Calibration

Instrumentation Calibration,

Instrumentation Calibration,

Design and Techniques

Instrumentation and instrument

Instrumentation and instrument

What is instrumentation?

What is instrumentation?



_In

_{In general}

_{general defnition}

_{defnition this}

_{this can}

_{can be}

_be

defned as the

defned as the art 

art  and

 and science

science o

 o

measurement and/or control.

measurement and/or control.



_{Is achieved by using an}

_{Is achieved by using an}

“

Instrumentation based on

Instrumentation based on

industrial application:

industrial application:

“It is the application o instrument or

“It is the application o instrument or

the purpose o

the purpose o

measuring, observing,

measuring, observing,

transmitting, indicating, recording,

transmitting, indicating, recording,

monitoring, and controlling any

monitoring, and controlling any

industrial process variable”.

What is an instrument?

_{Is any device used directly or indirectly in}

order to accomplish an objective or task.

 _{In Instrumentation, an instrument is any}

sensing, measuring, transmitting, indicating, or controlling device

associated with a process or system.

E. !easuring a body temperature using a thermometer.

Instrument application categories

and functional divisions.



_{Factory automation instruments}

_{Plant safety or safeguarding}

instruments



_{Product Quality monitoring/control}

instruments



_{Environmental condition}

monitoring /control instruments.



_{Process variable measurement and}

Implementing instrumentation

•

_{o! is instrumentation}

implemented?

". #ingle or #tand alone #ystem.

$. %omple #ystem

Instrumentation system

"nstrumentation system # is an

arrangement o two or more

instruments connected together to

perorm a unifed task.



 _{Each instrument operates}

independently according to its specifc

task. &ailure rom one member o

instrument, means ailure o the entire

instrument system.

Automation



 _{Is a system concept that utili'es}

instrumentation system to perorm a

certain task or se(uences o operations

in an automatic manner or without

human intervention.



 _{)oth maimi'ing (uantity o production}

and (uality and durability o produced

goods is greatly improved.

AUTOMAT! "#O$%%



 _{Is a process or se(uence o}

production activities done in an

automatic manner.

%&PE' (F )*%(+)%E

P-($E''



 _{*ighly !echani'ed +rocess}

What is Maintenance?



_{ll actions necessary or retaining an}

item, or restoring to it, a serviceable

condition, include servicing, repair,

modifcation, overhaul, inspection and

condition verifcation.



 _{-eep systems e(uipment in working}

order.



 _{o repair the e(uipment ater}

&uestion?

_{3hy do we need maintenance4} _{3hat are the costs o doing}

maintenance4

_{3hat are the costs o not doing}

maintenance4

_{3hat are the benefts o maintenance4} _{*ow can maintenance increase}

"urpose of Maintenance

•

_{ttempt to maimi'e perormance o}

production e(uipment e5ciently and

regularly

•

_{+revent breakdown or ailures}

_{!inimi'e production loss rom}

ailures

•

_{Increase reliability o the operating}

"rinciple Ob'ectives in Maintenance

•  _{o achieve product (uality and}

customer satisaction through adjusted and serviced e(uipment

• _{!aimi'e useul lie o e(uipment} • _{-eep e(uipment sae and prevent}

saety ha'ards

• _{!inimi'e re(uency and severity o}

interruptions

• _{!aimi'e production capacity 6 through}

Maintenance Ob'ectives

• _{!ust be consistent with the goals o}

production 7cost, (uality, delivery, saety8

• _{!ust be comprehensive and include}

Maintenance $osts

•

_{%ost to replace or}

repair

•

_{0osses o output}

•

_{9elayed shipment}

(ailure

_{&ailure 6 inability to produce work in}

appropriate manner

_{E(uipment / machine ailure on production}

:oor 6 worn out bearing, pump, pressure

leaks, broken shat, overheated machine etc.

_{E(uipment ailure in o5ce 6 ailure o power}

supply, air;conditioned system, computer network, photocopy machine

_{<ehicle ailure 6 brake, transmission, engine,}

Types of (ailure

 _{Functional Failure}

the inability to meet the specified performance standard

 _{Potential Failure}

a physical condition which indicates that the failure process has started

 _{Hidden Failure}

Failure is not apparent until the function is attempted

$urrent Maintenance %trategies

 _{Fix it when it fails or run until}

failure

 _{Time based (calendar time or}

running time)

Types of Maintenance

• _{Maintenance may be classified into four}

categories:

• _{(some authors prefer three}

categories-scheduled and preventive maintenances are merged)

•  _{Corrective or rea!down maintenance} •  _{"cheduled maintenance}

•  _{#reventive maintenance}

$orrective or )rea*do+n Maintenance

• _{Corrective or rea!down maintenance implies}

that repairs are made after the e$uipment is failed and can not perform its normal function anymore

