strong design, weak influence of external fields. Therefore, an induction wattmeter is an excellent technical device and is successfully used on distribution boards. The mechanism of an induction wattmeter is shown in Fig. 4.
Typically, wattmeters are made for moderate currents and voltages: 100-200 A, 120 V. For voltages up to 600 V, external additional resistances are used in the voltage circuit.
For currents greater than 200 A and voltages above 600 V, five-amp 100-120 V wattmeters are used in connection with current and voltage transformers. To measure the power of three-phase current, there are various special wattmeter designs: 1) single-phase wattmeter, connected to line current and phase voltage; the wattmeter measures phase power, but is calibrated to the power P of three-phase current: it is only suitable for a uniform load; 2) a single-phase wattmeter connected to line current and line voltage according to the diagram in Fig. 5; a choke is connected to the voltage circuit, giving an additional phase shift of the current in the voltage winding by 30°; the wattmeter is calibrated for the power of a three-phase current, but gives correct readings only when the load on all three phases is uniform; used in networks with an inaccessible zero point;
3) a wattmeter with two single-phase systems acting on a common axis; switched on to two line currents - I 1 and I 2 and two line voltages - E 1-3 and E 2-3 according to the diagram in Fig. 6; a wattmeter measures the power of three-phase current; suitable for uneven loads and for a three-wire system (without neutral wire);
4) a wattmeter with two single-phase systems acting on a common axis, each current coil consisting of 2 windings; switched on for two phase voltages - E 1-0 and E 2-0 and three currents according to the diagram in Fig. 7; a wattmeter measures the power of three-phase current; Suitable for uneven loads and for a four-wire system (three-phase with neutral wire).
One of the properties that characterizes the state of an electrical circuit is power. This property reflects the value of work performed by electric current in a certain time. The power of the equipment included in the electrical circuit should not exceed the power of the network. Otherwise, the equipment may fail, a short circuit or fire may occur. Electric current power is measured using special devices - wattmeters. In the case of direct current, power is calculated by multiplying the voltage by the current (you need an ammeter and a voltmeter). In an alternating current circuit, everything happens differently; you will need measuring instruments. A wattmeter is used to measure the operating mode of electrical equipment and record electricity consumption.
Scope of use
The main areas of use of wattmeters are industries in the electrical power industry, mechanical engineering, and repair of electrical devices. Wattmeters are also often used in everyday life. They are bought by electronics specialists, computer equipment specialists, and radio amateurs to calculate savings in electrical energy consumption.
Wattmeters are used for:
- Device power calculations.
- Carrying out tests of electrical circuits and some of their sections.
- Testing electrical installations as indicators.
- Checking the operation of electrical equipment.
- Accounting for electricity consumption.
Varieties
First, voltage is measured, then current is measured, and then power is measured based on these data. According to the method of measurement, conversion of parameters and output of results, wattmeters are divided into digital and analogue types.
Digital Wattmeters make measurements. The screen also displays voltage, current, and electricity consumption over a period of time. The measurement parameters are displayed on the computer.
Analog wattmeters are divided into recording and indicating instruments. They determine the active power of a section of the circuit. The wattmeter screen is equipped with a scale and an arrow. The scale is graduated in divisions and power values, in watts.
Design features and operating principle
Analog wattmeters are widely used, accurate measurements, and are devices of an electrodynamic system.
The principle of their operation is based on the interaction of two coils. One coil is stationary, with a thick winding wire, a small number of turns and low resistance. It is connected in series with the consumer. The second coil is moving. Its winding consists of a thin conductor having a significant number of turns, its resistance is high. It is connected in parallel with the consumer and is equipped with additional resistance to prevent short circuits of the windings.
When the device is connected to the network, magnetic fields arise in the windings, the interaction of which forms a torque that deflects the moving winding with an attached arrow to a calculated angle. The value of the angle depends on the product of voltage and current at a particular time.
