Data Acquisition

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Data Acquisition
Presented by- Md. Bashir Uddin Roll
1215502 Dept. of BME KUET, Khulna-9203
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What is Data Acquisition?

• Data acquisition is the process of sampling
  signals that measure real world physical
  conditions and converting the resulting samples
  into digital numeric values that can be
  manipulated by a computer.
• Data acquisition systems (abbreviated with the
  acronym DAS or DAQ) typically convert analog
  waveforms into digital values for processing.

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Data Acquisition SystemBlock Diagram
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Physical System
Physical system shows real world physical
conditions which are represented as physical
variables such as-

• Displacement
• Level
• Force
• Electric signal
• Etc.

• Temperature
• Pressure
• Light
• Sound

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Transducers

• A transducer is a device that changes one form of
  energy into another.
• Sound
  Electric signal
• Electric signal
  Sound

Microphone
Speaker

• A transducer is placed at the input of a
  measurement system.

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Signal Conditioning

• Signal Conditioning is the process in which noisy
  electrical signals are conditioned so that they
  can be used by an analog input board.
• Signal Conditioner is an integrated device
  (defined as converter) that converts the output
  of the transducer into an electrical quantity
  suitable for operation.

Electrical Quantity Suitable for Operation to A/D
Converter
Noisy Electrical Signals from Transducer
Signal Conditioner
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Steps of signal conditioning

• Signal Amplification
• Linearization
• Conversion
• Filtering

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Signal Amplification

• First step of signal conditioning is signal
  amplification by using amplifier.
• For maximum resolution, the voltage range of the
  input signals should be approximately equal to
  the maximum input range of the A/D converter.
• Amplification expands the range of the transducer
  signals so that they match the input range of the
  A/D converter.
• For example,

Amplifier (Gain10)
input signal Amplitude 1v
output signal amplitude 10v
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Linearization
Conversion Filtering

• Convert one type of electrical variation to
  another.
• Filtering is used to pass the signals with
  desired frequencies and blocks the unwanted
  frequencies to the A/D converter input.

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Converter

• Converter is an electronic circuit that converts
  signal in one form to another form.
• Types of converters 2 types
• A/D ( Analog to Digital) converter
• D/A ( Digital to analog) converter

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A/D Converter

• A/D converter converts analog signal into digital
  signal.
• Single chip integrated circuit
• A single input connection for the analog signal
• Multiple pins for digital output
• Each pin responds an output bit

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A/D Conversion
The process in which analog signal is converted
into digital signal is called A/D conversion.

• Steps of A/D conversion
• Sampling
• Quantizing
• Encoding

Sampler
Quantizer
Encoder
Analog Signal
Digital Signal
Sampled Signal
Quantized Signal
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Sampling

• Sampling is the process in which a continuous
  time signal is sampled to produce descrete time
  signal.
• Sampling Rate is the number of sample per second.
• The higher the sampling rate, the better
  reconstruction of original signal.

8 Samples/cycle
Analog Input
4 Samples/cycle
16 Samples/cycle
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Sampling (Cont.)

• Aliasing Acquired signal gets distorted if
  sampling rate is too small(less than Nyquist
  Rate)
• Nyquist Rate2Frequency of original signal

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Quantizing Encoding
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Quantization Error

• When a signal is quantized, we introduce an error
  - the coded signal is an approximation of the
  actual amplitude value.
• The difference between actual and coded value
  (midpoint) is referred to as the quantization
  error.
• The more zones, the smaller ? which results in
  smaller errors.

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D/A Converter

• D/A converter converts digital signal into analog
  signal.
• Single chip integrated circuit
• A single output connection for the analog signal
• Multiple pins for digital input
• Each pin takes an input bit

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Functions of Software

• Process, analyze, store, and display the acquired
  data with the help of software.

• Different alternatives
• Programmable software.
• Data acquisition software packages.

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Programmable Software

• Involves the use of a programming language, such
  as
• C, visual C
• BASIC, Visual Basic Add-on tools (such as
  VisuaLab with VTX)
• Fortran
• Pascal
• Advantage flexibility
• Disadvantages complexity and steep learning
  curve

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Data Acquisition Software

• Does not require programming.
• Enables developers to design the custom
  instrument best suited to their application.
• Examples
• TestPoint, SnapMaster, LabView,
  DADISP, DASYLAB, etc.

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THANK YOU