Similarities and differences between ammeter and voltmeter use

Ammeters and voltmeters.

Both ammeters and voltmeters are important electrical instruments. They have both similarities and differences in structure and use. Let's introduce it to the students in detail.

An ammeter, also known as an ampere meter. It is used to measure the magnitude of the current in the circuit. The ammeter has three binding posts and two ranges; Both ranges share a " " or " " binding post, marked with " is a positive or negative binding post.

The dial of the ammeter is marked with the symbol A and a scale indicating the current value, the "0" point of the ammeter is usually at the left end, and when the current in the circuit under test is zero, the pointer points to the 0 point. When there is current, the pointer is deflected, and the scale pointed after the pointer is stable is the current value in the circuit under test. When using " " or " and " and ", the range is 0, each large cell and each small cell is; If " " or " " and " and "3" are used, the range is 0 3a, 1a for each large cell and yes for each small cell.

The ammeter should be used in series in the circuit. The internal resistance of the ammeter itself is very small, so it is absolutely not allowed to connect the ammeter directly to the two poles of the power supply without passing through any electrical appliances, which will make the current through the ammeter too large and burn the ammeter.

Voltmeter, also known as voltmeter. Used to measure the voltage in the circuit, the voltmeter also has three binding posts, one negative binding post, and two positive binding posts. The student voltmeter generally has 3V, 15V two, when the measurement is selected according to the voltage size of the range of "15V", each large grid on the dial represents 5, each small grid represents the minimum graduation value; When the range is "3", each large cell on the dial represents LV, and each small cell represents the minimum graduation value.

The voltmeter should be used in parallel in the circuit, and the voltage at both ends of the electrical appliance should be measured in parallel with which electrical appliance; Unlike an ammeter, a voltmeter can be connected directly to the power supply without any electrical applicator, and the supply voltage is measured.

The steps of ammeter and voltmeter are basically the same, and they are divided into four steps: adjustment, selection, connection and reading

Tune – Adjust the pointer of the watch to the "zero scale" position before use.

Selection - select the appropriate range according to the actual situation of the circuit. In the case of not knowing the actual current or voltage, the method of "test touch" can be used to determine whether the range is exceeded, and it should be connected to a large range of binding posts during the test touch, and the action is fast when the test touch.

Connection - according to the respective connection methods of the ammeter and the voltmeter, the meter is correctly connected to the circuit, and at the same time pay attention to the relationship between the positive and negative binding posts of the meter and the current flow direction, and it must be ensured that the current flows in from the positive binding post of the meter and flows out from the negative binding post.

Reading - Correctly read the value shown by the table pointer, and be sure to pay attention to the selected range and the corresponding minimum scale value when reading

Similarities between voltmeter and ammeter:

The current should flow in from the "+" terminal post and flow out from the "-" binding post.

Neither the current nor the voltage to be measured exceeds the maximum measured value marked next to the selected range or binding post;

3. When you don't know the approximate value of the measured current or voltage in advance, you need to test the touch with a large range first.

Difference Between Ammeter and Voltmeter:

1. The ammeter measures the current and connects it in series on the measured current branch; The voltmeter measures the voltage, and is connected in parallel on the measured original;

2. The ammeter cannot be directly connected to both sides of the power supply, which will short-circuit and burn out the power supply; However, the voltmeter can be connected directly to both sides of the power supply, and the electromotive force of the power supply is measured.

3. The ammeter should be connected in series with the circuit, and the voltmeter should be connected in parallel with the circuit.

4. The law of series and parallel.

1) The law of series and parallel current:

Current law of series circuits: In series circuits, the currents are equal everywhere.

Parallel circuit current law: In parallel circuit, the trunk current is equal to the sum of the currents of each branch.

2) Series and parallel voltage rules:

Current law of series circuit: In a series circuit, the total voltage of the circuit is equal to the sum of the voltages of each department.

Parallel circuit current law: In a parallel circuit, the voltage at both ends of each branch is equal (also equal to the supply voltage).

Voltmeter, ammeter.

Connection. Parallel series test power supply.

Can or may not be used.

Voltage measurement, current measurement and current range.

0-3v，0-

0-3a

Electricity. Flow.

The directional movement of an electric charge is called a circuit, and the current is often denoted by i. The unit of current is amperes (a), and it is also commonly used in milliamperes (ma) or microamperes (ua). When measuring, connect the ammeter in series in the circuit, and select the range where the ammeter pointer is close to the full deflection.

This prevents the current from being too high and damaging the ammeter.

The ammeter cannot be connected directly in series at both ends of the power supply. Electricity. Press.

Voltage is responsible for the formation of electric current. In circuits, voltage is often expressed by u. The unit of electricity is volt (V), and it is also commonly used as a unit of millivolt (MV) or microvolt (UV).

When measuring, connect the voltmeter in parallel in the circuit, if the voltage on the circuit cannot be estimated, you should first use a large amount to refer to the rental range, and then use the appropriate range after a rough measurement. This prevents damage to the voltmeter due to excessive voltage. The voltmeter can be connected directly in parallel at both ends of the power supply.

The internal resistance of the ammeter is very small, the internal resistance of the voltmeter is larger, the meter must be connected in parallel at both ends of the circuit under test when using the voltmeter, when the ammeter is used, it will occur: 1. The circuit under test is short-circuited, and the circuit cannot work normally. 2. The ammeter will be damaged due to the large current flowing in the meter.

Therefore, voltmeters can only be used in parallel at both ends of the circuit, and ammeters can only be used in series in the circuit. When using both, it is necessary to choose the appropriate range.

The ammeter measures the current, which is connected in series on the measured current branch; The voltmeter measures the voltage, and is connected in parallel on the measured original; The ammeter cannot be directly connected to both sides of the power supply, which will short-circuit and burn out the power supply; However, the voltmeter can be connected directly to both sides of the power supply, and the electromotive force of the power supply is measured. Both voltmeters and ammeters are modified from sensitive galvanometers. Since the full bias current of the sensitive galvanometer is very small, the voltmeter has a large divider resistor connected in series in the sensitive galvanometer.

When used, it should be connected in parallel in the circuit. The ammeter has a small shunt resistor connected in parallel in a sensitive galvanometer. It is connected in series in the circuit when used.

The voltmeter simply shows the voltage. The ammeter can only read the value of the current.

1. Appearance. There is a letter "U" on the voltmeter, and there is a letter "A" on the ammeter, and the range is not the same, 2, usage. The ammeter should be connected in series in the electrical unit under test, and the voltmeter should be connected in parallel in the electrical vehicle under test. The reading is also different, one is an and the other is volt.

Appearance: The letter "U" has on the top of the voltmeter

The ammeter has the letter "A" on it

Usage: The voltmeter should be connected in parallel with the electrical unit under test.

The ammeter should be connected in series with the electroscope under test.

Similarities: They are all indicator instruments that rely on the current in the circuit to flow through the meter head.

Differences: The internal resistance of the ammeter is very low, and it can only work in series in the circuit, and the current of the branch is measured; The internal resistance of the voltmeter is very high, and it can only work in parallel in the circuit, and the voltage of the branch is measured.