Rec101 unit iv emi
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The document discusses electronic instrumentation, focusing on digital voltmeters, digital multi-meters (DMM), and oscilloscopes, detailing their construction, operational principles, and applications. It highlights the importance of accurate measurements through historical examples of measurement failures and explains how digital devices convert physical quantities into electrical signals for display. Additionally, it covers specific measurement techniques using oscilloscopes, including voltage, frequency, and phase measurements, as well as the generation of Lissajous figures.
![Measurement of Voltage,
Frequency and Phase by CRO
10/2/2017 24
REC 101 Unit IV by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
Voltp2p = [volt peak to peak divisions x VOLTS/div]
Time Period = [horizontal divisions per cycle x Time/div]
Voltage Measurement: Peak to peak amplitude of a waveform can
be measured on oscilloscope
Time Measurement: Time period of a waveform can be measured
on oscilloscope.](https://image.slidesharecdn.com/rec101unitivemi-170921103917/85/Rec101-unit-iv-emi-24-320.jpg)
Rec101 unit iv emi
- 1. Electronic Instrumentation and Measurements Electronic Instrumentation and Measurements: Digital Voltmeter : Introduction, RAMP Techniques Digital Multi-meters: Introduction Oscilloscope: Introduction, Basic Principle, CRT , Block Diagram of Oscilloscope, Simple CRO, Measurement of voltage, current phase and frequency using CRO, Introduction of Digital Storage Oscilloscope and Comparison of DSO with Analog Oscilloscope. 10/2/2017 1 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad
- 2. Measurements • Measurement involves comparing the value to be measured with a known value (standard) • It is impossible to measure without comparison; • the act of measurement involves reading the value with an instrument. The instrument makes the comparison of the value with standard & gives reading. • Standard are object or prescription to which all other measurements are compared • Electronic measurement involves conversion of measured physical quantity in a corresponding electrical quantity (voltage or current) through transducer/ sensor and after comparison with a reference displaying the result. 10/2/2017 2 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad
- 3. Importance of measurement Gimli Glider Experiment : On 23 July 1983, an Air Canada jet ran out of fuel at 12.5 km above sea, but safely landed at Gimli (Manitoba) • Investigation revealed that amount of fuel loaded was less due to miscalculation due to confusion of system of units. Instead of 22,300 kg of fuel, they had 22,300 pounds of fuel Mars Climate Obiter Incident (Cost $125 million): during orbital manoeuvre in, 1999, lost radio contact & disintegrated in atmosphere. • Investigations found that orbiter reached very close to mars surface that led to disintegration. The cause of discrepancy was a software that calculated thrusters impulse in p-s, while software that updated position of spacecraft, expected results to be in N-s. Columbus reached America instead of Asia. He miscalculated the circumference of the earth using Roman miles instead of nautical miles, which is part of reason he landed in Bahamas instead of Asia. 10/2/2017 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad 3
- 4. Digital voltmeter systems 10/2/2017 4 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad ▪Digital voltmeters are basically analog to digital converters with digital display to indicate voltage E Vo Attenuator or range selector Amplifier High input/ low output impendence Rectifier Analog to digital converter Digital Display BCD to seven segment display
- 5. Ramp Type DVM • Ramp type uses comparison of input voltage with Ramp waveform. • Ramp output triggers counter, output of which is displayed when counting stops • Counting circuit, BCD to seven segment decoder and digital readout constitutes a 2000 scale counter display. 10/2/2017 5 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad + - Ramp generator Clock generator Decade Counter Latch BCD to seven segment drivers 1 9 9 9 V Vi Display Reset
- 6. Ramp Type DVM • Ramp starts at t=0, when ramp reaches to Vi (t=t1), comparator output switches. • Counting continues in period t1. • No counting in rest time period of ramp t2 • Latch separates display drivers from counters during counting (t1) • At end of t1, latch triggers transfer of counts to display through drivers. 10/2/2017 6 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad RampVi Comparator output t1 t2 Reset Latch Latch trigger to correct display Counting No Counting Clock pulse during t1 Accurate measurement in Ramp type DVM requires precise Ramp voltage and time period.
