---
title: "Short note: Digital multimeter (DMM)"
subject: "Basic Electronics Engineering"
chapter: 7
key: "semester_2/basic_electronics_engineering:short-note-dmm"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/short-note-dmm
site: BCT Engineering
---

# Short note: Digital multimeter (DMM)

Basic Electronics Engineering · Chapter 7: Application of Electronic System

- Asked in: 2075 Baisakh, 3 marks; 2073 Magh, 5 marks; 2071 Bhadra, 4 marks; 2070 Magh, 3 marks (asked 4 times)
- Video: [How to use a multimeter like a pro, the ultimate guide](https://www.youtube.com/watch?v=0loXukB302Q) — Anthony Mendez 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/short-note-dmm
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-7

## Question

Write a short note on Digital Multimeter (DMM).

## Short answer

A DMM measures DC/AC voltage, current, and resistance with high accuracy and a digital display. It uses an attenuator for voltage, a shunt resistor for current, and constant-current method for resistance, followed by an ADC and decoder/driver.

## Answer

A **Digital Multimeter (DMM)** is an electronic instrument that measures voltage (AC/DC), current (AC/DC) and resistance, and shows the value directly as numbers on a digital display (LCD or LED). Many DMMs also measure capacitance, frequency and temperature, and can test diodes and continuity.

#### Block diagram

```text
 Input -> Range   -> Signal      -> ADC -> Decoder/ -> Display
          selector   conditioner          driver
          (attenuator/ (amp, AC-DC          ^
           shunt)       converter, I-V)    Control logic + clock
```

#### Working

- **Voltage:** an attenuator scales the input, and the ADC converts it.
- **Current:** the current flows through a precision shunt resistor, and the voltage drop across it is measured.
- **Resistance:** a constant current is passed through the unknown resistor, and the voltage across it is measured.
- The ADC output goes to a decoder, which drives the display.

Advantages: high accuracy (0.1 % or better), high input impedance (about 10 MΩ) so little loading error, easy reading with no parallax error, auto-ranging and auto-polarity, and small size. Disadvantages: it needs a battery, and it is poor at showing quickly changing readings.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A digital multimeter differs from an analog meter because it:
   A. Uses a pointer on a calibrated scale
   B. Shows the value as numbers on a digital display
   C. Needs no ADC
   D. Measures only voltage
   Answer: B. A DMM converts the signal with an ADC and shows the value directly as digits. (Key point: What DMM shows)

2. How does a DMM measure resistance?
   A. It connects the unknown resistor to a shunt
   B. It scales the voltage with an attenuator
   C. It measures the power in the resistor
   D. It passes a constant current through it and measures the voltage across it
   Answer: D. With a constant current source, V is proportional to the unknown R, and the ADC measures that voltage. (Key point: Measuring resistance)

3. What is the benefit of the DMM's high input impedance (about 10 MΩ)?
   A. Little loading error in the circuit measured
   B. Larger current drawn from the circuit
   C. Faster display of rapid changes
   D. It removes need for a battery
   Answer: A. A high input resistance draws very little current, so it does not disturb the circuit being measured. (Key point: High input impedance)

## Related in Basic Electronics Engineering

- [Remote control or digital multimeter](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Aremote-control-or-dmm) — Basic Electronics Engineering, chapter 7
- [DMM block diagram: V, I and R measurement](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Admm-dc-voltage-current-resistance) — Basic Electronics Engineering, chapter 7
- [DMM block diagram, measuring DC current](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Admm-dc-current) — Basic Electronics Engineering, chapter 7