• _{%uite &ustified in small factories where:}

 _{'own times are non-critical and repair costs}

are less than other type of maintenance

 _{Financial &ustification for scheduling are not}

!isadvantages of $orrective

Maintenance

• _{rea!down generally occurs inappropriate times}

leading to poor and hurried maintenance

• _{xcessive delay in production  reduces output} • _{Faster plant deterioration}

• _{*ncreases chances of accidents and less safety for}

both wor!ers and machines

• _{More spoilt materials} • _{'irect loss of profit}

• _{Can not be employed for e$uipments regulated by}

%cheduled Maintenance

• _{"cheduled maintenance is a stitch-in-time}

procedure and incorporates  _inspection

 _lubrication

 _{repair and overhaul of e$uipments}

• _{*f neglected can result in brea!down} •  _{enerally followed for:}

 _{overhauling of machines}

 _{changing of heavy e$uipment oils}

"reventive Maintenance

,"M-_{#rinciple . /#revention is better than cure0} _{#rocedure - "titch-in-time}

_*t

1  locates wea! spots of machinery and e$uipments 1  provides them periodic2scheduled inspections and

minor repairs to reduce the danger of unanticipated brea!downs

Advantages of "M

•  _3dvantages:

 –_{4educes brea! down and thereby down time}  –_{5ass odd-time repair and reduces over time of}

crews

 –_{reater safety of wor!ers}

 –_{5ower maintenance and repair costs}

 –_{5ess stand-by e$uipments and spare parts}  –_{etter product $uality and fewer rewor!s and}

scraps

 –_{*ncreases plant life}

 –_{*ncreases chances to get production incentive}

"redictive

,$onditionbased-Maintenance

• _{*n predictive maintenance, machinery}

conditions are periodically monitored and this enables the maintenance crews to ta!e timely actions, such as machine ad&ustment, repair or overhaul

• _{*t ma!es use of human sense and other}

sensitive instruments, such as

 –_{audio gauge, vibration analy6er, amplitude meter,}

pressure, temperature and resistance strain gauges etc+

"redictive Maintenance

,$ontd.-• _{7nusual sounds coming out of a rotating}

e$uipment predicts a trouble

• _{3n excessively hot electric cable predicts a}

trouble

• _{"imple hand touch can point out many}

unusual e$uipment conditions and thus predicts a trouble

ffective Instrumentation

Maintenance Approach

5ocating the real cause of a problem can be the most difficult part of the troubleshooting process+ ut ta!ing a logical approach helps ensure a successful result+

(actors that $ould Influence the ffectiveness of an Instrumentation %ystem Maintenance:

 &amiliarity o the process

 +roper understanding o the problem  +roper evaluation o visible symptoms

 -nowledge in the application o di=erent

!easurement, +rocess %ontrol and !aintenance &undamentals

 -nowledge in the proper use o hand tools

and e(uipment

ffective Maintenance Approach:

". 1nderstand properly the etent o the

problem based on given acts, data and symptoms.

$. #tart troubleshooting by frst using

Elimination by Deduction  method. I the cause o the problem is highly identifed, perorm corrective action at once to solve the problem.

>.   %ontinue troubleshooting by applying

Elimination by Input / Output Test method.

limination by /!eductive

Approach0

 roubleshooting by eliminating one component rom the other component in a loop by deduction or logical thinking method.

limination by !eductive Approach

". 1nderstand properly the etent o the problem

based on given acts, data and symptoms.

$. #tart troubleshooting by frst using

Elimination by Deduction  method. I the cause o the problem is highly identifed, perorm corrective action at once to solve the problem.

>.   %ontinue troubleshooting by applying

Elimination by Input / Output Test method.

1uidelines in using !eductive Approach:

".naly'e the etent o the problem

based on given acts or symptoms.

$.%ome up with a probability per element

based on given acts and decide which element most likely to cause the problem.

>.2ectiy problem i already possible. ?.pply 2oot %ause nalysis 72%8.

limination by /Input2Output Test0

or /$ause 3 ffect Method0

 roubleshooting by applying an input

and monitoring the output per loop

component

based

on

elements

1uidelines in using Input2Output Test:

". Established the details o each loop

component o a given control loop.

$. 1sing the degree o probability based

on the result o your “9eductive pproach@, perorm “Input/Autput@  est.

>. 2ectiy problem encountered while

doing input/output test.

%ignificant use of /Input2Output

Test0 or /$ause 3 ffect0

Input/Autput

est

i

properly

administered is a very e=ective tool in

identiying

e(uipment

unctional,

potential and hidden ailures.

ny ailure identifed during the test

could trigger appropriate maintenance

action/s.

