What is strain gauge ?

Engineer

 

Strain gauge if a metal conductor is stretched or compressed , it resistance changes on account of the fact that both length  and diameter of conductor change also there is a change in the value of registivity of the conductor when it is strain and these property is called piezo resistive effect.

Therefore, resistance strain gauge also called piezo resistive gauge.

                          Strain gauge is passive transducer. That uses variation in electrical resistance in wires to sense the strain produce by a force on wire.

★ Classification of  strain gauge :-

Write Applications of CRO ?

Engineer

Applications of CRO :-

1. There are huge applications of CRO in radio stations. It is true that our conventional.

2. CRO is not used in those radio station but they almost the same to our conventional CRO.

3. The CRO are used in the radio station to observe the sending and receiving signal properties.

4. CRO is used with the resonance circuit to observe the bandwidth, wave shope, etc.

5. Cro lso used to observe the characteristics of amplitude modulation circuits, frequency modulation  circuits, etc.

Block Diagram of CRO and Explain each part of CRO?

Engineer

The CRO stands for cathode ray oscilloscope. CRO is an electron test instrument , it is used to obtained wave forms when the different input signals are given the oscilloscope observes the changes in the electrical signals overtime. By seeing the waveforms, we can analyze sum properties like ampitude, freqency, rise time, distorchan, time interval etc.

              CRO consist of a set of blocks .The function each box of CRO in mentioned below.

1) Vertical ampilifier :-

                                   It ampilifies the input signal , which is to be displayed on the screen of CRT.

2) Delay line :-

                         It provides sum amount of delay to the signal , which is obtained and the output of vertical ampilifier. This delayed signal is then applied  to vertical deflection plates of CRT.

3) Trigger circuit :-

                             It provides a triggering signal in order to syndronize both horizontal and vertical deflection of electron beam.

4) Time base generator :-

                                       It produces a sawtooth signal sawtooth wave wories linearly 

with time and it causes movement of spot on screen with constant velocity.

5) Horizontal ampilifier :-

                                       It ampilifier the sawtooth signal and then connects its to the horizontal deflection plates of CRT.

6) Power supply :-

                              Power supply produces both high low voltages. high voltage is given negative high voltage to the CRT and low voltage are applied to other circuits. The power supply DC in nature.

7) CRT :-

               CRT is the major and important block. it consists of four parts these are electron gun, vertical deflection plates, horizontal deflection plates and fluoresent  screen.

                            

Explain Schering bridge ?

Engineer

             R1

        ____________

       |             |

       |             |

   ----|             |----

  |    |             |    |

VAC ---|             |---- R2

  |    |             |    |

   ----|             |----

       |             |

       |   Cx (Unknown) |

       |             |

       |             |

   ----|             |----

  |    |             |    |

  |    |             |    |

  |    |             |    |

  |    |   C (Variable) |

  |    |             |    |

  |    |             |    |

  |    |             |    |

   ----|_____________|----

       |             |

       |             |

THis bridge is used to measure to the  capacitor of the capacitor , dissipation factor and neasurent of relative permitivity. let us consider the circuit of she ring bridge as shown below :n

Here ., C, is the unknown capacitance whose value is to be determined with series electrical resistance r.

C2 is a standard capacitor.

C4 is a variable capacitor.

r3 is a pure resistor.

and r4 is a variable non inductive resistor connected in parallel with variable capacitor C4. Now the supply is given to the bridge b/wthe paints a and C. The detector is connected b/w b and d. from the theory of ac bridges we have at  balance condition.

                                  I1 1/N²A

The Schering bridge, also known as the Wien bridge or AC bridge, is a type of electrical circuit commonly used for measuring capacitance and resistance at high frequencies. It was invented by the German engineer and physicist Ernst Werner von Siemens in the late 19th century.

The Schering bridge is specifically designed to measure the capacitance of a capacitor or the resistance of a resistor in the presence of high-frequency alternating current (AC) signals. It is often employed in radio frequency (RF) and audio frequency (AF) applications.

The basic configuration of the Schering bridge consists of four arms: two fixed resistors, one variable capacitor, and one unknown component (either a capacitor or a resistor). The bridge is typically driven by an AC source, and the goal is to determine the value of the unknown component.

