A person who is far from electrical circuits, voltages, currents and resistances will hardly be able to 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 reveal this topic in a little more detail. In particular, we will 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 DC or AC circuit. The range of the instrument 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 it is very often confused with the mains voltage, they should be separated from each other.
EMF and voltage: difference
So, EMF is a physical quantity that characterizes the work done by any forces of a non-electric nature to moveunit positive charge along the contour under consideration. In the most common case, it shows the ability of an energy source to create one or another potential difference at two spaced points in the circuit. It is measured, like voltage, in volts. It differs from it in that it characterizes the power supply at idle, that is, without connecting to the network.
When there is a current in the circuit, that is, it is closed, another more familiar concept appears - voltage. Moreover, it can be taken both for the power source itself at its terminals, and in any part of the circuit. Voltage measurement is the identification 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 the same, with the only difference being what physical process generates the potential difference between the two points at which the measurement is made.
Types of voltmeters
Here two main types should be distinguished: portable and stationary. The portable voltage measuring instrument can not only be dragged by hand. It usually includes functionality to check the currents and resistances in the circuit, as well as the temperature of the conductors, etc. Stationary devices are often structurally integrated with the network itself, in which the measurement is carried out, for example, in electrical switchboards, panels, etc.
Regarding classification according to the principleactions, then we can distinguish several types of electromechanical voltmeters and two types of electronic ones. The latter are analog and digital. Electromechanical voltmeters use a magnetic transducer system to obtain voltage readings. Electronic devices digitize the received signal using an ADC. Voltmeter readings, depending on the principle of data presentation, are shown either by an arrow pointer or on a special digital display.
One more classification - according to purpose. It allows you to divide the devices into DC and AC meters, as well as phase-sensitive, pulse and universal. For the latter, almost the entire range of signals is available, the voltage of which needs to be known.
Main 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, by the way, depends on the voltage range of the circuit section being studied.
Still important characteristics are, of course, errors, as well as the resolution of the scale or the minimum step of readings, if we are talking about a digital voltmeter. If the user has received a universal device for measuring voltage, the limits of the quantities with which he is able to work, for example, currents, resistances, temperatures, as well asranges, errors and frequencies for variable signals.
Working principle
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 value, the deviation of the pointer arrow, which is mechanically connected to the circuit, frame, or something else that is used to convert current in the circuit, also increases. The accuracy of such devices is not very high, since it does not allow obtaining high values of input resistance, which means that it introduces serious distortions into measurements, since parasitic conduction is added to the circuit.
Digital voltmeters, which have recently become widespread in everyday life, have a large number of electronics under the lid. This is due to the conversion of the analog signal received at the input of the device into digital form using an ADC. For those who are really interested, there is a large amount of literature on the topic. Such a voltmeter, the price of which fluctuates within a few hundred rubles, of course, does not claim to have a rich selection of possibilities and great accuracy, but it is quite capable of measuring the voltage at the terminals of a car battery or in a 220 V network.
Connection in a chain
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 connectionimplies 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 in the circuit. Otherwise, the user runs the risk of simply burning the device, without having time to find out what it was all about. Even if it survives such barbaric treatment, its readings should not be trusted, since the current in the circuit undergoes serious changes when the voltmeter is connected in this way, again pushing the possibility of knowing the actual voltage of the section in which the measurements are made into the unknown.
Operating safety precautions
Because the resistance of the voltmeter itself is quite large in most cases, and the connection circuit is accordingly used in parallel, the risk of any serious electric shock in a 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 \u200b\u200bof both voltages and, most likely, currents. Therefore, here safety precautions must be at the highest level, and without sufficient knowledge, rubber gloves, mats and other appropriate measures, of course, any activity is contraindicated. What the voltmeter measures is most likely very life-threatening, so we recommend not to tempt fate. In any case, you should not touch bare wires, even if the circuit is by definition low-voltage.
Conclusion
Answering the question of what the voltmeter measures, weconsidered in general terms its device, main technical characteristics, classification. Of course, this short review does not claim to be comprehensive, especially given the reader's lack of basic knowledge of electrical engineering.
Summarizing, it should be noted that the voltmeter measures, of course, the voltage in the section 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 using the device at home, since contact with high-voltage sections of the circuits is life-threatening.
