The error in voltage measurement by a multimeter
In a digital multimeter, the measurement process involves converting the measured quantity into a DC voltage signal via a conversion circuit. This analog voltage is then transformed into a digital value by an analog-to-digital (A/D) converter. An electronic counter tallies these digital values, and finally, the measurement result is directly shown as digits on the display.
The multimeter's capabilities to measure voltage, current, and resistance are realized through its conversion circuit. Since current and resistance measurements are both founded on voltage measurement, it can be said that the digital multimeter is an enhanced version of a digital DC voltmeter.
Example: When measuring a standard voltage of 10V with two multimeters-one set to the 100V range with an accuracy class of 0.5, and the other to the 15V range with an accuracy class of 2.5-which multimeter will yield a smaller measurement error?
For the first multimeter:
The maximum absolute allowable error △X1 = ±0.5% × 100V = ±0.50V.
For the second multimeter:
The maximum absolute allowable error △X2 = ±2.5% × 15V = ±0.375V.
By comparing △X1 and △X2, it's evident that even though the first multimeter has a higher accuracy class than the second one, the measurement error it produces is larger. This shows that when selecting a multimeter, a higher accuracy class doesn't always guarantee better results. Along with a high - accuracy multimeter, choosing an appropriate measurement range is crucial. Only by correctly selecting the range can the multimeter's potential accuracy be fully utilized.
In a digital DC voltmeter, the A/D converter changes the continuously varying analog voltage over time into a digital quantity. An electronic counter then counts this digital quantity to obtain the measurement result, which is subsequently displayed by a decoding display circuit. A logic control circuit ensures the coordinated operation of all components, enabling the entire measurement process to be carried out sequentially under the action of a clock.