- 7. Dual Slope Integrator DVM • Dual slope Integrator eliminates requirement of precise voltage and time period, by using a special ramp generator (integrator) 10/2/2017 7 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Clock generator Counters BCD to seven segment drivers 1 9 9 9 Vi Display Reset + - Integrator Zero crossing detector Frequency divider Constant current source • Integrator capacitor is charged from Vi and then discharged at constant rate. Discharge time is proportional to Vi • During discharge duration, counter counts. • Two slopes; charge & discharge gives its name dual slope. • Accuracy of Dual slope integrator DVM depends on current source
- 8. Dual Slope Integrator DVM • Integrator charges negatively from Vi. In fixed time duration t1 . The charge voltage Vo Vi • Capacitor discharge at constant rate till zero crossing detector output goes negative • Discharge time t2 Vo Vi. • During discharge, counter counts • Counted result is displayed. • If clock frequency drifts, both t1 & t2 change, thus not affecting result. 10/2/2017 8 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Clock pulse Start counting Stop counting t1 t2 Integrator control waveform Dual slope ramp from integrator Zero crossing detector output
- 9. Digital Multi-meters (DMM) • A DMM measures two or more electrical quantities, principally – AC/DC voltage (volts) – AC/DC current (amps) and – resistance (ohms) • DMM have high accuracy, reliability than analog meters • DMM also come with special features measurement – Frequency – Capacitance – Temperature – Continuity testing/ Diode testing • DMM works on Ohm’s law to measure, voltage/current/ resistance 10/2/2017 9 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad
- 10. Digital Multi-meters (DMM) 10/2/2017 10 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Analog to Digital Converter BCD to seven segment drivers 1 9 9 9 ACV To resistance Constant current source Buffer Amplifier Calibrated attenuator Current to Voltage converter Current to Voltage converter Calibrated attenuator ACA DCA DCV Rectifier
- 11. Digital Multi-meters (DMM) Resolution, digits and counts • Resolution refers to smallest change in value that can be measured. • Digits and Counts are used to describe a multi-meter’s resolution. –A 3 1⁄2-digit meter can display 3 full digits (ranging from 0 to 9), and one “half” digit which display only 2 symbols (0 & 1), with maximum value 1. Thus a 3 1 ⁄2-digit meter can display up to 1,999 (2000 counts ). –A 4 1 ⁄2-digit meter can display up to 19,999 (20000 counts). –A 3 3 ⁄4-digit meter can display up to 3999 (4000 counts). –A 2000/20000-count meter may have volt ranges of 200 mV, 2 V, 20 V, 200 V, 750 V –As the range increase, resolution decrease –DMM are built with 3200, 4000, or 6000 counts. 10/2/2017 11 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad
- 12. Introduction to Oscilloscope & CRT 10/2/2017 12 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad CRT: Cathode Ray Tube CRO: Cathode Ray Oscilloscope CRT+ control & input circuitry CRT Block diagram: Electrode system in evacuated glass tube which ends at screen • Triode section • Focussing Lens • Deflection grids • Post deflection acceleration • Screen
- 13. CRT Construction 10/2/2017 13 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad 6.3 V -2 KV -2.050 KV -2 KV +12 KV Filament Cathode Grid Glass tube A1 A2 A3 Vertical deflection plate Horizontal deflection plate Isolation shield Resistive helixElectron beam Aquadag Screen Power Supply Triode section Focussing Deflection Post deflection acceleration Electron Gun
- 14. CRT Construction: Triode section 10/2/2017 14 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad • A electron beam is generated by a cathode heated by filament • Consists of a cathode , grid and anode • Grid is a Nickel cup with a hole in it • Cathode is Nickel cylinder, with flat oxide coated electron emitting surface towards the grid hole. Heating is provided by a filament • Cathode is kept at -2 KV and grid is adjustable in the range –2KV to -2.05 KV • Grid cathode potential controls electrons flow rate towards screen, thus Grid potential is brightness control.
