Chemical Process Instrumentation - Lecture 2 26 July 2024 (1).pdf

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1. Chemical Process
Instrumentation
LECTURE 2
Lecture by:
Nikita Dewangan
Department of Chemical Engineering
IIT Kharagpur

2. 2
Primary sensing
Element (PSE)
Variable
manipulation
element
Data
Presentation
Element
Variable
conversion
element
Data
Transmission
Element
Quantity to be
measured
Observer
QUICK RECAP:
GENERAL BLOCK DIAGRAM FOR MEASUREMENT SYSTEM

3. 3
EXERCISE:
Find out functional elements
and its sequence ?

4. PSE
VCEVME
DTEVCE
Measurand
Measured medium:
Fluid
Presented data Output
Observer
Piston
Force
Piston
Rod
Spring
Force
Motion
Linkages
DPE
Motion
Pointer & Scale

5. EVOLUTION OF INSTRUMENTS
Mechanical
✓Reliable for slow and static changing conditions
✓Easy to build and design.
✓No further power source is needed.
✓Unable to indicate remotely.
✓Cause commotion and produce inaccurate results
Electrical
✓A faster indication than mechanical
Involves translating an electrical amount into
mechanical motion on a scale.
✓Use electrical methods to report the output
Electronic
✓Quickly react to changing and dynamic conditions.
✓Lightweight, small, using little electricity, and very reliable.
✓Possess excellent sensitivity, adaptability, and the capability
of distant indication.
✓It is also feasible to measure without making contact.

6. 6CLASSIFICATION OF INSTRUMENTS
❑Classification on the basis of energy consideration
❑Operation on null and deflection principles
❑Classification on the basis of analog and digital
❑Automaticand manual type of instruments
❑Classification on the basis of contacting and non -contacting type

7. 7
❑Classification on the basis of energy consideration –Active and Passive
Often used where high degree
of accuracy is not required Active Passive
Quantity is measured with
the help of external power
Power source is used to
amplify or manipulate the
signal passing through it
High level of accuracy
and precision.
Designed to operate at a
wide range of frequencies
making them more versatile.
Do not require external
power source
Directly measure the signal
passing through them
Limited frequency range
•The change in petrol level moves a potentiometer arm, and the output signal
consists of a proportion of the external voltage source applied across the two
ends of the potentiometer. The energy in the output signal comes from the
external power source: the primary transducer float system is merely modulating
the value of the voltage from this external power source.
Ex:
Float type level indicator
•The pressure of the fluid is translated into a movement of a pointer against
scale. The energy expanded in moving the pointer is derived entirely from the
change in pressure measured. In this passive instrument. there are no other
energy inputs to the system.
Ex:
Pressure measuring device

8. 8
❑Operation on null principles
CLASSIFICATION OF INSTRUMENTS
Null type : An instrument in which zero or null indication determines the magnitude of measured
quantity such type of instrument is called a null type instrument. It uses a null detector which
indicating the null condition when the measured quantity and the opposite quantity are same.
Such type of instrument has high accuracy and also it is very sensitive. For the operation of the
null type instrument, thefollowing condition requires.
1.The opposing effects whose value are accurately known. It is necessary for measuring for
determining the numerical value of the measured quantity accurately.
2.A detector which detects the null conditions, i.e., adetector is a device which indicates zero
deflection when the balance condition occurs.
3. The null instrument includes a differential comparator, which compares and computes the
difference between these two inputs.
The measurand and the known quantities
balance one another in a null instrument
A null instrument requires input from two
sources for comparison

9. 9
❑Operation on deflection principles
CLASSIFICATION OF INSTRUMENTS
➢This type of instruments uses the deflection method for measurement.
➢A deflection instrument is influenced by the measurand so as to bring about a proportional response within the instrument.
➢This response is an output reading that is a deflection or a deviation from the initial condition of the instrument. In a typical
form, the measurand acts directly on a prime element or primary circuit so as to convert its information into a detectable
form.
➢The name is derived from a common form of instrument where there is a physical deflection of a prime element that is
linked to an output scale, such as a pointer or other type of readout, which deflects to indicate the measured value. The
magnitude of the deflection of the prime element brings about a deflection in the output scale that is designed to be
proportional in magnitude to the value of the measurand.
A deflection instrument requires input from only one source, but
may introduce a loading error
The logic flow chart for a deflection instrument is straightforward

