Transcript Data Acquisition

Basics of Data Acquisition Systems
Dr inż. Zdzisław Pólkowski
Badea George-Cosmin
http://www.geo-integration.com/products/G001.htm
Content
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Definition
A data acquisition system consists
Block Diagram
Transducer
Converters U/I and I/U
Converters R/U
Converters C/U
AO- amplifier
Amplifiers with modulation-demodulation
Differentiator and Integrator Circuits
Logarithmic and exponential amplifiers
Multiplexer / Demultiplexer
Conversion circuits analog and digital signals
Conclusion
Definition
• 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 easy processing.
http://www.ni.com/data-acquisition/what-is/
A data acquisition system consists:
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.
http://www.slideshare.net/amoldude/data-acquisition-system-33836067?qid=d49e6c85-1fa7-4a71-ac861ff0db642725&v=default&b=&from_search=2
Block Diagram
Physical
System
Transducer
Sensor
Signal
Conditioning
Noisy
Electrical
Signal
Physical
Variable:
Temperature
Pressure
Motion
Flow
A/D
Converter
Computer
Digitized
Signal
Filtered
And
Amplified
Signal
8-Bit
Binary
Code
http://www.slideshare.net/sumeetpatel21/data-acquisition-system-40835631?related=2
Block Diagram
Physical
System
 Physical System/Conditions:
• Physical condition that can be used as input of DAS or which can be
represented in Digital form are as under…
 Temperature;
 Pressure;
 Light;
 Force;
 Displacement;
 Level;
 Electric signals;
 ON/OFF switch.
http://www.slideshare.net/sumeetpatel21/data-acquisition-system-40835631?related=2
Block Diagram
Transducer
 Transducers:
Sensor
• A transducer converts temperature, pressure, level, length, position,
etc. into voltage, current, frequency, pulses or other signals.
• A transducer thus converts the physical conditions in electrical
waveform for easy signal processing
http://www.thomasnet.com/articles/engineering-consulting/transducer-signals
Block Diagram
Signal
 Signal Conditioning:
Conditioning
• Signal conditioning circuits improve the quality of signals generated
by transducers before they are converted into digital signals by the PC’s
data acquisition hardware.
• Most common signal conditioning functions are amplification,
linearization, cold-junction compensation, filtering, attenuation, excitation,
common-mode rejection, and so on.
http://www.ni.com/white-paper/4084/en/
Block Diagram
A/D
Converter
 Analog Digital (A/D) converter:
• Analog to digital (A/D) conversion changes analog voltage or current
levels into digital information.
• The conversion is necessary to enable the computer to process or
store the signals.
• A/D converters are electrical circuits that have the following
characteristics:
1. The input to the A/D converter is a voltage;
2. The output of the A/D converter is a binary signal.
http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Interfaces/ConvAD.html
Transducer
•
•
Converts a physical phenomenon into a measurable electrical signal.
Variety of transducers:
Phenomena
Transducer
Temperature
Thermocouples
Resistance temperature detectors
Light
Vacuum tube photo sensors
Photoconductive cells
Sound
Microphones
Force and pressure
Strain gages and load cells
Position (displacement)
Potentiometers
Optical encoders
Fluid flow
Head meters
Rotational and ultrasonic flowmeters
pH
pH electrodes
https://www.futek.com/DataAcquisitionHowto.aspx
Converters U/I and I/U
Source: http://www.mediacollege.com/glossary/q/quantization.html
Converters U/I and I/U
1. Converters voltage-current:
•
Voltage-current converters are common functional blocks in the
structure measuring and control electronic equipment.
• Voltage-current converters can generate unidirectional current (of one
polarity) or bidirectional (both polarities):
a) Unidirectional voltage-current converters come from constant power
generators with bipolar transistor or field effect voltage reference being
replaced by a variable control voltage.
b) The easiest bidirectional voltage-current converter for floating tasks
can be achieved by connecting the load impedance intrareieşire
reaction resistance instead of an operational amplifier in inverting
assembly.
http://media1.wgz.ro/files/media1:4b51fa8487a9d.pdf.upl/Ccsm2.pdf
Converters U/I and I/U
2.
Converters current-voltage:
•
Current-voltage converters are widely used in instrumentation control
structure, which ranks among basic blocks, along with amplifiers,
multipliers, memory-sampling circuits, voltage-current converters,
analog-digital or digital-to-analog and so on.
•
The simplest current-voltage converter is a resistance cuadripolară
called when the shunt used to measure current. The converter with
which receives the voltage across the shunt should have a much
higher input resistance than the shunt to not introduce unacceptable
errors.
•
Shunt current-voltage converters with high current is not used as input
current is closed by power sources and output operational amplifiers
used, increasing power dissipation.
http://media1.wgz.ro/files/media1:4b51fa8487a9d.pdf.upl/Ccsm2.pdf
Converters R/U
•
Converters Resistance to Voltage:
• Many sensors exhibit a change electrical resistance in response to the
quantity that they are trying to measure.
• There are two ways to convert resistance of a sensor to a voltage. The
first, and simplest way is to apply a voltage to a resistor divider network
composed of a reference resistor and the sensor as shown:
• The voltage that appears across the
sensor is then buffered before being sent
to the ADC. The output voltage is given
by:
http://soundlab.cs.princeton.edu/learning/tutorials/sensors/node17.html
Converters C/U
•
Converters Capacitance to Voltage:
• We have seen that the electrical property of capacitance has been the
main physical principle behind many of the sensors that we have
discussed.
