CLASS NOTES ON ELECTRICAL MEASUREMENTS & INSTRUMENTATION 2. DISCLAIMER. This document does not claim any originality and cannot . In this module we will learn the most important principles of making electrical measurements in general, i.e., to obtain voltages and currents using the. LECTURE NOTES. On. Electrical & Electronics Measurement. (PCEE). 3 rd. Semester ETC Engineering. Prepared by,. Priyabrata Sethy. Prasanta Kumar.
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ELECTRICAL AND ELECTRONIC MEASUREMENTS. 1. LECTURE NOTES. ON. ELECTRICAL AND DEPARTMENT OF ELECTRICAL ANDELECTRONICS. Engineering Class handwritten notes, exam notes, previous year questions, PDF free download. Electrical and Electronics. Measurements and Instrumentation. Prithwiraj Purkait. Professor. Department of Electrical Engineering and. Dean, School of.
The adjustment knob s are calibrated to show resonant frequency for any given setting, and the frequency is read from them after the device has been adjusted for maximum indication on the meter. Essentially, this is a tunable filter circuit, which is adjusted and then read in a manner similar to a bridge circuit which must be balanced for a null condition and then read.
This technique is a popular one for amateur radio operators or at least it was before the advent of inexpensive digital frequency instruments called counters , especially because it doesn't require direct connection to the circuit. In frequency as in other types of electrical measurement, the most accurate means of measurement are usually those where an unknown quantity is compared against a known standard, the basic instrument doing nothing more than indicating when the two quantities are equal to each other.
This is the basic principle behind the DC Wheatstone bridge circuit and it is a sound metrological principle applied throughout the sciences. If we have access to an accurate frequency standard a source of AC voltage holding very precisely to a single frequency , then measurement of any unknown frequency by comparison should be relatively easy.
For that frequency standard, we turn our attention back to the tuning fork, or at least a more modern variation of it called the quartz crystal.
Quartz is a naturally occurring mineral possessing a very interesting property called piezoelectricity. Piezoelectric materials produce a voltage across their length when physically stressed, and will physically deform when an external voltage is applied across their lengths. This deformation is very, very slight in most cases, but it does exist. Quartz rock is elastic springy within that small range of bending which an external voltage would produce, which means that it will have a mechanical resonant www.
In other words, if a chip of quartz is struck, it will ring with its own unique frequency determined by the length of the chip, and that resonant oscillation will produce an equivalent voltage across multiple points of the quartz chip which can be tapped into by wires fixed to the surface of the chip. In reciprocal manner, the quartz chip will tend to vibrate most when it is excited by an applied AC voltage at precisely the right frequency, just like the reeds on a vibrating-reed frequency meter.
Chips of quartz rock can be precisely cut for desired resonant frequencies, and that chip mounted securely inside a protective shell with wires extending for connection to an external electric circuit. When packaged as such, the resulting device is simply called a crystal or sometimes xtal.
The schematic symbol is shown in Figure below. Crystal frequency determing element schematic symbol. Electrically, that quartz chip is equivalent to a series LC resonant circuit.
Figure below The dielectric properties of quartz contribute an additional capacitive element to the equivalent circuit. The capacitance shown in parallel due to the wire connections across the dielectric insulating quartz body is real, and it has an effect on the resonant response of the whole system.
A full discussion on crystal dynamics is not necessary here, but what needs to be understood about crystals is this resonant circuit equivalence and how it can be exploited within an oscillator circuit to achieve an output voltage with a stable, known frequency. Crystals, as resonant elements, typically have much higher Q quality values than tank circuits built from inductors and capacitors, principally due to the relative absence of stray resistance, making their resonant frequencies very definite and precise.
Because the resonant frequency is solely dependent on the physical properties of quartz a very stable substance, mechanically , the resonant frequency variation over time with a quartz crystal is very, very low. This is how quartz movement watches obtain their high accuracy: by means of an electronic oscillator stabilized by the resonant action of a quartz crystal. For laboratory applications, though, even greater frequency stability may be desired. To achieve this, the crystal in question may be placed in a temperature stabilized www.