- 15. CRT Construction: Deflection 10/2/2017 15 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad • If horizontal/ vertical plates are grounded, beam is not deflected. • With potential across plates, beam deflects to +ve potential. • Voltage to produce one cm at screen (V/cm) is referred as deflection factor. Deflection by 1 V (cm/V) is termed as deflection sensitivity • When ac is applied at deflection plates, horizontal/vertical lines are produced at the screen. Waveform to be displayed is fed to vertical plates while horizontal plates are fed with a ramp. • Grounded isolation shield is lie between horizontal/ vertical plates + E/2 - E/2 screen deflectionAxial Velocity Vertical Velocity Deflecting plates Electron beam Deflection Angle
- 16. CRT Construction: Screen 10/2/2017 16 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad • CRT Screen is formed by coating phosphor material to inside of the screen. When electron beam strikes, electrons in the phosphor material go to higher energy level and return to original statae while emitting the visible light (Glow). • The glow may persist for some time (ms to second) and may be of colour Red, Blue , Green or White depending on the material. • Phosphors are insulators. Secondary emission electrons are collected by a graphite coating “aquadag” around the neck of tube. • Post deflection acceleration is provided by helix of resistive material deposited inside of tube between deflection plate and screen with starting point at ground while ending point at aquadag (12 KV) • Thus electrons leaving deflection plates finds continuous acceleration before striking screen
- 17. CRO Block diagram 10/2/2017 17 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad 6.3 V -2 KV -2.050 KV -2 KV +12 KV Screen Power Supply Vertical Amplifier Delay Line Input signal Trigger Circuit Time base Circuit Horizontal Amplifier Attenuator Calibration input
- 18. CRO : Waveform Display 10/2/2017 18 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad +2 V -2 V 0 0 1 2 3 4 ms t Input to vertical deflection plate Input to horizontal deflection plate +2 V -2 V 0 1 2 3 4 5 6 7 8 9 Display • When ac is applied to vertical plates and horizontal plates are grounded, then spot on the screen produce a vertical line by moving up and down • If ramp (a period of saw tooth wave) is applied on horizontal plate, spot moves horizontally along with up and down movement, thereby producing a waveform
- 19. CRO time base: Horizontal sweep generator 10/2/2017 19 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad • To display a waveform, saw tooth wave (repetitive ramp) is applied on horizontal plate, generated by a horizontal sweep generator • Sweep generator consists of ramp generator and Schmitt trigger • A ramp output is produced by linear charging of capacitor. • Schmitt trigger output is saturated i.e +(VCC-1)V or –(VEE-1)V • If Schmitt trigger output is -ve, then then ramp grows • As the ramp becomes higher than ground, Schmitt trigger output switches to +ve saturation that triggers ramp below the ground in very short time thereby again switching the Schmitt trigger. • Capacitor selection switch (Time/ div switch of CRO) determines T.