The main principle of operation of a digital wattmeter is the preliminary measurement of voltage and current. For these purposes, the following are connected to the load consumer in a series circuit, and a voltage sensor in a parallel circuit. These sensors are usually made of thermistors, thermocouples, and measuring transformers.
The instantaneous parameters of the measured voltage and current, via a converter, are supplied to the internal microprocessor. It calculates power. The result of the information is shown on the screen and is also transmitted to external devices.
Electrodynamic type devices, which are widely used, are suitable for alternating and direct current. Inductive type wattmeters are used only for alternating current.
Some options for instruments (wattmeters).
Household appliances made in China
The instructions describe all operating modes of this device and technical characteristics.
Essentially, this is a device that measures the power of various electrical consumers. How does he work? You insert it into the socket, and into the socket of this device you insert the plug of the consumer whose power you want to measure. With this device you will measure the power of any consumer over a certain time and then with the help of it you can even calculate, for example, how much money your refrigerator or any other device spends on electricity.
The device has a built-in battery. It is needed to remember the power that you measured, and then you will use it to calculate the price. The front panel of the device has five buttons: switching modes, price indicator, up-down switch, reset button if the device catches any glitch.
The characteristics of the device are indicated on the body:
- Operating voltage 230 volts.
- Frequency 50 hertz.
- Maximum current 16 amperes.
- The range of measured power is 0-3600 watts.
Operation of the device.
We plug it into the socket.
Let's turn it on an LED table lamp.
The display immediately shows the time during which the power of the consumer, in this case the lamp, is measured. 0.4 watts is the power of the lamp when it is turned off. We turn on the lamp; in operating mode it consumes 10.3 watts. We did not indicate the price per kilowatt, so there are zeros there.
Our lamp can change the light power. As the lamp light increases, the power reading increases. When the second mode is turned on, the operating time is also shown at the top; in the second field, kilowatt hours, since the device has not yet worked for even one hour, zeros are shown. The number of days this consumer was measured is shown below.
In the next mode, the second field shows the mains voltage, and the current frequency is shown below. The time is shown at the top of the display in all modes. When switching to the next mode, the current strength is shown in the center. Below is a parameter of a certain factor, about which there is no data yet, since the device manufacturer is Chinese.
The fifth mode shows the minimum power. In the sixth mode - maximum power.
It will be interesting to see the readings of these modes when the computer is running. For example, in sleep mode, with a normal desktop open, or when running a powerful game.
In the next mode, the cost of electricity is set using the installation buttons to calculate the cost of energy consumption. This way you can measure and calculate the consumption of any of your home appliances and devices, and you will know which devices you have are economical and which ones consume too much electricity.
This device has a low cost, about $14. This is a small price to pay in order to optimize costs by calculating the power consumption of devices.
Digital multifunctional device SM 3010
The wattmeter is used to measure voltage, frequency, power, direct and alternating current with one phase. It is also designed to control such devices with less accuracy.
Current measurement range is 0.002 - 10 amperes.
Voltage measurements:
- Constant from 1 to 1000 volts.
- Variable from 1 to 700 volts.
- Frequency is measured in the range 40-5000 hertz.
Measurement error:
- Current, voltage, DC power + 0,1%.
- Current, voltage, AC power + 0.1% in the frequency range 40-1500 Hz.
- Relative error of frequency measurement in the range 40-5000 hertz + 0,003%.
The dimensions of the device body are 225 x 100 x 205 mm. Weight 1 kg. Power consumption is less than 5 watts.
Measuring device CPU 8506 – 120
Serves to measure the power of active and reactive 3-phase AC networks, shows the current value of the power parameter on the indicator, and converts it into an analogue signal.
The measurements taken are shown in the form of numbers on indicators in units of quantities that are included in the device, or at the input of the current or voltage transformer. In this case, the transformation coefficient is taken into account. The digital display is divided into four digits.
Purpose of the device – for measuring active and reactive power in 3-phase electric current networks with a frequency of 50 hertz.
Technical data
- Power factor – 1.
- Case dimensions 120 x 120 x 150 mm.
