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GENERALIZED CONFIGURATIONAND FUNCTIONAL DESCRIPTIONS

OF MEASUREMENT SYSTEMS

Lecture 3Instructor : Dr Alivelu M Parimi


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OUTLINE

Functional elements of an instrument

Active and passive transducers

Analog and digital modes of operation

Null and deflection methods

Input output configuration of measurement system

Methods of correction of modifying and interfering inputs


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Functional elements of an

instrument Operation of any instrument can be described in generalized

way in terms of functional elements (not physical)

Figure represents possible arrangement of functional

elements in an instrument.

3


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Explain the operation of servomechanism system

shown in Figure in terms of the functional elements

and arrange them from measured medium to

observer.Input voltage ei

Output displacement xo


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Solution


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Transducers

1. Sensing Element

The physical quantity or its rate of change is sensed and responded to by this part

of the transistor.

2. Transduction Element

The output of the sensing element is passed on to the transduction element. This

element is responsible for converting the non-electrical signal into its proportionalelectrical signal.


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Example

A transducer changes a signal from one form of energy to another. A

common transducer in anesthesia changes mechanical energy, e.g., an

arterial pulse, into electrical energy.

Microphones and speakers are also examples of transducers


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Active and passive transducers

A transducer is a device that converts one type of energy to another.

An active transducer is a transducer whose output is dependentupon sources of power, apart from that supplied by any of theactuating signals, which power is controlled by one or more of these

signals. They produce an electrical signal proportional to the input (physical

quantity). For example, a thermocouple is an active transducer.

While passivetransducersare those which does not need anexternal source. Passive transducers directly produce electric signals

without an external energy source. They produce an output signal in the form of some variation in

resistance, capacitanceor any other electrical parameter, which thanhas to be converted to an equivalent electric currentor voltagesignal
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Under nominal pressure the platform is

made to stay at zero position (midway)

with help of standard weights. Uponapplication of pressure, platform moves

up/down and standard weights are

added/subtracted to restore platform at

zero position, the weights put on the

platform to restore balance are an

indication of applied pressure. The

condition of force balance is indicated by

the platform remaining at rest between

the upper and lower stops. Since the

weights and the piston area are all known,

the unknown pressure may be computed.

Is this an active or passive transducer?


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Examples


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Answers

2.3 a. The incoming light waves have only minuscule power

while it takes significant energy to push the pedal through

some distance, so the driver is functioning as an active

transducer.

b. The cars motion is driven by the full power of the engine,whereas the energy taken from the human foot is small in

comparison, so the engine is clearly an active transducer with

a very large power amplification.


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Conclusion

Functional elements of an instrument

Examples

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