,#$A-What is a /#oot $ause Analysis0

It is a systematic approach to maintenance problem analysis. It emphasi'e mainly on the main cause or root cause o the problem not just the temporary solution.

 his concept could be well implemented by considering the = (uestionsB

 _{Is the problem clearly identifed and}

understood based on given symptoms4

 _{Is the corrective action done really}

Other factors need to be considered

in troubleshooting instrumentation

system problem:

•  _{0oop confguration / system integrity.} •  _{Instrument type, installation,}

calibration C physical conditions.

In general4 the follo+ing simple guide 5uestions +ill help an Instrument Technician perform effective maintenance:

• _{3hat is the problem4}

• _{3hat do we think caused the problem4} •  _{3hat evidence do we have about the}

causes4

•  _{3hat solution7s8 do you have in mind4} •  _{*ow will the solution7s8 eliminate the}

$orrecting Instrument Output

response:

3hat do you think will be your courses o actions i ater doing an input/output test, the actual measured values are signifcantly di=erent rom the desired values4

Why Instrument $alibration is

6ecessary?

 he successul operation o any automated industrial process depends on the accuracy  and perormance  o each instrument in the measurement and control loop.

Instrument calibration helps to ensure that a process operates e!ciently and saely  within plant specifcations and produces a product o optimum quality"

7ample

n Instrument technician is conducting an Input/Autput test o an I/+ converter shown in the fgure. Input is ?;$D m rom 2% and output is >;" psi.

 he resulting s &ound I/A  able is shown belowB

(indings

)ased on the s &oundB I/A test able below, the I/+ shows an error o D.$psi in every test point.

In;order to eliminate the error, the instrument sensitivity was adjusted. ter adjustment, another Input/Autput test was conducted, and the result is shown on the I/A able on the right. his time the error in psi per test point is D. the process o adjusting the error is what is called %0I)2IAF.

 he able that contains the data ater calibration is called s 0etB I/A est

“Calibration is an insurance policy that verifies the accuracy of test instruments.” 

%alibration is the act o checking and veriying the accuracy o a measurement instrument by comparison with a reerence standard. +roperly calibrated instruments perorm to manuacturers published specifcations. 2egularly calibrating measurement instruments ensures the accuracy o measurements that are relied upon during design and manuacturing test.

3hile most instruments that are evaluated and calibrated normally pass the test, instrument perormance can change over time. here are several actors that can contribute to this change including drit, normal wear and tear, lack o proper maintenance, user error, and improper use and abuse o e(uipment. 2egular calibration ensures that test and measurement instruments are operating at a known perormance level.

)y doing proper calibration procedure and through proper interpretation o the calibration results, instrument error/s can be identifed and be corrected.

%alibration is re(uired by law.

Why is $alibration

#e5uired?

  %alibration is not a one;time occurrence. Instruments must be calibrated periodically to ensure specifed perormance.

Each instrument re(uires a specifc interval between calibrations. his interval is determined by the instruments owner and is oten based on the manuacturers recommendations.

 he original e(uipment manuacturers 7AE!8 calibration intervals are typically based on conservative perormance or the average user. &or best results, the instrument owner should use several additional actors in determining the optimal calibration interval, includingB he re(uired accuracy or the application vs. the instruments specifed accuracy. he business impact o using AA

 he International Argani'ation or #tandardi'ation 7I#A8 is comprised o representatives rom various national organi'ations and has "G$ member countries. I#A develops standards or industry and trade. +artnering with I#A registered calibration providers ensures that the provider ollows standard practices.

I#A HDDD is a amily o standards that provide a

ramework or managing an organi'ations

processes and a set o standardi'ed re(uirements or a (uality management system.

I#A/IE%"JD$ is a standard used by testing and calibration laboratories. 0aboratories implement the

%alibration according to 2.. H$>G o $DD> 72E+1)0I% % FA. H$>G *E FIAF0 !E2A0AKL % A& $DD>8, is a set o operations establishing under specifed condition, relationship

between values indicated by a

measuring instrument or measuring system, or values represented by

material measure, and its

corresponding known values o

$alibration according to 8egal

Metrology

8ote: *M"  9M" are commonly !nown as C35*43T94"+

Instrument $alibration )loc*

!iagram

*nput Measurement

"tandard (*M") 7nit 7nder Test (77T)

9utput Measurement "tandard (9M")

".Aver a period o time ".Aver a period o time

$.%hange in process parameters $.%hange in process parameters

>.%hange in environmental conditions >.%hange in environmental conditions

?.%hange in instrument mounting ?.%hange in instrument mounting position

position .)eor

.)eore installation o ne installation o new instrumentew instrument G.ter any instrument repair

G.ter any instrument repair J.3hen process verifcation

J.3hen process verifcation is re(uiredis re(uired M.Kovernmental 2egulation 7i.e.2 H$>G8 M.Kovernmental 2egulation 7i.e.2 H$>G8 H.Ather reasons deemed necessary

H.Ather reasons deemed necessary

When is $alibration #e5uired?

