International Institute of Information Technology. Department of Electronics & Telecommunication

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1 International Institute of Information Technology Hinjawadi, Pune Department of Electronics & Telecommunication LABORATORY MANUAL FOR ELECTRONICS MEASURING INSTRUMENTS AND TOOLS (SE E&TC SEM I)

2 List of Assignments Sr. No. Work Load Exam Schemes Practical Term Work Practical Oral 02 hrs per week Title of Assignment Time Span (No. of weeks) 1 Carry out Statistical Analysis of Digital Voltmeter 01 2 Multimeter Cathode Ray Oscilloscope Digital Storage Oscilloscope True RMS Meter LCR- Q Meter Spectrum Analyzer Frequency Counter Calibration of Digital Voltmeter Function generator/arbitrary waveform generator. 01 Text Books: 1. R Albert D Helfrick, William Cooper, Modern Electronic Instrumentation and Measuring Techniques PHI EEE. 2. H S Kalsi, Elctronic Instrumentation, 3 rd edition McGraw Hill. 3. M S Anand, Electronic Instruments and Instrumentation Technology, PHI EEE, fourth reprint.

3 ASSIGNMENT NO.1 Reference Books: TITLE: Statistical analysis using voltmeter PROBLEM STATEMENT: Carry out Statistical Analysis of Digital Voltmeter. Calculate mean, standard deviation, average deviation, and variance. Calculate probable error. Plot Gaussian curve. OBJECTIVE: 1. To understand importance of statistical analysis. 2. To understand analysis parameters.. REQUIREMENT: Resistance, DC power supply, bread board, digital voltmeter. THEORY: Arithmetic Mean: The most probable value of a measured value is the arithmetic mean of the number of readings taken. The best approximation will be made when the number of readings of the same quantity is very large. Theoretically, an infinite number of readings would give the best result, although in practice, only a finite number of measurements can be made. The arithmetic mean is given by the following expression: X(m) = [(x1 + x2 + x3 + xn) / n ] = ( x )/ n ; Where X(m) = arithmetic mean x1, x2,.,xn = readings taken n = number of reading Deviation from the Mean: Deviation is the departure of a given reading from the arithmetic mean of the group of readings. The deviations from the mean can be expressed as d1 = x1 X (m); d2 = x2 - X (m); d3 = x3 - X(m); here d1, d2, d3 = deviations of the readings x1, x2, x3, respectively. Note that the deviations may have a positive or a negative value but, the algebraic sum of all the deviations must be zero.

4 Average Deviation: The average deviation is an indication of the precision of the instruments used in making the measurements. Highly precise instruments could yield a low average deviation between the readings. By definition, average deviation is the sum of absolute values of all the deviations divided by the number of readings. Average deviation may be expressed as D = [ ( d1 + d2 + d3 + dn ) / n ] = ( d ) / n Standard Deviation: In statistical analysis of random errors, the root mean square value or the standard deviation is a very valuable aid. By definition, the standard deviation of an infinite number of readings is the square root of the sum of all the individual deviations squared, divided by the number of readings. Expressed mathematically as σ = [ { (d1) 2 + (d2) 2 + (d3) 2 + (dn) 2 } / n ] 1/2 = { ( di ) 2 / n } 1/2 ; Variance: Another expression for essentially the same quantity is the variance or mean squared deviation. The variance is a convenient quantity to use in many computations becoz variances are additive. The standard deviation, however, has the advantage of being of the sane units as the variable, making it easy to compare magnitudes. Most scientific results are now stated in terms of standard deviation. Variance (V) = mean square deviation = (σ) 2 ; Probable Error: The probable error is a value describing the probability distribution of a given quantity. It defines the half-range of an interval about a central point for the distribution, such that half of the values from the distribution will lie within the interval and half outside. Thus it is equivalent to half the inter quartile range The term also has an older meaning (sometimes stated as the only meaning), that has been deprecated for some time: it is denoted γ and defined as a fixed multiple of the standard deviation, σ, where the multiplying factor derives from the normal distribution, more specifically. γ = σ Gaussian Curve: In probability theory, the normal (or Gaussian) distribution is a very common continuous probability distribution. Normal distributions are important in statistics and are often used in the natural and social sciences to represent real-valued random variables whose distributions are not known.

5 PROCEDURE: 1. Take the 50 resistors of same value. 2. Connect two resistors in series with each other. 3. Apply 2V to the circuit. 4. Measure voltage across one resistor. 5. Change that Resistor each time. 6. Take 50 readings. 7. Calculate the mean, deviation, standard deviation, average deviation using the given formula. 8. Calculate Probable error. OBSERVATION TABLE: Resistance (Ω) Voltage (V) Mean Deviation Average deviation Standard Deviation Variance Probable Error CONCLUSION:

6 ASSIGNMENT NO. 2 TITLE: Multimeter PROBLEM STATEMENT: Perform following using Multimeter 1. Measurement of dc voltage, dc current, ac (rms) voltage, ac (rms) current, resistance and capacitance. Understand the effect of decimal point on resolution. Comment on bandwidth 2. To test continuity, PN junction and transistor. OBJECTIVE: To understand the functionality of multimeter. To use Multimeter for various application. REQUIREMENT: Resistors, Capacitors, Diode, Transistor, Multimeter, DC power supply, Bread board, Function generator. THEORY: The digital multimeter is one of the most versatile electrical instruments, capable of acquiring a variety of measurements. Digital multimeters are easy to use and are a necessity when testing and debugging electronics or electrical circuits. Digital multimeters have multiple functionality and serve as a voltmeter, ammeter, and ohmmeter combined in one package. Controls of DMM:- a) Digital Display Liquid crystal display with automatic decimal point positioning. Updated two times per second. When the meter is turned on, all display segments appear while the instrument performs a brief power-up self-test. b) Functions Selector Rotary Switch Turn to select any of 10 different functions, or OFF. Volts-dc Millivolts-dc Ohms (resistance), also conductance in nanosiemens (ns) Continuity or diode test Milliamps or amperes dc Microamps dc Milliamps or amperes ac Microamps ac

