generalized measuring systems2

7/29/2019 GENERALIZED Measuring Systems2

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GENERALIZED

MEASURING SYSTEM

Stage 1 : A detector- transducing

or sensor-transducer stage Stage 2 : An intermediate stage,

which is called the signal

conditioning stage

Stage 3: A terminating or readoutstage



• Measured are classified according to their

time relationship .

According to the rate of variation of themeasured with respect to time: is classified

into static and dynamic.

According to the fashion of variation withtime: is classified as analog and digital.

INUPUT IDENTIFICATION



INUPUT IDENTIFICATION

Static:

The measured does not change or not rapidly

change with time. Of course, the non-changed measured is the most easily

measured quantity. The meter pointer has no

difficulty in eventually reaching a definiteindication

Static or Dynamic



Static or Dynamic

a)Static quantity

Dynamic

•Steady-state &Transient

The measured rapidly changed with respect to time.

This case represents a real measurement challenge.

There are two general form of dynamic input:

steady-state periodic and transient.

The steady-state periodic quantity is one whose

magnitude has a definite repeating time cycle.

The time variation of a transient magnitude does

not repeated.

This condition represents the most severe

measuring state.



Analog quantity

The measured varies with time in a

continuous manner. For instance, the speed

of an automobile, as it starts from rest, and

the voltage in utility power lines.

Temperature, fluid flow, pressure, stress, and

strain are normally behave in analog manner.

Analog or Digital



Analog or Digital

quantitry c) Analog

•Digital quantity is that quantity varies in a stepwise

manner between two distinct magnitudes: a high

and a low voltage, for instance.

• Digital quantities are preferred in measuring

systems. Noise problem is reduced or eliminated,

data transmission is simpler, and computers are

designed to process digital information.

• Therefore it may be preferred in some cases to

convert analog type input to an equivalent digital

signal

Digital quantity



d)Digital quantity

•The primary function of this stage is to detect or sensethe measured.

• A transducer is a device that transforms one physicaleffect to another. In most cases , the physical variable is

transferred into an electric signal

Transducer classified as:-

-Mechanical : Bourdon tube

-Hydraulic-pneumatic : Float, propeller

-Optical :Photographic film, photoelectric cell

- Electrical :Resistance, coil, condenser.

FIRST STAGE

SENSING-TRANSDUCING STAGE



FIRST STAGE

SENSING-TRANSDUCING STAGE

The purpose of the second stage is to modify thetransduced signal so that it will be suitable for the third stage.

• increase the amplitude of the signal to the level required to drive the final terminating stage.

• Filtration process is carried out at this stage, whereasThe desired signal is extracted from the extraneousinput.

•Modification of the signal to be suitable for remotecontrolling is also carried out in this stage.

• In addition basic operation such as, integration,differentiation, summation could be performed in this

stage.

SECOND or INTERMEDIATE STAGE SIGNAL-CONDITIONING STAGE



SECOND or INTERMEDIATE STAGE SIGNAL-CONDITIONING STAGE The final stage expresses the measured in

comprehensible to one of the human sense or to acontroller. The output device may be

Indicators Displacement type: moving pointer and scale, movingscale and index, light beam and scale, electron beamand scale (CRO), liquid column

Digital type : Direct alphanumeric readout -Recorders: Digital printing, inked pin and chart, lightbeam and photographic film, magnetic recording.

Processors : Various type of computing systems or

controlling systems

THIRD OR TERMINATING or FINAL STAGE



THIRD OR TERMINATING or FINAL STAGE

Gage for Measuring Pressure in Automobile Tires

The piston-cylinder combination constitutes a

force-summing apparatus sensing and

transducing pressure to force. As a secondarytransducer, the spring converts the force to

displacement. Finally, the transduced input is

transferred without signal conditioning to thescale and index for read out



EXAMPLE OF MEASURING SYSTEM



Fig. 2.3 Gage for measuring pressure in automobile tires

• As shown in Fig. below, The accelerometer

provides an analogous voltage to the acceleration.

• A filter is used to eliminate the unwanted high

frequency components.

• The signal is then integrated w.r.t. time, thereby

providing a velocity-time relation.

• The signal is then amplified to the level necessary

to drive the read out stage.

• Finally, the output may be in the form of a trace

on a photographic paper.



Measuring System for Measuring the

Velocity of a Vibrating Body

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