DRAFT RECOMMENDED PRACTICE

ISA-dRP105.00.01-201XCD14

Management of a Calibration Program For Monitoring And Control Systems

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Quality Management System for Implementation and Maintenance of an Industrial Calibration Program

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Copyright © 201X by ISA, the International Society of Automation. All rights reserved. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher.

ISA67 Alexander DriveP.O. Box 12277Research Triangle Park, North Carolina 27709USA

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Preface

This preface, as well as all annexes, is included for information purposes and is not part of ISA-dRP105.00.01-201X.

This document has been prepared as part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standards@isa.org.

The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing & Materials as IEEE/ASTM SI 10-97, and future revisions, will be the reference guide for definitions, symbols, abbreviations, and conversion factors.

It is the policy of ISA to encourage and welcome the participation of all concerned individuals and interests in the development of ISA standards, recommended practices, and technical reports. Participation in the ISA standards-making process by an individual in no way constitutes endorsement by the employer of that individual, of ISA, or of any of the standards, recommended practices, and technical reports that ISA develops.

CAUTION — ISA DOES NOT TAKE ANY POSITION WITH RESPECT TO THE EXISTENCE OR VALIDITY OF ANY PATENT RIGHTS ASSERTED IN CONNECTION WITH THIS DOCUMENT, AND ISA DISCLAIMS LIABILITY FOR THE INFRINGEMENT OF ANY PATENT RESULTING FROM THE USE OF THIS DOCUMENT. USERS ARE ADVISED THAT DETERMINATION OF THE VALIDITY OF ANY PATENT RIGHTS, AND THE RISK OF INFRINGEMENT OF SUCH RIGHTS, IS ENTIRELY THEIR OWN RESPONSIBILITY.

PURSUANT TO ISA’S PATENT POLICY, ONE OR MORE PATENT HOLDERS OR PATENT APPLICANTS MAY HAVE DISCLOSED PATENTS THAT COULD BE INFRINGED BY USE OF THIS DOCUMENT AND EXECUTED A LETTER OF ASSURANCE COMMITTING TO THE GRANTING OF A LICENSE ON A WORLDWIDE, NON-DISCRIMINATORY BASIS, WITH A FAIR AND REASONABLE ROYALTY RATE AND FAIR AND REASONABLE TERMS AND CONDITIONS.  FOR MORE INFORMATION ON SUCH DISCLOSURES AND LETTERS OF ASSURANCE, CONTACT ISA OR VISIT WWW.ISA.ORG/STANDARDSPATENTS.

OTHER PATENTS OR PATENT CLAIMS MAY EXIST FOR WHICH A DISCLOSURE OR LETTER OF ASSURANCE HAS NOT BEEN RECEIVED. ISA IS NOT RESPONSIBLE FOR IDENTIFYING PATENTS OR PATENT APPLICATIONS FOR WHICH A LICENSE MAY BE REQUIRED, FOR CONDUCTING INQUIRIES INTO THE LEGAL VALIDITY OR SCOPE OF PATENTS, OR DETERMINING WHETHER ANY LICENSING TERMS OR CONDITIONS PROVIDED IN CONNECTION WITH SUBMISSION OF A LETTER OF ASSURANCE, IF ANY, OR IN ANY LICENSING AGREEMENTS ARE REASONABLE OR NON-DISCRIMINATORY.

ISA REQUESTS THAT ANYONE REVIEWING THIS DOCUMENT WHO IS AWARE OF ANY PATENTS THAT MAY IMPACT IMPLEMENTATION OF THE DOCUMENT NOTIFY THE ISA STANDARDS AND PRACTICES DEPARTMENT OF THE PATENT AND ITS OWNER.

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ADDITIONALLY, THE USE OF THIS DOCUMENT MAY INVOLVE HAZARDOUS MATERIALS, OPERATIONS OR EQUIPMENT. THE DOCUMENT CANNOT ANTICIPATE ALL POSSIBLE APPLICATIONS OR ADDRESS ALL POSSIBLE SAFETY ISSUES ASSOCIATED WITH USE IN HAZARDOUS CONDITIONS. THE USER OF THIS DOCUMENT MUST EXERCISE SOUND PROFESSIONAL JUDGMENT CONCERNING ITS USE AND APPLICABILITY UNDER THE USER’S PARTICULAR CIRCUMSTANCES. THE USER MUST ALSO CONSIDER THE APPLICABILITY OF ANY GOVERNMENTAL REGULATORY LIMITATIONS AND ESTABLISHED SAFETY AND HEALTH PRACTICES BEFORE IMPLEMENTING THIS DOCUMENT.

