The principle of magnetoelectric ammeter, what is the working principle of magnetoelectric ammeter

A brief description of the principle of a multimeter.

Note that this is a "brief description" and does not describe the structure of the multimeter in detail. I try to use the most ordinary language as much as possible so that even people who have no basic knowledge of electricians can understand it.

The multimeter is fundamentally an ammeter - its job is to measure the current and calculate it using a simple formula (Ohm's law, the formula is i=u r, the current is equal to the ratio of voltage to resistance), and get the result we want.

The actual usage of the multimeter and the principle of each function are explained in detail.

So how does it measure current? This is the soul of the multimeter - the magnetoelectric DC ammeter (also known as the micro-ampere meter), which is extremely accurate, but can withstand very small current. In order to prevent the micro-ampere meter from being burned, the multimeter will internally connect a resistor in parallel with the micro-ampere meter to split the current.

The parallel resistance and the resistance of the microampere meter are known, and the actual circuit size in the line can be easily calculated by using the formula i=i1*(r1+r2) r2 (r2 is the resistance value of the shunt resistor) - the resistor connected in parallel at this time is called the "shunt resistor".

The actual usage of the multimeter and the principle of each function are explained in detail.

When measuring voltage, a resistor is connected in parallel with the microampere meter, which can play the role of voltage division (this resistance is called multiplier resistance). The partial pressure formula is U Doubling: U Measurement = R Multiplication:

R micro-ampere meter - U multiplication can use a micro-ampere meter to measure the current of the multiplication resistor, which is obtained according to i=u r. As a result, the measurement result can be easily calculated.

The voltage and current of direct current can be measured directly, but the voltage and current direction of alternating current are changing all the time, so how to measure it? In fact, it is not difficult, it is to add a half-wave rectifier circuit inside the multimeter to turn the alternating current into direct current, and then test.

The actual usage of the multimeter and the principle of each function are explained in detail.

When measuring resistance, the battery inside the multimeter comes into play – the battery is used to pressurize both ends of the object to be measured and measure the current passing through the object at that time. The value of the pressure is known, so the resistance of an object can be easily calculated using the Ohm's law formula.

If the line is turned on (the resistance meter is smaller), the current can be returned to the multimeter, and the small horn in the multimeter can be turned on, and the beep sound will be emitted - generally when using the buzzer file test, the resistance value in the line will be displayed on the display screen at the same time.

Share the basic knowledge of electricians and learn electrician meters.

The working principle of magnetoelectric ammeter is as follows:When a small current is introduced into the coil, the current is deflected by the force of the magnetic field, and the hairspring is also a spring, when the coil is deflected, the hairspring will produce a torque in the opposite direction, and finally the coil will stop in one position. It can be proved that the angle of rotation of the coil is directly proportional to the current in the coil.

The difference between electromagnetic meters and magnetoelectric meters.

1) The two types of instruments can be distinguished from the dial. In addition to the difference in graphic symbols, the scale of the magnetoelectric ammeter and voltmeter is basically uniform, while the scale of the electromagnetic instrument changes from dense to sparse.

2) From the point of view of performance, the magnetoelectric meter reflects the average value of the current passing through it, so it can only be used to directly measure the DC current or voltage; An electromagnetic meter, on the other hand, reflects the effective value of the current passing through it.

The principle of the ammeter is that the energized conductor is affected by the force of the magnetic field in the magnetic field, and then drives the pointer to swing. The structure of the ammeter is made up of three binding posts. There are two kinds of binding posts + and -, such as (+, 3) or (-, 3) pointers, scales, etc. (there are no positive and negative binding posts for AC ammeters).

When there is a current passing through, the current passes through the magnetic field along the spring and the rotating shaft, and the current cuts the magnetic inductance line, so it is affected by the magnetic field force, which makes the coil deflect, and drives the rotating shaft and pointer to deflect. Since the magnitude of the magnetic field increases with the increase of the current, the magnitude of the current can be observed by the degree of deflection of the pointer.

How the ammeter works.

When there is a current passing through, the current passes through the magnetic field along the spring and the rotating shaft, and the current cuts the magnetic inductance line, so it is affected by the magnetic field force, which makes the coil deflect, and drives the rotating shaft and pointer to deflect.

Since the magnitude of the magnetic field increases with the increase of the current, the magnitude of the current can be observed by the degree of deflection of the pointer. It's called a magnetoelectric ammeter, and it's the kind we usually use in our labs.

If the galvanometer is connected in parallel with a small resistance, it becomes an ammeter, and the resistor connected in parallel plays a shunt role, otherwise the galvanometer is easy to burn out.

Electromagnetic induction, also known as magnetoelectric induction, refers to the phenomenon that a part of the conductor of a closed circuit moves in a magnetic field to cut magnetic inductance lines, and an electric current is generated in the conductor. This phenomenon of using a magnetic field to generate a wide current is called electromagnetic induction.

The current generated is called the galvanic current.

August 1831, Faraday.

Wrap the two coils around an iron ring, coil A is connected to the DC power supply, and coil B is connected to the ammeter.

He found that when the circuit of coil A is turned on or off, an instantaneous current is generated in coil B. Faraday discovered that an iron ring was not necessary. Take away the iron ring and do this experiment again, the above phenomenon still occurs, but the current in coil B is weaker.

In order to thoroughly study the phenomenon of electromagnetic induction, Faraday did a number of experiments. On November 24, 1831, Faraday presented himself to the Royal Society.

In a report submitted, this phenomenon was named "electromagnetic induction phenomena" and summarized five types of induced currents: varying currents, varying magnetic fields, moving constant currents, moving magnets, and conductors moving in a magnetic field.

The principle of the ammeter:

It is made by the action of the energized conductor in the magnetic field by the force of the magnetic field. The coil is subjected to a magnetic moment in a magnetic field with uniform amplitude distribution, and the coil rotation causes the coil spring to be twisted, resulting in a rotational torque. When the rotational torque of the spring is balanced with the magnetic moment, the coil stops rotating.

The precautions for the ammeter are as follows:

1. Correct wiring. When measuring current, the ammeter should be connected in series with the circuit under test; When measuring voltage, the voltmeter should be connected in parallel with the circuit under test. When measuring DC current and voltage, it is necessary to pay attention to the polarity of the instrument, which should be consistent with the polarity of the measurement.

2. Measurement of high voltage and high current. When measuring high voltages or currents, voltage transformers or current transformers must be used. The range of the voltmeter and ammeter should be consistent with the rated value of the transformer. The general voltage is 100V and the current is 5A.

3. Expansion of measuring range. When the measured circuit exceeds the range of the instrument, an external shunt or voltage divider can be used, but care should be taken that the accuracy level should match the accuracy level of the meter.

4. It should also be noted that the use environment of the instrument should meet the requirements and be kept away from the external magnetic field.