When is $alibration #e5uired?

)y practice, the re(uency o calibration )y practice, the re(uency o calibration depends upon the classifcation o the depends upon the classifcation o the instrumentsB

instrumentsB

Critical#

Critical# n n instrument instrument which, which, i i notnot conorming to specifcation, could potentially conorming to specifcation, could potentially compromise product or process (uality and compromise product or process (uality and saety. 7ypical is twice yearly8

saety. 7ypical is twice yearly8

$on%critical#

$on%critical# n instrument whose unction is n instrument whose unction is not critical to product or process (uality, but not critical to product or process (uality, but whose unction is more o an operational whose unction is more o an operational signifcance. 7ypical is yearly8

signifcance. 7ypical is yearly8

Reerence Only#

Reerence Only#  n instrument whose  n instrument whose unction is not critical to product (uality, not unction is not critical to product (uality, not

9o+ often instrument is calibrated? 9o+ often instrument is calibrated?

%alibration can be easily ignored or cycles %alibration can be easily ignored or cycles etended beyond their recommended time etended beyond their recommended time rame, which may increase operational risk or rame, which may increase operational risk or regulatory compliance. Feglecting routine regulatory compliance. Feglecting routine calibration schedules can lead to (uality and calibration schedules can lead to (uality and regulatory issues, increasing downtime, and regulatory issues, increasing downtime, and increase epenses.

increase epenses.

I a company is unable to meet its customer I a company is unable to meet its customer or regulatory re(uirements, they introduce or regulatory re(uirements, they introduce signifcant risk o business interruption, loss o signifcant risk o business interruption, loss o operating privileges, or compromised public operating privileges, or compromised public saety.

saety.

3hen compared with the signifcant business 3hen compared with the signifcant business risks associated with non;compliance, calibration risks associated with non;compliance, calibration

$ost and #is* of 6ot $alibrating $ost and #is* of 6ot $alibrating

%alibration utili'ing deal conditions such as room temperature, humidity, room pressure, vibration C etc.

 )ench %alibration is perormed in the shop on the bench with power supplied rom an eternal source. It may be perormed upon receipts o new instruments prior to installation. his provides an assurance that the instrument received is undamaged. his also allows confguration and calibration in a avourable environment.

Wor*shop4 8aboratory or )ench $alibration

Advantages !isadvantages ;+ *nstrument is removed, cleaned and

inspected+

;+ #roblem may encounter during pull-out and installation+

<+ Calibration done in an ideal conditions+ <+ =ero ad&ustment usually re$uired after installation to compensate for field

ambient operating conditions+ >+ Fixed calibration set-up and utilities+

Typical )ench $alibration %etup

%alibration utili'ing actual feld conditions such as feld ambient temperature, barometric pressure, vibration, utilities, position C etc.

&ield %alibrations are perormed “in;situ@ or in;place, as installed. he instrument being calibrated is not removed rom the installed location. &ield calibration may be perormed ater installation to ensure proper connections and confguration. +eriodic calibrations are more likely to be perormed in the feld.

(ield $alibration

Advantages !isadvantages ;+ May save calibration time+ ;+ 5oop elements

performance2condition may not be individually chec!ed+

<+ May identify and allow

troubleshooting of installation problems+ >+ 'one in actual field ambient operating conditions+

$haracteristics of

$alibration

". %ompliance to the 2e(uired ccuracy 2atio o #tandards

$. raceability o %alibration #tandards >. 1ncertainty o !easurements

. Accuracy #atio of

%tandards

 his term describe the relationship between the accuracy o the calibration standard and the accuracy o the 11.  good rule o thumb is to ensure an accuracy ratio o ?B". his means that the accuracy o the calibration standard is our times better than the accuracy o the 11.

 o determine whether a measurement is accurate and precise, it must be compared to a known #F929.  measurement standard is one that has been established as a model.

Instruments that are used as measurements standards 7%alibrators8 are calibrated according to internationally accepted standards 7+rimary #td.8. hese certifed standard instruments are then used to calibrate test e(uipment 7#econdary #td.8. est e(uipment is, in turn, used to calibrate process instruments.

The Importance of $alibration

%tandards ,$alibrators-:

%tandards or $alibrators

Instrument $alibration )loc*

!iagram

*nput Measurement

"tandard (*M") 7nit 7nder Test (77T)

9utput Measurement "tandard (9M")

b - a  c

a  ?@A b  ?@+;A c  @+;A

%alibration

#tandard

is

an

internationally

accepted

and

traceable instrument or material

used as reerence in calibrating

instruments.