THE USER OF THIS DOCUMENT SHOULD BE AWARE THAT THIS DOCUMENT MAY BE IMPACTED BY ELECTRONIC SECURITY ISSUES. THE COMMITTEE HAS NOT YET ADDRESSED THE POTENTIAL ISSUES IN THIS VERSION.

The following people served as members of ISA Committee ISA105:

NAME COMPANY

This recommended practice was approved for publication by the ISA Standards and Practices Board on __________.

NAME COMPANY

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Table of Contents1 Scope........................................................................................................................................... 11

2 Normative References................................................................................................................11

3 Definition of Terms and Acronyms............................................................................................11

3.1 Terms................................................................................................................................. 113.2 Acronyms........................................................................................................................... 12

4 Establishing a Calibration Program..........................................................................................13

4.1 Calibration Program Concepts........................................................................................134.2 Calibration Program..........................................................................................................14A calibration program for an industrial monitoring and control system formalizes a

methodology to periodically verify the performance accuracy of the components in that monitoring and control system and, when necessary, make adjustments to those components to bring them within their manufacturer rated accuracy and the loop within its required performance accuracy.......................................................14

Each user company/facility is encouraged to establish a calibration program specific to its needs. This recommended practice discusses the essential features of a calibration program and provides guidance how to establish such a program..........14

This proposed approach to a calibration program for automation instrumentation and systems takes into consideration all known loop measurement errors and establishes calibration tolerances based on the process requirements. Successful implementation of this approach requires management commitment to make this a living process. Critical steps in the process include:..........................14

a) Establish a loop/instrument tagging system..................................................................14b) Develop a comprehensive list of loops and instrumentation equipment requiring

calibration.......................................................................................................................... 14c) Establish a loop criticality system and criticality ratings for each of those loops......14d) Establish tolerance requirements for each loop............................................................14e) Establish loop calibration verification intervals (frequencies).....................................14f) Establish calibration equipment requirements..............................................................14g) Establish loop/instrument calibration record forms and calibration record-

keeping system.................................................................................................................14h) Establish necessary calibration procedures..................................................................14i) Establish staff qualifications and training requirements...............................................14j) Perform calibration checks at required intervals and document results .....................14Establish a calibration program verification methodology......................................................144.1.1 Device Calibration.............................................................................................................144.1.2 Loop Calibration................................................................................................................144.1.3 Test Equipment.................................................................................................................15

4.2.4 Competency.........................................................................................................154.3 Calibration Program Planning.........................................................................................15

4.3.1 Loops and components in the calibration program..........................................154.3.2 Component and Loop Criticality Determination................................................154.3.3 Establishing Required Loop Tolerance.............................................................154.3.4 Calculating theoretical loop tolerance...............................................................164.3.5 Calibration Confirmation Intervals.....................................................................164.3.6 Calibration equipment.........................................................................................17

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4.3.7 Calibration Record System.................................................................................184.3.8 Calibration Procedures.......................................................................................194.3.9 Calibration personnel..........................................................................................194.3.10 Responsibilities....................................................................................................20

5 Loop and Component Performance Verification......................................................................20

6 Calibration Program Management............................................................................................21

6.1 Control............................................................................................................................... 216.2 Assurance..........................................................................................................................216.3 Improvement......................................................................................................................21

7 Examples..................................................................................................................................... 21

Annex A – Example Documentation................................................................................................27

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IntroductionPurpose

The purpose of this recommended practice is to provide the basic framework for developing and maintaining a consistent calibration program for industrial automation and control systems, including instrumentation used in safety instrumented systems. The recommended practice provides guidance on methodologies for verification and calibration of monitoring and control systems by considering the accuracy of each loop required by the process and then adjusting loop component(s) to achieve the desired loop or component accuracy.

Accurate, reliable, and repeatable operation of loops in monitoring and control systems is vital to maintaining the safety and reliability of a facility. A well-considered calibration program, properly implemented and maintained, can directly contribute to the assurance of the desired operation of the monitoring or control system for the facility. A calibration establishes periodic assessments to be performed to monitor performance of instrumentation over time. Data acquired during these assessments not only aids in the establishment of future calibration intervals, but also is critical in the allocation of capital and operational resources. Clearly defined policy and procedures support the efforts of maintenance planners to schedule adequate labor and equipment for calibration both during and between facility outages. Following calibration procedures reduces the likelihood of human errors due to improper practices, ensures the desired results of the calibration efforts, and promotes the proper operation of monitoring and control systems.

