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Mr.C.MAGESH KUMAR / Ms. M.SURYA EIE/AIHT

ANAND INSTITUTE OF HIGHER TECHNOLOGY, Kazhipattur, Chennai-603 103 DEPARTMENT OF ELECTRONICS AND INSTRUMENTATION ENGINEERING

2 Marks and 16 Marks QUESTION BANK

Course code / Course Name: EI2251 / INDUSTRIAL INSTRUMENTATION I

YEAR / Semester: II A & B / IV Academic year: 2013-2014

COURSE CO-ORDINATOR: Mr.C.MAGESH KUMAR / Ms. M.SURYA

UNIT I - MEASUREMENT OF FORCE, TORQUE AND VELOCITY

Electric balance Different types of load cells Hydraulic, pneumatic strain gauge- Magneto elastic and

Piezo electric load cell Different methods of torque measurements: strain gauge-Relative angular twist-

Speed measurement:-Capacitive tacho-Dragcup type tacho-D.C and A.C tachogenerators Stroboscope.

PART-A (2 Marks)

1. Define Force. Force is defined as a mechanical quantity, an influence that causes an object to undergo a

certain change, either concerning its movement, direction, or geometrical construction.

Force may be defined as a cause that produces resistance or obstruction to any moving body, or

changes the motion of a body, or tends to produce these effects.

Force measurement is also done by electric means in which the force is first converted into

displacement at an elastic element and the displacement is measured. A vector quantity has both

magnitude and direction. Newton's second law states that the net force acting upon an object is

equal to the rate at which its momentum changes with time.

If a force of magnitude, F, is applied to a body of mass, M, the body will accelerate at a rate, A

(m/sec2), according to the equation: F = MA. Unit of force is the Newton (S I unit)

2. Define Stroboscope. (May 2013, May 2010) The stroboscope is a simple, portable manually operated device which may be used for

measurement of periodic or rotary motions.

A stroboscope having a scale that reads in flashes per minute or in revolutions per minute; the speed of a rotating device is measured by directing the stroboscopic lamp on the device,

adjusting the flashing rate until the device appears to be stationary, then reading the speed

directly on the scale of the instrument.

3. What are the applications of load cell? (Dec 2012) LOAD CELL are also called as FORCE METER

A load cell is a device that converts force into pressure. If the area on which the load is placed is

known then the calibration of force can be done directly.

Measurement of torque, force, pressure etc

4. What is the principle of DC tachogerator? (Dec 2012) Electromagnetic induction.

An emf is induced due to change in permanent magnetic flux. The induced emf is proportional

to flux and rotational speed.

DC tachogenerator converts mechanical energy into electrical energy when a conductor moves in

a magnetic field.

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Mr.C.MAGESH KUMAR / Ms. M.SURYA EIE/AIHT

5. Define load cell. (Dec 2009) / What is the function of load cell (Dec 2010) LOAD CELL are also called as FORCE METER

A load cell is a device that converts force into pressure. If the area on which the load is

placed is known then the calibration of force can be done directly.

It is defined as a transducer that converts an input mechanical force into an electrical output

signal. It is commonly known as Load transducers or load sensor.

6. What are the types of Load cell? (May 2013, Dec 2011, May 2011) i. Hydraulic Load Cell

ii. Pneumatic Load Cell iii. Magneto Elastic Load Cell iv. Piezo Electric Load Cell v. Strain Gauge Load Cell

7. What is the principle of Strain Gauge measurement? This type of load cell converts the load acting in them into electrical signal. The strain gauges are

bonded onto the beam that deforms when weight is applied. This change in the dimension of the

strain gauge causes its resistance to change. This change in resistance becomes a measure of the

applied force / quantity.

8. Define magneto-elastic effect? Magneto-elastic load cell works in principle of Magneto elastic principle called as Villari effect.

When a ferromagnetic material undergoes a mechanical stress, it changes the magnetic

permeability of the material. The level of change in permeability property is proportional to

applied force / stress.

Depends on permeability property of magnet defined as The measure of the ability of a material

to support formation of magnetic field within itself

This effect is based on the change in permeability of ferromagnetic material under applied stress.

