Transcript Module - 4 - SNGCE DIGITAL LIBRARY

MODULE 4
RECORDERS
• Recorder records an electrical or nonelectrical
quantities as a function of time . Classified into
• Analog recorders
A) Graphic recorders( Strip Chart Recorders ,X-Y
recorders)
B) Oscilloscopic Recorders
C) Magnetic tape recorders
• Digital recorders
• A) Incremental
• B)Synchronous
Strip Chart Recorders (X-t Recorder)
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Records one or more variables with respect to time.
Consists of
A long roll of graph paper moving vertically
A system for driving the paper at a uniform speed
A stylus for making marks on the moving graph paper ( moves
horizontally in proportional to the quantity being recorded)
• A Stylus driving system.
• Event marker to mark edges of chart
• Different types are
a)Galvanometer Type – Deflection principle
b)Null Type – Comparison Basis/ self balancing Type
Strip Chart Recorders (X-t Recorder)
Galvanometer Type
• Use D Arsonval galvanometer
• As the current flows through the coil, it deflects.
• The deflection is produced by a galvanometer which
produces a torque on the account of current passing
through the large moving coil situated in a strong
magnetic field.
• Greater the amplitude of the incoming signal (proportional
to the quantity being measured), the grater is the deflection.
• Instrument should be critically damped to avoid
overshoot.
• Does not suitable for fast variations in current ,voltage or
power. Only records the average value.
Galvanometer Type
Null Type
• Change in input produced by the signal upset the balance
of the measuring circuit of the recorder. As a result of this
unbalance, an error signal is produced that operates on
some devices which restore the balance or bring the
system to null conditions.
• Eg: Potentiometric Recorders , Bridge Recorders, LVDT
Recorders.
Strip chart Recorder
• Advantages:
Conversion of data is easier when rectangular
coordinated are used.
• The rate of movement of the chart can easily be
changed to spread out the trace of the variable
being observed
• Disadvantages:
Observing the behavior several hours or days
back is not as easy.
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X-Y Recorder
• Records one or more parameters with respect to
some other
• Or
• x-y recorder is an instrument which gives a
graphic record of the relationship between two
variables.
• In some type recorders ,Pen moves in two axes
• In X-Y recorders, an emf is plotted as a function
of another emf.
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X-Y Recorder
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Basic X-Y Recorder
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X-Y Recorder
• This is done by having one self-balancing potentiometer
control the position of the rolls.
• While another self-balancing potentiometer controls the
position of the recording pen.
• In some X-Y recorders, one self-balancing potentiometer
circuit moves a recording pen in the X direction
• While another self-balancing potentiometer circuit
moves the recording pen in the Y direction, while the
paper remains stationary.
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X-Y Recorder
• Attenuators are used to bring the input
signals to the levels acceptable by the
recorder.
• XY recorder is Expensive than strip chart
recorder
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X-Y Recorder
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X-Y Recorder
• A signal enters each of the two channels.
• The signals are attenuated to the inherent full
scale range of the recorder, the signal then
passes to a balance circuit where it is
compared with an internal reference voltage.
• The error signal ,the difference between the
input signal voltage and the reference voltage
is fed to a chopper which converts d.c signal
to an a.c signal.
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X-Y Recorder
• The signal is then amplified in order to
actuate a servomotor which is used to
balance the system and hold it in balance as
the value of the quantity being recorder
changes.
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Application X-Y Recorder
• Speed torque characteristics of motors
• lift Drag wind tunnel tests
• Plotting of characteristics of vaccum tubes, zener diodes
rectifiers and transistors etc
• Regulation curves of power supplies
• Plottering stress-strain curves, hysteresis curves and
vibrations amplitude against swept frequency
• Electrical characteristics of materials such as resistance
versus and temperature plotting the output from
• Electronic calculators and computers
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Wave Analyzers
DEEPAK.P
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Wave Analyzers
• Complex Waveform is made up of a fundamental
frequency and its harmonics.
• Wave Analyzers are used to measure the amplitude of
fundamental frequency and each harmonics
individually. (AF range only)
• Wave analyzers are also referred to as frequency
selective voltmeters such that it is tuned to the
frequency of one component whose amplitude is
measured
Wave Analyzers
• The analyzer consists of a primary detector : LC circuit passes only
the frequency to which it is tuned and provides a high attenuation to
all other frequencies . The full wave rectifier is used to get the
average value of the input signal . The indicating device is a D.C
voltmeter, used to read the peak value of the sinusoidal
Heterodyne Wave Analyzer
• Heterodyne wave analyzers are used to analyze signal
in the RF range and above (MHz range).
Heterodyne Wave Analyzer
• Attenuator is used to modify the amplitude of the
input signal .
• In this analyzer, the input signal is mixed with the
internal signal to produce a higher IF frequency.
• The local oscillator is tunable to get all the frequency
components of the input signal.
• The first mixer stage produces an output of 30Mhz
which is a difference between the input and oscillator
signal.
• This 30MHz signal will be amplified by IF amplifier and
fed to the second mixer.