In automation systems, more hardware faults occur in measuring instrumentation, transmitters, and control valves than in the control/logic systems. A calibration program can aid in early detection of failures. Reduction or elimination of instrument and control system calibration and maintenance of instrumentation and control systems may increase the likelihood of system problems, including:

Inaccuracy of measurements and control

System not responding correctly or as desired

Reduced awareness of instrument performance and actual need for calibration and maintenance

Potential for incorrect reporting of environmental data

However, targeted reduction, or increase, using data derived from an instrument asset management program can both reduce maintenance costs and improve reliability/safety.

Various definitions of the term calibration can be found:

The formal definition of calibration by the International Bureau of Weights and Measures is the following: "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 (of the calibrated instrument or secondary standard) and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication."

NIST Handbook 150:2001: 1.5.8 Calibration: Set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realized by standards.

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NOTE 1 The result of a calibration permits either the assignment of values of measured to the indications or the determination of corrections with respect to indications.

NOTE 2 A calibration may also determine other metrological properties such as the effect of influence quantities.

NOTE 3 The result of a calibration may be recorded in a document, sometimes called a calibration certificate or a calibration report.

According to standards ISO 9001:2008 7.6 and ANSI/NCSL Z540.3-2006, calibration is a comparison of the device being tested against a traceable reference instrument (calibrator) and documentation of this comparison. Although calibration does not formally include any adjustments, in practice, adjustments are possible and often included in the calibration process.

Maintenance practices for devices such as gauges and indicators, unfortunately, may occur only when the error in reading becomes large enough to be obvious to the operator or technician. Maintenance personnel routinely make decisions based on these devices. A faulty indication on such a device could lead to the release of energy or other unsafe action. A well-considered calibration program that periodically measures actual loop accuracy can drive the calibration intervals for these devices.

Instrumentation based on newer technology, e.g. “smart” devices, is more accurate than older technology devices and more stable, requiring less frequent calibration monitoring. A calibration program should also accommodate these types slightly differently, such as calibration check frequency and accuracy of calibration equipment required.

Companies striving to maintain a safe working environment while ensuring the reliability of their facilities may use calibration as a means of verifying the functionality and accuracy of their equipment.

Like other aspects of maintenance, there are many things to consider when establishing a company calibration program. Certainly, this is the case with the calibration of monitoring and control loops in a control system. This document presents a recommended approach to developing, implementing and maintaining a calibration program that is intended to lead to increased accuracy and reliability of monitoring and control systems, decreased production costs, and quality control improvements. More important, this approach is also intended to lead to increased safety of operation as the result of increased accuracy and reliability of the instrumentation.

This approach to calibration has proven successful when companies have adhered to the concepts set forth in these guidelines, enabling those companies to realize the full benefits from a standardized approach to calibration.

The intended audience for this document is any company or industry that utilizes instrumentation in the monitoring and control of a process or facility.

Organization

This recommended practice is organized to provide recommendations on :

Establishing a calibration program

Calibration program activities

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1 Scope1.1 General Applicability

The recommended practice detailed in this document defines a baseline definition and model of a quality management system that can be utilized to implement and maintain a calibration program for industrial monitoring and control systems. It is applicable to all industrial monitoring and control systems.

1.2 Inclusions and exclusions1.2.1 Manufacturer specific calibration procedures

This document does not provide or recommend manufacturer-specific calibration procedures for specific instruments as these are established by the instrument manufacturer and are outside the scope of this document.

1.2.2 BPCS and SIS functionality

This document does not include any consideration for how instrumentation and control signals are handled within the BPCS (Basic Process Control System) or /SIS (Safety Instrumented System) other than including indication of the signal in loop accuracy calculations.

1.2.3 Control value calibration

This document does not cover control valve maintenance.

1.2.4 Regulatory requirements

Regulatory requirements related to loop/instrument accuracies are not included in this RP.

1.2.5 SIS instrument calibration

The calibration of monitoring and control loops that are part of safety instrumented systems is included in the scope of this recommended practice. The documentation and management of these instruments as part of safety instrumented systems is excluded. For more information, see ANSI/ISA 84 and all its parts.

1.2.6 Instrument criticality

This document mentions criticality as it applies to a calibration program. This document does not modify any guidelines for establishing criticality provided in ISA TR91.00.02.

1.2.7 Control loop performance

The performance of final control elements and the tuning of control loops are excluded from the scope of this recommended practice.

2 Normative References NIST Handbook 150:2001

ISA TR91.00.02-2003 Criticality Classification Guideline for Instrumentation

ANSI\ISA 5.1-2009 Instrumentation Symbols and Identification

3 Definition of Terms and Acronyms3.1 Terms3.1.1 Accuracy- the degree of conformity of a device’s output to its actual input value.