When the bridge is balanced, meaning that the voltage across the bridge is zero, the ratio of the resistances on one side of the bridge is equal to the ratio of the capacitances on the other side. This condition is achieved by adjusting the variable capacitor until the bridge is balanced.

By measuring the values of the known components and the settings of the variable capacitor when the bridge is balanced, it is possible to calculate the value of the unknown component. The balance condition can be determined by either measuring the voltage across the bridge using a voltmeter or by observing the null indication on an oscilloscope.

The Schering bridge is particularly useful for accurate measurement of small capacitance values, especially in applications where the effects of parasitic capacitances and stray capacitances need to be minimized. It is widely used in the design and testing of electronic circuits, especially in the field of telecommunications and audio equipment.

Overall, the Schering bridge is a versatile and effective tool for measuring capacitance and resistance at high frequencies, providing a reliable method for determining the values of unknown components in electrical circuits.

Explain Maxewell inductance bridge ?

Engineer

 

AC bridge is used for measureing the unknow impedence where  as DC bridge used for measuring unknow resistance.

                                             AC components are present in the arm ( resistive or reactive ) in DC bridges the arm contain resistiv3e components only maxewell bridge is madiflication to the wheatstone bridge , used to measure unknown impedence in terms of collibrated resistance and induction or resistance and capacitor.

The bridge circuit measure and inductance by comparison with a variable  standard self inductance with respect to diagram.

 

1) R1L1  are unknown parameters.

2) R2 is the coil resistance/ decand resistance.

3) R2 & L2 are variable resistance and inductance respectively.

4) R3 & R4 are fixed resistance a normally R3 & R4 are a selection of values from 10 , 1000 & 10,000Ω

★ Maxewell inductance capacitance bridge.

Maxewell inductance capacitance bridge here unknown self inductance to be determine is compared with standard unknown capacitor.

The Maxwell inductance bridge, also known as the Maxwell-Wien bridge, is a type of bridge circuit used for measuring inductance. It was developed by the Scottish physicist James Clerk Maxwell and the German physicist Wilhelm Eduard Weber in the 19th century. This bridge configuration is particularly useful for accurately determining the value of an unknown inductance in terms of known resistance and capacitance values.

The Maxwell inductance bridge consists of four arms or branches: two ratio arms, one of which contains a variable resistance (R) and an unknown inductance (L), and the other containing a fixed resistance (R') and a fixed capacitor (C). The remaining two arms consist of a known resistance (R1) and a known capacitor (C1) connected in series.

The primary principle behind the Maxwell inductance bridge is based on the balance condition, where the ratio of the impedance of the L-C branch to the impedance of the R-C branch is equal to the ratio of the resistances in the ratio arms. When the bridge is balanced, the voltage across the galvanometer connected between the two junction points of the ratio arms becomes zero.

By manipulating the variable resistance (R) in one of the ratio arms and observing the null indication on the galvanometer, the unknown inductance (L) can be determined. At the balanced condition, the inductance (L) can be calculated using the formula:

L = R' * C * (R1 / C1)

Where R' is the fixed resistance, C is the fixed capacitor, R1 is the known resistance, and C1 is the known capacitor.

The Maxwell inductance bridge is a highly accurate method for measuring inductance because it eliminates the need for precise calibration of the bridge components. By adjusting the variable resistance, the bridge can be balanced regardless of the absolute accuracy of the resistors and capacitors used.

Overall, the Maxwell inductance bridge provides a practical and reliable means of measuring unknown inductance values in various applications, including electrical engineering, electronics, and physics research.

★ Advantage of using standard capacitor.

1) low cost  compared to the stable and accurate standard inductor.

2) Capacitors used here are loss less and their is less possibility of loosing energy.

3) Capacitors are independent of external magnetic field.

            W.R.T diagram :-

1)  L1 is the unknown inductance to be measure.

2) R1 resistance of unknown inductor.

3)R2 &R3 are R2 & R3 each can be selected to 10, 100, 1000, 10,000Ω

4) R4 standard non inductive variable resistance.

