what is instrument, selection criteria, and importance of Calibration? Zafar Ali student of Mehran UET jamshoro, Sindh,pk

1. Topic: Selection and Calibration of Instruments
Teacher name:Prof.Dr Aziza Aftab
Subject:Instrumentation and Process Control
Group members.
Zafar Ali 16CH55 (G.L)
Mohsin Ali 16CH33(AGL)
M.Suleman 16CH21
Sadam Hussain 16CH53
Department of Chemical Engineering

2. KEY WORDS
 WHAT IS INSTRUMENTS
 TYPES
 SELECTION CIRTERIA
 CALIBRATION – Comparison
 IMPORTANCE

3. An instrument may be defined as a device for determining the value or magnitude of a quantity or variable.
The instruments may be classified as follows:
i) Mechanical, electrical and electronic instruments
ii) Absolute and secondary instruments
iii) Manual and automatic instruments
iv) Analogue and digital instruments

4. Instrument Selection Criteria
 Identify all operating cases, such as normal operation at minimum, normal and maximum flow,
alternative operating modes, start-up, commissioning and emergency operation
 process data fluid name and phase, physical properties, corrosiveness and toxicity
 environmental conditions Instrument should be chosen that are as insensitive as possible
to operating environment.
 durability, maintainability and consistency of performance
 Published literature is of considerable help in the choice of suitable instrument for a
particular measurement situation
 Instrument choice is a compromise between its performance characteristics, ruggedness,
durability, maintenance requirements and purchase cost.

5. Pressure sensors:
 Manometers are commonly used when just a visual indication of low pressure level
 Bourdon tube type pressure gauge is used medium pressure or vacuum sensing ,Bellows-types
instruments are also sometimes used for this purpose, but much less frequently.
 The resonant-wire devices are popular choice. Deadweight gauges If very high measurement
accuracy is required. Deadweight gauges, because of their superior accuracy, are used in
calibration procedures of other pressure measuring devices.
 vacuum ranges, that is, below 1.0132bar
 Bourdon tubes measure pressures down to 0.1mbar
 Diaphragms can be designed to measure the pressure down to 0.001mbar
For differential pressure measurement, diaphragm-type sensors are the preferred option.

6. Manometers are also sometimes used to give the visual indication of differential pressure values
especially in the liquid flow rate indicators.

7. Temperature sensors:
. If the medium is solid this choice is restricted to thermocouples, thermopiles, resistance
thermometers, thermisters, semiconductor devices and color indicators.
For the fluid temperatures can be measured by any of the instruments with the exception of
radiation thermometers.
The most commonly used devices in the industry for the temperature measurement is the base-
metal thermocouple.
Semiconductor devices have better linearity than thermocouples and resistance thermometers and
similar level of accuracy
radiation thermometers or optical pyrometers could be used. They are used to monitor
temperature above 600C in industrial furnaces

8. Flow sensors:
 These include the temperature and pressure of the fluid, its density, viscosity, chemical properties
and abrasiveness, whether it contains particle, whether it is liquid or gas, etc.
 visual indication of flow rate is needed, variable-area meter is popular
 rotating devices such as turbine meters and positive displacement meters and at the same time
increased use of ultrasonic and vortex meters.

9. Calibration (Old Definition)
“Calibration is the comparing of an unknown measurement device against equal or better
known standard under specified conditions”

10. “Operation that, under specified conditions, in a first step, establishes a relation between
the quantity values with measurement uncertainties provided by measurement
standards and corresponding indications with associated measurement uncertainties, and
in a second step, uses this information to establish a relation for obtaining a measurement
result from an indication ”

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Importance of Calibration
 Assurance of accurate of measurements
 Ability to trace measurements to International standards
 International acceptance of test/calibration reports
 Correct diagnosis of illness (medical reports)
 Consumer protection (legal metrology)
 Meeting the requirements of ISO 9000 and 17025