With the advancement of technology in intergrated circuits, instruments are becoming increasingly compact and accurate. This revision covers in detail the digital. Overview: This revised and up-to-date edition provides essential understanding on the working principles, operation and limitations of the electronic instruments. Sensors for Transducers Potentiometers, Differential transformers, Resistance strain gauges, Capacitance sensors, Eddy-current sensors, Pizoelectric.
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Electronic Instrumentation and Measurement - site edition by Rohit Khurana. Download it once and read it on your site device, PC, phones or tablets. Text book Electronic Instrumentation and Measurements David A bell 2nd edition .pdf. Wajeeh Rehman. Loading Preview. Sorry, preview is currently unavailable. Electronics Measurements and Instrumentation eBook & Notes - Download as PDF File .pdf), Text File .txt) or read online.
Well, the height of a person depends on how straight she stands, whether she just got up most people are slightly taller when getting up from a long rest in horizontal position , whether she has her shoes on, and how long her hair is and how it is made up.
These inaccuracies could all be called errors of definition. A quantity such as height is not exactly defined without specifying many other circumstances.
Even if you could precisely specify the "circumstances," your result would still have an error associated with it. The scale you are using is of limited accuracy; when you read the scale, you may have to estimate a fraction between the marks on the scale, etc. If the result of a measurement is to have meaning it cannot consist of the measured value alone. An indication of how accurate the result is must be included also.
Indeed, typically more effort is required to determine the error or uncertainty in a measurement than to perform the measurement itself. Thus, the result of any physical measurement has two essential components: For example, a measurement of the width of a table would yield a result such as Significant Figures: The significant figures of a measured or calculated quantity are the meaningful digits in it.
There are conventions which you should learn and follow for how to express numbers so as to properly indicate their significant figures. Any digit that is not zero is significant. Thus has three significant figures and 1. Zeros between non zero digits are significant. Thus has four significant figures.
Zeros to the left of the first non zero digit are not significant. Thus 0. This is more easily seen if it is written as 3. For numbers with decimal points, zeros to the right of a non zero digit are significant. Thus 2.
For this reason it is important to keep the trailing zeros to indicate the actual number of significant figures. For numbers without decimal points, trailing zeros may or may not be significant. Thus, indicates only one significant figure. To indicate that the trailing zeros are significant a decimal point must be added. For example, Exact numbers have an infinite number of significant digits. For example, if there are two oranges on a table, then the number of oranges is 2.
Defined numbers are also like this. For example, the number of centimeters per inch 2. There are also specific rules for how to consistently express the uncertainty associated with a number. In general, the last significant figure in any result should be of the same order of magnitude i. Also, the uncertainty should be rounded to one or two significant figures. Always work out the uncertainty after finding the number of significant figures for the actual measurement.
For example, 9. But in the end, the answer must be expressed with only the proper number of significant figures. After addition or subtraction, the result is significant only to the place determined by the largest last significant place in the original numbers. After multiplication or division, the number of significant figures in the result is determined by the original number with the smallest number of significant figures.
For example, 2. Refer to any good introductory chemistry textbook for an explanation of the methodology for working out significant figures. The Idea of Error: The concept of error needs to be well understood. What is and what is not meant by "error"? A measurement may be made of a quantity which has an accepted value which can be looked up in a handbook e. The difference between the measurement and the accepted value is not what is meant by error.
Such accepted values are not "right" answers. They are just measurements made by other people which have errors associated with them as well. Nor does error mean "blunder.
Electronic instrumentation fundamentals.
Obviously, it cannot be determined exactly how far off a measurement is; if this could be done, it would be possible to just give a more accurate, corrected value. Error, then, has to do with uncertainty in measurements that nothing can be done about.
If a measurement is repeated, the values obtained will differ and none of the results can be preferred over the others. Although it is not possible to do anything about such error, it can be characterized.
For instance, the repeated measurements may cluster tightly together or they may spread widely. This pattern can be analyzed systematically. Classification of Error: Generally, errors can be divided into two broad and rough but useful classes: Systematic errors are errors which tend to shift all measurements in a systematic way so their mean value is displaced.
This may be due to such things as incorrect calibration of equipment, consistently improper use of equipment or failure to properly account for some effect. In a sense, a systematic error is rather like a blunder and large systematic errors can and must be eliminated in a good experiment. But small systematic errors will always be present. For instance, no instrument can ever be calibrated perfectly.
Other sources of systematic errors are external effects which can change the results of the experiment, but for which the corrections are not well known. In science, the reasons why several independent confirmations of experimental results are often required especially using different techniques is because different apparatus at different places may be affected by different systematic effects.
Aside from making mistakes such as thinking one is using the x10 scale, and actually using the x scale , the reason why experiments sometimes yield results which may be far outside the quoted errors is because of systematic effects which were not accounted for.
