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Syllabus :, , , , - Indicating and display device : D’Arsonval movement, PMMC, moving iron, LCD, LED., - Analog and Digital meters : Type of analog and digital meters, volimeter, ammeter, ohmmete;, extension of measuring range of meters, applications of meters, Calibration of meters., , ae, , , , , , - The signals which continuously vary and take infinite, values for a given range are called as analog signals., The meter that produces analog signals is called as an, analog meter., , - Inanalog system the function continuously varies., , — Examples of analog instruments are deflection type, instruments like PMMC ammeter, voltmeter, null, deflection instruments like DC potentiometer,, Wheatstone meter bridge etc., , — The signals which vary in discrete steps and take finite, different values in the given range are called digital, signals. The meter which produces digital signals is, called as digital meter., , | me 2.2 Advantages of Digital Meters, , over Analog Meters, , , , , , , , , , , , , ua. 224 State ny two. disadvantage of, __. instruments. (Ans. : Refer Section, , 2 051(A)(c)2S-1742.Marks'B, State any {wo advantages. of digital, instruments over an. analog instruments, + Refer Section 2.2) —, , CQO Gans, , , , , , , , , , , , , , , , , , , , , , , , , , , @ The output of digital meter is in digital form. So output |, can be given to floppy disk, computers, printers for |, storage and future computations., , Gi) The power require of a digital meter is small as |, compared to analog meter. |, , (iii) The readings are clearly indicated in decimal numbers. |, So errors of reading on scale (i.e. human errors are ), avoided)., , (iv) The readings can be carried upto any number of, significant digits by placing the decimal point. So, |, accuracy of the digital meter can be increased., , (v) The resolution of digital meters is more than that of, , analog meters as the number of bits is more in digital |, meters., , Disadvantages of digital instrument, , 1. The main drawbacks of digital meters are that they are, , Costly and some of instruments are complex., , 2. So, inspite of these advantages the digital meters are, , not completely replaced by analog meters due to the, fact that analog meters are cheap and simple.

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Gm anew) Pane moe TEERCRION sal, , ‘efer Section 2.3), , , , CRIMEA eee, iQ. (a), S-17,.Q. 2(c), S-18. 4 Marks, , Q.'4(c),'S-18,°4 Marks, Q:4(b),‘W-18,"4 Marks, , , , BCs, , , , , , , , , , , , , , , , The meter that displays analog signals is, , The meter that displays digital signals is called as, , , , , , 1. | Principle, called as an analog instrument. a digital instrument., 2. | Accuracy Less The accuracy of digital is more as compared to, analog meter., 3. | Resolution The resolution of analog meters is less. The The resolution of digital meters is more. The, digital meters can be made with a resolution of, , analog meters can be made with a resolution, , " of one part in several hundreds., , one part in several thousands., , , , , , 4. | Power required, , The analog meters require more power. They, may even load the circuit under measurement, , resulting in erroneous measurement., , The digital meters require negligible power., , , , , , , , , , 5. | Cost Analog meters are cheap. Digital meters are expensive., , 6. | Portability The analog meters are extremely portable. The digital meters are not easily portable. They, They can be moved from one location to require an external source of power. However, another easily. modem developments have made the digital, , instruments extremely portable and cheap., , 7. | Observational | Analog meters have considerable Digital meters‘are absolutely free from the, , errors observational errors. observational errors., Logical analyzer, signature analyzer, computers,, , , , Examples, , , , , , , , PMMC instrument, Potentiometer, DC, ammeter, DC voltmeter etc., , , , microprocessor based instruments etc., , , , , , , , , , Took A-— D., — A SACHIN SHAH Venture, , , , , , __ Where Authors inspire innovation

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Electronics Measurements & Instrumentation (MSBTE) 2-3, , , , §= Indicating and display device, , The essential Torque in all measuring instruments :, There are three types of torques :, , Deflecting Torque (T,), , The deflecting torque moves the pointer (The moving, system of the instrument) on a calibrated scale., , This torque is proportional to quantity under, measurement. It is produced by using effects of electric, , current such as magnetic effect, heating effect,, chemical effect etc., , 2. Controlling Torque (T,), , 1, , The function of the controlling torque is :, “ (1). To stop the pointer at the correct position., (2) To bring the pointer back to the zero position, when the quantity under measurement is zero., The magnitude of the controlling torque is directly, Proportional to the deflection of the pointer and acts in, opposite in direction to the deflecting torque., When certain quantity (voltage or current) is applied to, the measuring instrument deflecting torque is produced., Magnitude of deflecting torque is directly proportional, to the quantity under measurement. The pointer get, deflected., As soon as pointer get deflected, controlling torque is, produce. Its magnitude goes on increasing as the, deflection of pointer increases., When T, = T, the pointer becomes stationary and, shows the steady reading., Controlling torque is produced by two methods, , (1) Spring control method and, (2) Gravity control method, , r i, , This is the most common method of providing, controlling torque. It makes use one or two spiral hair, springs attach to the spindle of the meter., , The inner ends of both the springs are attached to the, spindle while the outer end of the upper spring is attach, to a lever and the outer end of the lower spring is fixed., The two springs are oppositely wound., , Spring control, , , , , , , , , , , , Ani and Digitay Meten, - The material used for these springs shoulg be Electronics, magnetic having low specific resistance ang c 7 Advanta, ture coefficient of resistance,, temper “. (1) The sprin, — Material such as Phosphor — Bronze, Silicon-Brogy, eel aa is, German silver are used for this purpose. tg) Io ac, —. Some time these springs act as current leads for the coi these spr, attached to the spindle. coil of th, (3) As the s, ‘Scale no incre, KA high to, ; the ratic, Pointer TF = Balanced weight torque.), the spi, Gi SH Lever a, [ (4) Contro, { 5 ‘Spiral spring 7 Disady, (1) Chang:, BAR Jewel bearings pee, (2) Accid, Fig. 2.3.1 (a) : Spring control spring, o , . their e, — With the deflection of the pointer the spring are with, stay in opposite direction to the motion of the pointer wD ¢, and produce controlling torque., — It is indicated by T,. The magnitude of this torque is, directly proportional to the deflection of the pointer, Hence T, <@, }, Where @ = The angular deflection of the pointer in |, degree | ', - Magnitude of T, goes on increasing and it becomes ), equal to deflecting torque and the pointer shows steady, reading. If meter is an ammeter, deflecting torque (Ty), is directly proportional to current (T, wD, Hence @ «I ‘ Cs T.=T), - Hence in spring control instrunients the deflection of, pointer is directly proportional to the quantity under, measurement and hence the scale of these type of, » meters are uniform., Uniform scale, Fig. 2.3.1 (b) : Uniform scale Tech-Neo, , , , , , Tech Neo Publications... Where Authors inspire ianovation, , sewed SACHIN SHAH Venture