7 c) Volt, Ohms, Diode test input terminal - Input terminal used in conjunction with the volts, mv (ac or dc), ohms, or diode test position of the function selector rotary switch. d) COM Common Terminal Common or return terminal used for all measurements. e) Milliamp/Microamp Input terminal Input terminal used for current measurements upto 320 ma (ac or dc) with the function selector rotary switch in the ma or µa positions. ma (ac or dc) with the function selector rotary switch in the ma or µa positions f) A amperes Input Terminals- Input terminal used for current measurements up to 10 A continuous. g) Overload Indication These symbols indicate the input is too large for the input circuitry. ( The location of the decimal point depends on the measurement range) h) Overflow Indication These symbols indicate the calculated difference in the Relative mode is too large to display (> 3999 counts) and that the input is not overloaded. Measurement of Parameters:- a) Voltage Measurement A digital multimeter can be used as a voltmeter to determine the potential voltage difference across several leads of an electrical component or from a lead referenced to ground. To measure the voltage across two leads, place the positive terminal on the lead with higher voltage (if known) and the negative terminal on the lead with a lower voltage. To measure the voltage of a specific location referenced to ground. Connect the positive terminal to the desired location and the negative terminal to ground. When used as a voltmeter, the digital multimeter has very large input impedance and thus draws very little current. b) Current Measurement A digital multimeter can be used as an ammeter to determine the current flow through a wire or electrical component. This measurement is accomplished by placing the digital multimeter in series with the wire that the current is flowing through, When used as an ammeter, the digital multimeter has a very small impedance (resistance) resulting in a small voltage drop across the multimeters leads. c) Diode and transistor testing Diode, Transistor testing is critical for the semiconductor and telecommunications industries. Because of this demand a select number of digital multimeters have a mode that easily allows the user to make diode measurements. The process for

8 taking a diode testing involves supplying the diode with a constant current source and reading the resulting voltage drop across the leads. PROCEDURE: 1. Measuring DC voltage and DC current i. Select Mode as DC. ii. Connect two resistors in series with each other. iii. Apply 5V DC supply across resistors. iv. Measure voltage across one resistor and current in series. v. Note down the reading. vi. Select a range with a maximum greater than we expect the reading to be. vii. Connect the meter, making sure the leads are the correct way round. viii. If the reading goes off the scale, immediately disconnect and select a higher range. 2. Measuring rms voltage and rms current i. Select Mode as AC. ii. Connect two resistors in series with each other. iii. Apply 5V AC sine signal from function generator. iv. Measure voltage across one resistor and current in series. v. Note down the reading. vi. Select a range with a maximum greater than we expect the reading to be. vii. Connect the meter, making sure the leads are the correct way round. viii. If the reading goes off the scale, immediately disconnect and select a higher range. 3. Measuring Resistance. i. Use multimeter in Ohm mode. ii. Connect two probes of multimeter to leads of resistor. iii. Note down the reading. iv. Select a range with a maximum greater than we expect the reading to be. v. Connect the meter, making sure the leads are the correct way round. vi. If the reading goes off the scale, immediately disconnect and select a higher range. 4. Measuring Capacitor. i. Use multimeter in capacitance measuring mode. ii. Insert capacitor in capacitance measurement slot on multimeter. iii. Note down the reading. iv. Select a range with a maximum greater than we expect the reading to be. v. Connect the meter, making sure the leads are the correct way round. vi. If the reading goes off the scale, immediately disconnect and select a higher range.

9 5. Testing continuity. i. Place the rotary switch on continuity position. ii. Connecting two probes, there is beep indicating continuity. 6. Testing diode. i. Place the rotary switch on diode position. ii. Use multimeter in capacitance measuring mode. iii. Connect the red (+) lead to the anode and the black (-) to the cathode. The diode should conduct and the meter will display a value (usually the voltage across the diode in mv, 1000 mv= 1 V). iv. Reverse the connections. The diode should not conduct this way so the meter except for a 1 on the left. 7. Testing transistor. i. Place the rotary switch on diode position. ii. Test each pair of leads both ways: The base emitter (BE) junction should behave like a diode and conduct one way only. The base collector (BC) junction should behave like a diode and conduct one way only. The collector emitter (CE) should not conduct either way. iii. Place the rotary switch on hfe point. iv. Connect transistor in n-p-n-p (hfe) transistor testing slot. v. Observe the display value. If hfe value should be in the range

10 OBSERVATION TABLE: Sr. No. Parameter Theoretical Value Practical Value 1 DC - Voltage DC - Current 2 AC - Voltage AC - Current Resistor 3 4 Capacitor 5 6 Diode Transistor CONCLUSION:

11 ASSIGNMENT NO.3 TITLE: Cathode Ray Oscilloscope PROBLEM STATEMENT: Perform following using CRO 1. Observe alternate, chop modes. 2. Measure unknown frequency and phase using XY mode. 3. Perform locking of input signal using auto, normal, external, rising and falling edge trigger modes. 4. Verify calibration, level, astigmatism, ac, dc, ground, attenuator probe operations OBJECTIVE: To understand the functionality of CRO. How to use CRO for various applications. REQUIREMENT: Function generator, CRO. THEORY: The cathode-ray oscilloscope (CRO) is a common laboratory instrument that provides accurate time and amplitude measurements of voltage signals over a wide range of frequencies. Its reliability, stability, and ease of operation make it suitable as a general purpose laboratory instrument. The heart of the CRO is a cathode-ray tube shown schematically in Fig.. 1. The cathode ray is a beam of electrons which are emitted by the heated cathode (negative electrode) and accelerated toward the fluorescent screen. The assembly of the cathode, intensity grid, focus grid, and accelerating anode (positive electrode) is called an electron gun. Its purpose is to generate the electron beam and control its intensity and focus. Between the electron gun and the fluorescent screen are two pair of metal plates - one oriented to provide horizontal deflection of the beam and one pair oriented to give vertical deflection to the beam. These plates are thus referred to as the horizontal and vertical deflection plates. The combination of these two deflections allows the beam to reach any portion of the fluorescent screen. Wherever the electron beam hits the screen, the phosphor is excited and light is emitted from that point. This conversion of electron energy into light allows us to write with points or lines of light on an otherwise darkened screen

12 Fig 1. Front panel of CRO The device consists mainly of a vacuum tube which contains a cathode; anode, grid, X&Y-plates, and a fluorescent screen (see Figure below). When the cathode is heated (by applying a small potential difference across its terminals), it emits electrons. Having a potential difference between the cathode and the anode (electrodes), accelerate the emitted electrons towards the anode, forming an electron beam, which passes to fall on the screen. When the fast electron beam strikes the fluorescent screen, a bright visible spot is produced. The grid, which is situated between the electrodes, controls the amount of electrons passing through it thereby controlling the intensity of the electron beam. The X&Y-plates are responsible for deflecting the electron beam horizontally and vertically. A sweep generator is connected to the X-plates, which moves the bright spot horizontally across the screen and repeats that at a certain frequency as the source of the signal. The voltage to be studied is applied to the Y-plates. The combined sweep and Y-voltages produce a graph showing the variation of voltage with time, as shown in Fig. 2 Fig 2. Internal structure of CRT As you can see, the screen of this oscilloscope has 8 squares or divisions on the vertical axis, and 10 squares on divisions on the horizontal axis. Usually, these squares are 1 cm in each direction.

13 Front Panel Controls: 1. XY: Switch when pressed cut off the time base & allows access to the external horizontal signal to be fed through CH2 (used for X-Y display). 2. CH1/2, Trig ½ : Switch selects channel & trigger source(released CH1 & pressed CH2) 3. Ext: Switch when pressed allows external triggering signal to be fed from the socket marked Trigger input. 4. Alt: Selects alternate trigger mode from CH1 & CH2.In this mode both the signals are synchronized. 5. Slope (+/-): Switch selects the slope of triggering, whether positive going or negative going. 6. Auto/level: Selects Auto/level position. Auto is used to get trace when no signal is fed at the input. In Level position the trigger level can be varied from the positive peak to negative peak with level control. 7. Level : Controls the trigger level from peak to peak amplitude of signal. 8. Trigger Input : Socket provided to feed external trigger signal in External Trigger mode. 9. AC/ DC /GND: Input coupling switch for each channel. In AC the signal is coupled through 0.1MFD capacitor. 10. Alt / Chop/Add: Switch selects alternate or chopped in Dual mode. If Mono is selected then this switch enables addition or subtraction of channel i.e.ch1 ± CH Intensity: Controls the brightness of the trace. 12. Mono/dual: Switch selects Mono or Dual trace operation. Operating Modes: For selecting either channel, CH1/CH2 is pressed or released, while selecting either channel; it also selects triggering of respective channels. For selecting both the channels, Dual is pressed The alternate or chop can be selected by pressing Alt/Chop switch. For addition of channel, release Mono/Dual switch & press Alt/Chop push button, which will display addition of CH1 & CH2? Similarly, subtraction of CH1- CH2 can be achieved by pressing Invert CH2 & Add mode. For X - Y operation the "XY" button must be pressed. The X signal is connected via the input of channel 2. Measure unknown frequency and phase using XY mode: Two sinusoidal inputs are applied to the oscilloscope in X-Y mode and the relationship between the signals is obtained as a Lissajous figure. To generate a Lissajous pattern two

14 different signals are applied to the vertical and horizontal inputs of the CRO. Earlier this technique used to measure frequencies before the frequency meter were discover. A signal generally sine wave of unknown frequency was applied to horizontal input and a frequency whose value is known applied to the vertical input of CRO. The pattern observed was depending on the ratio of the two frequencies applied to the vertical and horizontal inputs. Fig 3 Lissajous pattern for Phase shift Fig 4 Lissajous pattern for Phase shift PROCEDURE: Observe Alt/Chop Mode: 1. Alt: Alternate mode draws each channel alternately - the oscilloscope completes one sweep on channel 1, then one sweep on channel 2, a second sweep on channel 1, and so on. Use this mode with medium- to high-speed signals, when the sec/div scale is set to 0.5 ms or faster. 2. Chop mode causes the oscilloscope to draw small parts of each signal by switching back and forth between them.