Random errors are errors which fluctuate from one measurement to the next. They yield results distributed about some mean value. They can occur for a variety of reasons. They may occur due to lack of sensitivity.
For a sufficiently a small change an instrument may not be able to respond to it or to indicate it or the observer may not be able to discern it. They may occur due to noise. There may be extraneous disturbances which cannot be taken into account. They may be due to imprecise definition.
They may also occur due to statistical processes such as the roll of dice. Random errors displace measurements in an arbitrary direction whereas systematic errors displace measurements in a single direction.
Some systematic error can be substantially eliminated or properly taken into account. Random errors are unavoidable and must be lived with. Many times you will find results quoted with two errors. The first error quoted is usually the random error, and the second is called the systematic error. If only one error is quoted, then the errors from all sources are added together.
In quadrature as described in the section on propagation of errors. A good example of "random error" is the statistical error associated with sampling or counting. For example, consider radioactive decay which occurs randomly at a some average rate. If a sample has, on average, radioactive decays per second then the expected number of decays in 5 seconds would be Behavior like this, where the error, , 1 is called a Poisson statistical process.
Typically if one does not know that,. Mean Value Suppose an experiment were repeated many, say N, times to get, , N measurements of the same quantity, x. If the errors were random then the errors in these results would differ in sign and magnitude.
So if the average or mean value of our measurements were calculated,. This is the best that can be done to deal with random errors: It should be pointed out that this estimate for a given N will differ from the limit as the true mean value; though, of course, for larger N it will be closer to the limit.
In the case of the previous example: Doing this should give a result with less error than any of the individual measurements. But it is obviously expensive, time consuming and tedious. So, eventually one must compromise and decide that the job is done. Nevertheless, repeating the experiment is the only way to gain confidence in and knowledge of its accuracy.
In the process an estimate of the deviation of the measurements from the mean value can be obtained. Measuring Error There are several different ways the distribution of the measured values of a repeated experiment such as discussed above can be specified. Maximum Error The maximum and minimum values of the data set, In these terms, the quantity,. And virtually no measurements should ever fall outside. Probable Error The probable error, measured values.
Standard Deviation For the data to have a Gaussian distribution means that the probability of obtaining the result x is, , 5.
Because of the law of large numbers this assumption will tend to be valid for random errors. And so it is common practice to quote error in terms of the standard deviation of a Gaussian distribution fit to the observed data distribution. This is the way you should quote error in your reports. It is just as wrong to indicate an error which is too large as one which is too small.
Certainly saying that a person's height is 5' 8. Standard Deviation The mean is the most probable value of a Gaussian distribution. In terms of the mean, the standard deviation of any distribution is,.
The best estimate of the true standard deviation is,. The true mean value of x is not being used to calculate the variance, but only the average of the measurements as the best estimate of it. Thus, as calculated is always a little bit smaller than , the quantity really wanted.
In the theory of probability that is, using the assumption that the data has a Gaussian distribution , it can be shown that this underestimate is corrected by using N-1 instead of N. However, we are also interested in the error of the mean, which is smaller than sx if there were several measurements. An exact calculation yields,. The number to report for this series of N measurements of x is where. This means that out of experiments of this type, on the average, 32 experiments will obtain a value which is outside the standard errors.
Suppose the number of cosmic ray particles passing through some detecting device every hour is measured nine times and the results are those in the following table.
Principles of electronic instrumentation and measurement
Random counting processes like this example obey a Poisson distribution for which So one would expect the value of to be This is somewhat less than the value of 14 obtained above; indicating either the process is not quite random or, what is more likely, more measurements are needed.
The same error analysis can be used for any set of repeated measurements whether they arise from random processes or not. For example in the Atwood's machine experiment to measure g you are asked to measure time five times for a given distance of fall s. The mean value of the time is, , 9 and the standard error of the mean is,.
For the distance measurement you will have to estimate [[Delta]]s, the precision with which you can measure the drop distance probably of the order of mm. Propagation of Errors: Frequently, the result of an experiment will not be measured directly. Rather, it will be calculated from several measured physical quantities each of which has a mean value and an error.
What is the resulting error in the final result of such an experiment? A first thought might be that the error in Z would be just the sum of the errors in A and B. After all, 11 and. This could only happen if the errors in the two variables were perfectly correlated, i. If the variables are independent then sometimes the error in one variable will happen to cancel out some of the error in the other and so, on the average, the error in Z will be less than the sum of the errors in its parts.
A reasonable way to try to take this into account is to treat the perturbations in Z produced by perturbations in its parts as if they were "perpendicular" and added according to the Pythagorean theorem,.