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3.1.2 Calibration – the act of determining (by comparison with a standard) and, if necessary, adjusting a device to meet the standard within the device’s stated accuracy.

3.1.3 Calibration Work Instructions – Step by step instruction for performing a calibration on a specific device or loop.

3.1.4 Device - A piece of instrument hardware designed to perform a specific action or function.

3.1.5 Device Calibration A calibration performed on only one device.

3.1.6 Error – the difference between an indicated value and the actual value.

3.1.7 Instrument Asset Management – coordinated work processes of an organization to ensure the intended capability of assets is available.

3.1.8 Loop – combination of two or more instruments or control functions arranged so that signals pass from one to another for the purpose of measurement, indication, or control of a process variable.

3.1.9 Loop Accuracy – the degree of conformity of a loop’s measured or controlled variable indicated value to the variable’s actual value.

3.1.10 Loop Tolerance – the permissible limit of variation, from a known standard, in the loop indicated process measurement.

3.1.11 Management Program – activity that manages a group of related projects and/or work processes in a way that provides benefits and control not available by managing each activity individually and independently

3.1.12 Precision – the repeatability of measurements over time

3.1.13 Procedure – sequence of tasks with a defined beginning and end that is intended to accomplish a specific objective

3.1.14 Repeatability – The variation in measurements of a device or loop under the same conditions, and over a period of time.

3.1.15 Traceability – The property of the results of a measurement or the value of a standard whereby it can be related to a stated reference. Note: For example in the US, this is the National Institute of Standards and Technology or ILAC recognized laboratories.

3.1.16 Task - a single piece of work that needs to be done and does not have interacting elements requiring management

3.1.17 Verification – the act of checking the accuracy of a loop or loop component to determine whether it is performing within required tolerances.

3.1.18 Work Process - set of interrelated or interacting procedure(s) which transforms inputs into outputs

3.2 Acronyms3.2.1 NIST – National Institute of Standards and Technology (NIST) – A measurement standards laboratory, which is a non-regulatory agency of the United States Department of Commerce.

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3.2.2 ILAC – International Laboratory Accreditation Cooperation, organization with the aim of developing international cooperation for facilitating trade by promotion of the acceptance of accredited test and calibration results.

4 Establishing a Calibration Program4.1 General

A calibration Management program includes defined procedures, tasks and activities for the calibration of all the relevant instruments. On-going calibration is a fundamental part of instrument maintenance, which in turn is a fundamental part of the Plant’s / Facility’s maintenance. As such the management and scheduling of maintenance personnel, and other resources such as test equipment, to perform calibration activities is usually executed via Work Orders from the Plant’s / facility’s maintenance management system (computerized or otherwise). A broader reliability or Asset Management program in turn may guide this. Consequently, consideration should be given to how the calibration program interacts with other programs and systems in the Plant / Facility.

Where instrument and systems performance certification is mandated by regulating agencies, Federal, State or local, the owners should ensure that technicians involved in the calibration process are familiar with those requirements. Examples are EPA, NRC or CEMs permits for emissions and discharge to water bodies.

4.2 Calibration Program ConceptsMonitoring and control instrumentation and systems currently used in industry range from pneumatics to “smart” (microprocessor-based) digital electronics. These devices are as varied as the processes they monitor. Devices with moving parts require regular maintenance. These mechanical devices are much more susceptible to mechanical performance issues (e.g. binding and dragging due to environmental contamination) than are other automation instrumentation. Analog electronic instrumentation is subject to drift in settings and output. Digital instrumentation has multitudes of parameter settings that should be set properly to achieve desired operation. Devices not operating to their manufacturer’s specifications and/or not properly configured for the specific application can result in operational issues, such as off-spec quality, productivity issues, and safety issues. And then there is always the instrument failure. All of this results in a need for the loops important to safety, quality and correct operation of the facility to be periodically calibrated.

Understanding and adhering to the following guidelines, explained in the sections that follow, is required to achieve the full benefits of the recommended approach to a calibration program set forth in this document.

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4.3 Calibration ProgramA calibration program for an industrial monitoring and control system formalizes a methodology to periodically verify the performance accuracy of the components in that monitoring and control system and, when necessary, make adjustments to those components to bring them within their manufacturer rated accuracy and the loop within its required performance accuracy.

Each user company/facility is encouraged to establish a calibration program specific to its needs. This recommended practice discusses the essential features of a calibration program and provides guidance how to establish such a program.

