Faced with the need to find out the magnitude of the voltage on a section of an electrical circuit, many are wondering: how to connect a voltmeter? It's very simple, but you need to know a few simple rules.
Digital voltmeter circuit.
This device belongs to the measuring. It is used to read, measure voltage and electromotive force in electrical networks. It is connected in parallel with the load or power source.
Main characteristics of the device
Correctly connect a voltmeter will help knowledge of its structure and principles of operation. The type of conventional portable voltmeter is known to everyone. This is a rectangular box with a frontal screen, levers, buttons and connectors for contacts. It is equipped with a handle on which it can be put in a raised position, it also serves to carry it. There are also very compact options, similar to an ammeter. It's just a little box with terminals and a scale with an arrow.
Some devices similar to an ammeter can be distinguished by the sign V on the display. In schemes, he is depicted in the same letter, but in a circle. Just like the first, at one end there is a “+” sign. It must be connected to the positive end of the source, that is, to a point with a positive value of the circuit. Otherwise, the pointer will point in the opposite direction.
Table of characteristics of a digital voltmeter.
The greater the resistance inside the device, the better, because in this case the resistance has the least effect on the object of measurement, therefore its readings are more accurate and the range of application is wider.
There are quite a number of modifications:
- according to the principle of operation (electromechanical, static, electronic);
- by purpose (pulsed, DC / AC, phase-sensitive, selective, universal);
- stationary, shield, portable.
A more technical definition of a voltmeter sounds like this: a galvanometer with high sensitivity, considerable resistance, equipped with a display, which displays indicators of potential difference, or an electrical excitatory indicator in volts.Back to table of contents
The principle of operation of the voltmeter
It measures the various values of the current flowing through the device. The principle of operation is the same for all devices, and the design can be very diverse.
Wiring diagram of a voltmeter with a pulse stabilizer.
Some such devices of outdated production consist of a coil of thin wire; it is located between the ends of a magnet in the shape of a horseshoe with an iron arrow that moves on an axis. Current flows in this coil. The magnetized pointer moves on the current: the stronger it is, the greater its deviation (that is, the greater the potential difference between the ends of the coil wire).
Some do not have magnets, the current passes through the coil, taking in a thin metal tube, in other words, the cylinder of metal, located on the axis, moves relative to the coil.
In devices designed for alternating current, the current is passed through a specially installed wire, which causes it to heat up, thereby changing its size, which the indicator displays.
When measuring, it is necessary to take into account the resistance during heating and to calculate the correction, therefore, the design of some devices is already done in such a way as to measure with the amendment.
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Connecting a voltmeter to the circuit: recommendations
The first thing you need to know: if you turn on the device in a chain in a sequential way, it can fail.
Parallel connection is used because it reduces the current.
Connection diagram of the voltmeter to the circuit.
The voltmeter is connected in such a way that its powerful resistance does not change the measurement results. With a serial connection, the current capacity in the circuit will be minimal.
Correctly the device is connected to the circuit parallel to its part: it does not affect the flow of currents, therefore, the resistance is necessary large. Do not confuse a voltmeter with an ammeter, which is connected in series, because there should be a minimum resistance in it.
The current that flows through the device is much less than that flowing through the test area of the circuit. There are no influencing forces inside it. The difference of the ends of the terminals is the same with the voltage, because it measures it.
Connecting the device looks like this. To measure the voltage, which is between the two selected points in the electrical circuit, it simply needs to be connected to them so that such a connection is parallel to the power source. A voltmeter has virtually no effect on the current, due to its passage through itself, since it is created specifically for this with considerable resistance. Therefore, it does not cause any loss of energy.
In order to extend the range of measurements consistently to the winding of the device, an additional resistor is mounted. In this case, only a part of the measured current goes to the meter, it is proportional to the resistance of the device. With a known resistor resistance of a voltmeter, a voltage indicator is determined.
Such a resistor is built into the device, it is simultaneously used to reduce the influence of medium temperatures on the voltmeter. To do this, it is made of a material with a low temperature coefficient, its resistance is less than that in a coil, and therefore the total resistance of the device is almost independent of temperature.Back to table of contents
Voltmeter for a regular car
To measure the current in the automotive network will help voltmeter. How to connect it, every driver must know. For a machine with a computer on board, this is not a problem, since the computer will show the voltage of the on-board network, but there are many cars without a computer that have to use a voltmeter.
The whole body of the car is a "minus", so the negative pole is connected to it, that is, at any point it is "mass". The positive terminal from the voltmeter is connected to the positive of the generator: they immediately recognize the voltage they produce, as a rule, it is 14 volts. Plugged wires are recommended to choose thicker, it will reduce errors in measurements. If the device does not have a fuse, it should be installed in the circuit. Regarding the voltage in the onboard network, we recall that it should be greater than on the battery terminals.
When working with electricity, you must adhere to safety rules: do not touch bare wires, use rubber gloves and other means of protection.