This idea can be used to derive a general rule. If A is perturbed by then Z will be perturbed by. Similarly the perturbation in Z due to a perturbation in B is,. Combining these by the Pythagorean theorem yields. Errors combine in the same way for both addition and subtraction. You should be able to verify that the result is the same for division as it is for multiplication.
For example,. It should be noted that since the above applies only when the two measured quantities are independent of each other it does not apply when, for example, one physical quantity is measured and what is required is its square. If a variable Z depends on one or two variables A and B which have independent errors and then the rule for calculating the error in Z is tabulated in following table for a variety of simple relationships.
These rules may be compounded for more complicated situations. The design of a voltmeter, ammeter or ohmmeter begins with a current-sensitive element. Though most modern meters have solid state digital readouts, the physics is more readily demonstrated with a moving coil current detector called a galvanometer. Since the modifications of the current sensor are compact, it is practical to have all three functions in a single instrument with multiple ranges of sensitivity.
Schematically, a single range "multimeter" might be designed as illustrated. A voltmeter measures the change in voltage between two points in an electric circuit and therefore must be connected in parallel with the portion of the circuit on which the measurement is made.
By contrast, an ammeter must be connected in series. In analogy with a water circuit, a voltmeter is like a meter designed to measure pressure difference. It is necessary for the voltmeter to have a very high resistance so that it does not have an appreciable affect on the current or voltage associated with the measured circuit. Modern solid-state meters have digital readouts, but the principles of operation can be better appreciated by examining the older moving coil meters based on galvanometer sensors.
An ammeter is an instrument for measuring the electric current in amperes in a branch of an electric circuit. It must be placed in series with the measured branch, and must have very low resistance to avoid significant alteration of the current it is to measure. By contrast, an voltmeter must be connected in parallel. The analogy with an in-line flowmeter in a water circuit can help visualize why an ammeter must have a low resistance, and why connecting an ammeter in parallel can damage the meter.
The standard way to measure resistance in ohms is to supply a constant voltage to the resistance and measure the current through it. That current is of course inversely proportional to the resistance according to Ohm's law, so that you have a non-linear scale.
It is not an "Average" voltage and its mathematical relationship to peak voltage varies depending on the type of waveform. By definition, RMS Value, also called the effective or heating value of AC, is equivalent to a DC voltage that would provide the same amount of heat generation in a resistor as the AC voltage would if applied to that same resistor.
The heating value of the voltage available is equivalent to a volt DC source this is for example only and does not mean DC and AC are interchangeable.
The typical multi-meter is not a True RMS reading meter. As a result it will only produce misleading voltage readings when trying to measure anything other than a DC signal or sine wave.
Several types of multi-meters exist, and the owner's manual or the manufacturer should tell you which type you have. Each handles AC signals differently, here are the three basic types. A rectifier type multi-meter indicates RMS values for sinewaves only. It does this by measuring average voltage and multiplying by 1. Trying to use this type of meter with any waveform other than a sine wave will result in erroneous RMS readings.
Average reading digital volt meters are just that, they measure average voltage for an AC signal. Using the equations in the next column for a sinewave, average voltage Vavg can be converted to Volts RMS Vrms , and doing this allows the meter to display an RMS reading for a sinewave.
Bridge Measurements: A Maxwell bridge in long form, a Maxwell-Wien bridge is a type of Wheatstone bridge used to measure an unknown inductance usually of low Q value in terms of calibrated resistance and capacitance. It is a real product bridge. With reference to the picture, in a typical application R1 and R4 are known fixed entities, and R2 and C2 are known variable entities.
R2 and C2 are adjusted until the bridge is balanced. R3 and L3 can then be calculated based on the values of the other components:. To avoid the difficulties associated with determining the precise value of a variable capacitance, sometimes a fixed-value capacitor will be installed and more than one resistor will be made variable.
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The additional complexity of using a Maxwell bridge over simpler bridge types is warranted in circumstances where either the mutual inductance between the load and the known bridge entities, or stray electromagnetic interference, distorts the measurement results. The capacitive reactance in the bridge will exactly oppose the inductive reactance of the load when the bridge is balanced, allowing the load's resistance and reactance to be reliably determined. Wheatstone's bridge circuit diagram It is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.
Its operation is similar to the original potentiometer. Rx is the unknown resistance to be measured; R1, R2 and R3 are resistors of known resistance and the resistance of R2 is adjustable. R2 is varied until this condition is reached. The direction of the current indicates whether R2 is too high or too low. Detecting zero current can be done to extremely high accuracy see galvanometer. Therefore, if R1, R2 and R3 are known to high precision, then Rx can be measured to high precision.