15 Measurement of unknown frequency and phase: 1. Set the oscilloscope to XY mode 2. Ground or zero each channel separately and adjust the line to the center (vertical or horizontal) axis of the display. (On analog scopes, you can ground both simultaneously and center the resulting dot.) 3. Return to AC coupling to display the ellipse. Frequency Measurement: i. Two signal generators are used; consider the first generator as the standard frequency source where as frequency from the second function generator is considered as unknown frequency. ii. Set the frequency of generator one to 1 khz, vary the frequency of second function generator until a stable Lissajous pattern is displayed to the screen of CRO. iii. Trace the pattern, record the number of horizontal and vertical tangents and frequency of second function generator. iv. Repeat the procedure for 4-5 unknown frequencies it will give different Lissajous pattern. Phase Measurement: i. Two signal generators are used, consider the first generator as the standard signal source of known phase where as signal from the second function generator is considered as unknown phase. ii. Measure the horizontal width x1, x2, y1, y2 as shown in the figure below. iii. Repeat the procedure for 4-5 unknown frequencies it will give different Lissajous pattern. OBSERVATION TABLE: 1. Frequency 2. Phase - α = Sin -1 (Y 1 /Y 2 ) CONCLUSION: GRAPH: Draw waveform of alt, chop mode, XY mode for frequency and phase measurement.

16 ASSIGNMENT NO.4 TITLE: Digital Storage Oscilloscope. PROBLEM STATEMENT: Perform following using DSO Perform Roll, Average, Peak detection operations on signal Capture transients Perform FFT analysis of sine and square signals Perform various math operations like addition, subtraction and multiplication of two waves OBJECTIVE: To understand the functionality of DSO. How to use DSO for various applications. REQUIREMENT: Function generator, DSO. THEORY: Digital storage oscilloscopes (often referred to as DSOs) were invented to remedy many of the negative aspects of analog oscilloscopes. DSOs input a signal and then digitize it through the use of an analog-to-digital converter. Figure 1 shows an example of one DSO architecture used by Agilent digital oscilloscopes. The attenuator scales the waveform. The vertical amplifier provides additional scaling while passing the waveform to the analog-to-digital converter (ADC). The ADC samples and digitizes the incoming signal. It then stores this data in memory. The trigger looks for trigger events while the time base adjusts the time display for the oscilloscope. The microprocessor system performs any additional post processing specified before the signal is finally displayed on the oscilloscope. Having the data in digital form enables the oscilloscope to perform a variety of measurements on the waveform. Signals can also be stored indefinitely in memory. The data can be printed or transferred to a computer via a flash drive, LAN, or DVD-RW.

17 Fig.1 Block Diagram of DSO Trigger Type: The oscilloscope has six types of triggers: Edge, Video, Pulse Width, Slope, Overtime and Swap. Edge Trigger uses the analog or digital test circuits for triggering. It happens when the input trigger source crosses a specified level in a specified direction. Video Trigger performs a field or line trigger through standard video signals. Pulse Width Trigger can trigger normal or abnormal pulses that meet trigger conditions. Slope Trigger uses the rise and fall times on the edge of signal for triggering. Overtime Trigger happens after the edge of signal reaches the set time. Swap Trigger, as a feature of analog oscilloscopes, gives stable displays of signals at two different frequencies. Mainly it uses a specific frequency to switch between two analog channels CH1 and CH2 so that the channels will generate swap trigger signals through the trigger circuitry. Data Acquisition When you acquire an analog signal, the oscilloscope will convert it into a digital one. There are two kinds of acquisition: Real-time acquisition and Equivalent acquisition. The real-time acquisition has three modes: Normal, Peak Detect, and Average. The acquisition rate is affected by the setting of time base. Normal: In this acquisition mode, the oscilloscope samples the signal in evenly spaced intervals to establish the waveform. This mode accurately represents signals in most time. However, it does not acquire rapid variations in the analog signal that may occur between two samples, which can result in aliasing and may cause narrow pulses to be missed. In such cases, you should use the Peak Detect mode to acquire data.

18 Peak Detect: In this acquisition mode, the oscilloscope gets the maximum and minimum values of the input signal over each sample interval and uses these values to display the waveform. In this way, the oscilloscope can acquire and display those narrow pulses that may have otherwise been missed in Normal mode. However, noise will appear to be higher in this mode. Average: In this acquisition mode, the oscilloscope acquires several waveforms, averages them, and displays the resulting waveform. You can use this mode to reduce random noise. Equivalent Acquisition: This kind of acquisition can be utilized for periodic signals. In case the acquisition rate is too low when using the real-time acquisition, the oscilloscope will use a fixed rate to acquire data with a stationary tiny delay after each acquisition of a frame of data. After repeating this acquisition for N times, the oscilloscope will arrange the acquired N frames of data by time to make up a new frame of data. Then the waveform can be recovered. The number of times N is related to the equivalent acquisition rate. Time Base: The oscilloscope digitizes waveforms by acquiring the value of an input signal at discrete points. The time base helps to control how often the values are digitized. Use the SEC/DIV knob to adjust the time base to a horizontal scale that suits your purpose. DSO features: a) Pre- trigger function: (observation of waveforms before triggering) The DSO is capable of recording the waveforms preceding the triggering point. It continuously stores data until a trigger occurs storing is stopped at the predefined no. Of sampling after the trigger &then the stored data is displayed with the trigger point as reference. b) Observation of single shot events: A DSO can capture single _shot events such as power supply, start up characteristics, power resets, power failure detection counter measures against noise & instantaneous waveforms for areas that include mechanical equipments such as motors. The DSO can be used for failure monitoring purposes such as storing waveforms. c) Large memory capacity: DSO stores the observed data in memory. Memory capacity is unlimited. With a large memory capacity, phenomenon can be recorder over a long period. d) Computations: Since the collected waveform data is expressed as digital values, sophisticated computation processing can be performed on the waveform data &the