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g@ Advantages, , 4) The spring control meters. can be used in hori, well as in vertical position. sees, 2) In some instruments such as PMMC and dynamometer, these springs can be used as current lead: i, Is to the, coil of the meter. ere, 3) AS ve springs are light in weight, practically there is, no increase in the weight of the moving system hence, high torque to weight ratio (Torque to weight ratio is, the ratio of deflecting torque of meter to the frictional, torque.) Frictional torque is produce at the bearing of, the spindle. The magnitude of this torque is directly, proportional to the weight of the moving system. <, , 4 Controlling torque can be adjusted easily., , @ Disadvantages, , (1) Change of temperature affect the spring length and, , hence the magnitude of the controlling torque., , (2) Accidental stress in the springs may damage them and, springs may get a permanent set if stressed beyond, , their elastic limit., ® 2. Gravity control, T, csin@x/, , T, =wsin@x/, , T, = kgsin @, T, «sin®, 0, Pointer Scale, Spindle: Balance weight, Control weight, , (a), , , , 0), Fig. 2.3.2 : Gravity control, , , , umentation (MSBTE) 2-4, , Control weight, , , , In this type a small weight is placed on arm attach to, , the moving system., , The position of this weight is adjustable., , This weight produce controlling torque into gravity and, it is known as control weight., , Balance weight, , Balance weight is used to balance the weight of the, attached to the spindle. Hence it is present in spring, controlled and gravity controlled instrument., , When the pointer is on zero the magnitude of control, torque is zero and the control weight is in the position, , ” as shown in Fig. 1.7.2 (a)., , When the pointer get deflected through angle @, , j Fig. 1.7.2 (b) shows the position of control weight. Let, , the weight of the control weight is “w” and it is placed, at a distance / from the spindle., , Weight w acts vertically downward and can be resolved, into two component as w cos @ and w sin ©. Vertical, component produces the controlling torque which act in, , . opposite direction to the deflecting torque. Hence the, , controlling torque T, o w sin @, T, =Jwsind, T, =kgsin®, kg is known as gravity control constant weight., Thus, T, sin @, Thus the controlling torque is directly proportional to, , the sine of deflection angle., If Tye I the pointer become stationary when, , Ty =T,, , I sin®, , Hence the scale of gravity control instrument is non, uniform. It is cramped at the beginning and get, expanded towards the full scale deflection., , 0 7, Fig. 2.3.2(c), , A SACHIN SHAH Venture, , , , Tech-Neo Publications... Where Authors inspire innovation

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&, UQ. 2.4.1 Draw a diagram of D'Arsonval movement and stata its principle. RTE sea |, (Ans. : Refer Section 2.4) TTT mane, , UQ. 2.4.2 Draw the neat diagram of D' Arsonval movement meter. Derive the formula for pee oe, | (Ans. : Refer Section 2.4) 3 |, , 2 This type of construction consists essentially a moving Coil (current carrying element) which is Rectangular/Vertica ;,, shape and consist of a number of turns of fine wire., , Moving coil is suspended such that it is free to turn about its vertical axis of symmetry so and arranged in the air-gay, , between poles of a permanent horseshoe magnet and iron core. Iron core is cylindrical in shape if coil is rectangular,, , The coil is usually suspended by a Phosphor bronze or steel ribbon a few thousandths of an inch wide and less tha,, , 0.001 in. (0.025 mm) thick wire, or flat strip., , — This coil is free to rotate in the radial field between the shaped pole pieces of a permanent magnet, carries a small, mirror which serves as an optical pointer and indicates the coil position by reflecting a light beam onto a fixed scale., , , , , , Phosphor, bronze, ribbon, , , , , , , , , , Mirror, , Light, , source Aluminum —_ Upper, , frame Current source alent, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Qy (Bobbin) (Circuit under test), o—, Moving Mirror, Fixed coil Tron core, Seer iron core - ', wire on, bobbin, Horseshoe N u, permanent, magnet |, Former “suspension Permanent Let, magnet, Fig. 2.4.1 : Construction of D’Arsonval Instrument Fig. 2.4.2 : Construction of D’Arsonval Instrument, — The scale is away from the instrument about 1 m., Fe Current is conducted to and from the coil by the suspension ribbons., L The torque which deflects the indicating element is produced by the reaction of the coil current with the magnet field, | in which it is suspended., The strength of the fi field in the region occupied by the coil is increased by mounting a soft iron core in the central spac, Teet, , enclosed by the coil, the pole pieces being shaped to give a uniform field throughout the space in which the coil moves:, , , , Tech-Neo Publications...-.«.-WWhere Authors inspire innovation smu SACHIN SHAH Yeatart, , Es