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Active and passive Instruments

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Active and Passive Instruments: Active and passive Instruments Passive Instruments: The instruments where the output is produced completely by the quantity that is measured are called passive instruments. The example of passive instrument is a pressure gauge.Fig  shows a pressure gauge. Passive  Instrument As the pressure in the liquid changes, the piston moves.The pointer is connected to the piston. No other source of energy is used. The liquid pressure is the only source. Thus,the piston and pointer movement while measurement is entirely dependent on the liquid pressure. Active Instruments: Active instruments are the instruments in which the quantity to be measured activates the magnitude of external power input source that produces the measurement. The liquid level indicator is an example of an active instrument.Fig.1.4.2 shows a liquid level indicator. Active Instruments The power source is required in or...
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Classification of Instrumentation System

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Classification of Instrumentation System Instrumentation system Null and Deflection type Instruments: Deflection type instruments: The instruments in which deflection of the instrument forms the basis of measuremenl are called as deflection type instruments. The example of deflection type instruments is the permanent magnet moving coil (PMMC) ammeter. PMMC AMMETER The deflection of the coil is proportional to the current that is to be measured. Torque Td, that acts on the moving coil is proportional to current.The opposing effect is produced by a spring, having torque Tc which is proportional to the deflection. When the spring is balanced Tc=Td. The value of the current depends on the deflection.Thus,the value of the measured quantity depends upon the calibration of the instrument. Null type Instruments The instrument in which, a null or zero indication will lead to the determination of the magnitude of the measured quantity such instruments are c...
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Basic Principles of Transducer

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Basic Principles of Transducer Pressure Transducer The task of a process control system is to control the physical parameters like force, pressure, level etc and to maintain their value near the desired value.This is because the physical parameters may vary due to disturbances. To maintain these parameters at a required level certain corrective action requires to be taken. Fig. shows a process control loop. Process control loop The process control loop consists of four blocks process,parameter measurement, control element and controller. It is essential to measure the actual value of parameter P to achieve proper feedback. Nowadays most of the controllers are electronic and hence they require an electrical input. Thus,the feedback signal is required in electrical form. The measurement block includes two functions like to measure the parameter and to produce a suitable analog signal in electric form. Sometimes the parameter measurement...
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CLASSIFICATION OF NETWORKS

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CLASSIFICATION OF NETWORKS Classification of Network The electrical networks may be classified in a number of ways depending upon following. (i)the kind of elements of which the network is composed of and on the basis of their properties (ii)in terms of the general properties of its responses to excitation applied to its input terminals.Thus,we have linear and non linear networks, time invariant and time variant networks, active and passive networks etc.   Linearity: In a linear network, the voltage-current relationship is show by a linear equation. Suppose the network to be classified is under relaxed condition such that the initial condition is zero and an excitation e1(t)is applied for which the response is c1(t)and for excitation e2(t), the response is c2(t).Then the network is classified as linear if for excitation e1(t)+e2(t), the response is c1(t)+c2(t).This shows that a linearity follows superposition principle. Hence,from physical point of view, it ma...
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Basic Detail of Power Factor

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  Power Factor What is Power Factor ? It is the ratio of the active power of the fundamental wave the apparent power of  the fundamental waveform    Cause:    Inductive load which cause large difference of phase angle between current and voltage,Varying load,  industrial heating furnace, harmonic currents, electrical discharge lamp, AC motor, arc welder, furnaces, fluorescent lighting and air conditioning. Effect: overheating of motor and poor lightening.    Power factor correction: This is normally achieved by the addition of capacitors to the electrical network which compensate the active power. To reduce losses in the distribution system, and to reduce the clectricity bill, power factor correction, usually in the form of capacitors, is added to neutralize as ch of the magnetizing current as possible. Capacitor included leads the voltage, producing a leading power factor. The corrected power factor will be 0.92 to 0.95. Why to improv...
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