Very small changes in Rx disrupt the balance and are readily detected. This setup is frequently used in strain gauge and resistance thermometer measurements, as it is usually faster to read a voltage level off a meter than to adjust a resistance to zero the voltage. The desired value of Rx is now known to be given as:. If all four resistor values and the supply voltage VS are known, the voltage across the bridge VG can be found by working out the voltage from each potential divider and subtracting one from the other.
The equation for this is:. The Wheatstone bridge illustrates the concept of a difference measurement, which can be extremely accurate. Variations on the Wheatstone bridge can be used to measure capacitance, inductance, impedance and other quantities, such as the amount of combustible gases in a sample, with an explosimeter. The Kelvin bridge was specially adapted from the Wheatstone bridge for measuring very low resistances.
In many cases, the significance of measuring the unknown resistance is related to measuring the impact of some physical phenomenon - such as force, temperature, pressure, etc. Schering Bridge: A Schering Bridge is a bridge circuit used for measuring an unknown electrical capacitance and its dissipation factor.
The dissipation factor of a capacitor is the the ratio of its resistance to its capacitive reactance. The Schering Bridge is basically a four-arm alternating-current AC bridge circuit whose measurement depends on balancing the loads on its arms. Figure 1 below shows a diagram of the Schering Bridge. The Schering Bridge In the Schering Bridge above, the resistance values of resistors R1 and R2 are known, while the resistance value of resistor R3 is unknown.
The capacitance values of C1 and C2 are also known, while the capacitance of C3 is the value being measured. To measure R3 and C3, the values of C2 and R2 are fixed, while the values of R1 and C1 are adjusted until the current through the ammeter between points A and B becomes zero. This happens when the voltages at points A and B are equal, in which case the bridge is said to be 'balanced'.
In an AC circuit that has a capacitor, the capacitor contributes a capacitive reactance to the impedance. Thus, when the bridge is balanced: A Hay Bridge is an AC bridge circuit used for measuring an unknown inductance by balancing the loads of its four arms, one of which contains the unknown inductance. One of the arms of a Hay Bridge has a capacitor of known characteristics, which is the principal component used for determining the unknown inductance value. Figure 1 below shows a diagram of the Hay Bridge.
The Hay Bridge: As shown in Figure 1, one arm of the Hay bridge consists of a capacitor in series with a resistor C1 and R2 and another arm consists of an inductor L1 in series with a resistor L1 and R4. The other two arms simply contain a resistor each R1 and R3. The values of R1and R3 are known, and R2 and C1 are both adjustable. The unknown values are those of L1 and R4.
Like other bridge circuits, the measuring ability of a Hay Bridge depends on 'balancing' the circuit. Balancing the circuit in Figure 1 means adjusting R2 and C1 until the current through the ammeter between points A and B becomes zero. This happens when the voltages at points A and B are equal.
Substituting R4, one comes up with the following equation: A Wien bridge oscillator is a type of electronic oscillator that generates sine waves. It can generate a large range of frequencies.
The circuit is based on an electrical network originally developed by Max Wien in The bridge comprises four resistors and two capacitors. It can also be viewed as a positive feedback system combined with a bandpass filter. Wien did. The modern circuit is derived from William Hewlett's Stanford University master's degree thesis. Hewlett, along with David Packard co-founded Hewlett-Packard. Their first product was the HP A, a precision sine wave oscillator based on the Wien bridge.
The A was one of the first instruments to produce such low distortion. Amplitude stabilization: The key to Hewlett's low distortion oscillator is effective amplitude stabilization. The amplitude of electronic oscillators tends to increase until clipping or other gain limitation is reached.
This leads to high harmonic distortion, which is often undesirable. Hewlett used an incandescent bulb as a positive temperature coefficient PTC thermistor in the oscillator feedback path to limit the gain. The resistance of light bulbs and similar heating elements increases as their temperature increases. If the oscillation frequency is significantly higher than the thermal time constant of the heating element, the radiated power is proportional to the oscillator power.
Since heating elements are close to black body radiators, they follow the Stefan-Boltzmann law. The radiated power is proportional to T4, so resistance increases at a greater rate than amplitude.
If the gain is inversely proportional to the oscillation amplitude, the oscillator gain stage reaches a steady state and operates as a near ideal class A amplifier, achieving very low distortion at the frequency of interest.
At lower frequencies the time period of the oscillator approaches the thermal time constant of the thermistor element and the output distortion starts to rise significantly. Light bulbs have their disadvantages when used as gain control elements in Wien bridge oscillators, most notably a very high sensitivity to vibration due to the bulb's microphonic nature amplitude modulating the oscillator output, and a limitation in high frequency response due to the inductive nature of the coiled filament.
Modern Wien bridge oscillators have used other nonlinear elements, such as diodes, thermistors, field effect transistors, or photocells for amplitude stabilization in place of light bulbs. Distortion as low. This is due to the low damping factor and long time constant of the crude control loop, and disturbances cause the output amplitude to exhibit a decaying sinusoidal response.
