--- title: "Digital data acquisition system block diagram" subject: "Instrumentation I" chapter: 6 key: "semester_4/instrumentation_i:digital-data-acquisition-system" source: https://www.bctengineer.com/q/semester_4/instrumentation_i/digital-data-acquisition-system site: BCT Engineering --- # Digital data acquisition system block diagram Instrumentation I · Chapter 6: Digital Instrumentation - Asked in: year not given, 8 marks - Video: [Data Acquisition Systems | Block Diagram | Part-1/2 | Electrical Instruments ( EIM ) | Lec - 85](https://www.youtube.com/watch?v=jRbw2n2PA0E) — Education 4u - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/instrumentation_i/digital-data-acquisition-system - Whole chapter: https://www.bctengineer.com/md/semester_4/instrumentation_i/chapter-6 ## Question Explain digital data acquisition system with the help of block diagrams. ## Answer A **data acquisition system (DAS)** collects information about one or more physical quantities, converts it to digital form, and then processes, displays and stores it. A digital DAS converts the signals to digital form early, so the data can be handled by a computer. #### Block diagram of a multi-channel digital DAS ```text Transducer 1 -> [Signal cond.] -+ Transducer 2 -> [Signal cond.] -+-> [Analog MUX] <------+ Transducer n -> [Signal cond.] -+ | | v | [Amplifier] | | [Control logic] v [ and clock ] [Sample & hold] <-----+ | | v | [ ADC ] <--------+ | v [Digital processor / computer] | +----------------+--------------+ v v v [Display] [Recorder/printer] [Storage] ``` #### Function of each block 1. **Transducers:** convert physical variables (temperature, pressure, strain) into electrical signals. 2. **Signal conditioning:** amplifies, filters (including the anti-aliasing low-pass filter), linearises, provides excitation to the transducers, and isolates. 3. **Multiplexer:** connects the channels one at a time to a single ADC through analog switches, which reduces cost. 4. **Sample-and-hold (S/H):** freezes the signal level during A/D conversion so that the value does not change. 5. **A/D converter:** converts the held analog value into a binary number (e.g. a successive-approximation type). 6. **Control logic and clock:** generate the channel address, the S/H command and the conversion-start signal, and synchronise them. 7. **Digital processor / computer:** scales, linearises, analyses, checks limits, stores and controls. 8. **Display, recorder, printer, storage:** present the output to the operator; the data can also be sent over a network. #### Other points - The sampling rate per channel is fs = total ADC rate / number of channels, and it must satisfy the Nyquist condition for each signal. - A single-channel DAS needs no multiplexer. Uses: industrial process monitoring, laboratory testing, medical monitoring, weather stations. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the role of the multiplexer in a multi-channel DAS? A. Freeze the signal during conversion B. Connect channels one at a time to a single ADC, reducing cost C. Amplify the signal D. Display the data Answer: B. Analog switches select one channel at a time so one ADC serves all channels. (Key point: Multiplexer role) 2. Why is a sample-and-hold circuit used before the ADC? A. To amplify the transducer output B. To select the channel C. To keep the signal level constant during A/D conversion D. To filter noise Answer: C. S/H freezes the value so it does not change while the ADC converts. (Key point: Sample and hold) 3. If the ADC converts 80 kS/s total across 8 channels, the sampling rate per channel is: A. 80 kHz B. 640 kHz C. 8 kHz D. 10 kHz Answer: D. fs per channel = total rate / channels = 10 kHz, which must satisfy Nyquist for each signal. (Key point: Per-channel rate) 4. Which function is part of signal conditioning in a DAS? A. Amplification, anti-alias filtering and giving excitation to transducers B. Storing data on a disk C. Generating clock pulses D. Printing the result Answer: A. Signal conditioning amplifies, filters, linearises, excites and isolates transducer signals before multiplexing. 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