19 results are displayed on the screen in real time. This enables various functions such as auto set up function. e) Data output: Digitization of waveforms data allows various forms of output. For e.g. by incorporating a printer in the digital oscilloscope, the display on the screen can be immediately printed out and time consuming. Application: Automotive technicians use oscilloscopes to diagnose electrical problems in cars. University labs use oscilloscopes to teach students about electronics. Research groups all over the world have oscilloscopes at their disposal. Cell phone manufacturers use oscilloscopes to test the integrity of their signals. The military and aviation industries use oscilloscopes to test radar communication systems. R&D engineers use oscilloscopes to test and design new technologies. Oscilloscopes are also used for compliance testing. Examples include USB and HDMI where the output must meet certain standards.. PROCEDURE: 1. Connect sine input from function generator to DSO. 2. Observe the waveform in Roll mode on low time scale. 3. Observe the waveform Average and peak detection mode. 4. Using MATH menu perform FFT of Sine and square wave. 5. Connect two inputs from signal generator to both channel of DSO. 6. Now perform mathematical operation form MATH menu as Addition, Subtraction and multiplication. 7. Plot all the observed waveforms on graph paper. OBSERVATION TABLE: CONCLUSION: GRAPH: Draw waveform of roll mode, average detection, peak detection, addition, subtraction, multiplication, FFT of sine and square.

20 ASSIGNMENT NO.5 TITLE: True RMS Meter. PROBLEM STATEMENT: Study of true RMS meter Measure RMS, peak, and average voltages for half controlled rectifier or Full controlled rectifier by varying firing angle. OBJECTIVE: To understand use of true RMS meter. How to use RMS meter in different applications. REQUIREMENT: True RMS meter, half controlled rectifier, full controlled rectifier, probes. THEORY: Complex waveforms are most accurately measured with a true RMS responding voltmeter. This instrument produces a meter indication by sensing waveform heating power, which is proportional to the square of the RMS value of the voltage. This heating power can be measured by feeding an amplified version of the input waveform to the heater element of a thermocouple whose output voltage is then proportional to E 2 RMS. One difficulty with this technique is that the thermocouple is often non-linear in its behavior. This difficulty is over come in some instruments by placing two thermocouples in the same thermal environment, as shown in the block diagram of the true RMS responding voltmeter of Figure 1. The effect of the non-linear behavior of the couple in the input circuit (the measuring thermocouple) is cancelled by similar non-linear effects of the couple in the feedback circuit (the balancing thermocouple). The two couple elements form part of a bridge in the input circuit of a DC amplifier. The unknown AC input voltage is amplified and applied to the heating element of the measuring thermocouple. The application of heat produces an output voltage that upsets the balance of the bridge. The unbalance voltage is amplified by the DC amplifier and fed back to the heating element of the balancing thermocouple. Bridge balance will be re-established when the feedback current delivers sufficient heat to the balancing thermocouple, so that the voltage outputs of both couples are the same. At this point the DC current in the heating element of the feedback couple is equal to the AC current in the input couple. This DC current is therefore directly proportional to the effective, or RMS, value of the input voltage and is indicated on the meter movement in the output circuit of the DC amplifier. The true RMS value is measured independently of the waveform of the AC

21 signal, provided that the peak excursions of the waveform do not exceed the dynamic range of the AC amplifier. Fig. 1 Block diagram of True RMS Meter A typical laboratory-type RMS responding voltmeter provides accurate RMS readings of complex waveform having a crest factor (ratio of peak value to RMS value) of 10/1. At 10 per cent of full-scale meter deflection, where there is less chance of amplifier saturation, waveforms with crest factors as high as 100/1 could be accommodated. Voltages throughout a range of 100 μv to 300 V within a frequency range of 10 Hz to 10 MHz may be measured with most good instruments. True RMS Meters: Only meters that are specified as true RMS can determine the true RMS voltage of waveforms other than sine waves. Fig 2. Mater displaying rms voltage of inputs On some true RMS voltmeters, the true RMS value must be determined with two measurements.

22 1. Set voltmeter to volts DC and record the value. 2. Set voltmeter to volts AC and record the value = Vac TRMS Calculate V TRMS = (V dc 2 +Vac TRMS 2 ) Some true RMS meters will display the true RMS value directly. The meter measures Vac TRMS and V dc then completes the calculation below and displays the true RMS value. CONCLUSION:

23 PROBLEM STATEMENT: Study of programmable LCR-Q meter 1. Measure L, C & R. 2. Measure Q and Dissipation factor. OBJECTIVE: To understand the Functionality of LCR meter. How to use meter to measure L, C, R, Q and D. REQUIREMENT: LCR Q meter, resistors, capacitors, inductors, bread board, Meter probe, connecting wires. THEORY: ASSIGNMENT NO. 6 TITLE: Programmable LCR-Q meter. A digital LCR meter is used to measure Inductance (L), Capacitance (C), and Resistance (R), Quality factor and Dissipation factor. It has various ranges and desired range can be selected with the help of selector switch. The block diagram of LCR-Q meter is as shown in fig below. Fig 1. Block diagram of LCR-Q Meter