This proposed approach to a calibration program for automation instrumentation and systems takes into consideration all known loop measurement errors and establishes calibration tolerances based on the process requirements. Successful implementation of this approach requires management commitment to make this a living process. Critical steps in the process include:

a) Establish a loop/instrument tagging system

b) Develop a comprehensive list of loops and instrumentation equipment requiring calibration

c) Establish a loop criticality system and criticality ratings for each of those loops

d) Establish tolerance requirements for each loop

e) Establish loop calibration verification intervals (frequencies)

f) Establish calibration equipment requirements

g) Establish loop/instrument calibration record forms and calibration record-keeping system

h) Establish necessary calibration procedures

i) Establish staff qualifications and training requirements

j) Perform calibration checks at required intervals and document results

Establish a calibration program verification methodology

4.4 Device CalibrationDevice calibration ensures that discrete components within the loop have been compared and adjusted, if necessary, to a reference standard. This is typically done before the component or instrument is installed and is used as an initial benchmark to ensure accuracy and then is periodically checked to ensure device accuracy.

Device calibration is also used when loop calibration is not practical.

4.5 Loop CalibrationA key concept of this recommended practice is establishing required tolerance and performing calibration of the entire loop, which may include multiple devices, where practical. The concept of loop calibration is when the loop indication is not within the desired loop tolerance, the devices in the loop are individually checked and adjusted as necessary to bring the loop indication within the desired tolerance.

For example, a temperature transmitter could be calibrated as a single device but when installed with the sensor and indicator, the loop indication might not be within the desired tolerance. The key parameter is whether the entire loop is providing a measurement within the tolerance needed for proper operation of the process. Each component in a loop has a rated accuracy. The inaccuracy or error of each component in the loop results in the total loop inaccuracy greater than that of any component.

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4.6 Test EquipmentThe test equipment used to validate and calibrate a loop or component should be of sufficiently greater accuracy (typically three to four times better accuracy) than that loop or component.

4.7 CompetencyProperly trained personnel are essential to the success of a calibration program. This includes understanding the process, regulatory requirements, calibration tools, and instrument\systems training required by the manufacturer.

5.0 Calibration Program PlanningComponents and systems require periodic calibration to operate safely, efficiently, and in compliance with regulations. To ensure such calibrations occur as necessary, companies should create a program with the following attributes:

A structured calibration program

A formalized methodology that applies to all components and systems covered by the program, consisting of standards, procedures, and tasks

Activities for verifying performance accuracy and adjusting or replacing deficient/defective components/systems as necessary to ensure operation occurs in accordance with manufacturer rated accuracy parameters and/or required performance tolerances

5.1 Introduction5.2 Loops and components in the calibration programIf it does not already exist, an identification (tagging) system should be established which assigns a unique identification (tag) to each loop and component. This provides a uniform means of identifying a loop and each loop device, its inherent functions, and related system(s). The ANSI/ISA-5.1 standard for Instrumentation Symbols and Identification provides guidance for developing an identification system. Proper identification of the components in the calibration program is important to efficient and proper operation of the calibration program, including proper documentation and tracking of components.

Using the unique tags established, a comprehensive list of all loops and instrumentation in the facility to be included in the calibration program should be developed.

5.3 Component and loop criticality determinationIf it does not already exist, establish a loop criticality classification system for loops in the facility. The criticality of each loop is one of the driving factors for establishing calibration intervals. ISA technical report TR91.00.02 provides a structured technique for establishing criticality classifications. Classification examples from that document include safety, environmental, and asset protection.

Using the criticality classification system established, the applicable criticality classification for each component in the calibration program should be identified.

5.4 Establishing required loop toleranceEach loop should be evaluated against and calibrated to a specified tolerance, which is the permissible deviation from the actual value or loop tolerance.

The tolerance for each loop may be established in either of two ways: (1) by establishing the required accuracy of the loop necessary to meet safety, quality, and/or production requirements of the process, or (2) by establishing the theoretical tolerance of the loop based on the rated

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accuracies of all of its components. In both methods, the theoretical tolerance of the loop should be calculated to demonstrate whether the loop is capable of meeting the required accuracy (in method 1) or to establish the target tolerance for the loop (in method 2).

Establishing an acceptable tolerance for each loop:

a) Clearly defines the level of acceptable performance for each loop

b) Provides a defined measure to use in the periodic check of loop performance

c) Facilitates tracking of loop performance over time

d) Focuses calibration efforts to the areas that provide the most benefits

e) Provides management with a measure for auditing loop performance and calibration work (staff and equipment performance)

f) Clarifies loop performance expectations for operations and maintenance, including regulatory requirements where applicable

5.5 Calculating theoretical loop toleranceTheoretical loop tolerance is calculated by using the Root-Sum-Square (RSS) method, which combines the rated accuracy of each component in the loop. Each of the listed

Tolerance=√ (error 1 )2+(error 2)2 +(error3)2+(etc . error)2

effects on accuracy is squared and all squared terms are added together. The square root of this sum provides a combined uncertainty in either percentage or engineering units of the loop. Section 7 provides examples for calculating loop tolerance by using the manufacturers’ data and the RSS method.

