What should be paid attention to in the process of voltage and current measurement?

When measuring voltage, we must pay attention to the multimeter and the measured signal source in parallel, of course, if the measurement of relatively high DC voltage and AC voltage, you must add a high-voltage probe on the meter pen, there is a voltage attenuator inside the high-voltage probe, and if you don't know whether the measured voltage is a DC signal or an AC signal, and don't know how big the voltage value is, you should hit the highest range of the AC voltage block to measure, and when measuring the voltage, it is also important to check the meter pen insulation, generally the meter pen insulation is 1000V Available in 10A and 1000V 20A.

When measuring the current, it should also be noted that the multimeter must be connected in series with the signal source being measured, (except for the clamp meter) the clamp ammeter is to measure the current on the card, the current measurement with the multimeter must be disconnected from the circuit under test first, and then the multimeter to the current block, if you do not know the range, you must hit the maximum range, and then connect the red and black pen into the circuit to measure, when measuring the current, it is best not to take the pen with two hands, it is best to hold the pen with one hand, in order to prevent the poor insulation performance of the pen and cause electric shock accidents, When using the 20A current jack of the digital multimeter to measure the large current, when the current is higher than 5A, you must pay attention to the time, the general time can not exceed 20-30 seconds, otherwise the manganese copper manifold inside the current block will be heated and the measurement error will become larger.

When measuring voltage and current data, there are different measurement methods: different meanings, different methods.

First, the meaning is different:

The magnitude of the current is used with an ammeter.

For measurement, the ammeter should be connected in series with the electrical appliance to be measured. The connection method of the positive and negative binding posts should be correct: the current flows in from the positive binding post and flows out from the negative binding post, commonly known as positive in and negative out.

The measured current should not exceed the range of the ammeter, and the range can be determined by the method of test touch. Because the internal resistance of the ammeter is too small (equivalent to a wire), it is absolutely not allowed to connect the ammeter directly to the two poles of the power supply without passing through the electrical appliance.

Second, the way is different:

When measuring, the ammeter should be connected in series on the low-potential side of the circuit under test. When measuring DC, it is necessary to pay attention to the symbol of the end button of the ammeter, for a single current limit meter, the measured current should flow from the end button marked with "early +", and flow out of the ammeter from the end button marked with "—"; For multi-meter current limit meters, the one marked with "*" is the common end button.

If the other end buttons are marked with a "+" symbol. Then the measured current should flow in from the "+" end button and flow out from the "*" end button; If the other end knobs are marked with a "—" symbol, then the connection is exactly the opposite of the above.

If the magnitude of the voltage.

and the direction does not change with time, it is called a steady voltage or constant voltage, referred to as DC voltage, represented by a capital letter u. If the magnitude and direction of the voltage change over time, it is called a fluctuating voltage. For circuit analysis, one of the most important fluctuating voltages is the sinusoidal alternating current voltage (abbreviated as alternating voltage), which changes periodically in magnitude and direction according to the sinusoidal law over time.

The instantaneous value of the AC voltage is indicated by the lowercase letters u or u(t). The device that provides voltage in a circuit is a power supply.

The use and maintenance method of the voltmeter is similar to the use and maintenance method of the ammeter, and the following points should also be noted:

1) When measuring, the voltmeter should be connected in parallel to the circuit under test.

2) Since the voltmeter and the load are connected in parallel, the internal resistance RV is required to be much greater than the load resistance RL.

3) When measuring DC, first connect the "—" button of the voltmeter to the low potential end of the circuit to be tested, and then connect the "+" button to the high potential end of the circuit under test.

4) For multiple limit voltmeters, when it is necessary to change the limit limit, the voltmeter should be disconnected from the circuit under test, and then the limit should be changed.

Summary. When measuring current, the ammeter should be connected in series in the circuit.

When measuring voltage, the voltmeter should be connected in parallel at both ends of the resistor being measured.

