SIGNAL CONDITIONING

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SignalConditioning(Mult
iplexer, Data Acquisition,DSP, Pulse Modulation)
PE-4030 Chapter 3 Part two

• Professor Charlton S. Inao
• Professor Mechatronics System Design
• Defence Engineering College
• Bishoftu, Ethiopia

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Instructional Objectives

• In this lesson, the students shall be able
  to understand the principle of Signal
  Conditioning focusing mainly on the following
  topics
• 1. Multiplexers
• 2. Data Acquisition
• 3. Digital Signal Processing
• 4. Pulse Modulation

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Multiplexing

• Multiplexing is the process of handling multiple
  measurement inputs from the analog sensors or a
  number of different measurements from different
  locations in quick succession over a period of
  time before sampling and holding process, and
  eventually to analog to digital conversion(ADC).

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Sample and Hold
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Multiplexing with AA Filter
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1) Multiplexers

• Frequently there is a need for measurements to be
  sampled from a number of different locations, or
  perhaps a number of different measurements need
  to be made.
• Rather than use a separate microprocessor for
  each measurement , a multiplexer can be used.
• The multiplexer is essentially a switching device
  which enables each of the inputs to be sampled in
  turn.

Sequence of digital Signals
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Multiplexers

• A multiplexer (or mux) is a device that selects
  one of several analog or digital input signals
  and forwards the selected input into a single
  line.
•  A multiplexer of 2n inputs has n select lines,
  which are used to select which input line to send
  to the output.
•  Multiplexers are mainly used to increase the
  amount of data that can be sent over
  the network within a certain amount of time
  and bandwidth.

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Multiplexer as a Controlled Switch
Schematic of a 2-to-1 Multiplexer. It can be
equated to a controlled switch.
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Mux - DeMux
The basic function of a multiplexer combining
multiple inputs into a single data stream. On the
receiving side, a demultiplexer splits the single
data stream into the original multiple signals.
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Types of Multiplexers
A 2-to-1 mux
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2) Data Acquisition

• 2.1 Methodology
• 1.1 Source
• 1.2 Signals
• 2 .2DAQ hardware
• 2.3 DAQ software

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Data Acquisition System
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2) 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.

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The components of data acquisition systems
include

• Sensors that convert physical parameters to
  electrical signals.
• Signal conditioning circuitry to convert sensor
  signals into a form that can be converted to
  digital values.
• Analog-to-digital converters, which convert
  conditioned sensor signals to digital values.
• .

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DAQ Software

• Data acquisition applications are controlled by
  software programs developed using various general
  purpose programming languages such
  as BASIC, C, Fortran, Java, Lisp, Pascal

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DAQ-Methodology- Source

• Source
• Data acquisition begins with the physical
  phenomenon or physical property to be measured.
  Examples of this include temperature, light
  intensity, gas pressure, fluid flow, and force.
  Regardless of the type of physical property to be
  measured, the physical state that is to be
  measured must first be transformed into a unified
  form that can be sampled by a data acquisition
  system. The task of performing such
  transformations falls on devices called sensors.

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• The ability of a data acquisition system to
  measure differing properties depends on having
  sensors that are suited to detect the various
  properties to be measured.
• There are specific sensors for many different
  applications. DAQ systems also employ
  various signal conditioning techniques to
  adequately modify various different electrical
  signals into voltage that can then be digitized
  using an Analog-to-digital converter(ADC).

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DAQ-Methodology- Signals

• Signals
• Signals may be digital (also called logic
  signals sometimes) or analog depending on the
  transducer used.
• Signal conditioning may be necessary if the
  signal from the transducer is not suitable for
  the DAQ hardware being used. The signal may need
  to be amplified, filtered or demodulated. Various
  other examples of signal conditioning might be
  bridge completion, providing current or voltage
  excitation to the sensor, isolation,
  linearization.

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DAQ Hardware
DAQ hardware is what usually interfaces between
the signal and a PC. It could be in the form of
modules that can be connected to the computer's
ports (parallel, serial, USB, etc.) or cards
connected to slots (S-100 bus, AppleBus,
ISA, MCA, PCI, PCI-E, etc.) in the motherboard.
Usually the space on the back of a PCI card is
too small for all the connections needed, so an
external breakout box is required. The cable
between this box and the PC can be expensive due
to the many wires, and the required shielding.
MCA
S-100 Bus
Peripheral Component Interconnect
Industry Standard Architecture(ISA)
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DAQ System Hardware
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DAQ Hardware

• DAQ cards often contain multiple components
  (multiplexer, ADC, DAC, TTL-IO, high speed
  timers, RAM). These are accessible via a bus by
  a microcontroller, which can run small programs.
• A controller is more flexible than a hard wired
  logic, yet cheaper than a CPU so that it is
  permissible to block it with simple polling
  loops. For example Waiting for a trigger,
  starting the ADC, looking up the time, waiting
  for the ADC to finish, move value to RAM, switch
  multiplexer, get TTL input, let DAC proceed with
  voltage ramp.

