DAQ DATA ACQUISITION VIRTUAL INSTRUMENTATION

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

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

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DAQ - Block Diagram
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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

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TEMPERATURE SENSORActive Sensor
Temperature
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Input - Output RATIO C/mV
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EXAMPLE
K 2 oC/mV
Vout 5 mV
Temp. k Vout
Temp. 10 oC
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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

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Conditioning the Signal

• Amplification of the signal
• linearization throughout the range
• filtering unwanted signals
• isolation
• etc

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

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AMPLIFIER
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EXAMPLE

• Measured output voltage of amplifier Vout 50
  mV, Kprobe2 oC/mV
• Kamplif.10

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DAQ - Block Diagram
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A/D CONVERTER

• What is ANALOG (CONTINUES) Signal?
• What is DIGITAL (DISCONTINUES) Signal?

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Analog Signal - Consider

• single or differential input,
• range,
• resolution,
• sampling rate,
• accuracy,
• noise.

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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
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• 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?

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Comparison of Analog and Digital Signal
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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

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File on the PC

• DAQ software allows to
• select sampling rate,
• graph in real time,
• perform statistics,
• generate reports
• No need to transfer data

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LIVE DATA COLLECTION

• Lets collect same live data
• live data collection of dc signal (battery
  voltage)
• live data collection of ac signal (speed sensor)