How should the ammeter be connected to the circuit when measuring current? What should be the way the voltmeter should be used when measuring voltage.

When measuring the current, the ammeter should be connected in series in the circuit, and when measuring the voltage, the voltmeter should be connected in parallel at both ends of the resistor to be measured.

Glad to answer for you, any other physical questions.

What is Ampere Meter Connection? What is Ampere Meter Attachment Method?

1. The resistance to be measured by the internal connection method is connected in series with the ammeter in series and in parallel with the voltmeter, and the measured current is correct, but because the ammeter has internal resistance, the ammeter will divide the voltage, and the voltage measured by the voltmeter is the sum of the voltage of the ammeter and the resistance. Therefore, the measured value R1=U1 I1 is greater than the true value of the external method: the measured resistance to be measured is connected in parallel with the voltmeter and connected in series with the ammeter, and the measured voltage is correct, but because the voltmeter has internal resistance, the voltmeter will also have current through, then the current measured by the ammeter is the sum of the current through the voltmeter and the resistance.

So the measured value r2 = u2 i2 is less than the true value r.

Okay, thanks.

The choice of type. When the measurement is DC, the DC meter should be selected, that is, the instrument of the magnetoelectric measuring mechanism. When the measurement is AC, the waveform and frequency should be noted.

If it is a sine wave, only the effective value needs to be measured and converted to other values (such as maximum value, average value, etc.), and any AC table can be used; If it is a non-sine wave, it should be distinguished what value needs to be measured, the effective value can be selected by the instrument of the magnetic system or ferromagnetic electric system measuring mechanism, and the average value can be selected by the instrument of the rectifier system measuring mechanism. Instruments of motorized measuring mechanisms are often used for precise measurement of AC current and voltage.

Selection of accuracy. Because the higher the accuracy of the instrument, the more expensive it is, and the more difficult it is to maintain. Moreover, if other conditions are not properly coordinated, even the highest accuracy level of the instrument may not be able to get accurate measurement results.

Therefore, if the measurement requirements can be met by using an instrument with low accuracy, do not choose a high-accuracy instrument. Ordinary and grade instruments are selected as standard tables; Grade and grade instruments are used as laboratory measurements; Instruments below the grade are generally selected as engineering surveys.

Choice of measuring range. In order to give full play to the role of filial piety in the accuracy of the instrument, it is also necessary to reasonably select the instrument limit according to the size to be measured, if the selection is not appropriate, the measurement error will be very large. Generally, the indication of the instrument to the measured range is greater than 1 2 2 3 of the maximum range of the instrument, but not more than its maximum range.

Selection of internal resistance. When selecting the instrument, the internal resistance of the instrument should also be selected according to the size of the measured impedance, otherwise it will bring a large measurement error. Because the size of the internal resistance reflects the power consumption of the instrument itself, when measuring the current, the ammeter with the smallest internal resistance should be selected; When measuring voltage, a voltmeter with as much internal resistance as possible should be used.

Voltmeter for voltage measurement, ammeter for current measurement.

The voltmeter should be connected in parallel with the measured object, the ammeter should be connected in series with the measured object, pay attention to the range, and estimate the amount of current and voltage before use, and finally connect the battery, do not directly contact the wire, prevent electric shock, and protect your own safety.

Pay attention to the positive and negative poles, and pay attention to protect yourself.

The measuring range should also be taken care not to exceed the measuring range.

1. The voltmeter is connected in parallel in the circuit;

2. The ammeter is connected in series in the circuit;

3. Estimate the size of the measured value before measuring, and select the appropriate range;

4. When measuring large currents, clamp ammeters should be used;

5. When adjusting the range switch, disconnect the power supply to avoid damaging the instrument;

6. Pay attention to safety and prevent electric shock.

Note that there are many things to do, for different electricity.

Pressure gauge (digital analogue.