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DAQ Software

• DAQ software is needed in order for the DAQ
  hardware to work with a PC. The device driver
  performs low-level register writes and reads on
  the hardware, while exposing a standard API
  (Application Programming Interface) for
  developing user applications.
• A standard API such as COMEDI allows the same
  user applications to run on different operating
  systems, e.g. a user application that runs on
  Windows will also run on Linux.
• Available Software in the industry are NI Lab
  View , Vis Sim, Simulink

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DAQ Graphical Software

• Test point
• Snap Master
• NI LabView
• DADISP
• Dasy Lab
• LabTech
• LabWindows
• Simulink
• Matrixx
• VisSim

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3) Digital Signal Processing
From a high-level point of view, a DSP system
performs the following operations Accepts an
analog signal as an input. Converts this analog
signal to numbers. Performs computations using
the numbers. Converts the results of the
computations back into an analog signal.
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3) Digital Signal Processing
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DSP for Microphone
As in the analog case, the sound waves impact the
microphone and are converted to electrical
signals. These electrical signals are then
amplified to a usable level. The electrical
signals are measured or, in other words, they are
converted to numbers. These numbers can now be
stored or manipulated by a computer just as any
other numbers are. To play back the signal, the
numbers are simply converted back to electrical
signals. These signals are then used to drive a
speaker.
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3) Digital Signal Processing

• Digital signal processing (DSP) is concerned with
  the representation of discrete time signals by a
  sequence of numbers or symbols and the processing
  of these signals.
• Digital signal processing and analog signal
  processing are subfields of signal processing.
  DSP includes subfields like audio and speech
  signal processing, sonar and radar signal
  processing, sensor array processing, spectral
  estimation, statistical signal processing, digital
  image processing, signal processing for
  communications, control of systems, biomedical
  signal processing, seismic data processing, etc.

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3) Digital Signal Processing

• The goal of DSP is usually to measure, filter
  and/or compress continuous real-world analog
  signals. The first step is usually to convert the
  signal from an analog to a digital form,
  by sampling it using an analog-to-digital
  converter (ADC), which turns the analog signal
  into a stream of numbers.

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3) Digital Signal Processing

• However, often, the required output signal is
  another analog output signal, which requires
  a digital-to-analog converter (DAC). Even if this
  process is more complex than analog processing
  and has a discrete value range, the application
  of computational power to digital signal
  processing allows for many advantages over analog
  processing in many applications, such as error
  detection and correction in transmission as well
  as data compression.

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3) Digital Signal Processing

• DSP algorithms have long been run on standard
  computers, on specialized processors
  called digital signal processor on purpose-built
  hardware such as application-specific integrated
  circuit (ASICs). Today there are additional
  technologies used for digital signal processing
  including more powerful general
  purpose microprocessors, field-programmable gate
  arrays (FPGAs), digital signal controllers (mostly
  for industrial apps such as motor control),
  and stream processors, among others.

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Summary -DSP
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4) Pulse Modulation

• What is pulse modulation?
• The transmission of analog data or speech which
  is in continuous form is known as pulse
  modulation.
• At some certain levels or points, the wave
  formation can be seen in a pulse modulation
  system.
• In this synchronizing, pulses are sent with the
  information related to the signal at different
  time samples.

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• In electronics and telecommunications, modulation 
  is the process of varying one or more properties
  of a high-frequency periodic waveform, called
  the carrier signal, with a modulating
  signal which typically contains information to be
  transmitted.
• This is done in a similar fashion to
  a musician modulating a tone (a periodic
  waveform) from a musical instrument by varying
  its volume, timing and pitch.

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• The three key parameters of a periodic waveform
  are its amplitude ("volume"), its phase ("timing")
  and its frequency ("pitch").
• Any of these properties can be modified in
  accordance with a low frequency signal to obtain
  the modulated signal.
• Typically a high-frequency sinusoid waveform is
  used as carrier signal, but a square wave pulse
  train may also be used.

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Pulse Amplitude Modulation
A problem that is often encountered with dealing
with transmission of low level dc signals from
sensors is that the gain of an op amp used to
amplify them may drift and so resulting to the
output drifts. This problem can be overcome if
th signal is alternating rather than direct. The
conversion of the signal to alternating can
assistin the elimination of external inference
from the signal.
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• One way this conversion can be achieved is by
  chopping the dc signal in way suggested in the
  figure.
• The output from the chopper is a chain of
  pulses, the heights of which is related to DC
  level of the input signal.
• This process is called pulse amplitude
  modulation.
• After amplification and any other signal
  conditioning, the modulated signal can be
  modulated to give a dc output.
• With pulse amplitude modulation. The height of
  the pulses is related to the dc voltage.
• An alternative to this is the pulse width
  modulation where the width that is the duration
  of a pulse depends on the size of the voltage.

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• The PWM refers to the dc signals, however it is
  often necessary to modulate ac signals.
• This enables data transmission at much higher
  frequencies and so allows the use of high pass
  filters to eliminate the noise signals that
  usually occur at much lower frequencies.
• Modulation techniques used are amplitude
  modulation, phase modulation and frequency
  modulation.

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Pulse Width Modulation(PWM)
An alternative to this is the pulse width
modulation where the width that is the duration
of a pulse depends on the size of the voltage.
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Frequency
Amplitude
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Application of PWM

• Varying the speed of fan and motors by varying
  the duty cycle(10 or 50)
• Controlling of dim lights
• Controlling or changing the amount of Power
  delivered to output devices
• Speed control of radio controlled toy car
• Dimming of laptop or computer monitor

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PWM Kit
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PWM Circuit
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Voltage range 0-10 voltsduty cycle 50, 50 on
, 50 off wave form
Average voltage 5 V
50 duty cycle
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10 Duty cycle, Average voltage 1 Volt
Effective Average 1 volt
10 of 10 Volts 1 Volt, average voltage
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Summary

• PWM-the techniquewhereby changing the width of
  the pulse, the average voltage can be changed.
  Potentiometer can be used to change the duty
  cycle in the circuit.

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The End