--- title: "Measurement and measurement system block diagram" subject: "Instrumentation I" chapter: 1 key: "semester_4/instrumentation_i:measurement-system-block-diagram" source: https://www.bctengineer.com/q/semester_4/instrumentation_i/measurement-system-block-diagram site: BCT Engineering --- # Measurement and measurement system block diagram Instrumentation I · Chapter 1: Instrumentation Systems - Asked in: year not given, 8 marks - Video: [Instrumentation 01- functional blocks of measurement system](https://www.youtube.com/watch?v=WlhRBvM-EK0) — ABC Electricals - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/instrumentation_i/measurement-system-block-diagram - Whole chapter: https://www.bctengineer.com/md/semester_4/instrumentation_i/chapter-1 ## Question Define measurement and measurement system. Explain the measurement system with the help of block diagrams. ## Short answer Measurement is comparing an unknown quantity with a standard. A measurement system comprises primary sensing element, variable conversion, signal conditioning, and presentation. Its block diagram shows measurand → sensor → transducer → signal processing → display, with optional transmission and storage. ## Answer **Measurement** is the process of comparing an unknown quantity (the measurand) with a standard of the same kind, to find its magnitude as a number and a unit. **A measurement system** is the set of devices that senses the measurand, converts and processes the signal, and presents the result in a form an observer or a controller can use. #### Generalized measurement system ```text Measurand +-----------+ +-------------+ +------------+ ------------->| Primary |-->| Variable |-->| Signal | (pressure, | sensing | | conversion | | processing | temp, ...) | element | | element | | (amplify, | +-----------+ +-------------+ | filter) | +-----+------+ | +-----------+ +-----------+ +--------------+ | | Data |<--| Data |<--| Data |<-+ | storage/ | | display/ | | transmission | | control | | record | | (if needed) | +-----------+ +-----------+ +--------------+ ``` #### Functional elements 1. **Primary sensing element (sensor):** senses the measurand and gives a related physical response. Example: a Bourdon tube or diaphragm gives a displacement for a pressure. 2. **Variable conversion element (transducer stage):** converts the sensor output into a more convenient variable, usually electrical. Example: an LVDT or strain gauge converts displacement to voltage or resistance. 3. **Variable manipulation / signal conditioning:** amplification, filtering, modulation or demodulation, linearisation and A/D conversion, without changing the physical nature of the variable. 4. **Data transmission element:** carries the signal between distant stages (wires, telemetry). 5. **Data presentation element:** an indicator, recorder, printer or display, so the observer can read the value. 6. **Data storage and control:** stores the data or uses it in a feedback controller. #### Simple block diagram (electrical measurement) ```text Input --> [Transducer] --> [Amplifier/ --> [Indicator/ quantity Conditioner] Recorder] --> Reading ``` **Example (temperature):** a thermocouple (sensor and transducer) gives a few millivolts; an amplifier raises this; an ADC and microcontroller process it; and an LCD shows the temperature in °C. A good measurement system has high accuracy, sensitivity and repeatability, and a low loading effect on the measured source. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which statement correctly defines measurement? A. Reading a number from a digital display B. Comparing an unknown quantity with a standard of the same kind to get its magnitude as a number and unit C. Converting a physical quantity into a voltage D. Finding the error between two instruments Answer: B. Measurement compares the measurand with a standard of the same kind and expresses it as a number with a unit. (Key point: Definition of measurement) 2. What is the job of the primary sensing element in a measurement system? A. To amplify and filter the signal B. To display the value to the observer C. To sense the measurand and give a related physical response D. To store data for a controller Answer: C. The primary sensing element senses the measurand first, e.g. a Bourdon tube giving displacement for pressure. (Key point: Primary sensing element) 3. In the generalized measurement system, which is the correct order of the first three stages? A. Signal processing, sensing element, variable conversion B. Variable conversion, sensing element, signal processing C. Sensing element, signal processing, variable conversion D. Primary sensing element, variable conversion element, signal processing Answer: D. The measurand passes through the sensing element, then variable conversion, then signal processing. (Key point: Order of elements) 4. Which of these is done by the variable manipulation / signal conditioning stage? A. Amplification, filtering and A/D conversion without changing the nature of the variable B. Carrying the signal between distant stages only C. Sensing the measurand directly D. Showing the reading on an LCD Answer: A. Signal conditioning amplifies, filters, linearises or digitises the signal; transmission and display are separate elements. (Key point: Signal conditioning) ## Related in Instrumentation I - [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 - [Analog versus digital measurement system](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_i%3Aanalog-vs-digital-measurement) — Instrumentation I, chapter 1 - [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 - [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 - [Communication system and AM block diagram](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Adefine-comm-am) — Basic Electronics Engineering, chapter 5 - [Instrumentation system with block diagram](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Ainstrumentation-system) — Basic Electronics Engineering, chapter 7, asked 3× - [Digital control system block diagram and advantages](https://www.bctengineer.com/question.md?key=semester_6%2Fdigital_control_system%3Adcs-block-diagram-advantages) — Digital Control System, chapter 1, asked 3×