What does a voltmeter measure? Device for measuring voltage

A person, far from electrical circuits, voltages, currents and resistances, can hardly answer this question: what does a voltmeter measure? Since the answer is obvious, if you just read the second half of the title of the article, let's expand on this subject. In particular, consider the measurement of voltage in everyday life, the characteristics of devices, the principle of operation.

Definition

The voltmeter is a measuring device that allows you to obtain the voltage or electromotive force in a DC or AC circuit. The range of the device can extend up to 1000 V and more. Everything depends on its purpose. To better understand what this is, consider the definition of electromotive force. Since very often it gets confused with the voltage in the network, they should be separated from each other.

EMF and voltage: the difference

So, the EMF is a physical quantity that characterizes the work done by some non-electrical forces on the displacement of a single positive charge along the contour under consideration. In the most ordinary case, it shows the ability of the energy source to create a particular potential difference at two spaced points of the circuit. It is measured, like voltage, in volts. It differs from it in that it characterizes the power source at idle speed, that is, without connecting to the network.

When there is a current in the circuit, that is, it is closed, there is one more, more familiar concept - tension. And it can be taken both for the power supply at its terminals, and in any part of the circuit. Voltage measurement is the detection of the potential difference between two spaced points. For a power source, it is usually somewhat less than the electromotive force, when it is included in the consumption circuit. In fact, both EMF and voltage are one and the same, with a difference only in what physical process generates the appearance of a potential difference between the two points in which the measurement is performed.

Types of voltmeters

Here it is necessary to distinguish two main types: portable and stationary. A portable device for measuring voltage can not only be manually dragged. It usually includes a functional for checking the currents and resistance in the circuit, as well as the temperature of the conductors, etc. Stationary instruments are often structurally integrated with the network itself, in which measurement is carried out, for example, in electrical switchboards, panels, etc.

As for classification according to the principle of operation, it is possible to distinguish several types of electromechanical voltmeters and two types of electronic voltmeters. The latter are analog and digital. Electromechanical voltmeters use a magnetic conversion system to obtain voltage values. Electronic devices digitize the received signal by means of ADC. The voltmeter readings, depending on the principle of data presentation, are indicated either by a pointer or by a special digital display.

Another classification - by appointment. It allows you to divide the instruments into meters of direct and alternating current, as well as phase-sensitive, pulsed and universal. For the latter, almost all gamma signals are available, the voltage of which must be known.

Main technical characteristics

Depend on the purpose of the device. For example, a DC voltmeter usually has several measurement ranges, so their number will be one of the most important technical characteristics. In addition, almost all devices have a certain input resistance, depending, by the way, on the extent to which the voltage of the investigated section of the circuit is located.

Still important characteristics are, of course, the errors, as well as the resolution of the scale or the minimum step of the indication, if it is a digital voltmeter. If the user has got a universal device for measuring the voltage, the limits of the quantities with which he is able to work, for example, currents, resistances, temperatures, as well as ranges, errors and frequencies for variable signals, can be added to the above.

Principle of operation

The general scheme of the functioning of the device strongly depends on the implementation. If this is an electromechanical voltmeter, there is a magnetic system sensitive to the flowing current. Depending on its magnitude, the deviation of the pointer arrow, mechanically related to the contour, frame or something else that is used to convert the current in the circuit, also increases. The accuracy of such devices is not very high, since it does not allow to obtain high values of the input resistances, and therefore introduces serious distortions in the measurements, since parasitic conductivity is added to the circuit.

The digital voltmeters that have been widely used in everyday life have a large amount of electronics under the lid. This is due to the conversion of the analog signal received at the input of the instrument into a digital form using an ADC. To whom it is really interesting, it is possible to familiarize with a considerable quantity of the literature on a theme. Such a voltmeter, whose price fluctuates within several hundred rubles, certainly does not pretend to have a rich choice of possibilities and great accuracy, but it is quite capable of measuring the voltage at the terminals of a car battery or in a 220V network.

Connection to the circuit

The voltmeter in the circuit is always connected in parallel with the load or power supply, if it is necessary to measure its EMF or voltage at the terminals. That is why there are such stringent requirements to the input resistance of the device, since such a connection implies the appearance of additional conductivity in the circuit.

In no event should you connect a voltmeter, the price of which is at least as large as possible, into the circuit in series. Otherwise, the user runs the risk of corny burning the device, and not having time to figure out what it was all for. Even if he survives such a barbaric treatment, his testimony should not be trusted, since the current in the circuit undergoes serious changes with such a connection of the voltmeter, again pushing back to an unknown opportunity to find out the actual voltage of the section in which the measurements are made.

Operational safety measures

Since the resistance of the voltmeter in most cases is large enough, and the connection scheme, respectively, uses parallel, the risk of getting any serious electric shock in the low-voltage circuit is minimal. However, if we are talking about industrial devices, especially in the stationary version, this implies huge values of the measured values of both voltages and, most likely, currents. Therefore, safety engineering must be at the highest level, and without sufficient knowledge, rubber gloves, rugs and other appropriate measures, naturally, any activity is contraindicated. What a voltmeter measures is most likely very dangerous for life, so we recommend that you do not test fate. In any case, touch bare wires, even if the circuit is by definition low-voltage, should not be.

Conclusion

Answering the question about what the voltmeter measures, we have examined in general outline its structure, basic technical characteristics, classification. Of course, this small survey does not pretend to be a comprehensive completeness, especially in the absence of basic knowledge of electrical engineering in the reader.

Summing up, it should be noted that the voltmeter measures, of course, the voltage in the circuit section to which it is connected in parallel. Otherwise, his testimony will be unreliable, not to mention the danger of possible loss of expensive equipment. The reader should be careful when operating the device at home, since contact with high-voltage circuits is dangerous for life.