This can be used as a rough figure of merit, as the greater the amplitude bounce after a disturbance, the lower the output distortion under steady state conditions. Input admittance analysis If a voltage source is applied directly to the input of an ideal amplifier with feedback, the input current will be:. Where vin is the input voltage, vout is the output voltage, and Zf is the feedback impedance. If the voltage gain of the amplifier is defined as:.
If Av is greater than 1, the input admittance is a negative resistance in parallel with an inductance. The inductance is:. If a capacitor with the same value of C is placed in parallel with the input, the circuit has a natural resonance at:.
If the net resistance is negative, amplitude will grow until clipping occurs. Similarly, if the net resistance is positive, oscillation amplitude will decay. Notice that increasing the gain makes the net resistance more negative, which increases amplitude. If gain is reduced to exactly 3 when a suitable amplitude is reached, stable, low distortion oscillations will result.
Amplitude stabilization circuits typically increase gain until a suitable output amplitude is reached. As long as R, C, and the amplifier are linear, distortion will be minimal. Important Questions: What are the functional elements of an instrument? What is meant by accuracy of an instrument? Define international standard for ohm? What is primary sensing element? What is calibration? What are primary standards?
Where are they used? When are static characteristics important? What is standard? What are the different types of standards? Define static error. Distinguish reproducibility and repeatability. Distinguish between direct and indirect methods of measurements. With one example explain Instrumental Errors. Name some static and dynamic characteristics.
State the difference between accuracy and precision of a measurement. What are primary and secondary measurements? What are the functions of instruments and measurement systems? What is an error? How it is classified? Classify the standards of measurement? Define standard deviation and average deviation. What are the sources of error? Define resolution. What is threshold? Define zero drift. Write short notes on systematic errors. What are random errors? PART B 1. Describe the functional elements of an instrument with its block diagram.
And illustrate them with pressure gauge, pressure thermometer and DArsonval galvanometer. Draw the various blocks and explain their functions. Discuss in detail the various static and dynamic characteristics of a measuring system. Cathode-Ray Oscilloscope: The cathode-ray oscilloscope CRO is a common laboratory instrument that provides accurate time and aplitude 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. 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 ot 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 coversion of electron energy into light allows us to write with points or lines of light on an otherwise darkened screen. The signal applied to the verical plates is thus displayed on the screen as a function of time.
The horizontal axis serves as a uniform time scale. The linear deflection or sweep of the beam horizontally is accomplished by use of a sweep generator that is incorporated in the oscilloscope circuitry. The voltage output of such a generator is that of a sawtooth wave as shown in Fig. Application of one cycle of this voltage difference, which increases linearly with time, to the horizontal plates causes the.
When the voltage suddenly falls to zero, as at points a b c , etc The horizontal deflection of the beam is repeated periodically, the frequency of this periodicity is adjustable by external controls. To obtain steady traces on the tube face, an internal number of cycles of the unknown signal that is applied to the vertical plates must be associated with each cycle of the sweep generator. Thus, with such a matching of synchronization of the two deflections, the pattern on the tube face repeats itself and hence appears to remain stationary.
The persistance of vision in the human eye and of the glow of the fluorescent screen aids in producing a stationary pattern. In addition, the electron beam is cut off blanked during flyback so that the retrace sweep is not observed. CRO Operation: A simplified block diagram of a typical oscilloscope is shown in Fig.
In general, the instrument is operated in the following manner. The signal to be displayed is amplified by the vertical amplifier and applied to the verical deflection plates of the CRT. A portion of the signal in the vertical amplifier is applied to the sweep trigger as a triggering signal.
The sweep trigger then generates a pulse coincident with a selected point in the cycle of the triggering signal. This pulse turns on the sweep generator, initiating the sawtooth wave form. The sawtooth wave is amplified by the horizontal amplifier and applied to the horizontal deflection plates.
Usually, additional provisions signal are made for appliying an external triggering signal or utilizing the 60 Hz line for triggering. Also the sweep generator may be bypassed and an external signal applied directly to the horizontal amplifier.
CRO Controls: The controls available on most oscilloscopes provide a wide range of operating conditions and thus make the instrument especially versatile.
Since many of these controls are common to most oscilloscopes a brief description of them follows. Turns instrument on and controls illumination of the graticule. Focus the spot or trace on the screen. Regulates the brightness of the spot or trace.
Controls vertical positioning of oscilloscope display. Selects the sensitivity of the vertical amplifier in calibrated steps. Variable Sensitivity: Provides a continuous range of sensitivities between the calibrated steps. Normally the sensitivity is calibrated only when the variable knob is in the fully clockwise position.