10. Activity:
Provide an example of null and deflection type instruments used in Chemical Industry?

11. 11
❑Operation on analog and digital type
CLASSIFICATION OF INSTRUMENTS
ANALOG DIGITAL
The type of instrument which works on electromagnetic effects and
produces the output in analog form (wave or deflection of pointer) is
called an analog instrument.
The type of instrument which consists of solid state components and
shows the results in the digital form (digits on a screen) is known as
digital instrument
Analog instruments show the output by the deflection of a pointer on
a dial or scale.
Digital instrument shows the output on a digital display screen as a text
or number
Analog instruments can show the change in output by the movement
of pointer.
Digital instruments do not show the change in output quantity.
With the analog instruments, there is a possibility of considerable
observational errors like parallax error.
Digital instruments are free from observational errors.
Analog instrument uses continuous variation of the signal and records
its waveforms.
Digital instruments use sampling techniques for the conversion of input
signal into binary signal (or digital signal).
Analog instruments are less accurate Digital instruments are more accurate with high resolution
The common examples of analog instruments are Permanent magnet
moving coil instrument, galvanometer, needle type speedometer of
automobile, moving iron instrument, mercury thermometer, etc.
Some examples of digital instruments are digital multimeter, digital
ammeter and voltmeter, clamp-meter, etc.

12. 12
❑Operation on automatic and manual
CLASSIFICATION OF INSTRUMENTS
Manual instrument needs the services of an operator, whereas in automatic instruments there is no need for an operator.
Asmeasurementofrotationalspeedbyahandoperatedtachometeranoperatorisrequiredtomakethecontactofthe
instrumentwiththerotatingshaft.Formeasurementoftemperaturebyaresistancethermometerbywheat-stonebridgein
itscircuitanoperatorisrequiredtoindicatethetemperaturebeingmeasured.Ontheotherhand,inmeasurementof
temperaturebymercury-in-glassthermometer,nooperatorisrequired.anexample,
Automatic bomb calorimeterTachometer

13. 13
❑Classification on the basis of contacting and non -contacting type
CLASSIFICATION OF INSTRUMENTS
Contacttemperature sensorsmeasure temperature by coming into direct contact with the object
of interest. They are the most common type of temperature sensor and are used in various
industrial applications. Contact sensors work by measuring the heat energy that is transferred
from the object to the sensor.
•Contact sensors are often used in situations where accuracy is paramount and contact with
the object is possible, such as in medical, pharmaceutical and food processing applications.
•The main disadvantages of contact sensors are the potential logistical limitations of coming
into contact with the object of interest.
Ex: thermocouples, thermistors, and resistance temperature detectors
Non-contact temperature sensorsmeasure temperature without coming into contact with the object
of interest. They are often referred to as infrared sensors because they use infrared radiation (heat)
to measure temperature. Non-contact sensors tend to be quicker than contact sensors and are used
in a variety of industrial applications.
•The main advantages ofnon-contact sensorsare their accuracy, speed, and versatility.
•The main disadvantage of non-contact sensors is that they aren’t as precise as contact sensors.
Additionally, they are subject to errors due to background radiation and can be blocked by water
droplets, dust or dirt.
Ex: thermal sensors,infrared thermometers, pyrometers, andthermographic cameras.

14. SMART INSTRUMENTS IN PROCESS INDUSTRY
❑A smart sensor is a device that can measure physical quantities and give an output correlated to the measured value just likea
normal sensor, but it also has the capability to do some data analysis to this measured quantity using a built-in computing
resource and use these data to take some actions to increase the efficiency of theautomation process.
❑Smart sensors can also provide more accurate measurements. The computing resources built inside which filters out any
signal noise and converts the measured signal into a usable digital format without the need for a transducer as in a normal
sensor.
❑Smart sensors also have built-in communication capabilities that enable them to transmit data over the internet or a similar
network and give them the ability to communicate with external devices, which is the main reason why smart sensors are very
crucial elements in theinternet of things(IoT) and industry 4.0
Microprocessor
Communication Module
Power
source
Base sensor
Memory
Normal sensor responsible for
detecting the physical quantity
To feed power to the
computing resource and
maybe the sensor base.
This is the computing element, which enables the
sensor to make some data calculations to measure
quantities and take actions based on these analyses.
Dedicated to storing the measured values, and
calculated data and also storing the incorporated
software logic that controls how the sensor handles
these data.
To transmit and receive data between
the sensor and external devices over a
similar network or the internet.
Data outData in