What is $alibration

%tandard?

1. Primary Reference Standard or Material

-. _{9irectly traceable to international}

standards.

-. _{ standard which has highest}

metrological (uality in a specifed feld. $. Secondary or Certied Reference

Standard or Material

-.  _{raceable only to manuacturers}

reerence standards.

-. _{Ane which value is fed by}

$lassification of $alibration

;. Traceability of %tandards

ll calibrations should be perormed

traceable to a nationally or

internationally recogni'ed standard.  raceability is defned by F#I/F%#0 N?D;";"HH? as “the property of a result of a measurement whereby it can be related to appropriate standards,

through an unbroken chain of

Traceability <

Traceability < the property of a result of a measurement relating to appropriatethe property of a result of a measurement relating to appropriate standards, generally national or international through an unbro!en chain of standards, generally national or international through an unbro!en chain of comparison+

comparison+

9ierarchy of $alibration %tandards 3 9ierarchy of $alibration %tandards 3 Tr

,I%A-In the +hilippines, calibration is legally In the +hilippines, calibration is legally supported under 2.. H$>G 6 “the supported under 2.. H$>G 6 “the Fational !etrology ct o $DD>@.

Fational !etrology ct o $DD>@.

It is an act establishing a Fational It is an act establishing a Fational

!easurement Inrastructure #ystem

!easurement Inrastructure #ystem

7F!I#8 or standards and measurements, 7F!I#8 or standards and measurements, and or other purposes.

and or other purposes.

8ational Metrology 5aboratory of the

8ational Metrology 5aboratory of the

#hilippines (8M5#B*5)

=. Uncertainty of measurements

=. Uncertainty of measurements

1ncertainty analysis is re(uired or

1ncertainty analysis is re(uired or

calibration labs conorming to I#A

calibration labs conorming to I#A

"JD$

"JD$ re(uir

re(uirements.

ements.

1ncertainty analysis is perormed to

1ncertainty analysis is perormed to

evaluate

and

identiy

actors

evaluate

and

identiy

actors

associated

with

the

calibration

associated

with

the

calibration

e(uipment and process instrument

e(uipment and process instrument

that a=ect the calibration accuracy.

Measurement

Uncertainty

Why Measure?

 he objective o a measurement

is to determine the value o the

measurand  or the value o the

particular

(uantity

to

be

Measurement rrors4 effects

and corrections:

In

general,

measurement

has

imperections that give rise to an

error in the measurement result.

%ommonly, an error is classifed into

three types, namelyB a random

error, systematic error and spurious

error.

#andom rror ,Accuracy

rror-2andom errors are unavoidable errors, which are introduced into the measurement process at random or by chance. he e=ects o such variations known as random e=ects, give rise to variations in repeated observations o the measurand.

lthough it is not possible to compensate or the random error o measurement result, it can usually reduced by increasing the number o observations.

%ystematic rror ,)ias or "recision

rror-#ystematic error, like random error, cant be eliminated but it too can oten be reduced. I the in:uence o systematic error known as systematic e=ect can be (uantifed and i it is signifcant in si'e relative to the re(uired accuracy o the measurement, correction actor or bias can be applied. ter the correction, the epected value o the error arising rom the systematic e=ect is 'ero.

%purious rror 

#purious errors are error, such as

human

mistakes

or

instrument

malunction, which invalidate a

measurement. #uch errors cant be

treated with statistical analysis and

the

measurement

should

be

discarded.

Measurement and Measurand

In

general,

the

result

o

a

measurement

is

only

an

appro!imation or estimate of the

"alue of the measurand  and thus is

complete only when accompanied by

a statement o the

uncertainty o

that estimate.

What is U6$#TAI6T>?

)ased on defnition under $.$ o the I#A Kuide to the Epression o 1ncertainty in !easurement 7K1!8, the word “uncertainty@ means 9A1), and thus in its broadest sense “uncertainty o measurement@ means doubt about the validity o the result o a measurement.

Measurement Uncertainty $oncept

Measured alue @ .B m)ar C Uncertainty of measurement

$ommon %ources of Uncertainty

 _{Environmental conditions}

 _{+ersonal bias in reading values}

 _{&inite instrument resolution}

_{%alibration o standards}

 _{2ounding o measurement}

  _{!ethods C procedures o}

measurement

Ishi*a+a ,fishbone diagram-:

nvironment 5uipment Man

Measurement method 3 procedure Measurement system 3 utilities Temperature #ressure ibration  others  3ccuracy 4esolution "tability  others ias rror  9thers 'irect or *nferred 9thers Connection  wire resistance_{"tability of} utilities 9thers

Uncertainty can be e7pressed in

terms of the follo+ing:

".

