Working with electrical networks may be necessary in various life situations: car repairs, wiring in the house or at work. One of the quantities that often needs to be measured when carrying out work of this nature is voltage. It can be determined using a special device called a voltmeter. The principle of its operation, device, as well as methods of connection will be discussed below.
Device and principle of operation
If we talk about the principle of operation, then all devices of this type that allow various measurements in electrical networks are of 2 types:
- electromechanical type;
The first category is switch devices. In them, the arrow is attached to a special frame where the cable is wound. Such a coil will be located next to the magnet in those devices that are usually used for DC networks. Or next to another coil - if the device is intended for AC current.
Here it should be clarified that the model calculated for networks with a variable character of current will not work permanently in the network.
But if a diode bridge is used for connection, then it will be able to carry out the necessary measurements in the AC network, but with a slight loss of accuracy.
When an electric current passes through the winding, an electromagnetic field appears in it, which interacts with a magnet or other winding, and the frame rotates. The spring prevents the coil from rotating where the arrow is located. For this reason, the angle of rotation of the frame will correspond to the current that goes through it and the potential at the terminals.
To reduce the arrow oscillations, the device has an electromagnetic damper.
It can be piston, made of a cylinder and a piston, or made of an aluminum plate. To increase the accuracy of the readings, the arrow has special counterweights, which eliminate the effect of gravity. And the system itself is made of this type of steel, as alloyed, in order to reduce its wear.
The sensing element in electronic analogs is an electronic board that transforms the incoming signal into instrument readings. This device can work either from the voltage that is being measured, or from batteries or external power. By themselves, electronic voltmeters are divided into 2 categories:
In devices belonging to the first category, there is a converter of the input signal to the angle of turnout, which shows the value of the voltage being investigated, which is displayed on the scale. The disadvantage of such devices will be the need to recalculate the scale readings in the event of a change in the measuring limit.
The digital voltmeter is equipped with a corresponding display, as well as a converter, thanks to which the signal becomes digital. If the device is connected to a network where there is direct current, the polarity of the connection can be seen on the display. The distinctive features of such a device will be compactness, as well as accuracy. True, the last point will depend on the model of the built-in controller.
General recommendations for connection
Now we will give small recommendations on how to properly connect a voltmeter so that it shows the most accurate data. The first point is that the device cannot be connected to the electrical circuit sequentially, otherwise it will break due to a decrease in current . The connection should only be carried out in parallel, because this does not affect the current flow. And the resistance should be great.
Many people very often confuse a voltmeter with an ammeter, in which everything will be the other way around.
The connection diagram of the device will look so that to measure the voltage that is present in the circuit between 2 points , it is connected so that the switch is located opposite the power source. The device does not affect the current due to the fact that it passes it through itself. That is why his resistance is so great.
To expand the measuring range, an additional resistor can be connected to the winding of the device.
Then only part of the current will go to the meter, which will be proportional to the resistance of the device. If we know the resistance of the resistor at the voltmeter, then we can determine the voltage indicator.
The resistor itself is installed inside the voltmeter and is simultaneously used to reduce the influence of various factors on the measurement results. Therefore, it is made from a material that has the lowest possible temperature coefficient. Its resistance will be less than in the coil, due to which the total resistance will not depend on the temperature regime.
If we talk about a constant voltage, then to measure the indicators of an electrical circuit, you should have a so-called constant current compensator. Although a simpler solution would be to use a conventional digital device. To measure values starting from tens of millivolts and ending in hundreds of volts, the following devices are used:
With this type of measurement, additional resistances can also be used.
When measuring this type of voltage of several kilovolts, electrostatic voltmeters are usually used. Less commonly - other types of devices that are connected through a divider.
In order to correctly measure the characteristics of the alternating current with the device in question, you need to have a so-called measuring transformer. It is used to carry out such measurements and to improve the safety of people by allowing galvanic isolation from the high voltage circuit. By the way, this method will be the only correct one in general, because for safety reasons it is forbidden to carry out measurements without such transformers.
The use of such transformers will make it possible to increase the measurement limits of devices, that is, you can measure high voltages and currents by means of low-voltage and low-current devices. If an alternating current is measured to values in units of volts, then apply:
- digital voltmeters;
If up to hundreds of volts - electrodynamic, rectifier and electromagnetic. If it is up to several tens of megahertz, then measurements should be carried out with electrostatic and thermoelectric voltmeters.
Installation on an amplifier
Installing a voltmeter on an amplifier in a car is relatively easy. To implement it, the following elements are required:
- insulating tape;
- wire PVA 3x75.
First, in the case where the pocket above the radio tape recorder is located, you need to drill a hole with a diameter of about 1.6 millimeters, where you should install the corresponding connector with a wire connected to it.
Now you need to run the wire to the trunk itself, simultaneously attaching it with electrical tape to the power cable of the amplifier itself, and fix it on the amplifier terminals. The REM cable that controls the radio, as well as the amplifier, are connected to a voltmeter so that it turns on simultaneously with them. It is thanks to this that it will be possible to see the exact voltage at the amplifying terminals, when necessary.
This system is very easy to operate and the costs required to build it are very low.
How does it connect to the battery?
To successfully monitor the state of charge of a car battery, you need to know how you can connect a voltmeter and correctly decode its measurements. Since the advent of cars, where an on-board computer is responsible for controlling the systems, the need for a separate device has disappeared. But not everyone can afford such cars. And not everywhere in such machines the function of monitoring the state of the battery charge is implemented. And in winter it will be extremely important.
The most realistic readings will be given by devices that are connected directly to the dashboard. While they can be tricky to install, it pays off when you know all about charging your car's battery.
Most of the devices that can be found on the market today have 2 or 3 wires for connecting to the mains. Recently, 4-pin models have appeared. But, as a rule, most have three wires, so let's focus on marking the marking of 3-wire models:
- a red wire will mean a plus;
- black - minus;
- white will be responsible for turning the device off and on, as well as controlling the brightness of the backlight.
Sometimes it happens that the device shines very dimly or does not work at all. The reason for this is a slightly different cable marking. In this case, the white wire will be a minus, and the black one will control the device. The voltage sensor is placed in the place where the clock is usually located, but in some cases it happens that there is no free space on the dashboard, so you have to make a special hole.
Speaking directly about the connection, let's say that there are a large number of schemes.
But we will consider how to do this using the example of a voltmeter that is equipped with a pulse stabilizer. The body of the device can have a relief type surface. That is, we are talking about the fact that the frame around the display will protrude above the surface of the car panel. Because of this, the voltmeter will not fall inward and will hide the uneven edges of the homemade hole.
Usually, the voltmeter is connected via three contacts that are located on the sensor body. Then for this you still need a four-wire cable from a conventional computer drive. The wide IDE connector is cut off, and the rest of the wires are soldered to the car's wiring pins. The four-pin contact provides an excellent connection and, if necessary, allows you to quickly and without any serious effort and time to replace the voltmeter if it fails.
Regardless of which voltmeter has a structure, before installing it in the car, you should study the wiring diagram in detail, and also carefully read the instructions that come with the device.
See below for more details.