Digital Multimeter Measurement Error Analysis

The error of human reading is one of the reasons that affect the measurement accuracy. Pay special attention to the following points during use.

(1) Place the multimeter horizontally before measurement to perform mechanical zero adjustment

(2) The eye should be perpendicular to the pointer when reading

(3) When measuring the resistance, it must be zeroed every time the gear is changed. When the temperature is not adjusted, the new battery should be replaced, and the metal part of the test pen cannot be pinched by hand to avoid the shunting of the human body resistance and increase the measurement error.

(4) When measuring the resistance in the circuit, the power supply in the circuit is cut off, and the capacitor is discharged, and then the measurement is performed.

The accuracy level of the multimeter is generally divided into 0.1, 0.5, 1.5, 2.5, 5, and so on. For DC voltage, current, AC voltage, current, etc., the accuracy accuracy level is indicated by the maximum absolute allowable error Δx and the percentage of the selected range full scale value.

The multimeter measures the error caused by the voltage, and the error caused by measuring the same voltage by a multimeter with different accuracy is different. When the multimeter is selected, the higher the accuracy, the better. With a highly accurate multimeter, you need to choose the right range to get the potential accuracy of your multimeter. The error caused by measuring the same voltage with different ranges of a multimeter is also different. When the value of the signal to be measured is satisfied, the range with a small range should be selected as much as possible, so that the accuracy of the measurement can be improved. Therefore, when measuring the voltage, the measured voltage should be indicated above 2/3 of the multimeter's range, so as to reduce the measurement error.

When using a multimeter to measure the same resistance, the errors produced by using different ranges are different, and the errors produced by the measurement vary greatly. When selecting the gear range, try to make the measured resistance value at the center of the arc length of the range scale, and the measurement accuracy will be higher.

The rectifying meter in which the multimeter's magnetoelectric measuring mechanism and the rectifying circuit are combined indicates the average value of the alternating voltage. In engineering technology, it is usually necessary to measure the effective value of the AC voltage or current. To meet this need, the scale of the multimeter AC voltage is scaled according to the effective value of the sinusoidal AC voltage.

The multimeter AC voltage file is an average voltmeter. When the AC voltage is measured, although the dial is scaled according to the effective value, the rectifier circuit actually detects the voltage average. The ratio of the effective value U of the voltage to the average value /U is called the gauge coefficient of the meter, and is represented by K, which reflects the proportional relationship between the multimeter's AC voltage reading and the average value of the measured voltage.

The indication when measuring the sine wave voltage at the rated frequency with a multimeter is:

a=U

In the formula:

U is the reading of the multimeter's AC voltage file;

U is the effective value of the sine wave voltage.

It can be seen that the sine wave voltage is measured by the multimeter AC voltage file, and the reading a is the effective value of the measured voltage; the measurement of the non-sinusoidal voltage has no direct physical meaning, and only 0.9a is equal to the average of the measured voltage. value. If the form factor of the measured voltage is known, the effective value of the measured voltage can be obtained by conversion.

The form factor Kf is defined as the ratio of the effective value of the AC voltage to the average value, ie:

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