The following influencing parameters of a device need to be considered when calculating loop tolerance:

a) Hysteresis,

b) Drift,

c) Effects of influencing parameters

d) Resolution,

e) Maximum permissible error,

f) Dead band.

g) Range,

h) Bias,

i) Repeatability,

j) Stability

k) Measurement uncertainty

As an example, a manufacturer lists the following parameters for their differential pressure transmitter:

Long term stability

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Line pressure effect per 1000 psi (68,95 bar)

Ambient temperature effect per 50oF (28oC)

Mounting position effect

Vibration effect

Power effect

Electromagnetic compatibility (EMC)

5.6 Calibration Confirmation Intervals The calibration confirmation interval for a particular component or loop is a function of (a) criticality of the component/loop, (b) the performance history of the component/loop, (c) the ruggedness of the component(s), and (d) the operating environment. The user must determine the applicable verification frequency for each component/loop. Historical performance information and/or Instrument Asset Management diagnostics maintained by the user can be very helpful in this effort.

Records obtained using statistical data techniques for measurement frequency etc. can be useful in determining whether or not to modify calibration confirmation interval. Initial frequencies may consider manufacturer’s recommendations if no other data is available and then be adjusted as calibration performance data is obtained. Shown below is an illustrative example of a calibration intervals using criticality ranking. The example is not intended to be used directly.

5.6 Calibration equipment Equipment used to measure a loop’s tolerance or to calibrate a device should be:

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a) Certified, typically by the manufacturer or a third party on a regular, fixed period (annually or otherwise as recommended by the manufacturer) to be operating properly and within all manufacturers’ specifications. A sticker should be affixed to the equipment documenting the most recent date of re-certification. For calibration equipment, the device’s calibration should be traceable to a national or other acceptable standard.

b) At least a factor of three times better than the specified tolerance of the loop/component being calibrated (For example, if the loop tolerance is 3%, the aggregate calibration equipment accuracy should be 1% or less. If the component accuracy is 0.25%, the aggregate calibration equipment accuracy should be less than 0.08%. If multiple calibration equipment components are used, the aggregate accuracy should be calculated using the RSS method.)

c) Properly corrected for the effects of local conditions (e.g. ambient temperature, atmospheric pressure, etc.)

Control of Access to Calibration Adjustments - Access to adjusting means on devices after they have been confirmed or calibrated, whose setting affects the performance, should be sealed or otherwise safeguarded to prevent unauthorized changes. Seals or safeguards should be designed and implemented such that tampering will be detected. The calibration process procedures should include actions to be taken when seals or safeguards are found damaged, broken, bypassed or missing.

5.6.1 The following is a list of common test equipment:a) Digital multimeter (voltage, resistance, current)

b) Digital thermocouple, millivolt simulators(may be included in a))

c) Thermostatically controlled temperature bath

d) Digital frequency meter/timer(may be included in a))

e) Special test equipment required by the vendor of the device being tested/calibrated

f) Stabilized DC power supply

g) Dead weight tester

h) Precision pressure gauge

i) Current and/or voltage generator

j) Precision wire wound resistor decade box

k) Sine wave generator

l) Wobulator

m) Stop watch

n) Digital manometer

o) Digital Pneumatic\hudraulic Pressure calibrators

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q) Vacuum pumps (manually operated)

r) Sets of standard (precision) mercury-in-glass thermometers

s) Inclined manometer

5.7 Calibration Record SystemA calibration record system is necessary to provide documentation of when calibration activities have been undertaken on which pieces of equipment, what the results were, and what (if any) corrective action was taken. The system should include forms to be used to record the calibration activities and the method for storage of all calibration records to facilitate future access. This system may be paper- or electronic-based. The calibration service record (CSR) provides essential information on a particular loop/component. This includes the calibration points with the acceptable loop/component tolerances. Using the CRS allows staff to capture the “as found” and “as left” data, which highlights how much drift has occurred in the loop/component since the last calibration. An example of a CSR is provided in the Annex.