15. 15
Transducer Microprocessor
Analog to digital
converter
VME
Process variable
Display with
interface
Input
devices
Control Unit
Memory
Arithmetic and
logic unit
Output
devices
Microprocessor : Operational computer
Functions of microprocessor
1)to monitor and control operations of
Industrial devices by measuring key
parameters like temperature, pressure,
speed
2)in instruments to raise an alert or warning on
extreme conditions
3)to automate office work / business
processes and improve white collar
productivity
4)to speed up the information exchange
through Telephone and Satellite network
SMART INSTRUMENTS IN PROCESS INDUSTRY

16. 16
•Pressuresensorscapturepressurechangesandtransformthemintoelectricalsignals,wheretheappliedpressuredefinesitsquantity.
Theseelectro-mechanicaldevicesidentifyforceinliquidsorgasesandprovidedisplaydeviceswithcontrolsignals.Pressuresensorscan
alsodetectatmosphericchanges.Forexample,barometricpressuresensorscandetectchangesintheatmosphereandhelptopredict
weatherpatternsandchanges.
•Inindustrialproduction,atemperaturesensorcollectsinformationabouttemperaturefromthesurroundingenvironmentandconvertsitinto
specificvalues.Digitaltemperaturesensorscontaindigitaltemperaturesensorsamplingcardsandareubiquitousinindustrialautomation.
Theproductusesafilteringmethodcombiningrecursivehardwarecircuitfilteringandaveragedigitalsoftwarefilteringtominimiseexternal
interferencetosampling,withgoodconsistency,highfull-scaleaccuracy,strongstability,andfastresponse.
•Flowsensors:Thesesensorscansensethemovementofsolids,gases,orliquidsflowingthroughapipeoraconduit.Flowsensorsare
extensivelyusedinprocessingindustriesandallowoptimalperformanceofmachines.Aflowsensorcanbeelectronic,usingultrasonicflow
sensing,orpartiallymechanical.Electromagneticflowmetersfindprimaryuseinwatermanagement,lifesciences,andfoodindustries.
•Infraredsensorusesinfraredwavelengthsignalstocreateandprocessdatawithoutdirectcontacttothetargetobjectduringmeasurement.
Thebenefitofnophysicalcontactmeansthatthereisnofrictionbetweenthetargetandthesensor.
•Imagesensorsconvertstheopticalimageintoanelectricalsignal.Thesesensorsareusedinbothanaloganddigitaltypeelectronic
imagingdeviceslikecomputervision,imagingtoolsusedformedical,cameramodules,nightvisiontoolslikeradar,thermalimaging
devices,sonar,digitalcamerasetc.
Which all sensors were commonly used during COVID -19 Pandemic ?
SMART INSTRUMENTS IN PROCESS INDUSTRY

17. 17
What is a SCADA system used for?
Supervisory Control and Data Acquisition(SCADA) system is to monitor and control equipment in
industrial processes. Thus, SCADA systems are seen almost everywhere. Typically, SCADA systems
are used in:Manufacturing, Transportation, Water Management, Renewable Energy, Oil & Gas,
Power Distribution and Control
The connecting link in the SCADA architecture are the Programable Logic Controllers (PLCs) or
Remote Terminal Units (RTUs). These are microcomputers that interact with both the equipment
(also called field devices) on the one hand, and HMIs, which are Human Machine Interfaces, on
the other hand. HMIs are also referred to as graphical user interfaces.
https://scada-international.com/what-is-scada/#:~:text=What%20does%20SCADA%20stand%20for,data%20from%20the%20industrial%20equipment.
TECHNOLOGY ENHANCEMENT IN PROCESS INDUSTRY

18. Future trends in process instrumentation
1.Integration with IoT
Process instruments are increasingly being integrated with IoT, enabling real-time data monitoring and
analysis for improved classification and performance.
2. Use of artificial intelligence for predictive maintenance
Artificial intelligence is being utilized for predictive maintenance of process instruments, ensuring optimal
performance and longevity, which impacts their classification and reliability.
3. Development of more robust and precise sensors
Advancements in sensor technology are leading to the development of more robust and precise sensors,
enhancing the accuracy and capabilities of process instruments, thereby influencing their classification.
4. Enhanced data analytics capabilities
The enhancement of data analytics capabilities allows for deeper insights and analysis of process instrument
data, contributing to more accurate classification and performance optimization.