5) C4 standard capacitance variable.

what are kelvin double bribge ?

Kelvin double bridge posses and extra ratio are connected in the bridge circuit and hence it is call (DSC). The first ratio are is P & Q the second ratio are p & q is used to connect the golvanometer to a point d at the  appropriate potential between points m & n to eliminate the effect of connecting lead of resistance r between the resistance are and standard resistance.

The Kelvin double bridge, also known as the Kelvin Varley bridge, is a specialized type of bridge circuit commonly used for precise resistance measurements. It was developed by the Scottish engineer William Thomson, also known as Lord Kelvin, in the 19th century. The Kelvin double bridge is designed to minimize errors caused by contact resistances and lead wire resistance, allowing for highly accurate resistance measurements.

The Kelvin double bridge is an extension of the basic Wheatstone bridge configuration and incorporates additional ratio arms and measurement techniques to improve accuracy. The bridge consists of four arms or branches: two ratio arms, one containing a variable resistance (R) and an unknown resistance (Rx), and the other containing fixed resistors (R1 and R2). The remaining two arms are used for voltage measurements and are known as the ratio arms.

The primary principle behind the Kelvin double bridge is based on the balance condition, where the ratio of the voltage across the unknown resistance (Rx) to the voltage across the variable resistance (R) is equal to the ratio of the resistors in the ratio arms. When the bridge is balanced, the voltage difference across the galvanometer connected between the two junction points of the ratio arms becomes zero.

The key advantage of the Kelvin double bridge is its ability to minimize errors caused by contact resistances and lead wire resistance. This is achieved by using a four-wire Kelvin connection, where two additional separate connections, known as the Kelvin sense leads, are made to the measurement points of the unknown resistance (Rx). By passing the measuring current through one pair of leads and sensing the voltage across the other pair of leads, the impact of contact resistances and lead wire resistance is effectively eliminated, allowing for accurate measurements of low-resistance values.

The Kelvin double bridge is widely used in applications where high precision resistance measurements are required, such as in metrology laboratories, calibration facilities, and electronic manufacturing. It provides a reliable and accurate method for determining unknown resistance values with minimal errors caused by contact and lead wire resistances.

                                    

What is range extension with shunt multiplier ?

RANGE EXTENSION :-

                                          The purpose of shunt is to increase the range of ammeter and the shunt resistance is connected in parallel with PMMC golvanometer without shunt , normal range of ammeter is 0 to 5 MA to 0 - 20 MA, with internal shunts ammeter range can be increased upto 0 - 200 A , while with externl shunts more range can be increased.

DC AMMETER :-

                              Current is the rate of flow of electronic charge. if this electronic charge flow only in one direction , then the resultant current is called DC current the instrument which is used to measure the DC is called DC ammeter.

                             If we place a resistance in parallel with the PMMC golvanometer , then the PMMC entire combination acts as DC ammeter. THe parallel resistnce which is used in DC ammeter is called shunt resistance or simply shunt.

                                       V = IR 

                                     ISH RSH = ImRm 

                                      RSH == ImRm/ Ish 一 (1) 

                                 Apply KCL o+ anode 1

                                         -I+ Ish+ Im = 0 

                                        Ish = I- Im

                              Substitute in eq ท

                                  RSh = ImRm/ISh 

                                   RSh = ImRm/ Im( I/Im -1)

                                    RSh = Rm/ I / Im -1

                             

                                       Multiplying factor

                                          m =I/Im 

                                    ∴ RSh = Rm/m-1

      ★   RSh is the shunt resistance .

      ★   Rm is internal resistance of golvanometer.

     ★    I is the DC current.

Circuit Diagram of Electronic Multimeter

The voltmeter which uses for increase sensitivity is known as electronic voltmeter. It is used measuring the voltages of both AC & DC devices. The electronic voltmeter gives the accurate reading because of it high input resistance.

The given diagram shows analog electronic voltmeter. this particular circuit is having. three stages.

 

1) Input attenuator

2) Amplifier circuit

3) voltage measurment stage

1) Input Attenuator:-

                                 In voltmeter range selection switch with the switch at position a, can  attenuator import of 1 volt is passed to the voltages measuring stage to gives (FSD) we can change the position of selection switch if it is at position D, as per voltage divider theorem attenuator.

