23871687 Calibration

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CALIBRATION

Procedures, StandardAnd

Methodologies

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Introduction

• In this section, the procedures andmethodologies to carry out a

calibration will be discussed. Inaddition, the approach to calculateerrors in a calibration will be shown.

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Objective Of Calibration

• The prime objective of calibration isto ensure that measurements takenare accurate at all times taking intoconsideration wear and tear,degradation and abuse. It is with thisin mind that we need to adopt and

appropriate methodology to do aproper calibration.

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Scope of Calibration

In developing a calibration program, the followingshould be taken into consideration :

Involve all testers or those who use measuringand test equipment

Calibration must be conducted on all equipmentused to verify product compliance.

Engineering measuring equipment must all becalibrated.

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Hierarchy of Standards• The hierarchy of standards used in a calibration is shown as

follows :

Primary or National standards are the ultimate reference standards for determining ameasurement. As an example, a standard measurement of a meter is set by a steel rodof this length which is the primary standard. All other standards used to conduct acalibration must be checked with reference to this standard from the working to thereference standard

PrimaryStandard

Reference Standard

Working Standards

Measuring & Test Equipment

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Standard Adequacy

• Working standard used to calibrate internal measuringequipment must be traceable to either a National or PrimaryStandard. In addition, their accuracy must be 4 to 10times more accurate compared to the equipment to becalibrated. For instance, portable water analyzer such as pH

meter, NTU meter with the standard measurement scale,can be calibrated internally by using the standard solutionthat provided.

• Occasionally, an equipment may be state of the art and

hence, there is no reference standard available. In thiscase, this equipment can be calibrated with anotherequipment of the same type, make and model.

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Traceability of Calibration

• In a country, a calibration must be traceable to a National

Standard held by a national body (eg. SIRIM or othergovernment agencies of Malaysia). If this national standardis not available. The calibration must be traceable toanother country. Traceability of a calibration is importantas an incorrect reference standard used will not ensure

that the equipment calibrated has the required accuracy.

• As most companies send out their equipment for calibration,mandatory that they check the capability of the calibrationagent. Those that are certified to the ISO 9000 Guide 25

will be able to provide an appropriate traceability. Forothers, you will need to check the reference standards usedand their respective traceability.

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Factors to Consider in a Calibration

• Calibration Environment

• Interval of Calibration

• Accuracy of Standard Master

• Out of Tolerance Equipment

• Subcontractor Controls• Uncertainty of Measurement

• Handling the Storage

• Identification and Status of Calibration

• Training• Documentation and Records

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Calibration EnvironmentEnvironment conditions which could affect a calibration are as follows. This willlargely dependent on the sensitivity of an equipment to the various conditions. Consult

the equipment manufacturer to determine the appropriate environmental conditionsrequired to do a calibration.

• Temperature• Humidity• Vibration• Dust

• Noise• Light• Air Movement• Magnetic Field

Some examples where controlling certain environment factors is critical for thedifferent types of measurement are as follows :

Chemical Analyses – pH value and NTU are critical

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Interval of Calibration• Interval between one calibration to another is an important aspect to

ensure the continuing accuracy of an equipment. This must be establishedfor all measuring and test equipment, each may be set at differentintervals dependent on the degree of usage and other factors such as:

> Stability

> Frequency of Use

> Accuracy> Purpose of Use

• If you are unsure which is the best interval to choose, always follow theequipment manufacturer’s recommendations. This interval should bereviewed from time and as a rule of thumb, it should be adjusted based on

the calibration history. For example, if an equipment is calibrated on a sixmonthly basis and it is found to be out of calibration frequently, then thecalibration interval should be changed either 2 or 3 monthly.

C LIBR TION INTERV L

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CALIBRATION INTERVAL

• What actions and the calibration interval on the equipment would you recommend tothe user for the following :

1. An instrument is found to have failed 2 times in the last 2 calibrations

performed at 6 monthly intervals.

2. A newly purchased pH on-line analyzer which will be used in production daily.

Calibration interval recommended by manufacturer is 3 monthly.

3. A Magnetic Flow Meter used to measure the flow of water with

specification of 0.5 to 1 % accuracy.

Accuracy of Magnetic Flow Meter is 0.5 to 1% with Calibration interval of

yearly using the Flow Meter Verificator.

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ACCURACY OF REFERENCE STANDARD

• As discussed in the previous section, thereference standard used to do a calibration mustbe at least 4 to 10 times more accurate than the

equipment. In general, a 95% confidence level ispreferred and this gives a + 2 sigma (standarddeviation) or 4 sigma capability in a measurement.

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OUT OF TOLERENCE EQUIPMENT

• When an equipment is found to be out of tolerance or not having the requiredaccuracy, certain steps must be taken. Actions to be taken include decisions on

whether the equipment can be used or not and what needs to be done on the affectedproducts as follows :

> Review all measurements prior to and after adjustment is made to the

affected equipment.

> Decide on whether the equipment can be used or has to be thrown away

or used for lesser accuracy measurements.> Review previous batches of products ( 1 week or more) where

measurements have been taken using this out of tolerance equipment

prior to and after an adjustment has been made to correct the out of

calibration situation. Decide whether they meet specification or not.

> If the equipment can be used but needs correction to their readings, then the

compensation or offset factors must be stated on the equipment.