#tandard 1ncertaintyB ui

%ombined 1ncertaintyB uc

>.

Epanded 1ncertaintyB # $ uc

Methods of valuating %tandard

Uncertainty ui $omponents:

". ype  Evaluation 7o uncertainty8 6

is the method o evaluating

uncertainty by the statistical analysis o a series o observations. In this case, the standard uncertainty is the eperimental standard deviation o the mean that ollows rom an averaging procedure.

$. ype ) Evaluation 7o uncertainty8 6 method o evaluation o uncertainty by means other than the statistical analysis o series o observations. In this case the evaluation o the standard uncertainty is based on some pool o inormation such asB

• _{previous measurement dataO}

• _{eperience with or general knowledge o the}

behavior and properties o relevant materials and instrument

• _{manuacturers specifcations}

• _{data provided in calibration and other certifcates}

%ample: $alculating %tandard Uncertainty ,ui) of (lo+meter and "roving Tan* in terms of %tandard !eviation ,%T!-:

 "D;validation runs were conducted on a :owmeter calibration system using >DDD batch si'e. 2esults were tabulated and #9< o the :owmeter and the proving tank were calculated. 2esults shown on the let table.

ui o &lowmeter is >."> ui o +roving tank is ".D

The $ombined %tandard Uncertainty

,u 

-:

 he combined standard uncertainty o a measurement result, suggested symbol uc, is taken to represent the

estimated standard deviation o the result. It is obtained by combining the individual standard uncertainties ui,

whether arising rom ype  or a ype ) evaluation, using the usual method or combining standard deviations.

$alculating the $ombine %tandard

Uncertainty

,u 

c 

-

Combine

7ncertainty (uc  ) =

ui  of Flowmeter is >+;> and ui of #roving Tan! is

;+@?

(ui of Flowmeter)D E (ui of #roving Tan! )D

(>+;>)D E (;.0 )D

7panded Uncertainty ,U -:

 (uantity defning an interval about the result o a measurement that may be epected to encompass a large raction o the distribution o values that could

reasonably be attributed to the

measurand. he epanded uncertainty denoted by * is obtained by multiplying the combined standard uncertainty uc by a coverage actor k. husO #Puc7k8

$alculating the 7panded Uncertainty

,U -

xpanded 7ncertainty (") = uc (#)

= !.! ($) = %&' . 

here:

uc = Combine standard uncertainty # = Coverage Factor 

%tatement of Uncertainty of Measurement

in $ertificates

In calibration certifcates , the complete result o the measurement consisting o the estimate y  o the measurand and the associated epanded uncertainty *  shall be given in the orm 7y /# *.

 o this an eplanatory note must be added which in the general case should have the ollowB

he reported e*panded uncertainty of measurement is stated as the standard uncertainty of measurement multiplied by the covera+e factor #=$, -hich for a normal distribution corresponds to a covera+e probability of appro*imately / level of confidence.

8evel of $onfidence:

!ost o epanded uncertainty calculations are based on coverage actor 7kP$8 and confdence level o HQ 7" chance in $D that the value o the measurand lies outside the interval8.

D

. $ompliance to I%OEF;G

%alibration technical re(uirements per +F# I#A/EI% "JD$B$DDD

 _{*uman &actors 7+ersonnel8}  _{Environmental %onditions}

 _{est C %alibration !ethods and}

!ethod <alidation

 _{est/calibration e(uipment}  _{raceability}

Overall benefits of having a

regular instrument calibration:

 _{Enhances production e5ciency}

 _{Enhances product (uality assurance}  _{Increases plant saety}

 _{2eduction in production cost}  _{Improves proft margin}

#ange

#ange and

and %pan

%pan

 o o ully ully understand understand the the concept concept oo calibration, it is essential to understand calibration, it is essential to understand the range and span o an

the range and span o an instrument.instrument. Range

Range is the set o values 702< C 12<8 is the set o values 702< C 12<8 over which a measurement can be over which a measurement can be made without changing the made without changing the instrum

instruments ents sensitivsensitivityity.. &pan

&pan is the distance 7or di=erence8is the distance 7or di=erence8 between the upper range vale 712<8 between the upper range vale 712<8 and lower range value 702<8.

!ifference bet+een instrument

!ifference bet+een instrument

Measuring #ange and $alibration

Measuring #ange and $alibration

#ange

#ange

'easuring Range

'easuring Range 6 reers to6 reers to instrument measuring capability

instrument measuring capability Calibration Range

Calibration Range  6 reers to  6 reers to range

range the the instrument instrument is is calibratedcalibrated to produce a scaled output.

