How to read the measurement results of a digital multimeter?

Most handheld or benchtop digital multimeters display measurements digitally. The number of digits displayed on the screen usually represents the measurement resolution of the digital multimeter. Resolution is the smallest detail that a digital multimeter can quantitatively determine when making a measurement. Therefore, the more digits a digital multimeter displays, the higher its resolution. Handheld digital multimeters are typically capable of displaying three-and-a-half and four-and-a-half digits. Benchtop digital multimeters are typically capable of displaying five and a half, six and a half, seven and a half, and even eight and a half digits.

A detailed look at the number of digits, accuracy and resolution of digital multimeters

What are the digits, accuracy and resolution of a digital multimeter?

Digital Multimeter (DMM)figure,accuracycap (a poem)resolution (of a photo)It is its core performance parameter, which directly affects the accuracy of the measurement results and the scope of application. The following is a detailed explanation:

1. Digits

• define: The number of digits indicates the number of digits that the multimeter can display, usually in the form of "½ digit" (e.g. 3½ digits, 4½ digits, etc.).
  • ½ position: The highest bit can only be displayed 0 maybe 1(For example, a 3½-digit multimeter with a maximum display value of 1999).
  • pantotope: All digits can be displayed 0-9(For example, a 4-digit multimeter with a maximum display value of 9999).
• significance::
  • The more digits, the higher the measurement range and resolution (e.g., 4½ digits is finer than 3½ digits).
  • Common digit grades:
    • 3½-bit: Basic model, suitable for daily maintenance (display range) 0-1999).
    • 4½-bit: Mid to high end, suitable for laboratories (display range) 0-19999).
    • 6½ and above: High precision scientific research or calibration purposes.

2. Accuracy

• define: Accuracy indicates how close the measurement result is to the true value and is usually expressed as a percentage error plus a fixed error term (e.g. ± (1% + 3d)).
  • percentage error: Range dependent (e.g., at 2V range) ±1% homologous ±0.02V).
  • Fixed error (d): Based on the minimum resolution (e.g. 3d (Indicates ±3 minimum display units).
• typical example::
  If the accuracy of the multimeter in the 2V range is ± (1% + 3d)The resolution is 1mV::
  • The measured values are 1.500V When the error is 1.500 x 1% + 3 x 0.001V = 0.015V + 0.003V = ±0.018VThe
• significance::
  • The higher the accuracy, the more reliable the measurements, but also the higher the cost.
  • Calibration, temperature drift and component quality all affect accuracy.

3. Resolution

• define: Resolution is the smallest amount of input change that the multimeter can recognize, i.e., the smallest display unit (e.g., the 1mV).
  • Determined by both the range and the number of digits: for example, the resolution of a 4½-digit multimeter in the 2 V range is 2000mV/19999 ≈ 0.1mVThe
• Difference with accuracy::
  • High resolution does not mean high accuracy (e.g., the resolution is shown up to 0.1mV(but the actual error may be much larger).
  • Resolution reflects "sensitivity" and accuracy reflects "confidence".
• practical application::
  • In auto-range mode, the multimeter automatically switches ranges according to the input, which may affect the resolution (e.g., the resolution decreases when switching to a higher range).

Relationship between the three and recommendations for selection

• Bits and Resolution: The more bits, the higher the resolution (e.g., 4½ bits are finer than 3½ bits).
• Accuracy and Resolution: High resolution needs to be supported by high accuracy, otherwise fine display is meaningless.
• Applicable Scenarios::
  • routine maintenance: 3½ positions (e.g. measuring battery voltage, on-off testing).
  • Electronic design/debugging: 4½ bits or more (e.g. to analyze sensor signals).
  • Precision Measurement: 6½ digits or more, in conjunction with high accuracy (e.g., calibrated instruments).

summary table

The choice needs to balance all three according to the needs: high digits and high accuracy are suitable for professional scenarios, while basic applications can be prioritized for cost-effectiveness.