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This contains the information about various components of DAS.
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By Shiv chamkure,2011BIN004 1
• What Is Data Acquisition?
• What data acquisition system consist of ?
• Block diagram of data acquisition system
• Signal conditioning
• Ground loops
• Data acquisition and control hardware
• Functions of a DAQ device
• Data Acquisition Software 2
What Is Data Acquisition?
Data acquisition (DAQ) is the process of
measuring an electrical or physical
phenomenon such as voltage, current,
temperature, pressure, or sound ,flow rate
with a computer.
A data acquisition system consists of :
1. Sense of physical variables ( transducers )
2. Signal Conditioning for electrical signal to make it
readable by an A/D board
3. Convert the signal into a digital format acceptable by
a computer(DAQ device)
4. Process, analyze, store, and display the acquired
data with the help of software
Improving the quality of signals
Noisy, Low-Level Signal Filtered, Amplified
Noisy, Low-Level Signal
Filtered, Amplified Signal
When the input signal is as small as microvolts, electrical
noise can drown out the signal itself, leading to
For reducing the effects of noise on your signal is to
amplify the signal as close to the source as possible.
Increases Signal to Noise Ratio (SNR)
e.g. A J-type thermocouple outputs a very low-level
voltage signal that varies by about 50 µV/°C.
To reject unwanted noise within a certain frequency
Many systems will exhibit 50 Hz periodic noise from
sources such as power supplies or machinery.
Simple RC Filter
Passive & Active Filters
Isolation is one way to eliminate ground loop errors.
Isolation breaks ground loops, rejects high common-mode
voltages, and protects expensive DAQ boards.
Protects from power lines, lightning.
Improper grounding of the DAQ system is the most common
cause of measurement problems and damaged DAQ boards.
There is no physical wiring between the input and output.
The input is normally transferred by converting it to an optical or
magnetic signal then it is reconstructed on the output.
To get correct measurements you must properly
ground your system.
Signal is referenced to a system ground
-Anything that plugs into an outlet
Grounded Signal Source
Signal is NOT referenced to a system
– earth ground
– building ground
– Isolation Amplifiers
– building ground
Floating Signal Source
Ground Loops : There are two grounds.
The grounds are at different potentials.
There is a galvanic path between the
Breaking this galvanic path can be accomplished by
optical isolation:- optical isolators,
magnetic isolation:- Transformers
ground loop isolators,
analog signal converters
analog signal isolators
Signal conditioners are also
sometimes referred to as:
Data acquisition and control hardware :
DAQ Hardware turns your PC into a
measurement and automation system
50 pin connector
Terminal Block and Cable
Terminal Block and Cable route
your signal to specific pins on
your DAQ device
Some things to consider:
Connection to the Internet
Is there software support?
Type of input channels - single-ended input channels
differential input channels.
Compatible with a variety of bus protocols
Number of analog input channels
Reduced board size
Plug-in data acquisition cards DAQ device
Functions of a DAQ device :
- analog input- digital output
- digital input- analog output
- counter/timer functions
Analog Inputs (A/D)
when selecting A/D hardware :
Number of input channels
Single-ended or differential input signals
Sampling rate (in samples per second)
Resolution (usually measured in bits of
Input range (specified in full-scale volts)
The higher the sampling rate,
the better signal we get
Acquired signal gets distorted if sampling
rate is too small.
Nyquist sampling theorem tells us that we must
sample the signal at more than twice the rate of
the maximum frequency component in the
analog input signal.
According to the Nyquist Theorem, the sampling rate
must be at least 2fmax.
Nyquist Sampling Theorem
Where , highest frequency component = fmax
Minimum and maximum voltages the ADC
Ranges are selectable
Pick a range that your signal fits in
Smaller range = more precise representation
of your signal
Number of bits the ADC uses to represent a signal
changes can be measured
Example: 12-bit resolution
2resolution = 212 = 4,096 levels
Larger resolution = more precise representation
Gain setting amplifies the signal for best fit
in ADC range
Gain settings are 0.5, 1, 2, 5, 10, 20, 50, or
100 for most devices
Proper gain = more precise representation
Code Width is the smallest change in the signal your
system can detect (determined by resolution, range,
code width =
gain * 2 resolution
Smaller Code Width = more precise representation
Analog Outputs (D/A)
D/A devices allow the computer to control real-
Analog output signals may directly control
The process can give feedback in the form of
analog input signals.
This is referred to as a closed loop control
system with PID control.
Counter/timer devices provide a variety of measurement
solutions, including measuring a number of time-related
Use counter/timers for:
Edge or event counting (totalizing)
pulse-width modulation (PWM)
Data Acquisition Software
It can be the most critical factor in obtaining reliable,
high performance operation
Transforms the PC and DAQ hardware into a complete
DAQ, analysis, and display system.
– Programmable software.
– Data acquisition software packages
Involves the use of a programming language,
– C++, Visual C++
– BASIC, Visual Basic + Add-on tools (such as
VisuaLab with VTX)
• Advantage: flexibility
• Disadvantages: complexity and steep
Data Acquisition Software Packages
• Does not require programming.
• Enables developers to design the custom
instrument best suited to their
• Examples: TestPoint, SnapMaster, LabView,
DADISP, DASYLAB, etc
Example of Computer DAQ System