           Output   →      Vi = E x R4 / R1+R2+R3+R4

                    E = Vi ( R1+R2+R3+R4/R4)

                      E = 1 (100 Ø)/4Ø )

                       E = 25V

                  Position,.

                                  A = 1V

                                  B = 5V

                                  C + 10V

                       Emox = 25V

2) Amplifier Stage :-  

                                 The main aim of this stage is to offer high input resistance and low output resistance. The amplifier has a voltage gain of one. It is said to be buffer between attenuator and voltage measure circuit. 

3) Voltage measurment stage:- 

                                                This is electromechanical (VMS) it is typically desined to give meter (FSD) for an amplifier output of one volt. lower value of voltages millivolt range can also be measure if amplifier gain is increased.

            

Advantages and Disadvantage of moving iron (MI) instrument ?

Advantages of moving iron :- 

★ It is a universal instrument which can be used for the measurment of AC and DC quantities.

 

★ The types of instrument have high value of torque to weight ratio.

★ It is very cheap due to simple.

 

Accuracy  of any instrument depend on its design and work man ship.

Disadvantage of moving iron instrument :-

  ★  These instruments suffer from error due to hysteresis , frequency change and stay losses.

  ★  THe scale o moving iron instrument is not uniform like PMMC instrument.

 

 ★    Power constraction is higher for low voltage range.

  ★    Change in frequency also caused error in aC measurement.

Write Advantage & Disadvantage of PMMC instrument ?

 →Advantage of PMMC:- 

★ The PMMC has uniformly divided scale.

    The scale may be very long , over about 250 degree.

★ The has very high torque to weight ratio.

 ★ THe PMMC has consumes low power.

 ★    The PMMC has very high occuracy.

→ Disadvantage of PMMC:-

★    It has comparitively high cost.

 ★   The PMMC has only suitable for DC measurement.

★    Again of permanent magnet and control spring introduces errors.

Explain moving iron instrument in detail ?

PRINCIPLE :- 

                             When iron pie is placed near the magnet it is attracted toward the magnet. The force of attraction depends on the strength of magnetic field.

           This type  of instrument is a used for measuring voltage or current.

Moving iron instrument are two types :-

 (1) ATTRACTION type MI. 

 (2) REPULSION type MI.

 

1. ATTRACTION type MI :- 

FIG:  Block diagram of Attraction type MI 

The figure shaws contructional detail of an attraction type moving iron instrument . The moving iron is a flate disc of a sector ecentrically mounted.

             The coil is also flate and has the narrow  slote like opening when the current flows through the coil, magnetic field is  produced and the moving iron moves from outside the coil to the stronger field inside the coil. 

The controlling torque is provided by spring.

Damping is provid by air friction with the  help of lite alluminium piston

2 REPULSION type :- 

FIG: block diagram of repulsion type MI 

In the repulsion type there are two vane or plate inside the coil one is fixed and another is movable . This are similarly magnetised when the current through the coil and there is the force of repulsion blue the vans resulting in the movement of moving vane. 

→ Two designs are possible in repulsion type MI.

1) Radical type 

2) Co-exiol type 

1) RADICAL type:- 

                                 In this type the vanes are radical streps of iron this trips are placed within the coil fixed vane to atteched to the coil and movable one is connected to the spindal. 

2) Co-exical type:-

In this type of instrument the fixed and moving vane are section of Co-exical cylender. The controlling torque is provided by spring gravity control can also be used in vertical movement instrument . The damping torque is produced by air , friction , as in attraction type instruments we can used both AC and DC the moving iron insturment are unpolorised instrument that is they are independent of the direction in which the current passes.

→ Derivation of moving iron instrument:- 

     Torque eq ท

   Small increase in curerent small deflection & same mechanical work will be done.

  TD→ Deflecting torque.

Mechanical → Torque x angular 

               deflection.

                       TD x DQ 一(1)

★ Due to change inductance , there is a change in energy strored in the magnetic field. current "I" is increased.

