Electric circuits have become an integral attribute of modern life. They permeate almost everything, and people do not even think that it is worthwhile to disappear by electric current, and our world will be in serious danger. What is current, can it be measured, and what will these indications give for an ordinary person?
The laws of current behavior are studied at school, and, in principle, every high school student knows about the directional movement of charged particles. This movement of electrons inside the conductor is called electricity. But any movement in nature - even the movement of water in a river, the movement of air masses or charges, can do some useful work. And this is already interesting from a practical point of view. Knowing the power, duration of exposure, the direction of application of any force, you can use it in solving certain vital issues.
Therefore, scientists are so busy studying the environment and creating instruments that allow everything to measure and calculate. To obtain ideas about the current, the ammeter device was invented. It allows you to determine the number of charged particles that per unit time pass through a known section of the conductor, that is, the current strength.
What is an ammeter, its types
An ammeter can measure the current in any electrical circuit. This device is not difficult to recognize, it is indicated by the Latin letter A. Since the current can be of different sizes, starting from milliamps and above, there are devices of different power or universal, in which the measurement limit changes. Moreover, for direct and alternating current , different types of ammeters are needed.
According to the principle of the device, there are devices :
- Electromagnetic performance.
- Magnetoelectric.
- Thermal.
- Detector type.
- Induction.
- Electrodynamic system.
- Photovoltaic.
- Thermoelectric.
A magnetoelectric device can determine the current strength in circuits connected to a constant voltage. Detector and induction type - measure alternating currents. All other species can be universal.
Ammeters of electrodynamic and magnetoelectric design have high sensitivity and accuracy of readings.
How to connect an ammeter to an electric circuit
An ammeter of any type is connected in series to a load in an electrical circuit. Then the same current passes through it as through the circuit. In order not to affect the current, not to interfere with it, the device is made with a small input resistance. It must be remembered that by connecting the ammeter in parallel with the load (incorrect connection), all current will go through it according to the principle of least resistance. Forgetting how to connect an ammeter, you can simply burn the device!
Before choosing a device, you need to find out the type of current - AC or DC. After that, taking the appropriate ammeter (the marking of the scale usually indicates the sign of the wave for alternating voltage and a straight line for constant), set the maximum measurement limit on it and only then think about how to connect the ammeter to the circuit. After that it is necessary to take readings of the device. If they are significantly less than the set measurement limit, for example, the arrow is in the first half of the scale, counting from zero, then it is necessary to rearrange the limit one down. The readings are considered more accurate when the arrow is located in the second half of the scale.
DC current measurement
Direct currents are present in many electronic circuits, especially for power supplies, various chargers. To fix such devices, masters just need to know how to connect an ammeter. In practice, an ordinary person who is not connected with radio electronics can also apply this knowledge, for example, to determine how much the battery in the camera holds the charge.
Take a fully charged battery. Suppose its rated voltage is 3.5 volts (V). A light bulb is selected for such a denomination and a circuit is assembled: battery - measuring device - light bulb. Record what the ammeter shows. For example, a light bulb consumes a current of 150 milliamps (mA), and the battery has a capacity of 1500 milliampere-hours (mAh), which means that a good battery should give a current of 150 mA for about 10 hours!
AC current measurement
Any household electrical appliance is a load that consumes alternating current. But, considering issues of domestic use of electricity, power remains an important concept, because it is paid precisely for kilowatts (kW). What is an ammeter in this case? Indirect measurement device. Using it, they recognize the current and applying the formula:
P = IU (Ohm's law), where I is the current strength (A), U is the voltage (V),
calculate the power (P) (W).
For example, the device lost information about its parameters, in this case, measurements can not be dispensed with. Or you need to calculate the power consumption of a building, where it is simply impossible to take into account all the devices. Then, at the entrance from the power panel, a powerful ammeter is connected and measurements are taken. But in the latter case, you need a clearance that only professional electricians have!
Non-contact current measurement method
Sometimes it’s technically impossible to break the electric circuit to turn on the measuring device, but it is necessary to measure the current (with regards to ordinary and high-voltage electric circuits). How to connect an ammeter in this case? For this, a non-contact current measurement device, current clamp, was developed. The principle of its operation is based on the fact that any current passing through a conductor creates a certain electromagnetic field. The magnitude of this field is greater, the greater the current strength. By measuring the field strength and converting these data, you get the real value of the force, expressed in amperes.
This is a very convenient way to take measurements, because you do not need to think long about how to connect an ammeter. To the charger and any electrical circuit, you can connect the pliers directly to the insulated wire and take readings.
Why do I need to control the charge current in the battery
It seems to be simpler: I connected the car battery to the charger, I waited ten hours and the job was done - it is charged. In fact, it is very important to control the charge current, overcharging is as harmful as an incompletely charged battery. This can lead to a reduction in its life. Therefore, it is advisable to think about how to connect the ammeter to the charger.
When the circuit is assembled and turned on, the ammeter shows the magnitude of the charge current. If the battery is working, but discharged, it will gradually take charge. That is, the charge current begins to decrease slowly (over several hours) until it stops at a certain value. When this happened, it is advisable to disconnect the battery from the charger. If there is a sharp decrease in current from the initial value (within half an hour), then the battery may be malfunctioning.
Very good chargers have a charging current adjustment function. Then at the beginning of the process it is necessary to set the charge current ten times less than the nominal battery capacity, which is indicated in its technical parameters.