• This has made it a useful tool in measuring small vibrations. Capacitance
can also be used to measure much greater distances than we have seen
so far.
• Capacitance can be measured in the same two ways discussed
previously for measuring resistance - a voltage divider or a bridge circuit.
Instead of using resistors, capacitors are used.
• The output voltage can be written as:
http://soundlab.cs.princeton.edu/learning/tutorials/sensors/node18.html
AO- amplifier
A method of amplifying:
• It is necessary that
. It appears a indeterminate:
•
It can be maintained at 0 by connecting impedance outside a
configuration AO negative reaction. These impedances with AO maintain
at zero and determine the output voltage
http://www.bel.utcluj.ro/dce/didactic/de/12_AO_amplificatoare.pdf
Amplifiers with modulation-demodulation
• Block diagram of a modulation-demodulation amplifier is shown below:
 FTJ1 = input filter
 M = modulator
 Aca = amplifier c.a.
 D = demodulator
 FTJ2 = output filter
 O = oscillator
http://iota.ee.tuiasi.ro/~czet/Curs/Masurari/C10%20Instrumente%20si%20dispozitive%20de%20masurare%20analogice.pdf
Differentiator and Integrator Circuits
1. Differentiator:
•
The right-hand side of the capacitor is held to a voltage of 0 volts, due
to the virtual ground effect. Therefore, current through the capacitor is
solely due to change in the input voltage. A steady input voltage won’t
cause a current through C, but a changing input voltage will
• The formula for determining
voltage output for the
differentiator is as follows:
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/differentiator-integrator-circuits/
Differentiator and Integrator Circuits
2. Integrator:
•
As before, the negative feedback of the op-amp ensures that the inverting
input will be held at 0 volts. If the input voltage is exactly 0 volts, there will
be no current through the resistor, therefore no charging of the capacitor,
and therefore the output voltage will not change.
•The formula for determining
voltage output for the
integrator is as follows:
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/differentiator-integrator-circuits/
Logarithmic and exponential amplifiers
1. Amplifier logarithmic:
•
•
Circuit limitations:
the range of variation of the output voltage is reduced by a few tens
mV;
the temperature dependence of the output voltage by
and .
http://www.bel.utcluj.ro/dce/didactic/cef/17_aplicatii_cu_AO.pdf
Logarithmic and exponential amplifiers
2.
Amplifier exponential:
http://www.bel.utcluj.ro/dce/didactic/cef/17_aplicatii_cu_AO.pdf
Multiplexer / Demultiplexer
• The basic function of the Multiplexer (MUX);
• The typical application of a MUX;
• The basic function of the Multiplexer (DEMUX);
• The typical application of a DEMUX;
http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf
Multiplexer / Demultiplexer
1. Multiplexer (MUX):
• A MUX is a digital switch that has
multiple inputs and a single output.
• The select lines determine which
input is connected to the output.
• MUX Types:
a. 2-to-1 (1 select line);
b. 4-to-1 (2 select lines);
c. 8-to-1 (3 select lines);
d. 16-to-1 (4 select lines).
http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf
Multiplexer / Demultiplexer
1. Typical application of a MUX:
http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf
Multiplexer / Demultiplexer
2. Demultiplexer (DEMUX):
• A DEMUX is a digital switch with a
single input and a multiple outputs.
• The select lines determine which
output the input is connected to
• DEMUX Types:
a. 1-to-2 (1 select line);
b. 1-to-4 (2 select lines);
c. 1-to-8 (3 select lines);
d. 1-to-16 (4 select lines).
http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf
Multiplexer / Demultiplexer
2.
Typical application of a DEMUX:
http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf
Conversion circuits analog and digital signals
http://www3.eng.cam.ac.uk/DesignOffice/mdp/electric_web/Digital/DIGI_13.html
Conversion circuits analog and digital signals
1. Digital-to-analog:
• Digital-to-analog conversion is a process in which signals having a few
defined levels or states are converted into signals having a theoretically
infinite number of states.
• A common example is the processing, by a modem, of computer data
into audio-frequency (AF) tones that can be transmitted over a twisted
pair telephone line. The circuit that performs this function is a digital-toanalog converter (DAC)
• But when a DAC is used to decode the binary digital signals,
meaningful output appears. This might be a voice, a picture, a musical
tune, or mechanical motion.
http://whatis.techtarget.com/definition/digital-to-analog-conversion-DAC
Conversion circuits analog and digital signals
1. Analog-to-digital :
• Analog-to-digital conversion is an electronic process in which a
continuously variable signal is changed, without altering its essential
content, into a multi-level signal.
• The input to an analog-to-digital converter (ADC) consists of a voltage
that varies among a theoretically infinite number of values.
• Digital signals propagate more efficiently than analog signals, largely
because digital impulses, which are well-defined and orderly, are easier
for electronic circuits to distinguish from noise, which is chaotic
http://whatis.techtarget.com/definition/analog-to-digital-conversion-ADC
Conclusion
 Data acquisition systems typically convert analog physical condition
into digital values for easy processing;
 DAS is advantageous as we can store a lot of physical condition data
in digitized form;
 DAS helps in easy processing of data as well as easy comparison can
be done;

Today DAS is used in almost every field, industry and companies.
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