Selects desired coupling ac or dc for incoming signal applied to vertical amplifier, or grounds the amplifier input. Selecting dc couples the input directly to the amplifier; selecting ac send the signal through a capacitor before going to the amplifier thus blocking any constant component. Selects desired sweep rate from calibrated steps or admits external signal to horizontal amplifier. Provides continuously variable sweep rates.
Calibrated position is fully clockwise. Controls horizontal position of trace on screen. Horizontal Variable: Controls the attenuation reduction of signal applied to horizontal aplifier through Ext.
Selects whether triggering occurs at a specific dc or ac level. Selects the source of the triggering signal. LINE - 60 cycle triger Level: Selects the voltage point on the triggering signal at which sweep is triggered.
It also allows automatic auto triggering of allows sweep to run free free run. A pair of jacks for connecting the signal under study to the Y or vertical amplifier. The lower jack is grounded to the case. Horizontal Input: A pair of jacks for connecting an external signal to the horizontal amplifier.
The lower terminal is graounted to the case of the oscilloscope. External Tigger Input: Input connector for external trigger signal. Provides amplitude calibrated square waves of 25 and millivolts for use in calibrating the gain of the amplifiers. Sensitivity is variable. Range of sweep is variable. Operating Instructions: Before plugging the oscilloscope into a wall receptacle, set the controls as follows: Plug line cord into a standard ac wall recepticle nominally V.
Turn power on. Do not advance the Intensity Control. Allow the scope to warm up for approximately two minutes, then turn the Intensity Control until the beam is visible on the screen. Set the signal generator to a frequency of cycles per second. Connect the output from the gererator to the vertical input of the oscilloscope.
Establish a steady trace of this input signal on the scope. Adjust play with all of the scope and signal generator controls until you become familiar with the functionof each. The purpose fo such "playing" is to allow the student to become so familiar with the oscilloscope that it becomes an aid tool in making measurements in other experiments and not as a formidable obstacle.
If the vertical gain is set too low, it may not be possible to obtain a steady trace. Measurements of Voltage: Consider the circuit in Fig.
The signal generator is used to produce a hertz sine wave. The AC voltmeter and the leads to the verticle input of the oscilloscope are connected across the generator's output.
The trace represents a plot of voltage vs. To determine the size of the voltage signal appearing at the output of terminals of the signal generator, an AC Alternating Current voltmeter is connected in parallel across these terminals Fig.
The AC voltmeter is designed to read the dc "effective value" of the voltage. The peak or maximum voltage seen on the scope face Fig. Agreement is expected between the voltage reading of the multimeter and that of the oscilloscope. In this position, the trace is no longer calibrated so that you can not just read the size of the signal by counting the number of divisions and multiplying by the scale factor.
However, you can figure out what the new calibration is an use it as long as the variable control remains unchanged. The mathematical prescription given for RMS signals is valid only for sinusoidal signals.
The meter will not indicate the correct voltage when used to measure non-sinusoidal signals. Frequency Measurements: When the horizontal sweep voltage is applied, voltage measurements can still be taken from the vertical deflection.
Moreover, the signal is displayed as a function of time. If the time base i. Frequencies can then be determined as reciprocal of the periods. Set the oscillator to Hz.
Display the signal on the CRO and measure the period of the oscillations. Use the horizontal distance between two points such as C to D in Fig. Set the horizontal gain so that only one complete wave form is displayed.
Then reset the horizontal until 5 waves are seen. Keep the time base control in a calibrated position. Measure the distance and hence time for 5 complete cycles and calculate the frequency from this measurement. Compare you result with the value determined above. Repeat your measurements for other frequencies of Hz, 5 kHz, 50 kHz as set on the signal generator.
Lissajous Figures: These stationary patterns are known as Lissajous figures and can be used for comparison measurement of frequencies.
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Use two oscillators to generate some simple Lissajous figures like those shown in Fig. You will find it difficult to maintain the Lissajous figures in a fixed configuration because the two oscillators are not phase and frequency locked. Their frequencies and phase drift slowly causing the two different signals to change slightly with respect to each other.
Testing what you have learned: Your instructor will provide you with a small oscillator circuit. Examine the input to the circuit and output of the circuit using your oscilloscope.
Measure such quantities as the voltage and frequence of the signals. Specify if they are sinusoidal or of some other wave character. If square wave, measure the frequency of the wave. Also, for square waves, measure the on time when the voltage is high and off time when it is low.
Q meter: For many years, the Q meter has been an essential piece of equipment for laboratories engaged in the testing of radio frequency circuits. In modem laboratories, the Q meter has been largely replaced by more exotic and more expensive impedance measuring devices and today, it is difficult to find a manufacturer who still makes a Q meter. For the radio amateur, the Q meter is still a very useful piece of test equipment and the writer has given some thought to how a simple Q meter could be made for the radio shack.
