---
title: "Short note: Digital voltmeter"
subject: "Basic Electronics Engineering"
chapter: 7
key: "semester_2/basic_electronics_engineering:short-note-digital-voltmeter"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/short-note-digital-voltmeter
site: BCT Engineering
---

# Short note: Digital voltmeter

Basic Electronics Engineering · Chapter 7: Application of Electronic System

- Asked in: 2072 Magh, 4 marks
- 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-digital-voltmeter
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-7

## Question

Write a short note on digital voltmeter.

## Short answer

A digital voltmeter scales the input voltage with an attenuator, amplifies it, and converts it to a digital number using an ADC. The value is displayed on an LCD/LED with auto-polarity and high input impedance (~10 MΩ), offering high accuracy and no reading error.

## Answer

A **digital voltmeter (DVM)** measures a voltage and displays it directly as decimal digits on a numeric display, instead of a pointer on a scale.

#### Block diagram

```text
 Input -> Attenuator -> Amplifier -> ADC -> Decoder -> Display
          (range)       (signal                driver   (LCD/LED)
                        conditioner)
                         ^
                 Reference voltage, clock, control logic
```

#### Working

1. The input is scaled by the attenuator (range switch) to suit the ADC.
2. The amplifier amplifies and buffers it (high input impedance).
3. The ADC (dual-slope, successive approximation or ramp type) converts the analog voltage to a binary or BCD number.
4. The decoder/driver converts it to seven-segment form and the display shows the value with a decimal point and polarity sign.
5. The control logic and clock set the timing.

**Advantages:** high accuracy and resolution, high input impedance (10 MΩ and above), no parallax or reading error, fast reading, auto-polarity and auto-range, easy interfacing with computers.

**Disadvantages:** needs power supply, costlier, and not good for watching a rapidly changing voltage.

## Check yourself

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

1. A digital voltmeter differs from an analog voltmeter in that it:
   A. Moves a pointer on a scale
   B. Displays the voltage as decimal digits
   C. Has low input impedance
   D. Cannot show polarity
   Answer: B. A DVM shows the voltage as numbers, removing parallax and reading error. (Key point: DVM display)

2. What does the attenuator (range switch) do?
   A. Converts the analog voltage to digital
   B. Drives the seven-segment display
   C. Scales the input to suit the ADC
   D. Provides the clock
   Answer: C. It scales the input voltage down to the range the ADC can handle. (Key point: Role of attenuator)

3. Which is a disadvantage of a DVM?
   A. Parallax error
   B. Low accuracy
   C. Low input impedance
   D. Not good for watching a rapidly changing voltage
   Answer: D. Digits change too fast to follow, and it needs a power supply and costs more. (Key point: Disadvantages)