For different circuits (AC and DC), it is different, and here are some general precautions:

1. Range: Judge the value of the measured voltage, and then select the range of the meter to avoid burning the voltmeter by measuring high voltage at too low voltage level;

2. Gear: AC gear for AC circuit, DC gear for DC circuit;

3. Matching: AC circuit measures voltage, pay attention to the signal frequency of the selected voltmeter and the measured loop, and the measurement is inaccurate when the difference is large; When measuring the voltage of the DC circuit, pay attention to the polarity of the meter pen;

4. Safety: When measuring high voltage, pay attention to the position of the pen and hand to avoid electric shock; At the same time, pay attention to the table pen not to cause a short circuit in the circuit, which will affect the safety of the circuit;

5. Reading: The digital meter can be read directly, and the analog meter needs to see the position of the pointer according to the gear in order to read accurately;

6. The safety of the voltmeter: if you use a multimeter to measure, check whether it is in the voltage gear before each measurement; Using other gears to measure voltage will not only cause a short circuit in the circuit, but also burn the voltmeter.

And so on, you can experience it carefully at work.

First, the connection method of the voltmeter:

Observe whether the pointer is pointing at the "zero" tick mark, if not, you need to adjust the zero button to adjust the pointer to "zero" first

The voltmeter must be connected in parallel with the appliance under test.

Note 1If the voltmeter and the electrical appliance under test are connected in series, the indication of the voltmeter will be equal to the power supply voltage, and the small bulb will not.

Luminous. 2 The voltmeter can be connected directly between the two stages of the power supply, so that the voltage value of the power supply can be measured.

3) Current must be allowed to enter from the positive terminal of the voltmeter (red binding post) and then flow out from the negative terminal (black binding post).

Note: If the positive and negative poles of the voltmeter are reversed, the pointer will be reversed.

4): The range of the voltmeter must be selected correctly.

Note: 1: If you can estimate the voltage again, estimate it first, and then select the appropriate range.

2: When it is impossible to estimate, use the test touch method to select the range.

The specific operation method of the test touch method to select the range:

1): First connect the range of 0-15V, close and disconnect the switch quickly, and observe whether the pointer exceeds the scale mark of the maximum range, if it exceeds the need to change to a voltmeter with a larger range.

2): If the deflection of the pointer does not exceed the range, but the voltage indication number is greater than 3V, the range of 0-15V should be connected.

3): If the number of voltage representations is less than 3V, the range of 0-3V should be connected.

Second, the reading of the voltmeter:

1): Specify the range of the selected voltmeter. (judging by the wiring used).

2): See the graduation value of each range: 0-3V range, the graduation value is.

0-15V range, the graduation value is.

3): Read the number of squares (the number of squares that clearly deflect the pointer to the right).

Note: The range of 0-3V = the number of grids deflected by V. The range of 0-3a = the number of cells deflected by v.

Before measuring, it seems that the clear range can meet the self-measurement requirements;

Whether the minimum fractional degree value corresponding to each range BAI meets the requirements of measurement accuracy;

The pointer is zeroed; When measuring, it is necessary to estimate the voltage to be measured first, select the appropriate range, and use the test touch method when it cannot be estimated;

In parallel with the measurement object, the binding post should pay attention to the positive in and negative out (red in and black out);

Finally, the pointer is read after it is stationary, and the line of sight is perpendicular to the pointer deflection plane when reading;

Voltage detection is relatively simple, and the voltage sensor is connected to the line end of the voltage to be measured.

Current sensing, in fact, also relies on voltage sensing to calculate the current. There are two ways to do this:

1. Mutual inductance detection method. Mutual inductance detection method is generally used in high-voltage and high-current occasions (AC). In the mutual inductance circuit, when the main winding flows through different currents, the secondary windings induce different voltages.

By reading out the voltage values of the interwindings, the current flowing through the main windings can be calculated.

2. Resistance detection method. Resistance detection method is generally used in low-voltage and low-current occasions. When a current flows through a resistor, a corresponding voltage is generated at both ends of the resistor, and the current flowing through the resistor can be calculated by reading out the voltage value.