19. 19Types of Instrument Errors
•Error is the difference between the time value of the measurand and the result obtained from
measurement.
i.Systematic errors
ii.Random errors
iii.Gross errors

20. Systematic Errors:
in experimental observations usually come from the measuring instruments. They may occur because:thereis something wrong
with the instrument or its data handling system, or because the instrument is wrongly used by the experimenter.
Systematic errors due to measurement system
a.Installation error: This arises due to defects (imperfections) in the construction and assembly of measurement systems.
b.Equipment Error: This is found even in perfectly manufactured instruments and are often caused by either the ageing of
components, friction and energy dissipation between moving parts, wear and tear (mechanical damage) and vibrations.
c.Offset error: This error occurs when a scale isn’t calibrated to a correct zero point. It’s also called an additive error or a zero-
setting error.
d.Scale factor error: This error occurs when measurements consistently differ from the true value proportionally (e.g., by 10%).
It’s also referred to as a correlational systematic error or a multiplier error.
Ex: 1) A thermocouple always reads 1
o
C higher than the actual temperature due to manufacturing defect
2) A weighing scale consistently adds 10% to each weight. A true weight of 10 kg is recorded as 11 kg, while a true weight of40kg
is recorded as 44 kg.

21. Random Errors:
Random error is a type of measurement error that is caused by the natural variability in the measurement process. It is
unpredictable and occurs equally in both directions (e.g., too high and too low) relative to the correct value. It is usuallycaused
byfactorssuch as limitations in the measuring instrument, fluctuations in environmental conditions, and slight procedural
variations.
## Statisticians often refer to random error as “noise” because it can interfere with the true value (or “signal”) of what you’re
trying to measure. If you can keep the random error low, you can collect more precise data.
Forexample,imagineyouwanttomeasuretheheightofatreeusingameasuringtape.Thetree’sheightis10feet,butdue
tovariationsinthemeasuringtape,theangleyoulookatthetape,thesuninyoureyes,thewindblowingthetape,etc.,you
getslightlydifferentmeasurementseachtimeyoumeasureit.Thefirstmeasurementis10.2feet,thesecondis9.9feet,
andthethirdis10.1feet.Thesedifferencesareduetorandomerror.
Sources or causes of random errors are listed below.
•Observational:Error in the judgment of the observer.
•Small disturbances:Small disturbances may introduce errors in the measurement
•Fluctuating Conditions:Sometimes, variations in temperature or the environment may lead to
errors in the measurement.
•Quality:Sometimes, if the quality of the object whose measurement is to be made is not
defined, it leads to an error.

22. 22How do we reduce or minimize error ?
Random Errors Systematic Errors
✓Take repeated measurements
✓Increase yoursamplesize
✓Increase the precision of measuring
instruments
✓Control other variables: In controlled
experiments, keep everything as consistent
as possible
✓Taking the average of multiple
measurements reduces the random error by
canceling out the positive and negative
errors.
✓Triangulation: use multiple techniques to
record observations so you’re not relying on
only one instrument or method.
✓Regular calibration: frequently comparing
what the instrument records with the value
of a known, standard quantity reduces the
likelihood of systematic errors affecting your
study

23. NEXT CLASS
•Types of instrument errors continue…
•How to calculate error with examples
•Input-output configuration of instruments

24. 24
TEXTBOOK REFERENCES:
1.Instrumentation fundamentals for Process Controls -Douglas O. J. deSâPublished 2019 by CRC Press
Taylor & Francis Group
2. Second edition , Measurement, Instrumentation, and Sensors Handbook Electromagnetic, Optical, Radiation,
Chemical, and Biomedical Measurement, John G. Webster HalitEren
3. Doeblin, E.O. (2004) –Measurement Systems : Application and Design, Tata McGrew Hill Publishing Company
Limited , New Delhi
4. Johnson, C.C. (2006), Process control instrumentation technology, Prentice Hall, New Delhi