How do I use ammeters and voltmeters?

1. Ammeter.

An ammeter is a tool that measures the magnitude of current.

The ammeter must be connected in series in the circuit to be tested, and the "+" pole of the ammeter must be extremely close to the "+" of the power supply"It is extremely necessary to follow the power supply"?"Extreme proximity.

2.The structure of a DC ammeter.

The structure of the DC ammeter mainly includes: three binding posts [there are two kinds of binding posts with "+", such as (+, 3) or (-, 3)], pointers, scales, etc. (there are no positive and negative binding posts for the AC ammeter).

3.Rules for the use of ammeters.

Rules: The ammeter should be connected in series in the circuit (otherwise it will be short-circuited); The current should be from the "+" terminal post and out from the "-" terminal post (otherwise the pointer will be reversed); The measured current should not exceed the range of the ammeter (damage the ammeter); It is absolutely forbidden to connect the ammeter to the poles of the power supply without passing through the electrical appliance (short circuit).

Ammeter reading: (1) See the range clearly.

2) See the scale value clearly.

Generally speaking, the scale 0 3a is a graduation value and 0 is.

3) Look at the position where the watch hand stays (be sure to observe it from the front).

5.Preparation before use:1Calibrate zero, change the cone with a flat mouth.

Adjust the zero button.

6.Selective range: empirically estimated or by test touch.

Second, the voltmeter.

A voltmeter is an instrument that measures voltage.

The voltmeter must be connected in parallel at both ends of the circuit to be tested, and note that the positive and negative poles cannot be reversed. When using the ammeter, its two binding posts must not be directly connected to the two poles of the power supply, so as not to burn out the ammeter due to excessive current.

2 How to use DC voltmeter:

The commonly used voltmeter has three binding posts, one negative binding post and two positive binding posts.

3 Problems that should be paid attention to when using a voltmeter.

The following points should be noted: (l) When measuring voltage, the voltmeter must be connected in parallel at both ends of the circuit under test.

2) "+ The binding post cannot be reversed.

3) Choose the range correctly, and the measured voltage should not exceed the range of the voltmeter. When used, it is connected to one positive and one negative, and is connected in parallel in the circuit; If connected in series, the power supply electromotive force is measured.

The AC voltmeter is not divided into positive and negative poles, the range is correctly selected, and the voltmeter is directly connected in parallel at both ends of the circuit under test.

The voltage measured by the AC voltmeter is the RMS value of the AC voltage.

Third, finally our company (CCID.

G) believes that it is also necessary to distinguish the similarities and differences between the two tables.

1.Similarities: The positive pole of both meters is close to the positive pole of the power supply.

Pay attention to the measurement range for both tables.

2.Differences: The ammeter must be connected in series in the circuit to be tested, and the voltmeter must be connected in parallel at both ends of the circuit to be tested.

The ammeter should not be directly connected to the poles of the power supply, the voltmeter.

It can be connected directly to the poles of the power supply.

Junior high school physics and electricity do not seem to mention the internal resistance of a power supply, that is, the Ohm's law problem of the whole circuit.

According to the figure, when the sliding contact of the variable resistance moves upward, that is, when the resistance value increases, the total resistance value of the series circuit composed of it and the series R3 and R4 in series increases, so that the "calculation formula of the total resistance of the parallel circuit" listed in **, the right side of the equation because the denominator of one of the fractions increases, that is, the fractional value decreases, so their sum decreases, and the reciprocal of the total resistance value decreases after paralleling, so the total resistance value increases (the total resistance increases, and its reciprocal decreases), ** The decrease in the total resistance value of r written above is a wrong conclusion. Because the total resistance of the parallel circuit increases as the p-point moves up, the total current flowing through the circuit, i.e., the reading of the ammeter, decreases. According to Ohm's law of the whole circuit, when the output current of the power supply decreases, the voltage drop on the internal resistance of the power supply decreases, and the voltage drop measured by the voltmeter in this circuit, that is, the voltage drop of the power supply electromotive force minus the internal resistance, will increase, that is, the voltmeter reading will increase.

This knowledge content seems to be learned at the high school level.

External method: when the internal resistance of the voltmeter is much greater than the resistance value of the resistance to be measured, the external method is used, and the current flowing through the voltmeter is very small and negligible, so the current measured by the ammeter is basically the current flowing through the resistance to be measured.

Internal method: when the internal resistance of the ammeter is much less than the resistance value of the resistance to be measured, the internal method is used, and the voltage obtained by the ammeter is very small and negligible, so the voltage measured by the voltmeter is basically the voltage at both ends of the electrical resistor.

Both methods are designed to measure more accurately, and once you have mastered the principle, you will be able to use it easily.

There is a permanent magnet inside the ammeter, which generates a magnetic field between the poles, there is a coil in the magnetic field, there is a hairspring spring at each end of the coil, the spring is connected to a binding post of the ammeter, between the spring and the coil is connected by a rotating shaft, and there is a pointer at the front end of the rotating shaft relative to the ammeter.

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.

In the case that it is impossible to estimate the measured current in advance, it is necessary to test the mountain with a larger range.

