MODULE 4

RECORDERSRecorder records an electrical or nonelectrical quantities as a function of time . Classified into Analog recordersA) Graphic recorders( Strip Chart Recorders ,X-Y recorders)B) Oscilloscopic RecordersC) Magnetic tape recordersDigital recordersA) IncrementalB)Synchronous

Strip Chart Recorders (X-t Recorder)Records one or more variables with respect to time.Consists of A long roll of graph paper moving verticallyA system for driving the paper at a uniform speedA 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 chartDifferent types area)Galvanometer Type Deflection principleb)Null Type Comparison Basis/ self balancing Type

Strip Chart Recorders (X-t Recorder)

Galvanometer TypeUse D Arsonval galvanometerAs 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 TypeChange 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 RecorderAdvantages: 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 observedDisadvantages: Observing the behavior several hours or days back is not as easy.

**X-Y RecorderRecords one or more parameters with respect to some otherOrx-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.

**X-Y Recorder

**Basic X-Y Recorder

**X-Y RecorderThis 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.

**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

**X-Y Recorder

**X-Y RecorderA 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.

**X-Y RecorderThe 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.

**Application X-Y RecorderSpeed torque characteristics of motorslift Drag wind tunnel testsPlotting of characteristics of vaccum tubes, zener diodes rectifiers and transistors etcRegulation curves of power suppliesPlottering stress-strain curves, hysteresis curves and vibrations amplitude against swept frequencyElectrical characteristics of materials such as resistance versus and temperature plotting the output fromElectronic calculators and computers

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Wave Analyzers

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 AnalyzersThe 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 AnalyzerHeterodyne wave analyzers are used to analyze signal in the RF range and above (MHz range).

Heterodyne Wave AnalyzerAttenuator 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 AnalyzerThe 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 1500HzThe 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 analyzerA 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

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 otherParallel filter bank Spectrum analyserParallel filter bank Spectrum Analyzer

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 distortionEf = the amplitude of fundamental frequency including fundamental frequency. E2,E3 ,En = the amplitude of the individual harmonics

Distortion AnalyzerConsists of three main Parts Input section withImpedancematcher, Notch filter andamplifier section, An output metering circuit.

Distortion AnalyzerThe input isimpedence -matched t with the help of anattenuator and an impedance matcher. This signal is then preamplifierto a desired level and applied to aWien 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 frequencyThe remaining signal after the fundamental has been suppressed, is amplified to a measurable level.

**Data Acquisition System

Data Acquisition System

Multi channel data acquisition system

Data Acquisition SystemSensors/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 OscilloscopeA 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.

Digital Storage OscilloscopeBasic 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 OscilloscopePretrigger 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

**Digital Storage Oscilloscope

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

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 ControlThe 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) controllerProportional 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) controllerProportional-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) controllerPD 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 ControlDigital 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 ControllersA 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 (PLCs) 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 ControllersThe 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 ControllersThe basic components of the PLC are Input module Output module Processor Memory Power supply Programming device

Programmable Logic ControllersPLC 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 ControllersA 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 ControllersDuring 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

PLCThe output result is calculatedbased on the ladder diagram.

Digital RecordingAn 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 RecordingDuring 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

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