MODULE 4

1. MODULE 4

2. 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

3. Strip Chart Recorders (X-t Recorder) 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

4. Strip Chart Recorders (X-t Recorder)

5. 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.

6. Galvanometer Type

7. 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.

8. 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.

9. 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.

10. X-Y Recorder

11. Basic X-Y Recorder

12. 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.

13. 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

14. X-Y Recorder

15. 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.

16. 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.

17. 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

18. Wave Analyzers DEEPAK.P

19. 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

20. 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

21. Heterodyne Wave Analyzer Heterodyne wave analyzers are used to analyze signal in the RF range and above (MHz range).

22. 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.

23. 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

24. 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

25. 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

26. Spectrum analyzer (swept receiver design) Spectrum analyzer using swept receiver design. For the RF or microwave signals, the swept technique is preferred

27. 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

28. 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

29. Distortion Analyzer Consists of three main Parts Input section with Impedance matcher, Notch filter  and amplifier  section, An output  metering circuit.

30. 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.

31. Data Acquisition System

32. Data Acquisition System Multi channel data acquisition system

33. 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.

34. 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.

35. 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.

36. 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

37. Digital Storage Oscilloscope

38. Digital Storage Oscilloscope

39. 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

40. Digital Storage Oscilloscope

41. 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)

42. 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

43. 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.

44. 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

45. 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:

46. 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:

47. PID (Proportional-Integral-Derivative)

48. PID (Proportional-Integral-Derivative)

49. 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.

50. Programmable Logic Controllers