For those who are unfamiliar with this type of instrument, a few introductory notes on the definition of Q and the measurement of Q, are included. The Q factor or quality factor of an inductance is commonly expressed as the ratio of its series reactance to its series resistance. We can also express the Q factor of a capacitance as the ratio of its series reactance to its series resistance although capacitors are generally specified by the D or dissipation factor which is the reciprocal of Q.
A tuned circuit, at resonance, is considered to have a Q factor. In this case, Q is equal to the ratio of either the inductive reactance, or the capacitive reactance, to the total series loss resistance in the tuned circuit. The greater the loss resistance and the lower the Q, the greater the power lost on each cycle of oscillation in the tuned circuit and hence the greater the power needed to maintain oscillation.
Another way to derive Q is as follows: Sometimes we talk of loaded Q such as in transmitter tank circuits and, in this case, resistance for calculation of Q is the unloaded tuned circuit series resistance plus the additional loss resistance reflected in series into the circuit from its coupled load. There are other ways of expressing Q factor. It can be expressed approximately as the ratio of equivalent shunt resistance to either the inductive or the capacitive reactance.
Series loss resistance can be converted to an equivalent shunt resistance using the following formula: To measure Q factor, Q meters make use of this principle. A basic Q meter is shown in Figure 1. Terminals are provided to connect the inductance Lx to be measured and this is resonated by a variable tuning capacitor C. Terminals are also provided to add capacitance Cx , if required. The tuned circuit is excited from a tunable signal source which develops voltage across a resistor in series with the tuned circuit.
The resistor must have a resistance small compared to the loss resistance of the components to be measured so that its value can be ignored. A resistance of a mere fraction of an ohm is necessary. Metering is provided to measure the AC injection voltage across the series resistor and the AC output voltage across the terminals of the tuning capacitor.
The output measurement must be a high input impedance circuit to prevent loading of the tuned circuit by the metering circuit. Q factor is calculated as the ratio of. In practice, the signal source level is generally set for a calibrate point on the meter which measures injected voltage and Q is directly read from calibration on the meter which measures output voltage. Some of the uses of Q Meter: The Q meter can be used for many purposes.
As the name implies, it can measure Q and is generally used to check the Q factor of inductors. As the internal tuning capacitor has an air dielectric its loss resistance is negligible compared to that of any inductor and hence the Q measured is that of the inductor. The value of Q varies considerable with different types of inductors used over different ranges of frequency. Miniature commercial inductors, such as the Siemens B types or the Lenox-Fugal Nanored types, made on ferrite cores and operated at frequencies up to 1 MHz, have typical Q factors in the region of 50 to Air wound inductors with spaced turns, such as found in transmitter tank circuits and operating at frequencies above 10 MHz, can be expected to have Q factors of around to Some inductors have Q factors as low as five or 10 at some frequencies and such inductors are generally unsuitable for use in selective circuits or in sharp filters.
The Q meter is very useful to check these out. The tuning capacitor C of the Q meter has a calibrated dial marked in pico-farads so that, in conjunction with the calibration of the oscillator source, the value of inductance Lx can be derived. Providing the capacitor to be tested is smaller than the tuning range of the internal tuning capacitor, the test sample can be easily measured. Firstly, the capacitor sample is resonated with a selected inductor by adjusting the source frequency and using the tuning capacitor set to a low value on its calibrated scale.
The sample is then disconnected and using the same frequency as before, the tuning capacitor is reset to again obtain resonance. The difference in tuning capacitor calibration read for the two tests is equal to the capacitance of the sample.
Larger values of capacitance can be read by changing frequency to obtain resonance on the second test and manipulating the resonance formula. A poorly chosen inductor is not the only cause of low Q in a tuned circuit as some types of capacitor also have high loss resistance which lowers the Q. Small ceramic capacitors are often used in tuned circuits and many of these have high loss resistance, varying considerably in samples often taken from the same batch. If ceramic capacitors must be used where high Q is required, it is wise to select them for low loss resistance and the Q meter can be used for this purpose.
To do this, an inductor having a high Q, of at least , is used to resonate the circuit, first with the tuning capacitor C on its own and then with individual test sample capacitors in parallel. A drastic loss in the value of Q, when the sample is added, soon shows up which capacitor should not be used. Direct measurement of Q in an inductor, as discussed in previous paragraphs.
Inductors also have distributed. High distributed capacitance is common in large value inductors having closely wound turns or having multiple layers. Actual Q can be calculated from Qe, as read, from the following: Two methods of measuring distributed capacitance are described in the "Boonton Q Meter Handbook". The simplest of these is said to be accurate for distributed capacitance above 10 pF and this method is described as follows: With the tuning capacitor C set to value C1 say 50 pF , resonate with the sample inductor by adjusting the signal source frequency.
