---
title: "Analog versus digital measurement system"
subject: "Instrumentation I"
chapter: 1
key: "semester_4/instrumentation_i:analog-vs-digital-measurement"
source: https://www.bctengineer.com/q/semester_4/instrumentation_i/analog-vs-digital-measurement
site: BCT Engineering
---

# Analog versus digital measurement system

Instrumentation I · Chapter 1: Instrumentation Systems

- Asked in: year not given, 4 marks
- Video: [Comparison of Analog and Digital Instruments](https://www.youtube.com/watch?v=MCExgH9razk) — bindas physics
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/instrumentation_i/analog-vs-digital-measurement
- Whole chapter: https://www.bctengineer.com/md/semester_4/instrumentation_i/chapter-1

## Question

Differentiate between analog and digital measurement system.

## Short answer

Analog systems represent the measurand as a continuous signal with a pointer on a scale, subject to parallax and limited accuracy. Digital systems use discrete numeric display, offer higher accuracy, better noise immunity, and easy data processing but require more complex circuits.

## Answer

An **analog** measurement system represents the quantity by a continuously varying signal (pointer position or voltage). A **digital** system represents it as discrete numbers (binary codes) and shows it as digits.

| Point | Analog system | Digital system |
|---|---|---|
| Signal | Continuous in amplitude and time | Discrete (quantised, sampled) |
| Display | Pointer on a scale | Numeric digits (LED/LCD) |
| Resolution | Limited by scale and reading skill | Fixed by number of bits/digits |
| Reading error | Parallax and interpolation errors | No parallax; direct reading |
| Accuracy | Lower (about 0.5 to 2 %) | Higher (0.01 % or better possible) |
| Noise immunity | Poor; noise adds to the signal | Good; only levels 0/1 matter |
| Data storage and processing | Difficult | Easy; interface to computers |
| Speed | Slow (mechanical movement) | Fast |
| Cost and complexity | Simple, cheap | More complex circuits (ADC, logic) |
| Example | PMMC voltmeter, moving-coil ammeter | Digital multimeter, digital frequency counter |

Digital systems also have a quantisation error of ±½ LSB, which analog systems do not have.

## Check yourself

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

1. How does a digital measurement system represent the quantity compared with an analog one?
   A. Continuously varying pointer position
   B. Discrete numbers (binary codes) shown as digits
   C. A continuously varying voltage only
   D. Using parallax-corrected scales
   Answer: B. Digital systems use discrete (sampled, quantised) values; analog systems use continuous signals. (Key point: Signal nature)

2. Why does a digital system have better noise immunity than an analog one?
   A. It uses a pointer on a scale
   B. It is slower
   C. Only the levels 0/1 matter, so small noise does not change the value
   D. Noise is added directly to the signal
   Answer: C. Digital signals need only distinguish two levels, so noise is rejected; in analog, noise adds to the signal. (Key point: Noise immunity)

3. Which error occurs in digital systems but not in analog systems?
   A. Parallax error
   B. Interpolation error
   C. Reading error from the pointer
   D. Quantisation error of ±1/2 LSB
   Answer: D. Digitising causes a quantisation error of ±1/2 LSB; parallax and interpolation errors belong to analog scales. (Key point: Digital-specific error)

## Related in Instrumentation I

- [Measurement and measurement system block diagram](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_i%3Ameasurement-system-block-diagram) — Instrumentation I, chapter 1
- [Digital data acquisition system block diagram](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_i%3Adigital-data-acquisition-system) — Instrumentation I, chapter 6
- [Types of measurement errors and minimization](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_i%3Ameasurement-errors-minimization) — Instrumentation I, chapter 1

## Related in other subjects

- [Digital transmission system; analog vs digital](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aanalog-digital-transmission-compare) — Instrumentation II, chapter 5
- [Analog vs digital multiplexing; 24-channel system](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aanalog-digital-mux-24-channel) — Telecommunications, chapter 3
- [Duplex digital communication system vs analog](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adigital-comm-duplex-vs-analog) — Communication Systems, chapter 1
- [Analog and digital system block diagrams; linear and non-linear distortion](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aanalog-digital-block-linear-nonlinear-distortion) — Communication Systems, chapter 1