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DAQ - DATA ACQUISITION VIRTUAL INSTRUMENTATION

This guide provides an in-depth overview of Data Acquisition (DAQ) systems, emphasizing the processes involved in capturing various signals and integrating them into PC environments. Topics covered include sensor types (biological, chemical, and physical), signal conditioning, analog-to-digital conversion, and the use of software for real-time data collection and analysis. Learn how to effectively measure and interpret electrical signals from non-electrical quantities, ensuring high accuracy and resolution in your data acquisition projects.

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DAQ - DATA ACQUISITION VIRTUAL INSTRUMENTATION

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  1. DAQ - DATA ACQUISITIONVIRTUAL INSTRUMENTATION Dr. Shahin H. Berisha Math and Science Division GateWay Community College Phoenix, Arizona, USA

  2. Signals Outline • 1.What is DAQ ? • 2.How do I get my captured SIGNALS into PC? • Live data capturing?

  3. Signal Conditioner A/D Converter Personal Computer Display Data Sensor Non-Elec. Quantity Electrical SIGNAL Elec. Analog Signal Digital SIGNAL Digital Display DAQ - Block Diagram

  4. SENSOR - PROBE • Converts any BIO, CHM. or PHY quantity into electrical voltage (SIGNAL) • BIO Sensor - Hart-rate (Sensor) into el. signal - voltage • CHM Sensor - pH (Sensor) into el. signal-voltage • PHY Speed - Speed (Sensor) into el. signal- voltage

  5. Fe Voltage Constantan TEMPERATURE SENSORActive Sensor Temperature

  6. SENSOR VOLTAGE TEMP. Input - Output RATIO C/mV

  7. EXAMPLE K = 2 oC/mV Vout = 5 mV Temp. = k Vout Temp. = 10 oC

  8. SIGNAL CONDITIONER Output signal of the sensor is usually very small signal - consequently: • Very difficult to measure - record • Interference is very high - noise • Signal need to be amplified

  9. Conditioning the Signal • Amplification of the signal • linearization throughout the range • filtering unwanted signals • isolation • etc

  10. Low -level signals are amplified to increase resolution - higher accuracy • Linearization of thermocouple voltage - Same correction factor • Filtering unwanted signals (hardware or software filter)

  11. AMPLIFIER

  12. EXAMPLE • Measured output voltage of amplifier: Vout =50 mV, Kprobe=2 oC/mV • Kamplif.=10

  13. Signal Conditioner A/D Converter Personal Computer Display Data Sensor Non-Elec. Quantity Electrical SIGNAL Elec. Analog Signal Digital SIGNAL Digital Display DAQ - Block Diagram

  14. A/D CONVERTER • What is ANALOG (CONTINUES) Signal? • What is DIGITAL (DISCONTINUES) Signal?

  15. Analog Signal - Consider • single or differential input, • range, • resolution, • sampling rate, • accuracy, • noise.

  16. 4,24 10,19 8,20 6,18 2,16 0,6 ANALOG SIGNAL - Variation of Temp. vs Time DIGITAL SIGNAL - Sampled every 2 minutes Sampling Frequency: Every 2 min. Fast changing Signals - this is very slow frequency

  17. PC finds the ORDERED PAIRS at every 2 minutes and stores in FILE: t 0 2 4 6 8 10 (min) T 6 16 24 18 20 19 (oC) • PC Plots ordered pairs - graph, • The two signals are not identical, • What to do so the digital analog signal are closer?

  18. 4,24 8,20 6,18 2,16 0,6 Comparison of Analog and Digital Signal

  19. Sampling Frequency • Is how often the A/D conversion occurs • How high can I go with sampling frequency to increase my accuracy (Nyquist Criteria) • Computer hardware • available memory • For Laboratory purposes • depend on the sampled quantity • every second or two

  20. File on the PC DAQ software allows to: • select sampling rate, • graph in real time, • perform statistics, • generate reports No need to transfer data

  21. LIVE DATA COLLECTION • Let’s collect same live data • live data collection of dc signal (battery voltage) • live data collection of ac signal (speed sensor)

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