The small changed in current and this inductance is change from L+ dl. 

              

          Initially stored energy =1/2 LI ²

  Change in stored energy 

               = [ 1/2 (L+dl) (L+dI)² ]  -1/2  LI²

                

            = 1/2 (L+dl) (I² + dI² +2IdI)  -1/2 LI²

            

             Negatcing higher order terms.

            

           Finally stored → IdI + 1/2 I² dL 一 (2)

★ To increase the current by dI ,applyed voltage must be increase (V ∝ I) 

    Voltage e = d∅/  dt - d/ dt  (LI) ⇒ IdL/dt + ldI/ dt 

                                                           Total electrical energy

= eIdt 

= put evalue

= I [ IdL /dt + ldI / dt ]

= I²dl + ILdI 一一(3) 

Low of conservation of energy electrical = increase in machanical energy supplied stored + work done energy.

          

           Added all eqท (1) + (2) + (3)

           I²dL + ILdL = IldI + 1/2 I²dL+ IdL

         Id = 1/2 I²dl/d∅

Spring produces controlling torque = Id

            

                   TC ∝ Q 

                 TC = KQ         

              eqท TC  &  Td                          Deflecting torque

                  1/2 I²dl /dQ = KQ                           equal

                       Q ∝ I²                             controlling torque 

                         

Write the principle working and constraction of PMMC instrument ?

Engineer

(PMMC) Permanent magnet moving coil.

The PMMC instrument in most accurate type  for DC measurement 

The working principle of this instrument is same as aersoal type gol vonometer.

PRINCIPLE :-

                          When a movable coil is placed in the magnetic field it experience a torque and move .It represent the capability of a for to produced change in the rotation motion of body PMMC is only measure direct current D.C  the PMMC can be used  for direct current measurment only and induction type for A.C current measurment only remaining all meter can be used with either direct current of alternating current.

CONSTRUCTION :- 

(1) Moving Coil :- The moving coil is wound or rectangular form is made up of jewel bearing. The coils moves freely in the field of permanent magnet.

(2) Magnetic System :- Magnet  systems is a leader in convesational mobile interfaces providing superior user experience powered by  chatbots and Al.

(3) Deamping :- Deamping torque is provided by movement of aluminium former moving magnetic field of the permanent magnet pointer and scale.

WORKING :- Due to instructin blue stationary magnetic field created by magnet and magnet produced by flowing the current in coil it deflecting torque is produced.

                                       Td= BIL neuton

               

                                     B = Flux density 

                                     I = Current

                                     L = Length of coil 

                                     B = bridth of coil 

                                     A = Totel area of coil 

                                     Td= NBIL

                                                ↳  No.of  terms 

                               Deflecting torque → NBIL x b / NBIA 

                                                           Force area of coil 

             

                                               Td ∝ I                  Td=K I 

                    

                              Controlling torque       TC ∝ ∅

                          TC = C∅ →  Angular deflection 

                                   TD = TC

                               C  Ø  = KI

                                ∅    =  k/C

                                ∅ = I        /       ∅ ∝ I

               I

                           

Fundamental of DC Circuit

 click on the link - https://infinite6260.blogspot.com/ 

Engineer

Introduction:-

                          concept of charge, current ,voltage, EMF, resistance, resistivity, , conductance, conductivity, power and energy, ohm laws, KCL and KVL, series and Parallel combination, of resistances , star- delta connection, star to delta and delta to star, transformation, simple numerical problems , working principle , and application of primary and secondary cell.

Concept of charge:-

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field.

There are two types of electric charge positive or negative ( commonly carried by portion and electrons respectively).

Electrons are negatively charged while protons are positively charged.

The S.I unit of charged is coulomb and it is denoted by C.

The coulomb is defined as the quantity of electricity transported in one second by a current of one ampere.

Current :-

Electric current is defined as the rate of flow of negative charged of the conductor. In other word the continuous flow of electrons o=in an electric circuit is called an electric current. The conducting material consist a large no. of force electrons which moves from on atom to the other at random.

Since the charge is measured in coulombs and time in second so the unit of electric current is coulomb / second or ampere.