24 The basic principle used in the digital LCR meter is to measure the voltage across the component and current passing through the component under test, when the test signal is fed to the component. Theses processed voltages and current signals from the component under test are then fed to the digital integrator unit which finally enables a digital display unit which directly gives the value of the component under test. The measuring test signal is applied by an inbuilt oscillator to the component, through a selectable source resistor Rs. The signal current then flows to a current to voltage converter, which is essentially an Op-amp with the range resistor R R, connected in its feedback path. The op-amp drives the junction of component and R R to a virtual ground and hence R R does not change the current through the component. The voltage E1 and E2 are the vector quantities. Thus they are completely defining the characteristics of the component at a particular test frequency and signal level. Capacitance C α E 2 /E 1 α I/V Inductance L α E 1 /E 2 α V/I These ratios are adopted in the measurement modes and are obtained by dual slope integration method. For inductance measurement, a series equivalent circuit of an inductor is assumed while for capacitance measurement, a parallel equivalent circuit of assumed for the five ranges. Depending on the impedance of the unknown component, the values of Rs and R R are selected. For inductance measurement, the impedance of component is usually low and hence Rs is chosen much higher. This achieves a constant current drives to the component. The Rs decides the value of the current. For capacitance measurement, the impedance of component is high and Rs is chosen to be much low. Thus constant voltage drives is provided to the component under test. The voltage E 1 is applied as one input to differential amplifier. E 1 is then fed to a control switch, along with E 2. The greater of two is fed to average voltage detector (AVD) and the lasser to phase sensitive detector (PSD). The signal given to AVD is also given to PLL and voltage controlled oscillator (VCO). These two produce the clock signals, which are locked in phase with reference signal. The clock signal is then divided into phase shifted 90 0 and These are given to PSD. The PSD detects the phase angle. The dc voltage outputs from AVD and PSD are given to digital integrator unit and finally to digital display unit where the value of the component is displayed. The basic accuracy of digital LCR meter is ±0.15% of the reading, for wide range of values. The range selection is fully automatic. It automatically differentiates between inductors and capacitors. The display used is normally 4 digit LEDs with automatic decimal point.

25 Q Meter: The Q factor is called quality factor or the storage factor. It is defined as the ratio of power stored in the element to the power dissipated in the element. It is the magnification provided by the circuit. It is also defined as the ratio of reactance to resistance of a reactive element. Thus for inductive reactance it is the ratio of X L to R while for capacitance reactance it is the ratio of Xc to R. The Q meter is and instrument which is designed to measure some of the electrical properties of the coils and capacitors. It is very useful instrument. Principle of working: The principle of working of this useful instrument is based upon well characteristics of resonant series R, L, C circuit. Fig 2. Series resonant circuit At Resonant Frequency (f 0 ) we have X C =X L Where, X C = Capacitive Reactance L X L = Inductive reactance = f 0 = Resonant freq = I 0 =Current at resonance = F/R From phasor diagram: E c = I 0 X c = I 0 X L = = I 0 w 0 L Input Voltage E = I 0 R Hence, input voltage E is magnified Q times.

26 A Practical Q meter: A practical Q meter consists of a self inductance contained variable frequency RF oscillator. This oscillator delivers current to a low value shunt resistance (R S4 ). This low resistance of the order of few hundred Ω. A typical value may be 0.02 Ω. Though this resistance a small value of voltage E is injected. In resonance circuit, this value is measured by thermo couple voltmeter. Since, the value of shunt resistance is very low it introduces almost no resistance into oscillator circuit and therefore represent voltage source of magnitude E with very small internal resistance A calibrated std. variable c is used for resonating the circuit. An electronic voltmeter is connected across this capacitor. The coil under test is connected to terminals T 1 and T 2. Fig. 3 A practical Q meter. PROCEDURE: 1. Measurement of Resistor. a. Connect different resistors to LCR meter through probe. b. Select R and note down reading. 2. Measurement of Capacitor. a. Connect different capacitors to LCR meter through probe. b. Select C and note down reading. 3. Measurement of Inductor. a. Connect different inductor to LCR meter through probe. b. Select L and note down reading. 4. To measure Q and D. a. Connect R and C in series using bread board. b. Press series button. c. Now press C and Note down Q/D reading. d. Connect R and C in parallel using bread board. e. Press parallel button. f. Now press C and Note down Q/D reading. g. Connect R and L in series using bread board. h. Press series button. i. Now press L and Note down Q/D reading.

27 j. Connect R and L in parallel using bread board. k. Press parallel button. l. Now press L and Note down Q/D reading OBSERVATION TABLE: Sr. No Parameter Theoretical Value Practical Value 1 Resistor 2 Capacitor 3 Inductor 4 RC Series 5 RC Parallel 6 RL series 7 RL Parallel Q = Q = D = D = Q = Q = D = D = Q = Q = D = D = Q = Q = D = D = CONCLUSION:

28 ASSIGNMENT NO.7 TITLE: Spectrum Analyzer PROBLEM STATEMENT: Study of spectrum analyzer. 1. Perform harmonic analysis and Total Harmonic Distortion (THD) measurement for sine and square waves 2. Verify frequency response of filters & high frequency (HF) amplifier. 3. Analyze Spectrum of AM & FM and to measure percent modulation and bandwidth. OBJECTIVE: To understand the Functionality of spectrum analyzer. How to use spectrum analyzer for different measurements. To know the various use of spectrum analyzer. REQUIREMENT: Spectrum analyzer, probes, connecting wires, digital function generator or arbitrary function generator. THEORY: The most common way of observing a signal is to display it on an oscilloscope, with time as the x-axis. This is a view of the signal in the time domain. It is also very useful to display signals in the frequency domain. This measurement method, often providing unique information unavailable, or practically unavailable, I the time-domain view, is called spectrum analysis. The instrument providing this frequency-domain view is the spectrum analyzer. On its CRT, the spectrum analyzer provides a calibrated graphical display, with frequency on the horizontal axis and voltage on the vertical axis. There are two types of spectrum analyzers: scanning types, which scan in frequency, and non scanning types, also called real-time spectrum analyzers. The scanning types are essentially swept receivers, both super heterodyne and tuned RF (TRF), whose tuning is electrically swept over the frequency range of observation by a scanning signal that also controls the horizontal position of the can only look at a single frequency at a given instant. The spectrum analyzer that we are using the laboratory is the swept spectrum analyzer.