9. Define Torque. The force which tends to change the linear motion or rotation of a body. It is also defined as the turning or twisting moment of a force about an axis. The force that tends to cause rotationUnit: Radian /sec

T= FD Where T=Torque , F=Force, D=perpendicular distance from the axis of

rotation of the line of action of the force.

10. What are the classifications of tachometer?

11. Define the principle of Capacitive Tachometer.

Capacitive Tachometer uses the principle of charging a capacitor and discharging through a meter

alternatively. The average discharge current would be proportional to the speed.

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Mr.C.MAGESH KUMAR / Ms. M.SURYA EIE/AIHT

12. What is pressductor? Magneto-elastic load cell works in principle of Magneto elastic principle called as Villari effect.

When a ferromagnetic material undergoes a mechanical stress, it changes the magnetic

permeability of the material. The level of change in permeability property is proportional to

applied force / stress.

Depends on permeability property of magnet defined as The measure of the ability of a material

to support formation of magnetic field within itself

Magneto-elastic type load cell is called pressductor .The degree of change has a direct

relationship with applied stress or force.

13. Give few Applications of Drag-cup tachometer? Drag-cup tachometer is used in Automobiles which measure the angular speed of the wheel, in Aircraft Engines, in

measuring locomotive speed.

14. What is meant by Strobotron? The Stroboscope consists of a source of flashing light whose frequency can be varied &

controlled .This Source is called strobotron.

An electronic stroboscope uses a (variable frequency flashing light) multivibrator type circuit to produce flashes of light at known and adjustable rates.

The variable frequency flashing light source is called strobotron.

15. Define speed. Speed is defined as rate of change of position of an object with respect to time.

Speed = velocity, Velocity is the rate of change of displacement, V = dx/dt

Speed is a variable refers to the revolutions per minute of some piece of rotating equipment.

16. What is revolution counter? Revolution counter is a device for counting or recording the number of revolutions made by a

rotating shaft of motor or engine.

17. What is prony brake? The prony brake is a device which is most popular for determining the torque exerted by engines

or motors .It consists of a hollow drum attached to the motor shaft and an arm attached to a band

with friction which passes around the drum

The free end of the arm is attached with the hanging scale.

18. What are the fundamental forces of nature? Gravitational Force, Electromagnetic force, Strong interaction force that hold atomic nucleus

together, Weak Interaction force.

19. What are the types of electromagnetic tachometer? The types of electromagnetic tachometer are AC Tachometer, DC Tachometer.

20. What are the types of electric tachometer? Eddy current or Drag type, Electric generator type, Contact less type, Frequency type, Ignition

type, Stroboscopic type.

21. What are the types of mechanical tachometer? Revolution counter with time period, Centrifugal force tachometer, Resonance tachometer.

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Mr.C.MAGESH KUMAR / Ms. M.SURYA EIE/AIHT

22. What are the limitations of AC tachometer? 1. The difficulty with this system is that at low speed the frequency of output voltage is low and

hence it is very difficult to smooth out the ripples in the output voltage wave shape.

2. High speeds also present a problem. At high speeds the frequency increases and therefore, the

impedance of coils of tachometer increases.

23. In a stroboscopic tachometer if four stationary marks are used, then what will be the speed of the tachometer?

A stroboscope is made to flash directly on the mark. The flashing is adjusted until the mark

appears stationary even though the shaft rotates.

At this condition, the speed of shaft (n in rpm) is equal to frequency (f in Hertz) of light flashed

on shaft. i.e., n = f

In general, if no. of marking in shaft is m, then n = f/m.

If no. of marking is 1, then n = f

If no. of marking is 2, then n = f/2

If no. of marking is 3, then n = f/3

Typically a gas-discharge or solid-state lamp is used, because they are capable of emitting light

nearly instantly when power is applied, and extinguishing just as fast when the power is

removed.

Speed n= f/4, Here f= frequency in hertz.

24. What are the factors affecting the accuracy of force measurement? Force must either be reasonably constant in value.

Force must act perpendicular to the platform of sc