5.8 Calibration ProceduresTo promote consistent methodology and results, calibration procedures, or calibration work instructions, should be established for each loop/component. These procedures should detail the method and equipment to be used to check and perform calibration. The procedure includes the following:

• Description of the component or loop to be calibrated

• Overview of the tasks to be performed

• Equipment and personnel requirements

• Procedure to be followed for the calibration

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5.9 Calibration personnel To ensure the safety and reliability of the measurement and control system, only competent personnel should be allowed to perform calibrations. Suggested areas of knowledge include:

1) General Maintenance skills

a) Operations and process safety

b) Electrical safety

c) Troubleshooting

2) Instrument Maintenance Skills

a) Instrumentation maintenance and repairs

b) Loop checking

c) Calibration

d) Calibration record keeping

Confirming the qualifications of the personnel involved in calibration can be achieved through the completion of an internal certificate program or through an recognized independent third party

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certification program. Once complete, a subject matter expert should evaluate an individual’s ability to perform a specific type of calibration. Supervisors should keep a register of qualified individuals by component type. It is important to understand that someone may be fully qualified to calibrate one type of component and not another. In addition, certain regulatory requirements may establish qualification for personal performing calibrations. Requirements for periodic training and re-certification to ensure continued competency of personnel should also be established.

5.10 ResponsibilitiesPreferably, a calibration program definition should be an integral part of the initial design and build capital expenditure phases of the facility’s life cycle phase. Whether the calibration program is being created for the initial facility build or created/rejuvenated during the operation phase of the life cycle, given the number of loops in a typical industrial facility, fully implementing an automation and control system calibration program is a major undertaking. It may well be part of a broader scoped instrument asset management or reliability program. As with any significant program, for it to be successful, company management will need to provide sufficient support to the creation and on-going execution of the program. To ensure consistency, a project team should be created to manage the project. The project will require support from the facility technicians, engineers and, most important, senior management.

The management of the plant, facility, or automation system should be responsible for establishing and owning the program and ensuring compliance with the automation and control system calibration program. This would include establishing a process for auditing compliance with, and updating, the program.

All aspects of the calibration program should be completely documented for an effective calibration program, including, but not limited to:

a) Calibration procedures (required method)

b) Calibration equipment (required accuracies, re-certification frequency and procedures, personnel training)

c) Personnel training and certification

d) Personnel responsibilities and accountabilities

e) Required loop tolerances

f) Required forms

g) Verification and calibration record keeping system

h) Required verification frequencies

6 Loop and Component Performance Verification6.1 Verifications and calibrations should be made using the “loop” calibration method whenever possible. In those cases where this is not possible, loop component accuracies should be verified and used to calculate loop accuracy, which is then compared to loop required accuracy.

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The verification portion of the calibration procedure should define the steps necessary to check the performance of a type of loop. This should include a task list providing specific steps necessary to perform the check, including equipment and methodology.

If the calibration confirmation of a loop/component reveals that the loop/component is not within the required tolerance, a calibration adjustment may be required to one or more loop components according to defined procedures. The calibration procedure for that component defines the overall steps necessary to calibrate a type of device. A task list provides the specific steps necessary to calibrate a specific component. If the desired tolerance cannot be achieve the component should be repaired or replaced.

Calibration confirmation is not achieved until and unless the fitness of the measuring equipment for the intended use has been demonstrated and documented. Calibration confirmation should include calibration and verification, any necessary adjustment or repair, and subsequent recalibration, comparison with the accuracy requirements for the intended use.

Software used in the calibration processes and calculations of results should be documented, identified and controlled to ensure suitability for continued use. Calibration Software - any revisions to it, shall be tested and/or validated prior to initial use, approved for use, and archived.

7 Calibration Program Management7.1 Control

An effective calibration program should include a means to track calibrations by device/loop, define required interval, forecast calibrations due, document calibrations, and trend results. Many third party software applications exist that can help automate a calibration program.

7.2 AssuranceAn effective calibration program should be periodically monitored for compliance. This includes verification that loop calibration checks are being performed at the required intervals; all calibration activities are being properly documented; and calibration equipment is properly maintained and has current certification. Management should ensure that this periodic monitoring is consistently performed and results documented.

7.3 ImprovementCalibration programs should be evaluated and updated on a periodic basis or when significant modifications or projects are completed to ensure the program is evergreen. Audits should not only consider if the loops/devices have been added or removed, but should also include a review of the criticality rating, process conditions, accuracy capability and requirements for each device/loop.

Periodically review results as trended over time to determine if drift performance is acceptable or if modified frequency of calibration or device technology should be considered in order to ensure desired loop performance is maintained.

