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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
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• 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
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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
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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.
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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
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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
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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
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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
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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
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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
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EXAMPLE OF MEASURING SYSTEM
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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.
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Measuring System for Measuring the
Velocity of a Vibrating Body
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