This document provides an overview of data acquisition systems. It discusses: 1) What a data acquisition system consists of including transducers to measure physical variables, signal conditioning to prepare analog signals for processing, and data acquisition hardware and software to convert the signals to digital and analyze the data. 2) Key aspects of signal conditioning like amplification to boost low-level signals, filtering to remove noise, and isolation to prevent ground loops. 3) Components of data acquisition hardware including terminals to connect to sensors, DAQ devices to convert analog to digital, and functions like analog input/output and counter/timer capabilities.

1. Data Acquisition
system
By Shiv chamkure,2011BIN004 1

2. • What Is Data Acquisition?
• What data acquisition system consist of ?
• Block diagram of data acquisition system
• Transducers(sensors)
• Signal conditioning
• Ground loops
• Data acquisition and control hardware
• Functions of a DAQ device
• Data Acquisition Software 2

3. 3
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.

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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

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Data Acquisition System
Block Diagram :

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What is a Transducer?
Transducer
converts a physical phenomenon into a
measurable electrical signal

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Variety of Transducers

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Signal Conditioning
Improving the quality of signals
Amplification
Filtering
Isolation
Noisy, Low-Level Signal Filtered, Amplified
Signal
Noisy, Low-Level Signal
Filtered, Amplified Signal

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Amplification :
When the input signal is as small as microvolts, electrical
noise can drown out the signal itself, leading to
meaningless data.
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.

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Filtering :
To reject unwanted noise within a certain frequency
range.
Many systems will exhibit 50 Hz periodic noise from
sources such as power supplies or machinery.
Butterworth Filter
Bessel Filter
Chebyshev Filter
Simple RC Filter
Passive & Active Filters
e.g

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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.
.
Isolation :
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.

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Grounding Issues
To get correct measurements you must properly
ground your system.
+
_
Vs
+
_
Vs
Grounded Floating
Signal Source

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Signal is referenced to a system ground
-earth ground
-building ground
Examples:
-Power supplies
-Signal Generators
-Anything that plugs into an outlet
Grounded Signal Source
+
_
Vs

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Signal is NOT referenced to a system
ground
– earth ground
– building ground
Examples:
– Batteries
– Thermocouples
– Transformers
– Isolation Amplifiers
– building ground
+
_
Vs
Floating Signal Source

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Ground Loops :  There are two grounds.
 The grounds are at different potentials.
 There is a galvanic path between the
grounds.

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Breaking this galvanic path can be accomplished by
isolators
optical isolation:- optical isolators,
photo-transistors
magnetic isolation:- Transformers

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Eliminating Ground Loop :

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signal transmitters,
ground loop isolators,
4-20ma transmitters,
4-20ma converters,
4-20ma isolators,
analog signal converters
analog signal isolators
Signal conditioners are also
sometimes referred to as:

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Computer
Your Signal
DAQ Device
Q Device
Terminal Block
Cable
Your Signal
Computer
Data acquisition and control hardware :
Terminal Block
Cable
DAQ Hardware turns your PC into a
measurement and automation system

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Your Signal
Terminal Block
Cable
50 pin connector
Terminal Block
Your Signal
Terminal Block and Cable
Terminal Block and Cable route
your signal to specific pins on
your DAQ device

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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
Sampling rate
Resolution
Accuracy
Reduced board size
Plug-in data acquisition cards DAQ device

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Functions of a DAQ device :
- analog input- digital output
- digital input- analog output
- counter/timer functions

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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
resolution)
 Input range (specified in full-scale volts)
 Gain

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A/D Converter:
Sampling Rate
 The higher the sampling rate,
the better signal we get
 Acquired signal gets distorted if sampling
rate is too small.

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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

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Minimum and maximum voltages the ADC
can digitize
Ranges are selectable
Pick a range that your signal fits in
Smaller range = more precise representation
of your signal
Range

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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
Resolution

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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
Gain

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Code Width
 Code Width is the smallest change in the signal your
system can detect (determined by resolution, range,
and gain)
range
 code width =
gain * 2 resolution
 Smaller Code Width = more precise representation

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Analog Outputs (D/A)
 D/A devices allow the computer to control real-
world events.
 Analog output signals may directly control
process equipment.
 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.

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Counter/timer devices provide a variety of measurement
solutions, including measuring a number of time-related
quantities.
Use counter/timers for:
 Frequency measurement
 Edge or event counting (totalizing)
 Pulse-width measurement
 Event timestamps
 pulse-width modulation (PWM)
Counters/Timers

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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.
Different alternatives:
– Programmable software.
– Data acquisition software packages

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

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Data Acquisition Software Packages
• 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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Computer
Timer
Digital Control
Circuit
Trigger
Interrupt
Parallel/Series
Input Port
Parallel/Series
Output Port
A/D
D/A
Filter
+
-
S/H
Sensor
Bridge
Instrumentation
Amplifier
Input
Strobe
Display
Control
Output Strobe
Example of Computer DAQ System

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Presented by
Shiv Chamkure
2011BIN004