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DAQ - DATA ACQUISITION VIRTUAL INSTRUMENTATION

DAQ - DATA ACQUISITION VIRTUAL INSTRUMENTATION. Dr. Shahin H. Berisha Math and Science Division GateWay Community College Phoenix, Arizona, USA. Signals. Outline. 1.What is DAQ ? 2.How do I get my captured SIGNALS into PC? Live data capturing?. Signal Conditioner. A/D Converter.

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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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