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Subcontractor Controls

• In choosing an appropriate subcontractor to perform yourcalibration, it is critical that an accredited calibrating labor agent is used (those certified to ISO 9000 Guide 25).Ask for a copy of their certification before selecting them.You will also need to ensure that the reference standards

used by the calibrating lab or agent is traceable to nationalstandard. The calibration method used should also bechecked to ensure they used an appropriate or recognizedprocedure. Both of these requirement can be verified ontheir Certificate of Calibration, which is issued to you uponcompletion of a calibration for each set of equipment.

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Uncertainty Of Measurement

The uncertainty of measurement of a calibration needs to becalculated to determine all the possible sources of errors. It isgiven by the formula :

Uncertainty of Measurement = + t (from a Students t-table) x s(standard deviation of variation).

As a rule of thumb, the uncertainty of measurement must not exceed30% of the tolerance of a measurement. If it does, it’s mean that theequipment is not suitable for use as its required accuracy is not

sufficient. A measurement taken using this equipment will give a falseor inaccurate value.

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Handling and Storage• The proper handling and storage of measuring equipment and their

reference standards are an essential part of establishing aneffective Calibration Program. Some of the guidelines to follow areas follows:

Handling – ensure the equipment is appropriately handled during use, storage andtransportation.

Proper Storage – ensure equipment is stored in their respective casing or specialstorage container under appropriate environmental conditions as required.

Proper Packing for Transportation – ensure the equipment is appropriately packed toprotected them from movement and damage during transportation (eg. Use “bubblebags” or impact absorbent materials).

Check that the calibration status is valid before issuing an equipment for use(especially newly purchased equipment).

Ensure that the equipment is appropriately sealed with a tamper-proof sticker ormarking, etc to prevent unauthorized adjustment or repair.

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Identification and Status of Calibration

• Upon completion of a calibration, each equipmentmust be appropriately labeled to indicate theirstatus. Depending on the size of the equipment, itmay not be possible to attach a calibration labelon all instruments. For an equipment such asthermometer it may not be practical to stick sucha label. Therefore, other means such as colorcoding can be used instead of a label to indicate

their calibration status. Alternatively, the labelmay be attached to the casing or container.

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Example of the various labels or identifications which can be used are asfollows:

• Passed Calibration

• Tamper Proof Label

These labels are used to prevent tampering on the equipment after it is calibrated.

An example is as follows :

ID#: DATE:

BY: DUE:

VOID Calibration Seal

If Broken

PBA

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• “DO NOT USE” Label

This label is used to indicate that a specific equipment cannot be usedeither because it is damaged or needs repair or malfunctioned or itscalibration is out of tolerance.

• “No Calibration Required” Label

This label is used to indicate those equipment which do not require anycalibration. These are mainly those used for rough measurement and forwhich accuracy is not important. Some examples are processinstrumentation such as chlorine analyzers and ultrasonic level sensor, etc.

DO NOT USE

PBA Perbadanan Bekalan AirPulau Pinang Sdn. Bhd.

CALIBRATION NOT

REQUIRED

Perbadanan Bekalan AirPulau Pinang Sdn. Bhd.PBA

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Training

• Personnel appointed to perform calibration mustbe appropriately trained together with propereducation and experience. They must understandthe characteristic and features of an equipment,and its usage (ie. Required accuracy, stability,

sensitivity, etc). Furthermore, the personnel mustknow the calibration procedures andmethodologies including the calculation ofuncertainty of measurement and sources oferrors. Various training courses are now availableand those responsible for performing calibrationmust attend these courses.

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Documentation and Records

• Appropriate documentation and records must be maintained aspart of a calibration program. Essential ones are as follows :

a) Master List of Equipment

A master list of equipment shall be maintained to indicate all the measuring equipment used in acompany. It should state as a minimum, the following details :

Equipment Identification (ID) Location

Required Accuracy

Measurement Range

Calibration Interval

Calibration Lab/Agent (internal or external)

Date Calibrated

Date due for Next Calibration

Pass / Fail Calibration

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b) Calibration Plan

For each type of equipment, a calibration plan shall be developed. This plan shalloutline all the steps to conduct a calibration including :

Reference standards to be used ;

Recording methodologies ;

Environmental conditions for calibration ;

Calculations ;

Approach to handle an out of tolerance situation.

The plan should also outline the recalling system to ensure each piece of equipment iscalibrated either on or before their due date. A reminder system or calibrationschedule is necessary.

c) Training Records

Training records shall be maintained for all personnel authorized to performcalibration.

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d) Out of Calibration Notice and Records

Notices advising the relevant department and personnel of an equipment found to be

out of calibration and the corresponding actions (s) taken shall be maintained.

e) Manufacturers’ Handbooks

Manufacturers’ handbooks or reference manuals used as part of calibration shall alsobe controlled and kept by the department responsible for calibration.

f) Calibration Certificate

Calibration certificate provide by an external calibrating organization must be kept asproof of calibration and are to be maintained as part of the calibration records.

Internal calibration certificate also required to be kept at the respective cost centre.

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g) Records of Usage

Records of usage are to show the persons who have used the equipment and toindicate the degree of usage and what measurements were taken.

h) Measurement Equipment History Record

A history record should be maintained for each piece of equipment. It should containthe following details :

make, model and type or brand

date of purchase

department using this equipment and its location use

date of first calibration

adjustment made during calibration (if any)

repair & service details

action taken on out of tolerance situation (if any)

date of disposal (when it is unusable).

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Thank youPrepared By:

Mohd Suhaimi Shariff

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23871687 Calibration