8 Examples Calculating theoretical loop accuracy examples

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Transmitter Accuracy 0.0750 0.0750System Accuracy 0.1000 0.1000Stability 0.0100 0.0100Ambient Temp Effect/oF 0.0036 0.0000 0.0036

Maximum Total Error 0.0886 0.1000 0.18860.0757 % 0.1000 % 0.1255 %2.27 PSI 3.00 PSI 3.76 PSI

Combined Uncertainties (±)

Transmitter Tolerance

Control System

Analog Input Card

Loop Combined Tolerance

Main Steam Pressure 0-3000 PSI

Calculating the theoretical tolerance using the RSS method, the loop is within calibration if the full-scale reading is between 2996.24 and 3003.75 PSI.

Tolerance=√ (0.0750 )2+(0.1000 )2 +( .0100 )2+ ( .0036 )2

Tolerance=±0.1255 %∨±3.76 PSI

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Transmitter Accuracy 0.2500 0.2500System Accuracy 0.1000 0.1000Stability 0.1000 0.1000Ambient Temp Effect/oF 0.0100 0.0022 0.0122

Maximum Total Error 0.3600 0.1022 0.4622

0.2694 % 0.1000 % 0.2875 %6.74 PSI 2.50 PSI 7.19 PSI

Combined Uncertainties (±)

First Stage Pressure 0-2500 PSI

Transmitter Tolerance

Data Logger Analog Input

Card

Loop Combined Tolerance

Transmitter Accuracy 0.0750 0.0750System Accuracy 0.5000 0.5000Stability 0.0100 0.0100 0.0200Ambient Temp Effect/oF 0.0036 0.0100 0.0136

Maximum Total Error 0.0886 0.5200 0.6086

0.0757 % 0.5001 % 0.5062 %1.89 PSI 12.50 PSI 12.65 PSI

First Stage Pressure 0-2500 PSI

Transmitter Tolerance

Control System

Analog Input Card

Loop Combined Tolerance

Combined Uncertainties (±)

Switch Repeatability 3.0000Temperature Effect per oF 0.0200Stability % per Year 0.0000

Maximum Total Error 3.0200

3.0001 %90.00 PSI

Combined Uncertainties (±)

Turbine EH System Pressure 200-3000 PSI

Switch Tolerance

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Gauge Accuracy 2.0000Temperature Effect per oF 0.1000Stability % per Year 1.0000

Maximum Total Error 3.1000

2.2383 %67.15 PSI

Boiler Feed Pump Turbine Pressure 0-3000 PSI

Combined Uncertainties (±)

Gauge Tolerance

These examples highlight the large differences in the uncertainties from system to system and from device to device. Far less accuracy is required to calibrate gauge (combined uncertainties 2.238%) than is required to calibrate loops on the inputs to a control system (combined uncertainties 0.1255%). It is important to note that there are actually more identifiable factors to uncertainty in the systems. However, none of these factors is significant enough to make a recognizable increase in the uncertainty of the loop.

Implementation example

o In 1995, the natural gas supplier started providing their technicians loop tolerances for all of the utility power plants. Shown below is March 2006 audit of the power plant meter run number one.

o Providing acceptable tolerance for each loop was a new concept for the natural gas supplier. Over time, the company realized the following benefits of this practice:

o Clearly defined levels of acceptable performance for each loop

o Focuses calibration efforts to the areas that provide the most benefits

o Provides management with a measurement for auditing the calibration work (staff and equipment performance)

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Bibliography

NIST (2001), Handbook 150:2001, Washington, National Institute of Standards and Technology

ISA (2009), 5.1-2009 Instrumentation Symbols and Identification, North Carolina, Inter-national Society of Automation

ISA (2003), TR91.00.02-2003 Criticality Classification Guideline for Instrumentation, North Carolina, International Society of Automation

Beamex (2009), Ultimate Calibration 2nd Edition, 2009, Finland, Beamex Oy Ab.

Cable, Mike (2005), Calibration: A Technician’s Guide, North Carolina, International Society of Automation

ISO 9001 (2015), Clause 7.6 Control of monitoring and measuring equipment, Switzerland, International Organization for Standards

ANSI/NCSL Z540.3-2006 (2006), Requirements for the Calibration of Measuring and Test Equipment, Boulder, Colorado, NCSL International

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Calibration Service Record

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Developing and promulgating sound consensus standards, recommended practices, and technical reports is one of ISA’s primary goals. To achieve this goal the Standards and Practices Department relies on the technical expertise and efforts of volunteer committee members, chairmen and reviewers.

ISA is an American National Standards Institute (ANSI) accredited organization. ISA administers United States Technical Advisory Groups (USTAGs) and provides secretariat support for International Electrotechnical Commission (IEC) and International Organization for Standardization (ISO) committees that develop process measurement and control standards. To obtain additional information on the Society’s standards program, please write:

ISAAttn: Standards Department67 Alexander DriveP.O. Box 12277Research Triangle Park, NC 27709

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