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ARINDA SAM COURSE WORK

1.Define the term instrumentation (1 mark)

y Instrumentation is the art and science of measurement and control.2.State any four aims of carrying out instrumentation (2 marks)

y To be precise and consistent.y To save life and property for example through use of alarm systems.y To control and maintain machines easily increasing their life time.y For efficiency and perfection.

3.Explain two reasons why electronic equipment are now more widely used than mechanical instruments

in engineering applications. (2 marks)

y Efficiency. Electronic equipment are more faster and requires less input to do a heavy workcompared to mechanical equipment.

y Portability. Electronic equipment are always portable and easy to move from one place to anothercompared to mechanical equipment.

4.Define the term transducer. (1 mark)

y A transducer is a device that converts one form of energy or physical quantity to another.5.State any four characteristics of an ideal transducer. (2 marks)

y Repeatability There should be a linear rAelationship between the measurand and the transducedsignal.

y Size: The transducer must be capable of being placed exactly where it is needed.y The transducer should have minimum sensitivity to external effects. Pressure transducers, for

example, are often subjected to external effects such as vibration and temperature.

y The natural frequency of the transducer should be well separated from the frequency andharmonics of the measurand.

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6. Briefly classify electrical transducers according to;-

I Variable control parameter type. (2 marks)

II Self generating excitation voltage (2marks)

III Briefly describe the principle of operation of a quartz crystal transducer(4 marks)

Solution.

I. Capacitance transducers, Inductive transducers and resistance transducers.

II. Electromagnetic transducers and piezoelectric transducers.

III. Quartz crystal units serve as the controlling element of oscillator circuits by conversion of mechanical

vibrations to electrical current at a specific frequency. This is accomplished by means of the

"Piezoelectric" effect. Piezoelectricity is electricity created by pressure. In a piezoelectric material, the

application of mechanical pressure along an axis will result in the creation of an electrical charge along an

axis at right angles to the first. In some materials, the obverse piezoelectric effect is found, which means

that the imposition of an electric field on the ends of an axis will result in a mechanical deflection along

an axis at right angles to the first.

7.A quartz crystal transducer has a sensitivity of 80pF/bar. Given that for an output pressure of 3bars, an

output voltage of 2 volts is produced, determine the capacitance of the device.

y Capacitance (C) = Sensitivity x output pressure= 80pf/bar x 3bar

= 240pf at 3bars.

8.Define the terms mechanical strain, electrical strain and gauge factor in relation to resistance straingauges.( 2 marks)

y Mechanical Strain is defined as the amount of deformation per unit length of an object when aload is applied.

y Electrical strain is defined as the change in electrical resistance to the original resistance of aconductor.

y Gauge factor is defined as the ratio of fractional change in electrical resistance to the fractionalchange in length.

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9.Determine the un axial strain in u strain sensed by a 100 strain gauge if it has a gauge factor of 2and the resistance change produced by the strain is 2.5 (2 marks)

Gauge factor=Fractional change in resistance

Axial strain

Therefore, 2= 2.5

100/u

2u=2.5/100

u=2.5/200

u=12.5x10-3=0.0125

10.Define the term pressure and state the SI units in which it is measured. (2 marks)

y Pressure is defined as force acting perpendicularly per unit area.y Its SI units are Pascals (Pa)y 1Pa=1N/m2

11. State two ways by which the sensitivity of a manometer can be increased. (2 marks)

y Inclining the smaller manometer tubey Decreasing the diameter of the manometer tube can lead to increased sensitivity due to increased

capillary action. However a very narrow tube will generate a greater capillary action effect that

will interfere with the operation of the manometer.

12Distinguish between gauge pressure and absolute pressure. (2 marks)

y Gauge pressure is that pressure that is measured relative to the atmospheric pressure whileabsolute pressure is defined as the pressure, measured relative to a perfect vacuum .

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13.Show that in a location where the acceleration due to gravity is g , the pressure p acting at a depth

h in a liquid of density is given by p= gh. (4 marks)

P = Force/Area......(i)

F = mg .................(ii)

substituting (ii) in (i),

P=mg/Area............ (iii)

From =m/v

m= v............(iv)

where m is the mass of the liquid

v is the volume of the liquid

But V=Ah.................(v)

Substituting (v) in (iv)

m= Ah................(vi)

Substituting (vi) in (iii)

P = Ahg

AHence P = gh. as required.