Types of Current :-

1. AC current

2. DC current

(1). Alternating Current (AC) :-

Charge in the circuit first move in one direction , then in other. 

(2). Direct Current (DC) :-

Flow of charge is one direction.

voltage is the pressure from an electrical circuit power source that bush charged electrons current through a conductivity loop ending them to do work such as aluminating a light.

In  brief voltage = Pressure and it is messured in volts(v).

Types of Voltage:-

1. AC voltage 

2. DC voltage

(1). AC voltage:-

→Reverse direction at regular intervals.

→Alternating voltage represented an a digital multimeter by V~.

(2). DC voltage:-

→Travels in a straight line and is one direction.

→ DC voltage represented an a digital multimeter by V-.

EMF :-

              Electromotive force is a measurement of the energy that causes current to flow through a circuit . It can also be defined as the potential difference in charge between two point in a circuit.

EMF is also known as voltage and it si measured in volts (V).

Resistance:-

Resistance is the measure of the opposite to the current flow in an electrical circuit.

It is denoted by R and its unit is ohm (Ω).

When an electric current of one ampere passes through a component across which a potential difference voltage of one volt exist then the resistance of that component is one ohm.

Low of Resistance:-

The value of resistance of a conductor or insulator depends upon the flowing factor.

1. The value of resistance of a conductor is directly proportional to its length i.e

                                                            R∝L.

2.The value of resistance of a conductor is inversely proportional to it cross sectional area.

                                                           R=L/A

3. The resistance of any conductor depends upon the types of material ar the resistivity of the conductor. 

                                                        R=FL/A

where, 

 R= Resistance in ohm

F= Resistivity in ohm cm

L= length of conductor in cm

A= Cross sectional area of conductor in Cm^2

Resistivity or specific Resistance :-

 Every conductor depending upon its shape or size oppose the flow of current flowing through its body this opposition flow of current is called resistivity.

Hence, the resistance of a conductor of 1cm in lenght having cross sectional area of 1cm^2 is called specific resistance of that conductor.

We know that-

                                                  R=∫L/A

   or, ∫= RA/L     =       ohm X cm^2/Cm           =        ohm - cm

unit is specific resistance is ohm-cm and is makes it is ohm - cm.

Conductor :-

Conductor is the measure of low easily electrical current can pass through a material conductor is the inverse of electrical resistance.

                             Conductor G= 1/R

unit of conductor is Mho (℧) or siemers.

Conductivity:-

Electrical conductivity or specific conductivity or specific conductance is the measure of material ability is conduct electric current.

conductivity or specific conductance.

                                        σ=1/∫

unit of conductance or specific conductance is siemen per cm or mho/cm.

Power & Energy:-

Power is defined as the time rate of doing work.

power= work done / time taken.

P=W/T

Horse power (HP) is the name of several unit of measurement of power.

1H.P= 746 Watt ( British system)

1 HP = 735.5 Watt ( Mks Unit)

Energy :-

Energy is defined as capacity or ability of doing work mathematically It is defined as a product of power & time.

Energy (E) Pxt

Where , P is NM or Watt

E= power X time

Ohm's low:-

Ohm low state that under constant temperature & constant Physical conditions the voltage (V) across a resister is directly proportional to current I flowing through the resister.

                                                    V∝I

Kirchhoff's Low:-

ohm low is not sufficient to analyse circuit . for analysis of circuit ohm's low is combines with kirchoff's low.

Kirchhoff's current low(KCL):-

kirchhoff's current low states that the algebri sum of combination meeting  at a point is zero.

                                       Σ^N ih= 0

                                       K=1

N is no. of branches connected to node point and K is the Kth current entering the node.

Since current I1, I3, and I4 are entering & I2, I5, are leaving the node.

I1+ I3+I4= I2+I5.

The sum of current entering a node is equal to the sum of the current leaving the nodes.

Kirchhoff's voltage low:-

Kirchhoff's voltage low state that the algebric sum of all voltage around a closed path is zero.

                                                     Σ^M Vl=0

                                                         l=1

M is the number of voltage in the losp and vl is the Lth voltage.

In  the given circuit diagram we start with the voltage source and go clockwise around the loop.

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