29 The Swept Super heterodyne Spectrum Analyzer Fig. 1 Basic Block Diagram of Swept super heterodyne SA Figure1 above is the basic block diagram of a spectrum analyzer covering the range of 500 khz to 1GHz which is representative of the super heterodyne type. The input signal is fed into a diode mixer, which is driven to saturation by a strong signal from the local oscillator, which is linearly tunable electrically over the range of 2 to 3, GHz. The input mixer multiplies (heterodynes) the input signal and local oscillator signal together and so provides two signals at its output that are proportional in amplitude to the input signal but of frequencies that are the sum and difference between the frequencies of the input signal and the local oscillator signal. The intermediate-frequency amplifier is tuned to a narrow band around 2 GHz. As the local oscillator is tuned over the range from 2 to 3 GHz, only input signals that are expected from the local-oscillator frequency by 2 GHz will be converted to the intermediate frequency band, pass through the intermediate frequency amplifier, be rectified in the detector, and produce a vertical deflection on the CRT. The spectrum analyzer will also be sensitive to signals from 4 to 5 GHz. A low-pass filter with a cutoff a little above 1 GHz at the input suppresses these spurious signals. Fig 2 below is a more detailed block diagram of the spectrum analyzer. The frequency of the first local oscillator is controlled with a select ably attenuated signal from the scan generator combined with an adjustable bias level from the centre frequency control in the voltage control block. The attenuator controls the frequency axis calibration of the display by controlling the frequency range over which the first local oscillator is scanned. The adjustable bias level sets the frequency about which the local oscillator is scanned and thus the centre frequency of the display. Several conversions are used in the intermediate-frequency amplifier chain, which ultimately gets down to a 3-MHz intermediate-frequency amplifier having a bandwidth of a few hundred hertz to provide this high selectivity over the whole range of the instrument. The high first intermediate frequency is necessary for wide image separation, the low last intermediate frequency is necessary for narrow-band filtering unobtainable at the first intermediate frequency.

30 Fig. 2 Block diagram of Spectrum Analyzer Frequency Resolution and Bandwidth - Frequency resolution is the ability of the spectrum analyzer to separate signals closely spaced in frequency. Two factors determine resolution, the bandwidth or selectivity of the intermediate-frequency amplifier and the frequency stability of the spectrum analyzer, as determined by the drift, residual FM, and phase noise of the local oscillators. The scanning action in the spectrum analyzer slides the input spectrum past the final intermediate-frequency amplifier filter. Because of this, the magnified display of a singlefrequency continuous-wave signal is a plot of the frequency selectivity characteristic of the intermediate-frequency amplifier filter. Therefore, two continuous-wave signals with a separation of less than the intermediate-frequency bandwidth would both be in the same passband at the same time and would not be distinguished. The other factor determining resolution is the frequency stability of the spectrum analyzer local oscillators. These oscillators must have greater absolute stability than any signals that are to be analyzed and resolved. Residual FM in the spectrum analyzer will smear the display, and phase noise will add noise skirts to the filter skirts, both reducing resolution. Sweep Desensitization - Sweep desensitization is an effect, caused by scanning a spectrum analyzer too fast, which results in loss of amplitude calibration, sensitivity, and resolution. During scan the signal must remain in the bandpass of the intermediate-frequency filter long enough to allow the amplitude of the signal in the filter to build up to the proper value. To avoid desensitization, the scan velocity in hertz must not exceed the square of the 3-dB

31 bandwidth of the intermediate-frequency filter in hertz. The frequency resolution of the spectrum analyzer is also reduced by this effect because the displayed time-domain transient response of the filter masks its frequency-selectivity characteristic. Sensitivity - The ability of the swept super heterodyne spectrum analyzer to measure small signals is determined by its own internally generated noise. Typical noise figures vary from 24 db at low frequency to 40 db at 12 GHz. The internally generated noise referred to the spectrum analyzer input exceeds basic thermal noise by these noise figures. The noise on the spectrum analyzer display is that contained only within the passband of its intermediate-frequency filter. Although the spectrum analyzer covers a wide frequency range it is a narrow-band instrument and therefore very sensitive to continuous-wave signals. Noise power is proportional to bandwidth, and so the highest sensitivity to continuous-wave signals is obtained by using the narrowest bandwidths. Dynamic Range - The dynamic range of the spectrum analyzer expresses its ability to display the true spectra of large and small signals simultaneously. With signal levels within the dynamic range of the instrument, spurious signals, which result from the distortion of the large signals by the analyzer itself and could either mask the small signals or erroneously appear as small signals, will not appear on the display. The dynamic range that is free of spurious signals can be defined as the ratio of the signal level to the noise level at signal levels where spurious distortion products just begin to become visible above the noise level of the display. Harmonic Mixing - Harmonic mixing is used to extend the frequency range of the swept super heterodyne spectrum analyzer. Harmonic mixers respond to several input frequencies simultaneously, but pre selection filter can be used to eliminate the confusion. Bandpass broadband filters can help with higher order harmonic mixing modes, but the most effective solution is a tracking narrow-band filter which can be adjusted to track a desired harmonic mixing mode as the spectrum analyzer is tuned and scanned. Such a filter is the YIG filter, consisting of one or more coupled yttrium-iron-garnet resonators whose resonant frequency is proportional to the strength of the field from an electromagnet in which they are placed. This filter can be biased and electrically swept to allow only the signal matching a desired mixing mode to enter the input mixer.