1. If the deflection of the gauge needle exceeds the larger range, it means that the ammeter is not available.

2. If the deflection of the watch hand exceeds the small range but does not exceed the large range, the large range is selected.

3. If the deflection of the Nashin pointer does not mark the small range, the small range is selected. This reduces the reading error.

For example, the figure above shows the deflection of the watch hand when trying to touch it with a large range (select the two binding posts "-" and "3"). The readings are out of the small range, so a large range should be used.

The purpose of the voltmeter: it is used to measure the voltage. The purpose of the ammeter: it is used to measure the current.

A voltmeter is an instrument that measures voltage. It is composed of permanent magnets, coils, etc. The voltmeter is a fairly large resistor, ideally thought of as an open circuit. The voltmeters commonly used in laboratories at the junior high school level have ranges of 0 3 V and 0 15 V.

An ammeter is a meter used to measure the current in an AC and DC circuit. In the circuit diagram, the symbol of the ammeter is:"Circle A"。The current value is expressed in "A" or "A.""is a standard unit.

As the name suggests, the ammeter is of course used to measure the current on the line, and it must be connected in series in the circuit under test; The voltmeter is used to measure the voltage, and it is connected in parallel in the circuit under test, and the gear must be adjusted when measuring the voltage and current, otherwise it will burn out the instrument, and it is best to measure it step by step from high grade to low gear.

The purpose of the voltmeter: it is used to measure the voltage. The purpose of the ammeter: it is used to measure the current.

A voltmeter is an instrument that measures voltage. It is composed of permanent magnets, coils, etc. The voltmeter is a fairly large resistor, ideally thought of as an open circuit. The voltmeters commonly used in laboratories at the junior high school level have ranges of 0 3 V and 0 15 V.

An ammeter is a meter used to measure the current in an AC and DC circuit. In the circuit diagram, the symbol of the ammeter is:"Circle A"。The current value is expressed in "A" or "A.""is a standard unit.

The difference between the internal and external methods of the ammeter: the internal and external connection are relative to the ammeter, the ammeter is externally connected outside the voltmeter, the ammeter is internalized in the voltmeter, the small resistance is externally connected, the measured value is smaller than the actual value, and the internal connection is used to measure the large resistance, and the measured value is larger than the actual value.

Ammeter internal method: The voltmeter measures the sum of the resistance and the voltage of the ammeter, which is larger. The measured current is accurate to the voltage.

Since the ammeter is connected in series with the resistance, the measured current is the current through the resistor, and the measured current is accurate, but the measured voltage is the voltage at both ends of the resistance and the ammeter in series, and the measured voltage is relatively wrong for measuring the voltage at both ends of the resistor.

When the resistance value to be measured is very large or the internal resistance of the ammeter is very small relative to the resistance value, the voltage error measured by this connection method is relatively small. Otherwise, the error will be large.

External ammeter method: The ammeter measures the sum of the current of the voltmeter and the resistance, which is larger. The measured voltage is more accurate than the current.

Because the voltmeter is connected in parallel with the resistor, the measured voltage is the voltage at both ends of the resistor, and the measured voltage is accurate, but the measured current is the current that is connected in parallel through the resistance and the voltmeter.

When the resistance value to be measured is very small or the internal resistance of the voltmeter is large relative to the resistance value, the flow error measured by this connection method is relatively small. Otherwise, the error will be large.

When the resistance value of the resistance to be measured is comparable with the resistance value of the ammeter, the external connection method is used;

When the resistance value of the resistor to be measured is much greater than that of the ammeter, the internal connection method is used;

When measuring with a meter, one should ensure that the measured voltage or current can not exceed the maximum measured value of the meter, and the second should try to improve the accuracy of the measurement under the premise of ensuring the safety of the meter, so the range of the meter should be selected according to the size of the voltage and current to be measured. In general, the range is selected by a touch test. The function of the touch test is to check whether the connection of the meter is correct; The second is to determine whether the range of the selected meter is appropriate.

Test touch: 1. When connecting the circuit, generally a wire connected to the meter binding post should be reserved first, do not connect first, after connecting the circuit, close the switch, use the reserved wire head to quickly contact with the binding post, and leave quickly, and observe the deflection of the meter pointer at the same time to determine whether the deflection of the pointer is correct. If the pointer is found to be reversed, the "+" "Sakuraku" "-" binding post of the voltmeter should be replaced.

2. If the size of the voltage or current to be measured cannot be determined or estimated, after connecting the circuit, the large range of the meter should be used to test the touch, that is, the reserved wire head should be held to quickly contact the terminal post of the large range of the meter, and at the same time look at the pointer of the voltmeter, if the pointer deflection angle is too small, it should be replaced with a small range; If you find that the pointer exceeds the range, you should use a voltmeter with a higher range instead. 3. The speed of the test touch should be fast, if it is too slow, it is easy to bend or damage the pointer when the pointer is reversed; If the range is too small, the pointer may be damaged or even the meter may be burned. The pointer of the meter can only ensure the safety of the meter and measure accurately only if it is positive and biased and the appropriate range is selected.

If the measuring range is too large, the measurement result is not accurate, and if the measuring range is too small, the meter may be burned out.