Heterodyne Wave Analyzer
• The second mixer will produce a 0 Hz signal which is
the difference between IF and crystal oscillator signal
• This signal will then be filtered by the active filter of a
bandwidth less than 1500Hz
• The amplitude of the selected frequency component
can be read from the output meter in Volt or dB.
• This wave analyzer is operated in the RF range of
10kHz – 18MHz
Spectrum Analyser
• Oscilloscope is used to display and measure signal in a
time domain.
• The instrument providing this frequency domain view
is the spectrum analyzer
• A spectrum analyzer display signal on its CRT with
frequency on the horizontal axis and amplitude
(voltage) on the vertical axis.
• Spectrum analyzers use either a parallel filter bank or a
swept frequency technique
Parallel filter bank Spectrum Analyzer
• In a parallel filter bank analyzer, the frequency range is covered by a
series of filters whose central frequencies and bandwidth are so
selected that they overlap each other
• Parallel filter bank Spectrum analyser
Spectrum analyzer (swept receiver design)
• For the RF or microwave signals, the swept
technique is preferred
Spectrum analyzer using swept receiver design.
Spectrum analyzer (swept receiver design)
• The sawtooth generator provides the sawtooth
voltage which drives the horizontal movement of the
scope and the frequency controlled element of the
voltage tuned oscillator.
• The voltage tuned oscillator will sweep from fmin to
fmax of its frequency band at a linear recurring rate.
• The frequency component and voltage tuned
oscillator frequency beats together to produce a
difference frequency, i.e. IF (intermediate frequency)
• This IF will be amplified and displayed on the CRT
screen of the spectrum analyzer
Distortion Analyser
•
Function of distortion analyzer : measures the total harmonic
power in the test wave rather than the distortion caused by each
component.
• Simplest method is to suppress the fundamental frequency of the
signal with a notch filter , leaving only harmonics plus noise.
• The total harmonic distortion (THD) can also be written as
• Where THD = the total harmonic distortion
• Ef = the amplitude of fundamental frequency including fundamental
frequency. E2,E3 … ,En = the amplitude of the individual harmonics
Distortion Analyzer
• Consists of three main Parts
Input section with Impedance matcher, Notch
filter and amplifier section, An output metering circuit.
Distortion Analyzer
• The input is impedence -matched t with the help of
an attenuator and an impedance matcher.
• This signal is then preamplifier to a desired level
and applied to a Wien bridge notch filter, tuned to
reject the fundamental frequency and balanced for
minimum output by adjusting the bridge controls.
• A feedback loop from the bridge amplifier output to
the pre-amp input helps to eliminate any remaining
contribution from the fundamental frequency
• The remaining signal after the fundamental has
been suppressed, is amplified to a measurable level.
Data Acquisition System
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Data Acquisition System
• Multi channel data acquisition system
Data Acquisition System
• Sensors/Transducers are used to generate the analog
signals.
• Then the signal is conditioned by scaling, amplification,
filtering etc.
• An Individual S/H circuit is assigned to each channel and
they are updated synchronously by the timing circuit.
• When a large no. of channels are monitored at the same
time , multiplexing the outputs of the S/H is commonly
preferred.
• The S/H outputs are connected to an A/D Converter
through a multiplexer resulting a sequential read out of
outputs.
Digital Storage Oscilloscope
• A digital storage oscilloscope is an oscilloscope which stores and
analyses the signal digitally rather than using analogue
techniques.
• The input analogue signal is sampled and then converted into a
digital record of the amplitude of the signal at each sample
time.
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Digital Storage Oscilloscope
• Basic advantage of digital operation is the storage capacity, stored
information can be repeatedly read out, processing capability and
analysis of the output.
• Furthermore, voltage and time scales can be easily changed after
the waveform has been recorded, which allows expansion of the
selected portions.
• Also cursor can be positioned at any desired point on the waveform
and time & voltage values are displayed digitally on the screen
• Split screen capabilities enables easy comparison of the two signals.
Digital Storage Oscilloscope
• Pretrigger capability is also significant advantage.
Slow read out of data is is possible for producing
hardcopy with external plotters.
• When more memory is needed, magnetic
memory expansion is possible.
• Analog input voltge can be sampled at adjustable
rates.
• But limited in bandwidth by the speed of the A/D
Converters
Digital Storage Oscilloscope
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Digital Storage Oscilloscope
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Digital Storage Oscilloscope
• Initially the input signal is attenuated and it is then applied
to the vertical amplifier.
• The input, is then digitized by an analog to digital
converter to create a data set that is stored in the memory
.it can be available in the digital form also.
• The stored digital data can be converted to analog signal
and can be applied to CRO for displaying it.
• The digital storage oscilloscope has three modes of
operation:
• 1. Roll mode ii) Store mode iii) Hold or save mode
• Roll mode is used to display very fast varying signals,
clearly on the screen. The fast varying signal is displayed as
if it is changing slowly, on the screen
Digital Storage Oscilloscope
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Electronic Control System
• Function of ECS is to keep the variables of a
system electronically at the desirable value.