Instrum

Instrument

ent Accuracy

Accuracy44

"recision and 1ain

"recision and 1ain

Accuracy in $alibration

Instruments are calibrated to make

them accurate within

manuacturers specifcations.

Accurate  calibration thereore is an essential actor in instrument perormance.

Ways of !etermining Instrument

Accuracy:

".

!anuacturers specifcations

)y calculations 7%alculated8

. As a percent of output

span

EampleB

 pressure transmitter has an output span o D psi. It measures an actual tank pressure o $ psig but reads $G psi. In this case, the transmitter is accurate within " psi or $Q o span.

ccuracy 7Q8 P !< 6 </#pan  "DD

7ample of accuracy

;. As a percent of measured

value

,M-EampleB

 pressure transmitter has an output span o D psi. It measures an actual tank pressure o $ psig but reads $G psi. In this case, the transmitter accuracy is ?Q o measured value.

ccuracy 7Q8 P !< 6 </!<  "DD

7ample of accuracy

What is an Accurate Instrument?

n accurate instrument is an instrument in which the output

accuracy always alls within

manuacturers specifcations every time an input is applied.

%ample: Accurate Instrument Manufacturers accuracy

statement is C2 F.GH of span

$ontrol $hart ,;"TF;F-(# $ement $orporation

Meaning and Importance of

Instrument "recision

(recision  is another important actor in instrument perormance.

 precise instrument will produce the same output every time it receives an identical input.  transmitter that produces the same output signal rom a constant input is precise.

%ample: "recise Instrument Manufacturers accuracy

statement is C2 F.GH of span

$ontrol $hart ,;"TF;F-(# $ement $orporation

%ample: "recise Instrument Manufacturers accuracy

statement is C2 F.GH of span

$ontrol $hart ,;"TF;F-(# $ement $orporation

Meaning and Importance of 1ain

in $alibration

 he level o accuracy to which an instrument can be calibrated is partially dependent on another actor known as )ain.

)ain reers to the amount o output change or each increment o input change. It is a key actor in

determining how accurately an

1ain $alculation

Transmitter ain is calculated by dividing the output span by the input span+

$alibration "rocedures

carried out in relation to

instruments input/output

relationship. It could be either a ; point or "D;point input/output relationship.

Gpoint $alibration "rocedures

 calibration procedure which utili'es a  input and  output test points.  his is the most widely used calibration procedure. est points commonly used are D, $, D, J and "DDQ o the input and output span.

Gpoint Input and Output relationship

Table

EampleB 9irect cting Electronic emperature %ontroller with calibration range o "DD 6 DD R%

Fpoint $alibration "rocedures

 calibration procedure which utili'es a "D input and "D output test points. his is the most widely used calibration procedure. est points commonly used are D, $, D, J, "DD, J, D, $ and DQ o the input and output span.

 his procedure is used to determine

instrument error known as

Fpoint Input and Output relationship

Table

EampleB 9irect cting Electronic emperature %ontroller with calibration range o "DD 6 DD R%

)asic %teps in $alibrating an Instrument:

". Identiy the type o 11 to be calibrated and record all necessary inormation re(uired or the calibration job.

$. Identiy and prepare the appropriate I!#, A!# and 1tilities re(uired or the calibration job.

>. #et;up the calibration system.

?. %alibrate 11 reerence to 11s maintenance manual or users established 3ork Instruction.

. Evaluate/correct instrument error. G. 9o housekeeping.

Types of $alibration rror 

Types of $alibration rror 

*nstrument error can occur due to a variety of *nstrument error can occur due to a variety of factors: drift, environment,

factors: drift, environment, electrical supply, electrical supply, addition ofaddition of components to the output loop, process changes, etc+ components to the output loop, process changes, etc+ "ince a calibration is performed by comparing or "ince a calibration is performed by comparing or applying a !nown signal to the instrument under test, applying a !nown signal to the instrument under test, errors are detected by performing a calibration+ 3n errors are detected by performing a calibration+ 3n error is the algebraic difference between the indication error is the algebraic difference between the indication and the actual value of the measured variable+

Types of $alibration rror 

Types of $alibration rror 

".

". 0inear Errors0inear Errors



 _{Nero #hitNero #hit} 

 _{#pan Error#pan Error} 

 _{Nero and #pan ErrorNero and #pan Error}

$.

$. Fon 6 linear ErrorFon 6 linear Error >.

Jero %hift

,8inear- *ero shit reers to a situation in which an instrument signal output is consistently higher or lower than would be epected throughout the input span.

It can also be described as a situation where the instrument is outputting consistently with inputs provided but starts at a point too high or too low on the output scale.