- 20. CRO time base: Horizontal sweep generator 10/2/2017 20 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Upper trigger level Lower trigger level Ramp generator output Schmitt trigger output (VCC – 1) V -(VEE -1) V T Ramp generator + - R3 R1 R2 -VEE VCC C Sync input Schmitt Trigger Trigger • To display a waveform correctly on screen input waveform and ramp waveform (saw tooth wave) must be perfectly synchronized, otherwise the displayed waveform will appear as sliding to the side of screen. Synchronization is done using sync input to Schmitt trigger and other automatic time base circuit components
- 21. Dual Trace Oscilloscope 10/2/2017 21 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad • Dual trace CRO are one which can display two waveforms. Two input terminals and set of controls are provided, identified as channel A and channel B. This allows comparison in terms of amplitude, time etc. • Construction of dual trace oscilloscope • Dual beam • Split beam • Alternate mode • Chop mode
- 22. Dual Trace Oscilloscope 10/2/2017 22 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Dual beam CRT • It contains pair of electron guns and vertical deflection plates for two waveforms in a single tube. • Saw tooth wave from time base is applied on single horizontal deflection plates for both beams for simultaneous screen sweep. Split beam CRT • Beam from electron gun is split in two beams before it passes through separate vertical deflection plates for two waveforms
- 23. Dual Trace Oscilloscope 10/2/2017 23 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Alternate mode CRT • Vertical deflection plates of CRT are fed by single amplifier • Input to amplifier is alternatively and repeatedly fed by two input channels. Switching frequency is controlled by time base circuit. • Repetition frequency is high enough so that two waveforms appear on screen simultaneously. Chop mode CRT • Time period of saw tooth is chopped in various time slots. • Input to amplifier of vertical deflection plates is alternatively and repeatedly fed by two input channels in chopped time slots. • Two waves are displayed in dash line trace with gaps that are virtually invisible for low frequency waveforms.
- 24. Measurement of Voltage, Frequency and Phase by CRO 10/2/2017 24 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Voltp2p = [volt peak to peak divisions x VOLTS/div] Time Period = [horizontal divisions per cycle x Time/div] Voltage Measurement: Peak to peak amplitude of a waveform can be measured on oscilloscope Time Measurement: Time period of a waveform can be measured on oscilloscope.
- 25. Measurement of Voltage, Frequency and Phase by CRO 10/2/2017 25 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Frequency= 1/ Time Period Frequency Measurement: Frequency is inverse of measured time period Phase Measurement: Phase between two waveforms can be measured by measuring the horizontal distance between peaks of two waveform and measuring the horizontal divisions in a cycle. cycleaindivisionhorizontal waveformsbetweendivisionshorizontal 360differencePhase 0
- 26. Measurement of Voltage, Frequency and Phase by CRO 10/2/2017 26 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad VOLT /DIV 4.8div 4 div 3.2div 3.4div Channel B Channel A Channel A Time period =4.8 div x 0.1 ms/div =0.48 ms Frequency =1/(0.48 ms) = 2.083 KHz Volt (p2p) = 4 div x 200 mV/div = 800 mV Channel B Time period =3.2 div x 0.1 ms/div =0.32 ms Frequency =1/(0.32 ms) = 3.125 KHz Volt (p2p) =3.4 div x 200 mV/div =680 mV TIME/DIV CAL
- 27. Oscilloscope: X-Y and Z display 10/2/2017 27 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad • When time base is disconnected, and input waveforms are applied on horizontal and vertical amplifiers, resulting display are called lissajou figures and depends on relationship of two waveforms. • Simple figures occur for waveforms of same frequency waveform, while for different frequencies quite complex figures are formed. For stationary figures there must be exact ratio of frequencies Vertical input Horizontal input Vertical input : sine wave Horizontal input: No input Vertical input : No input Horizontal input: sine wave Vertical input : Sine wave Horizontal input: In-phase Sine
- 28. Oscilloscope: Lissajou figures 10/2/2017 28 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Vertical input Horizontal input Vertical input : sine wave Horizontal input: anti phase sine wave Vertical input : No input Horizontal input: sine wave with 900 phase shift Vertical input : Sine wave Horizontal input: Sine wave with phase difference between 0-900 Vertical Input (f1) Horizontal Input (f2) f1:f2=2:1 f1:f2=3:2