32 PROCEDURE: 1. Apply 1 KHz sine wave from function generator to spectrum analyzer and observe the harmonic and total harmonic distortions. 2. Note the readings. 3. Do the same procedure for Square wave. 4. Generate AM signal from digital function generator or arbitrary waveform generator. Note down amplitude and frequency of carrier and modulating signal. 5. Calculate the modulation index, bandwidth and total power. 6. Connect AM signal to spectrum analyzer. Observe AM signal in frequency domain. 7. Note down Power in main lobe and side bands with frequency. 8. Note down bandwidth also. (Verify theoretical and practical values.) 9. Generate FM signal from digital function generator or arbitrary waveform generator. Note down amplitude and frequency of carrier and modulating signal. 10. Calculate the modulation index, bandwidth and total power. 11. Connect FM signal to spectrum analyzer. Observe FM signal in frequency domain. 12. Note down Power in main lobe and side bands with frequency. 13. Note down bandwidth also. (Verify theoretical and practical values.) OBSERVATION TABLE: Sr. No Parameter/ Signal Measurements Harmonic Analysis THD 1 Sine 2 Square Theoretical Values Practical Values 3 AM Vm= f m = Vm= f m = Vc= f c = Vc= f c = m = Pc = m = Pc = at f P LSB = P LSB = at f P USB = P USB = at f P t = BW = P t = BW = 3 AM Vm= f m = Vc= f c = m = Vm= f m = Vc= f c = m =

33 No. of sidebands = Pc = P LSB = P USB = No. of sidebands = Pc = at f P LSB = at f P USB = at f P t = BW = P t = BW = FORMULAE: A. For AM signal, 1. P T = P C + P USB + P LSB 2. BW= 2F m 3. m= Vm/Vc. 4. f LSB = fc + fm 5. f USB = fc - fm 6. P t = P c (1+m 2 /2) B. For FM Signal, 1. m = δ /fm 2. P T = P C + P USB1 + P LSB1 + P USB2 + P LSB2 3. BW= 2(δ + Fs) CONCLUSION:

34 ASSIGNMENT NO.8 TITLE: Frequency Counter PROBLEM STATEMENT: Study of Frequency Counter 1. Carry out measurements through different modes of measurement. 2. Measure frequency, time, ratio, events & pulse width. OBJECTIVE: To understand the Functionality of frequency counter. How to use frequency counter for different measurements. REQUIREMENT: Two function generator, Probes. THEORY: Frequency is the rate of a repetitive event. If T is the period of a repetitive event, then the frequency f is its reciprocal, 1/T. Conversely, the period is the reciprocal of the frequency, T = 1/ f. Since the period is a time interval expressed in seconds (s), it is easy to see the close relationship between time interval and frequency. The standard unit for frequency is the hertz (Hz), defined as events or cycles per second. The frequency of electrical signals is often measured in multiples of hertz, including kilohertz (khz), megahertz (MHz), or gigahertz (GHz), where 1 khz equals one thousand (10 3 ) events per second, 1 MHz equals one million (10 6 ) events per second, and 1 GHz equals one billion (10 9 ) events per second. A device that produces frequency is called an oscillator. The process of setting multiple oscillators to the same frequency is called synchronization. A digital counter is basically a very simple device. It is, in essence, a comparator.it Compares an unknown frequency or time period to a known frequency or a known time period, depending upon whether frequency or period measurements are being made. The results of the comparisons are presented in an easy-to-read digital format. A digital counter consists of four basic elements: 1. Time base generator 2. Decimal counting units with display 3. An electronic switch (gate) 4. Signal input and wave shaping circuitry The time base generator generally consists of a crystal oscillator operating either at 1MHz or 10 MHz followed by a multi-stage divider (some inexpensive counters use the 60Hz AC power line frequency as a time base). A high frequency crystal oscillator is used so that a very accurate time base can be generated. The multistage divider reduces the oscillator frequency to one Hertz (one cycle per second).

35 Fig. 1Block diagram of Frequency counter The decimal counting units are the counting portion of a digital counter. Each DCU counts from zero to nine, reset to zero, and starts over again. As a counting unit goes from nine back to zero, it generates an output signal that is suitable for driving another DCU. Therefore DCU s can be strung together to allow counting to any desired value. Because the count value must generally be read by humans, each DCU is connected to a digital display that shows the value that the DCU has counted to. The electronic switch (or gate) is the element that allows the signal being counted to pass into the DCU s or to be disconnected from them. Because the switch must operate very fast (so that high frequency signals can be measured), it is normally constructed from a digital logic gate that has turn-on and turn-off times of a few nanoseconds (a few billionths of a second). The signal input and wave shaping circuitry is required for several reasons. First it is desirable that the device or circuit generating the signal to be measured be disturbed as little as possible. This requirement is generally satisfied by constructing the counter so that it requires very little signal current to operate. This is another way of saying that the counter has high input impedance. Second, the signal to be measured may be very small and require amplification before it can cause the DCU's to operate. Third, the DCU's are digital devices that will not operate properly with a sine wave, or other signal that changes amplitudes relatively slowly, as an input. Therefore, a major function of the signal input and wave shaping circuitry is to cause all signal transitions to occur in a few nanoseconds at the input to the DCU's. There is an additional counter element that was not included in the list above. The element in question controls counter operation and is, in some ways, the most complex portion of the entire device. However, it is not necessary to consider exactly how the