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Data Acquisition

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Presented by-Md. Bashir Uddin Roll: 1215502 Dept. of BME KUET, Khulna-9203 – PowerPoint PPT presentation

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Title: Data Acquisition


1
Data Acquisition
Presented by- Md. Bashir Uddin Roll
1215502 Dept. of BME KUET, Khulna-9203
2
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.

3
Data Acquisition SystemBlock Diagram
4
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

5
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.

6
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
7
Steps of signal conditioning
  • Signal Amplification
  • Linearization
  • Conversion
  • Filtering

8
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
9
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.

10
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

11
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

12
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
13
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
14
Sampling (Cont.)
  • Aliasing Acquired signal gets distorted if
    sampling rate is too small(less than Nyquist
    Rate)
  • Nyquist Rate2Frequency of original signal

15
Quantizing Encoding
16
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.

17
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

18
Functions of Software
  • Process, analyze, store, and display the acquired
    data with the help of software.
  • Different alternatives
  • Programmable software.
  • Data acquisition software packages.

19
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

20
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.

21
THANK YOU
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