Presented by- Md. Bashir Uddin Roll: Dept. of BME KUET, Khulna-9203

 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.

Displacement Level Force Electric signal Etc. Temperature Pressure Light Sound Physical System Physical system shows real world physical conditions which are represented as physical variables such as-

 A transducer is placed at the input of a measurement system.  A transducer is a device that changes one form of energy into another. Sound Electric signal Electric signal Sound Microphone Speaker

 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. Signal Conditioner Noisy Electrical Signals from Transducer Electrical Quantity Suitable for Operation to A/D Converter

 Signal Amplification  Linearization  Conversion  Filtering

 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 (Gain=10) input signal Amplitude =1v output signal amplitude =10v

 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.

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

 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

The process in which analog signal is converted into digital signal is called A/D conversion. Steps of A/D conversion:  Sampling  Quantizing  Encoding SamplerQuantizerEncoder Analog Signal Sampled Signal Quantized Signal Digital Signal

 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. Analog Input 4 Samples/cycle 8 Samples/cycle 16 Samples/cycle

 Aliasing: Acquired signal gets distorted if sampling rate is too small(less than Nyquist Rate)  Nyquist Rate=2*Frequency of original signal

Quantizing & Encoding

4.16  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.

 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

 Different alternatives: ◦ Programmable software. ◦ Data acquisition software packages.  Process, analyze, store, and display the acquired data with the help of 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

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