Range selection and measurement error analysis of

2022-10-21
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Range selection and measurement error analysis of each gear of the multimeter

measuring with a multimeter will bring certain errors. Some of these errors are the maximum absolute errors allowed by the accuracy level of the instrument itself. Some are human errors caused by improper adjustment and use. The measurement error can be reduced by correctly understanding the characteristics of multimeter and the causes of measurement error, and mastering the correct measurement technology and method

human reading error is one of the reasons that affect the measurement accuracy. It is inevitable, but it can be minimized. Therefore, special attention should be paid to the following points in use: 1. Before measurement, place the multimeter horizontally and conduct mechanical zero adjustment; 2 keep your eyes perpendicular to the pointer when reading; 3. When measuring resistance, zero should be adjusted every time you change gear. Replace the battery when it cannot be adjusted to zero; 4 when measuring resistance or high voltage, do not hold the metal part of the probe with your hand, so as to avoid the shunt of human resistance, increase the measurement error or electric shock; 5 when measuring the resistance in RC circuit, cut off the power supply in the circuit and discharge the electricity stored in the capacitor before measuring. After excluding the artificial reading error, we will analyze other errors

1. Multimeter voltage and current range selection and measurement error

the accuracy grade of multimeter is generally divided into several grades, such as 0.1, 0.5, 1.5, 2.5, 5, etc. For DC voltage, current, AC voltage, current and other gears, the calibration of accuracy (accuracy) level is expressed by the percentage of its maximum absolute allowable error △ X and the full scale value of the selected range. Expressed by formula: a% = (△ x/full scale value) × 100%... 1

(1) the error caused by measuring the same voltage with a multimeter with different accuracy

for example: there is a 10V standard voltage, measured with two multimeter with 100V gear, 0.5 gear, 15V gear and 2.5 gear, which meter has a small measurement error

solution: from Formula 1: the first table measurement: the maximum absolute allowable error

△ x1= ± 0.5% × 100V=±0.50V。

measurement of the second meter: maximum absolute allowable error

△ x2= ± 2.5% × l5V=±0.375V。

comparing △ X1 and △ X2, we can see that although the accuracy of the first meter is higher than that of the second meter, the error caused by measuring with the first meter is larger than that caused by measuring with the second meter. Therefore, it can be seen that when selecting a multimeter, the higher the accuracy, the better. With a multimeter with high accuracy, we should also choose a suitable range. Only when the measuring range is correctly selected can the potential accuracy of the multimeter be brought into play

(2) the error produced by measuring the same voltage with different ranges of a multimeter

for example, the accuracy of mf-30 multimeter is level 2.5, and 100V gear and 25V gear are selected to measure a 23v standard voltage. Which gear has a small error

solution: maximum absolute allowable error of 100V gear:

x (100) = ± 2.5% × 100V=±2.5V。

25v gear maximum absolute allowable error: △ x (25) = ± 2.5% × 25V=±0.625V。 It can be seen from the above solution:

measure 23v standard voltage with 100V gear, and the reading value on the multimeter is between 20.5v and 25.5v. Measure 23v standard voltage with 25V gear, and the value shown on the multimeter is between 22.375v and 23.625v. From the above results, Δ x (100) is greater than Δ x (25), that is, the measurement error of 100V gear is much larger than that of 25V gear. Therefore, when a multimeter measures different voltages, the errors produced by measuring with different ranges are different. When the measured signal value is satisfied, the gear with small range should be selected as far as possible. This can improve the accuracy of measurement

(3) the error caused by measuring two different voltages with the same range of a multimeter

for example, the accuracy of mf-30 multimeter is 2, so as to improve the production efficiency Level 5. Measure a standard voltage of 20V and 80V with 100V gear. Which gear has a small error

solution: maximum relative error: △ a% = maximum absolute error △ x/measured standard voltage regulator × 100%, maximum absolute error of 100V gear △ x (100) = ± 2.5% × 100V=±2.5V。

for 20V, its indication is between 17.5v-22.5v. The maximum relative error is: a (20)%= (± 2.5v/20v) × 100%=±12.5%。

for 80V, its indication is between 77.5v and 82.5v. The maximum relative error is:

a (80)%= ± (2.5v/80v) × 100%=±3.1%。

comparing the maximum relative error of the measured voltage of 20V and 80V, it can be seen that the former is much larger than the latter. Therefore, when measuring two different voltages with the same range of a multimeter, whoever is close to the full gear value will have higher accuracy. Therefore, when measuring the voltage, the measured voltage should be indicated at more than 2/3 of the range of the multimeter. Only in this way can the measurement error be reduced

2. range selection and measurement error of resistance gear

each range of resistance gear can measure the resistance value of 0 ~ ∞. The scale scale of ohmmeter is a nonlinear and uneven inverted scale. It is expressed as a percentage of the arc length of the ruler. Moreover, the internal resistance of each range is equal to the multiplying factor of the central degree of the scale arc length, which is called "central resistance". In other words, when the measured resistance is equal to the center resistance of the selected gear range, the current flowing through the circuit is half of the full-scale current. The pointer indicates in the center of the scale. Its accuracy is expressed by the following formula:

R% = (△ R/central resistance) × 100%... 2

(1) when measuring the same resistance with a multimeter, the error caused by TBS choosing different measuring ranges

for example: mf-30 multimeter, its rxl0 gear has a year-on-year increase of 70.21%, and the center resistance is 250 Ω; R × The central resistance of l00 gear is 2.5k Ω. The accuracy level is 2.5. Use it to measure a standard resistance of 500 Ω and ask R × L0 gear and R × 100 gears to measure, which error is big? Solution: from formula 2:

r × L0 gear maximum absolute allowable error △ R (10) = Central resistance × R%=250Ω × (±2.5)%=±6.25Ω。 Using it to measure 500 Ω standard resistance, the indication value of 500 Ω standard resistance is between 493.75 Ω ~ 506.25 Ω. The maximum relative error is: ± 6.25 ÷ 500 Ω × 100%=±1.25%。

R × L00 gear maximum absolute allowable error △ R (100) = Central resistance × R%2.5kΩ × (±2.5)%=±62.5Ω。 Using it to measure 500 Ω standard resistance, the indication value of 500 Ω standard resistance is between 437.5 Ω ~ 562.5 Ω. The maximum relative error is: ± 62.5 ÷ 500 Ω × 100%=±10.5%。

the comparison of the calculation results shows that the measurement errors vary greatly with the selection of different resistance ranges. Therefore, when selecting the gear range, try to make the measured resistance value in the center of the arc length of the range scale. The measurement accuracy will be higher

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