• Implemented In two ways
• Analog (PID Controllers)
• Digital (ON/OFF / Digital Processors)
Analog Control
• The system to be controlled is the Plant /Process .A sensor
measures the quantity to be controlled. An actuator affects
the plant. A controller or control processor processes the
sensor signal to drive the actuator. Disturbance is a signal
from external of the plant that occurs unpredictably and
disturbs the plant from reaching the pre specified level
Proportional (P) controller
• Proportional control is the most basic control that is always
used in the controllers. This is easy to develop, but cannot
remove steady-state error.
• The equation of the P controller in time domain: u(t) = K p
e(t) where
K p -proportional gain.
Proportional-Integral (PI) controller
• Proportional-Integral controller is used to eliminate steady-state
error, but if integral gain is mistuned, the system can become
unstable and the response time can be slower.
• The equation of the PI controller in time domain:
where K
i : integral gain
Proportional-Derivative (PD) controller
• PD control increases the stability of the system and
makes the response time faster, but with the
presence of noise in the system.
• The equation of the PD controller in time domain:
PID (Proportional-Integral-Derivative)
• More than 80% of the feedback controllers are PID controllers in the
actual fields, because its performance is good and it is easy to tune.
• The equation of the PID controller in time domain:
PID (Proportional-Integral-Derivative)
PID (Proportional-Integral-Derivative)
Digital Control
• Digital devices such bas microcontrollers, Digital
Signal Processors, programmable logic controllers
or computer etc is used as the controller. Here ADC
& DAC are integrated to the System for proper
conversions from analog to digital and vice-versa.
Programmable Logic Controllers
Programmable Logic Controllers
• A digitally operating electronic apparatus which uses a
programmable memory for the internal storage of instructions for
implementing specific functions such as logic, sequencing, timing,
counting, and arithmetic to control, through digital or analog
input/output modules, various types of machines or process.
•
Programmable logic controllers (PLC’s) permit hardware control
devices such as relays, timers, counters, and drum controllers
(sequencers) to be replaced by programmable solid-state
components and programmed instructions.
• PLC reads the status of the external input devices, e.g. keypad,
sensor, switch and pulses, and execute by the microprocessor logic,
sequential, timing, counting and arithmetic operations according
the status of the input signals as well as the pre-written program
stored in the PLC.
Programmable Logic Controllers
• The generated output signals are sent to output devices as
the switch of a relay, electromagnetic valve, motor drive,
control of a machine etc.
• To do so, a ladder program, consisting of a set of
instructions representing the logic to be followed by the
PLC, is developed, entered, and downloaded to the PLC.
• The widely used language in designing a PLC program is
the ladder diagram
• It can also be programmed using assembly code,
sequential function Chart, Functional Block Diagram etc.
• PLC is the workhorse of industrial Automation.
Programmable Logic Controllers
• The basic components of the PLC are
• Input module
• Output module
• Processor
• Memory
• Power supply
• Programming device
Programmable Logic Controllers
• PLC memory,( Program memory- storing the instructions for logical
control operations & Data memory- stores status of switches, data
from various I/O devices , past value of data etc.) which contains the
program of logic, sequencing, and other input/output operations
•
The input module and output module: are the connections to the
industrial process that in to be controlled. The inputs to the controller
are signals from limit switches, pushbuttons, sensors, and other
on/off devices. Also, larger PLCs are capable of accepting signals
from analog devices . The outputs from the controller are on/off
signals to operate motors, valves, and other devices required to
actuate the process.
• The processor is the central processing unit (CPU) of the
programmable controller. It executes the various logic and
sequencing functions.
Programmable Logic Controllers
• A power supply is specially used to drive the PLC .
• The PLC is programmed by means of a programming device. The
programming device is usually detachable from the PLC cabinet so
that it can be shared between different controllers. It is used to
build,test and edit the logical sequence that PLC will execute
Programmable Logic Controllers
• During its operation, the CPU completes three
processes:
• (1) it reads, or accepts, the input data from the field
devices via the input interfaces,
• (2) it executes, or performs, the control program
stored in the memory system, and
• (3) it writes, or updates, the output devices via the
output interfaces. This process of sequentially
reading the inputs, executing the program in
memory, and updating the outputs is known as
scanning.
PLC
PLC
The output result is calculated
based on the ladder diagram.
Digital Recording
• An analog signal is converted to digital by an analog-to-digital
converter, which measures the amplitude of an analog signal at
regular intervals, which are specified by the sample rate, and then
stores these sampled & quantized numerical value in computer
hardware such as compact disc or hard` disk.
• Digital recordings are very accurate, the accuracy determined only
by the quality of the D/A and A/D converters.
• For optical disc recording technologies such as CDs or DVDs, a laser
is used to burn microscopic holes into the dye layer of the medium.
• A weaker laser is used to read these signals.
• This works because the metallic substrate of the disc is reflective,
and the unburned dye prevents reflection while the holes in the dye
permit it, allowing digital data to be represented.
Digital Recording
• During digital recording of the analog signal, analog to digital
(A/D) conversion takes place from continuous time-amplitude
coordinates to discrete time-amplitude coordinates
Digital Recording