- The height of the numbers on the display is 20 mm.
- The largest reading interval is 9999.
- Accuracy level: 0.5.
- Conversion time: less than 0.5 s.
- Operating temperature: from +5 to + 40 degrees.
- Protection class of housing and panel: IP 40.
- Power consumption: 5 watts.
- Weight less than 1.2 kg.
Different electrical appliances consume different amounts of energy. There are a lot of technologies that allow you to save energy without losing the quality of operation. Devices have been developed to measure energy consumption to help estimate all costs. One of them is a household wattmeter plugged into an outlet.
general information
Wattmeter is a combined device, a power meter in sockets. It can be called an electricity meter, but the functionality of the device does not end there. The device also serves as a voltmeter, showing the DC voltage in the network.
There are different types of wattmeters for sockets:
- digital;
- analog.
The former display all the necessary information on the display, the latter require simple calculations to be made independently, but are cheaper. Externally, the wattmeter resembles an adapter for a socket. The panel has control and adjustment buttons. It is important to purchase a device that can be plugged directly into the socket. When you plug the device into an outlet, it shows how many watts the appliances are using.
Household wattmeters in sockets do not require special connection diagrams. If the meter shows only the total power in the apartment, then these mini-devices will reflect the operation of each outlet separately. Their design includes a plug for connection to a socket and a socket for turning on the load.
The device consists of the following components:
- current and voltage sensors;
- analog-to-digital converter;
- microcontroller;
- keyboards (data input means).
High-quality wattmeters for sockets, which show how much electricity the device consumes, can simultaneously measure voltage, power factor, current, frequency and a number of other indicators. The measurement parameters of the device are the duration of operation of the equipment, the total number of kilowatts that the equipment can consume.
Some wattmeters will even display the amount you need to pay for electricity after entering the tariff. There are wattmeters in sockets with a power regulator: when the indicator is exceeded, the devices emit signals.
How does a wattmeter work?
The device is quite simple to use. It should be plugged into a power outlet, and the device that needs to be checked should be connected through it. The necessary information will be displayed on the screen.
The operating procedure for the digital device is as follows:
- Connect the device to the network.
- Make sure it shows “zero” and the previous digits are reset.
- Turn on household appliances.
- After a few seconds, evaluate the readings - the number of watts/hour and others.
The analog counter is simpler. It has rotating disks, from which information will have to be calculated using a stopwatch. Having turned on the stopwatch, you need to calculate how long it took the disks to turn around. Next, you need to multiply the kilowatts on the meter by 3600 and divide by the calculated time in seconds. This will give you the power factor.
Characteristics of wattmeters
A number of models have holes for accumulators and batteries, which will be required if functions for storing measured parameters and analysis and comparison of data are provided.
Typically, the technical characteristics of the devices are as follows:
- rated power - 3.6 kW;
- current - 16A;
- voltage - 190 – 270 V;
- frequency - 50 Hz;
- minimum measured power - 0.1 W;
- measurement accuracy - error up to 1%;
- total reflected energy consumption - up to 10,000 kW/h;
- own energy consumption - less than 0.5 W;
- The optimal ambient temperature is 5 – 40 degrees.
Most often, using wattmeters in sockets with a power consumption indicator, the operation of kettles, washing machines, heaters, and other household appliances is assessed.
Pros and cons of devices
The disadvantages include the maximum load limitation of 3.6 kW, although most home appliances fit within this figure. It will not be possible to check the operation of the equipment in severe frost: in an unheated room, the operation of the device will not be correct.
Wattmeters have many advantages:
- the ability to evaluate the operation of all appliances in the house;
- ease of use - even a beginner can handle it;
- no need for special switching circuits or the use of adapters;
- obtaining complete information about the operation of equipment;
- the ability to calculate costs and save in the future;
- reasonable price, availability.
Household wattmeters are multifunctional devices that should be in every home. The products will replace a number of other devices for electrical engineering enthusiasts and will help control energy consumption in the apartment.
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