- 29. Oscilloscope: Z-axis modulation 10/2/2017 29 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad • CRO have a intensity modulation input termed as Z-axis modulation • The input wave actually modulates the grid input of oscilloscope. This dims or blank out the traces. • For a lissajou figure ‘circle’ when z-axis modulation is applied, gaps are formed. Ratio of modulating frequency (fm) to deflecting plate signal frequency (fp) is equal to number gaps in the circle. • When fm:fp is an exact quantity, gaps in circle will be stable Vertical input Horizontal input fm:fp :: 3:1 fm:fp :: 8:1
- 30. Oscilloscope specifications and performance 10/2/2017 30 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Sensitivity: defines the amplitude that can be displayed on screen • Typically sensitivity ranges from 2 mV/div to 10 V/div. • Using the probe measuring sensitivity can be increased. Voltage Measurement Accuracy: • Accuracy of V/div sensitivity is typically 3%. • Reading accuracy is typically 5% per division. • For peak to peak voltage in 5 div, reading accuracy is 5%/5= 1%. Overall measurement accuracy becomes 1%+ 3%= 4% Frequency Response: • Highest and lowest frequency of waveform that may be displayed with no more than 3 dB attenuation • For CRO upper cutoff frequency (fH) having negligible effect on displayed waveform, signal frequency should not exceed fH/10
- 31. Oscilloscope specifications and performance 10/2/2017 31 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad Time Base Accuracy: • Accuracy of V/div sensitivity is typically 5%. • Reading accuracy of time base is typically 5% per division. • For peak to peak voltage in 5 div, reading accuracy is 5%/5= 1%. Overall measurement accuracy becomes 1%+ 5%= 6% Rise Time Measurement: • is rise time imposed on oscilloscope on an input pulse wave. • tro=0.35/fH
- 32. Digital Storage Oscilloscope (DSO) • DSO store and analyses the signal in digital form instead of analog. The signal is sampled and converted into digital form using ADC (Analog to digital converter) into binary form. To avoid aliasing, sampling frequency should be greater than Nyquist rate. • DAC is used to display on CRT or use a raster type digital display. • Most DSO sample with 8-bit resolution (1 in 255 or 0.4% resolution). If DSO can store 4000 samples it is said to have 4000 word memory or 4K memory • DSO have interpolation facility which improves display. • DSO’s high cut-off frequency is normally one fourth of sampling rate. Ex. 25 MHz DSO with sampling rate 100 M Samples/s • DSO’s use either real time sampling or equivalent sampling (as in sampling oscilloscope) 10/2/2017 32 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad
- 33. DSO Applications Auto set : Normally DSO’s have automatic selection of time and amplitude setting for best waveform display and display the settings Multichannel display: Normally DSO’s have four or more new and stored waveform display. Waveform Processing :Normally DSO’s have DVM, Digital frequency meter, and time measurement circuits. Two cursors are employed to select two points on waveform. Vrms, Vp-p, f, tr, T, pulse width, duty cycle etc. can be measured and displayed. Pre-Triggering and Post-Triggering: DSO’s can be used to display pre- trigger and post-trigger portions of the waveform. It is possible because input waveform is continually processed and stored. Zoom and Restart : Some DSO’s provide zoom and restart facility. It is essentially addition method of time delay selection. 10/2/2017 33 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad
- 34. DSO Applications Glitch and Runt Catching : High sampling rate DSO’s can catch Glitches (spikes) which are missed in normal CRO/ DSO. A runt is special glitch which is not large to produce triggering. A maximum/ minimum detector is employed in some DSO’s for the purpose. Baby Sitting Mode: Some waveform transits occur once in long duration. DSO can be put in baby sitting mode in which waveform is sampled/recorded continuously so that at any instant when anomaly is detected, many previous cycles are stored to be analysed later. Roll Mode: Many quantities can vary slowly over a longer period of time. DSO time base can be adjusted to give long sampling duration, samples are stored and played back at a faster speed . Documentation / Printing: DSO’s has storage and printing facilities. 10/2/2017 34 REC 101 Unit IV by Dr Naim R Kidwai, Professor & Dean, JIT Jahangirabad