--- title: "Data logger block diagram and operation" subject: "Instrumentation II" chapter: 5 key: "semester_5/instrumentation_ii:dl-block" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/dl-block site: BCT Engineering --- # Data logger block diagram and operation Instrumentation II · Chapter 5: Data Acquisition And Transmission - Asked in: 2074 Chaitra, 6 marks; 2073 Shrawan, 5 marks; 2068 Chaitra, 4 marks; 2076 Chaitra, 4 marks; 2068 Baisakh (old course), 4 marks; 2072 Chaitra, 2 marks (asked 6 times) - Video: [Microcontroller Based Data Logger System || CSE360 || BRAC University](https://www.youtube.com/watch?v=E1jkJIPHbk0) — SM Mohtasim Billah Fahim - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/dl-block - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-5 ## Question What is a data logger? Draw its block diagram and explain the operation of each block. ## Short answer A data logger automatically measures and records sensor signals over time. It consists of sensors, signal conditioning, a multiplexer, sample-and-hold, ADC, a controller with real-time clock, memory, display, and communication interface. ## Answer A **data logger** is an electronic instrument that automatically measures and records one or more physical quantities (temperature, pressure, voltage, etc.) with time, usually in internal memory, for later retrieval and analysis. It may work unattended for a long period. #### Block diagram ```text Sensors -> Signal -> Input -> S/H -> ADC --+ (1..n) conditioner scanner(MUX) v +--------------+ Real time clock ---------------------| Controller / |-> Display Keypad (setup) ----------------------| Microprocessor|-> Alarm/Output +------+-------+ | | Memory (storage) Communication (USB/RS-232/BT) Power supply (battery/mains) feeds all blocks ``` #### Operation of the blocks 1. **Sensors/transducers:** convert physical quantities into electrical signals. 2. **Signal conditioner:** amplifies, filters, linearises and level shifts the signals to the ADC range; also isolation and cold-junction compensation. 3. **Input scanner (multiplexer):** connects the channels one by one to the ADC, in a programmed sequence and rate. 4. **Sample and hold:** holds the signal constant during conversion. 5. **ADC:** converts the analog value into digital words. 6. **Controller (microprocessor/microcontroller):** controls scanning and timing, processes data (scaling, limit checking), time-stamps it, and manages memory and communication. 7. **Real-time clock:** supplies date and time for each sample. 8. **Memory/storage:** RAM, flash or memory card stores the data for later transfer. 9. **Display and keypad:** show readings and set sampling rate, channels, alarm limits. 10. **Communication interface:** transfers data to a PC (USB, RS-232, Ethernet, Bluetooth). 11. **Power supply:** mains or battery with backup so that no data is lost. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a data logger? A. A device that only displays readings live B. An instrument that automatically measures and records quantities with time, usually in memory, for later retrieval C. A power amplifier D. A type of printer only Answer: B. It works unattended, recording one or more physical quantities with time stamps. (Key point: Definition) 2. What does the input scanner (multiplexer) do? A. Connects channels one by one to the ADC in a programmed sequence and rate B. Converts signals to digital C. Stores data D. Supplies power Answer: A. It lets one S/H and ADC serve many sensor channels. (Key point: Input scanner) 3. What is the purpose of the real-time clock? A. To amplify signals B. To power the memory C. To supply date and time so each sample is time-stamped D. To convert voltage to current Answer: C. Time stamps allow later analysis of when each reading was taken. (Key point: Real-time clock) 4. Why is a sample and hold used before the ADC? A. To amplify the signal B. To filter noise C. To select the channel D. To keep the signal constant during conversion Answer: D. If the input changed during conversion, the digital result would be in error. (Key point: Sample and hold) ## Related in Instrumentation II - [Compact data logger characteristics and block diagram](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acompact-dl-block) — Instrumentation II, chapter 5 - [Data logger with Bluetooth scatternet](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Abt-datalogger-scatternet) — Instrumentation II, chapter 5 - [Characteristics of a data logger](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adl-characteristics) — Instrumentation II, chapter 5, asked 6× - [Data logger input scanner and conditioner design](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adatalogger-three-transducers) — Instrumentation II, chapter 5 - [Parallel transfer schemes and 8255A block diagram](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aparallel-transfer-8255-block) — Instrumentation II, chapter 2 - [8255 mode 2 operation with timing diagram](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Appi-mode2) — Instrumentation II, chapter 2 ## Related in other subjects - [Block diagram of data logger](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Adata-logger-block-diagram) — Basic Electronics Engineering, chapter 7 - [Data logger and remote control block diagrams](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Adata-logger-remote-control) — Basic Electronics Engineering, chapter 7 - [Frequency counter operation with block diagram](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Afrequency-counter) — Digital Logic, chapter 11, asked 14× - [PID control operation with block diagram](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Apid-operation-block-diagram) — Embedded System, chapter 7, asked 4×