Functional Elements of Instrumentation

FUNCTIONAL ELEMENTS OF INSTRUMENT

ANIL KUMAR PATHAK

ME(REGULAR)

INSTUMENTATION AND CONTROL

NITTTR, CHANDIGARH

FUNCTIONAL ELEMENTS OF ANINSTRUMENT

It is possible and desirable to describe both the operation and the performance of measuring instrument and associated equipments.

Performance is described in terms of static and dynamic characteristics.

Operation can be described in terms of functional elements.

Each functional element is made up of distinct component or group of components which perform the required and definite steps in measurement.

FUNCTIONAL ELEMENTS OF ANINSTRUMENT

PRIMARY SENSING ELEMENT

first receives energy from the measured medium andproduces an output depending , in some way ,on themeasured quantity (measurand).

An instrument always extracts some energy from themeasured medium. Thus the measured quantity isalways disturbed by the act of measurement, whichmakes a perfect measure theoretically impossible.

Good instruments are designed to minimize thisloading effect.

This stage is also known as detector transducer stage.

VARIABLE-CONVERSION ELEMENT

The output of primary sensing element may be any electrical signal i.e. voltage, frequency etc or any physical variable like displacement etc.

convert the output signal of the primary sensing element to another more suitable variable, while preserving the information content of the original signal.

VARIABLE-MANIPULATION ELEMENT

Sometimes it become necessary to manipulate the signal.

change, in numerical value according to the some definite rule but a preservation of the physical nature of the variable, e.g. an electronic amplifier (analog).

It does not necessarily follow the variable conversion element but may precede it.

The combination of variable conversion element and variable manipulation elements is called signal or data conditioning element.

These processes may be linear like amplification, integration ,addition etc or nonlinear like modulation , detection , sampling etc.

DATA-TRANSMISSION ELEMENT

when the functional elements are separated, it becomes necessary to transmit the data from one to another.

It may be as simple as shaft and bearing or as complicated as a telemetry system for transmitting the signals from satellites to ground.

DATA-PRESENTATION ELEMENT

presents the information about the measured quantity into a form recognizable by one of human senses.

This function includes the simple indication of a pointer moving over a scale.

These devices may be analog or digital indicating instruments like ammeter, voltmeter etc.

DATA-STORAGE/PLAYBACK ELEMENT Sometimes it is necessary to record the

measured data for further analysis. In case the data is to be recorded,

recorders like magnetic tapes, high speed camera, storage type C.R.T. , printers or microprocessors may be used.

Storage-pen/ink Storage/playback – Tape

recorder/reproducer, memory

FUNCTIONAL ELEMENTS OF PRESSURE GAUGE

FUNCTIONAL ELEMENTS OF PRESSURE THERMOMETER

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