A person who is far from electrical circuits, voltages, currents, and resistances can hardly immediately 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, we will open this topic in more detail. In particular, we consider the measurement of voltage in everyday life, the characteristics of devices, the principle of operation.
Definition
A voltmeter is a measuring device that allows you to get the value of voltage or electromotive force in a direct or alternating current circuit. The range of the device can extend up to 1000 V or more. It all depends on its purpose. To better understand what it is, consider the definition of electromotive force. Since very often it is confused with the voltage in the network, they should be separated from each other.
EMF and voltage: difference
So, EMF is a physical quantity that characterizes the work performed by any non-electric forces to move a single positive charge along the contour under consideration. In the most ordinary case, it shows the ability of the energy source to create one or another 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, that is, without connecting to the network.
When there is current in the circuit, that is, it is closed, another concept more familiar to the ear appears - voltage. Moreover, it can be taken both for the power source at its terminals, and in any part of the circuit. A voltage measurement is the detection of a potential difference between two spaced points. For a power source, it is usually slightly less than the electromotive force when it is included in the consumption circuit. In fact, both EMF and voltage are one and the same thing, with the only difference in what physical process gives rise to the potential difference between the two points at which the measurement is carried out.
Types of Voltmeters
Two main types should be distinguished here: portable and stationary. A portable voltage measuring device can not only be dragged manually. Usually it includes functionality for checking currents and resistance in a circuit, as well as temperature of conductors, etc. Stationary devices are often structurally integrated with the network itself, in which the measurement is carried out, for example, in electrical distribution panels, panels, etc.
As for the classification according to the principle of action, we can distinguish several types of electromechanical voltmeters and two types of electronic. The latter are analog and digital. Electromechanical voltmeters use a magnetic conversion system to obtain voltage values. Electronic devices digitize the received signal using the ADC. The voltmeter readings, depending on the principle of data presentation, are shown either with a pointer or on a special digital display.
Another classification is by designation. It allows you to divide the devices into meters of direct and alternating current, as well as phase-sensitive, pulsed and universal. For the latter, almost the entire gamut of signals is available, the voltage of which must be found out.
Key Specifications
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 impedance, which, incidentally, depends on the extent to which the voltage of the circuit section under investigation is located.
Other important characteristics are, of course, errors, as well as the resolution of the scale or the minimum step of the readings, if we are talking about a digital voltmeter. If the user got a universal device for measuring voltage, the above limits can be added to the values with which he is able to work, for example, currents, resistances, temperatures, as well as ranges, errors and frequencies for variable signals.
Principle of operation
The overall operation of the device is highly implementation dependent. If it is an electromechanical voltmeter, there is a magnetic system that is sensitive to the flowing current. Depending on its size, the deviation of the pointer arrow, mechanically connected with 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 input resistances, which means that it introduces serious distortions in the measurements, since parasitic conductivity is added to the circuit.
The most common digital voltmeters recently used in everyday life have a large number of electronics under the cover. This is due to the conversion of the analog signal received at the input of the device into digital form using the ADC. Who is really interested, you can read a lot of literature on the topic. Such a voltmeter, the price of which varies within a few hundred rubles, of course, does not pretend to have a wide choice of possibilities and great accuracy, but it is quite capable of measuring the voltage at the terminals of a car battery or 220 V.
Circuit connection
The voltmeter in the circuit is always connected in parallel with the load or power source, if you need to measure its EMF or voltage at the terminals. That is why there are such stringent requirements for the input impedance of the device, since such a connection implies the appearance of additional conductivity in the circuit.
In no case should you connect a voltmeter, the price of which is at least a little high, in series. Otherwise, the user runs the risk of trite to burn the device, without having time to figure out what it was all about. Even if he withstands such barbaric treatment, his testimony should not be trusted, since the current in the circuit undergoes serious changes with this connection of the voltmeter, again pushing into an unknown opportunity to find out the actual voltage of the section in which the measurements are made.
Operational Safety Precautions
Since the resistance of the voltmeter itself in most cases is quite large, and the connection circuit, respectively, is used in 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 a stationary version, this implies huge values of the measured values of both voltages and, most likely, currents. Therefore, here the safety precautions should be at the highest level, and without sufficient knowledge, rubber gloves, rugs and other appropriate measures, of course, any activity is contraindicated. What a voltmeter measures is most likely very life-threatening, so we recommend that you do not try your luck. In any case, touching bare wires, even if the circuit is by definition low voltage, should not be.
Conclusion
Answering the question about what a voltmeter measures, we examined its device in general terms, the main technical characteristics, and classification. Of course, this short review does not claim to be comprehensive, especially in the face of an insufficient amount of basic knowledge of electrical engineering from the reader.
Summing up, it should be noted that the voltmeter measures, of course, the voltage on the portion of the circuit to which it is connected in parallel. Otherwise, his testimony will be unreliable, not to mention the danger of a possible loss of expensive equipment. The reader should be careful when operating the device at home, since contact with high-voltage sections of the circuit is life threatening.