%pan rror

,8inear-&pan error is another type o instrument error. he readings or an instrument with span error either do not represent "DDQ o the output span or the output span does not match the input span.

Jero %hift and %pan rror

$ombination

,8inear-)oth *ero shit and span error can occur in the same instrument. In such case, an input/output graph produces a signal line that agrees with neither the origin nor the angle o the ideal line.

6on < linear rror 

$on%linearity  is a condition in which an instrument outputs signals that do not match inputs between upper and lower limits o the span. #evere non; linearity is not a simple adjustment problem and may re(uire instrument repair. nd i the magnitude of the nonlinear error is unacceptable and it cannot be ad&usted, the instrument must be replaced+

9ysteresis

+ysteresis is another common instrument problem. In this case, instrument produces di=erent signals depending upon the direction o the input procedure. !oving up or down through the input range produces di=erent output signals.

9ysteresis

$alibration $ertificate2#eport must at least contain the follo+ing elements as per G.F.; of "6% I%O2I$ EF;G;FFF.

•  _{ title}

• _{Fame and address o the laboratory}

where calibration was carried out.

• _{%ertifcate Identifcation}

• _{Fame and address o client}

• _{Identifcation o the method being}

used.

• _{9ate 1nit received C calibrated}

• _{raceability, 1ncertainty C}

Environmental %onditions

• _{est results C units o measurement} • _{&indings C observations}

• _{#tatement o the e=ect o the results}

relate only to item calibrated.

In addition4 calibration certificates shall

include the follo+ing4 +here necessary for the interpretation of calibration results:

". 3hen an instrument or calibration has been adjusted or repaired, the calibration results beore and ater adjustment shall be reported.

$.  calibration certifcate or label shall not contain any recommendation on the calibration interval ecept agreed with the client.

>. 3hen a calibration work has been contracted, the laboratory perorming the work shall issue the calibration certifcate to the contracting laboratory.

?. he ormat o the calibration certifcate shall be designed to accommodate data and to minimi'e the possibility o misunderstanding.

. 3hen it is necessary to issue a complete new calibration certifcate, this shall be uni(uely identifed and shall contain in a reerence to the original that it replaces. G. %alibration certifcates are part o the

Important 6otes #egarding

$ertificates:

should also include the page number and total number o pages.

$. It is highly recommended that a statement speciying that the test report or calibration certifcates shall not be reproduced ecept in ull, without written approval rom the issuing laboratory.

>. %alibration certifcates must be controlled and considered legal documents.

Introduction to

What is alidation2erification?

<alidation/verifcation 6 is the process o simulating an instrument with a known input and comparing the result to a %alibration olerance. I the di=erence is within the specifed tolerance, no action shall be taken. *owever, i not, %alibration must be perormed.

$haracteristics of a

alidation2erification

". %ompliance to the 2e(uired ccuracy 2atio o #tandards

$. raceability o %alibration #tandards >. 1ncertainty o !easurements

?. %ompliance to I#A;"JD$ " Acceptable Tolerance

G. Acceptable Tolerance

Every <alidation/<erifcation should be perormed to a specifed tolerance. he terms tolerance and accuracy are oten used incorrectly. he defnitions or each are as ollowsB

Accuracy#  he ratio o the error to the ull scale output, epressed in Q o span or the ratio o the error to the output, epressed in Q reading.

Tolerance# +ermissible deviation rom a specifed value. !aybe epressed in

alidation Tolerance

  _{should not be based on}

manuacturers accuracy statement only. It should include also the ollowingB

• _{2e(uirements o the process}

• _{%apability o available test}

e(uipment

• _{%onsistency with similar}

alidation2erification )loc*

!iagram

*s the diff+ more than the Cal+ ToleranceG

Calibrate b - a  c a c b y n %uit

alidation Acceptance $riteria:

•_{Error is within the given calibration}

tolerance.

• _{ypes and magnitude o error}

indicated by instrument is acceptable based on application.

•_{!easurement uncertainty is}

known/defned.

•_{Ather relevant criteria specifed by}

Gpoint alidation2erification

$urve

 3cceptable Calibration Tolerance

(E2- @+<A of "pan)

Measured alue

&uality Management %ystem

and Instrument $alibration

&uality Management

%ystem

Suality !anagement #ystem is a

part o the organi'ations

management system that ocuses on the achievement o results, in relation to the product (uality objectives.

&M% and Instrument

$alibration

#ince an accurately calibrated instrument contributes not only to the saety aspects o any automated industrial process but also much on e5ciency and product (uality, most o plants Suality !anagement #ystem 7S!#8 deals calibration issue as one o its main concern.

I#A;HDDD S!# standard specifcally item J.G thereo re(uires regular testing and calibration o any process instruments, which during malunction could a=ects product (uality.