For the ultimate in a frequency standard though, nothing discovered thus far surpasses the accuracy of a single resonating atom. This is the principle of the so-called atomic clock, which uses an atom of mercury or cesium suspended in a vacuum, excited by outside energy to resonate at its own unique frequency.
The resulting frequency is detected as a radio-wave signal and that forms the basis for the most accurate clocks known to humanity. National standards laboratories around the world maintain a few of these hyper-accurate clocks, and broadcast frequency signals based on those atoms' vibrations for scientists and technicians to tune in and use for frequency calibration purposes.
Two Marks 1.
Name the different essential torques in indicating instruments. Deflecting torque Controlling torque Damping torque 2. Name the types of instruments used for making voltmeter and ammeter. No hysterisis loss Very accurate High effuiciency. How the range of instrument can be extended in PMMC instruments. In ammeter by connecting a shunt resister In voltmeter by connecting a series resister. Free from hysterisis and eddy current errors. State the advantages of Moving iron type instruments Less expensive Can be used for both dc and ac Reasonably accurate.
State the advantages of Hot wire type instruments Can be used for both dc and ac Unaffected by stray magnetic fields Readings are independent of frequency and waveform. What are the constructional parts of dynamometer type wattmeter? Write down the deflecting torque equation in dynamometer type wattmeter. Td VI Cos www. State the disadvantages of Dynamometer type wattmeter. Readings may be affected by stray magnetic fields.
At low power factor it causes error.
EE 33-Measurements and Instrumentation
Name the errors caused in Dynamometer type wattmeter. Error due to pressure coil inductance Error due to pressure coil capacitance Error due to methods of connection Error due to stray magnetic fields Error due to eddy current. How the errors caused by pc inductance is compensated. By connecting a capacitor in parallel to the resister. How the errors caused by methods of connection is compensated By using compensating coil.
Name the methods used for power measurement in three phase circuits. What are the special features to be incorporated for LPF wattmeter? Pressure coil circuit Compensation for Pressure coil current Compensation for Pressure coil inductance.
Define Phantom loading. Method by which energizing the pressure coil circuit and current coil circuits separately is called phantom loading. State the use of phantom loading. Power loss is minimized. Vacuum instruments Introduction to Actuators and Control Pressure Controllers Flow Control Actuators Power Control Magnetic control devices Motors Introduction to flow Flow Formulas of Continuity equation Bernoulli equation Flow losses Flow Measurement Instruments of Flow rate Total flow and Mass flow Dry particulate flow rate and Open channel flow Humidity Humidity measuring devices Density and Specific Gravity Density measuring devices Viscosity Viscosity measuring instruments Position and Motion Sensing Position and motion measuring devices Force, Torque, and Load Cells Force and torque measuring devices Smoke and Chemical Sensors Sound and Light Sound and light measuring devices Sound and light application considerations Each topic is complete with diagrams, equations and other forms of graphical representations for better learning and quick understanding.
Electrical Instrumentation is part of Electronics, Signals, and Measurement for Electrical Engineering and Computer Science engineering education courses and technology degree programs of various universities.
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Statics and Dynamics By R. Hibbeler Book April Force and torque measuring devices Chips of quartz rock can be precisely cut for desired resonant frequencies, and that chip mounted securely inside a protective shell with wires extending for connection to an external electric circuit. Meter movements relying on the motion of a mechanical needle rectified D'Arsonval, iron-vane, and electrostatic all tend to mechanically average the instantaneous values into an overall average value for the waveform.
As this panel has been removed from service, there are no current-carrying conductors threaded through the center of the CT donuts anymore: Figure below www. While the device shown above is somewhat crude and would suffer from unique engineering problems of its own, the concept illustrated is very sound. State the disadvantages of Dynamometer type wattmeter.