Set the signal source to half the original frequency and re-resonate by adjusting C to a new value of capacitance C2. Calculate distributed capacitance as follows: State the principle of digital voltmeter. Give the importance of iron loss measurement. List two instruments for measurement of frequency. Write the function of instrument transformer. Brief the principle of digital phase meter.
Write any two advantages and disadvantages of digital voltmeter. Explain the purpose of Schmitt trigger in digital frequency meter. Which torque is absent in energy meter? What are the errors that take place in moving iron instrument? Explain the principle of analog type electrical instruments. How a PMMC meter can be used as voltmeter and ammeter? What is loading effect? State the basic principle of moving iron instrument. Why an ammeter should have a low resistance? Define the sensitivity of a moving coil meter.
What is the use of Multimeter? Write its advantages and disadvantages. Voltmeter has high resistance, why it is connected in series? What is an energy meter? Mention some advantages and disadvantages of energy meter. What is meant by creep adjustment in three phase energy meter? List some advantages and disadvantages of electrodynamic instrument.
List the advantages of electronic voltmeter. What is a magnetic measurements and what are the tests performed for magnetic measurements? Mention the advantages and disadvantages of flux meter. What are the methods used to determine B-H Curve? What are the errors in instrument transformers? What is frequency meter and classify it? What is phase meter and what are its type?
Discuss why it is necessary to carry out frequency domain analysis of measurement systems?
What are the two plots obtained when the frequency response of a system is carried out? Explain the function of three phase wattmeter and energy meter. A function generator is a device which produces simple repetitive waveforms. Such devices contain an electronic oscillator, a circuit that is capable of creating a repetitive waveform. Modern devices may use digital signal processing to synthesize waveforms, followed by a digital to analog converter, or DAC, to produce an analog output.
The most common waveform is a sine wave, but sawtooth, step pulse , square, and triangular waveform oscillators are commonly available as are arbitrary waveform generators AWGs. Function generators are typically used in simple electronics repair and design; where they are used to stimulate a circuit under test. The amount of resistance that a resistor offers is measured in Ohms. Variable Resistor Potentiometer A variable resistor is also known as a potentiometer. These components can be found in devices such as a light dimmer or volume control for a radio.
When you turn the shaft of a potentiometer the resistance changes in the circuit. These are often found in exterior lights that automatically turn on at dusk and off at dawn. Capacitor Capacitors store electricity and then discharges it back into the circuit when there is a drop in voltage.
A capacitor is like a rechargeable battery and can be charged and then discharged. Diode A diode allows electricity to flow in one direction and blocks it from flowing the opposite way. Light-Emitting Diode LED A light-emitting diode is like a standard diode in the fact that electrical current only flows in one direction. The main difference is an LED will emit light when electricity flows through it.
Inside an LED there is an anode and cathode. The longer leg of the LED is the positive anode side. Transistor Transistor are tiny switches that turn a current on or off when triggered by an electric signal. In addition to being a switch, it can also be used to amplify electronic signals. A transistor is similar to a relay except with no moving parts. Relay A relay is an electrically operated switch that opens or closes when power is applied.
Inside a relay is an electromagnet which controls a mechanical switch. This circuit contains electronic components like resistors and capacitors but on a much smaller scale. Integrated circuits come in different variations such as timers, voltage regulators, microcontrollers and many more. What Is A Circuit? Before you design an electronic project, you need to know what a circuit is and how to create one properly.
An electronic circuit is a circular path of conductors by which electric current can flow. A closed circuit is like a circle because it starts and ends at the same point forming a complete loop. In contrast, if there is any break in the flow of electricity, this is known as an open circuit.
All circuits need to have three basic elements. These elements are a voltage source, conductive path and a load. The voltage source, such as a battery, is needed in order to cause the current to flow through the circuit. In addition, there needs to be a conductive path that provides a route for the electricity to flow. Finally, a proper circuit needs a load that consumes the power.
The load in the above circuit is the light bulb. Schematic Diagram When working with circuits, you will often find something called a schematic diagram. These symbols are graphic representations of the actual electronic components. Below is an example of a schematic that depicts an LED circuit that is controlled by a switch. It contains symbols for an LED, resistor, battery and a switch.
By following a schematic diagram, you are able to know which components to use and where to put them.Measurement system any of the systems used in the process of associating numbers with physical quantities and phenomena. siteGlobal Ship Orders Internationally. What is meant by creep adjustment in three phase energy meter?
As was pointed out earlier, all signals have a time characteristic, so we must consider the behavior of a block in terms of both the static and dynamic states. Over a single sweep of frequency, RF output voltage from the device, as a function of time, is a plot of the filter response.
DPReview Digital Photography. Not Enabled.
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