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TitleCalibration and Measurement Process
TagsCalibration Reliability Engineering Uncertainty Measurement Confidence Interval
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Total Pages364
Table of Contents
                            Acronyms
1. INTRODUCTION
	1.1 Purpose
	1.2 Applicability
	1.3 Scope
2.0 QUALITY RECOMMENDATIONS
	2.1 Introduction
	2.2 Measurement Functions
	2.3 Measurement Quality Recommendations
		2.3.1 Requirement Definition
		2.3.2 Requirement Traceability
		2.3.3 Implementation Cost
		2.3.4 Uncertainty Identification
		2.3.5 Design Documentation
		2.3.6 Design Review
		2.3.7 Quality Control
		2.3.8 Quality Documentation
	2.4 Relevant Quality Provisions
3. MEASUREMENT REQUIREMENTS
	3.1 Objectives of the Measurement Process
	3.2 Defining Measurement Requirements
		3.2.1  Measurement Requirements Definition Sequence
		3.2.2 System Characteristics and Measurement Parameters
		3.2.3 Establishing Measurement Classifications
		3.2.4 Establishing Confidence level Requirements
		3.2.5 Establishing Measurement System Reliability Requiremen
		3.2.6 Finalizing Measurement Requirements
		3.2.7 Example—Measurement Requirement Definition of a Solar
		3.2.8 Compensating for Difficult Requirements
	3.3 Calibration Considerations
	3.4  Space-based Considerations
		3.4.1  Space-based Measurement System Implications
		3.4.2 SMPC for Space-based Hardware
	3.5 Software Considerations
		3.5.1 Software Requirements
		3.5.2 Software Development
	3.6 Considerations for Waiver of Requirements
4. MEASUREMENT SYSTEM DESIGN
	4.1 Measurement System Design Approach
	4.2 Identifying Physical Phenomena to be Measured
		4.2.1 Process Characteristics
		4.2.2 Measurement Mode
		4.2.3 Method of Transduction or Energy Transfer
		4.2.4 Measurement Location
		4.2.5 Measurement Range
		4.2.6 Measurement Uncertainty
		4.2.7 Measurement Bandwidth
	4.3 Selecting Candidate Equipment and Interpreting Specifica
		4.3.1 Specification Completeness
		4.3.2  Specification Interpretation
	4.4 Evaluating Measurement System Errors
		4.4.1  Sensing Errors
		4.4.2 Intrinsic Errors
		4.4.3 Sampling Errors
		4.4.4 Interface Errors
		4.4.5 Environment Induced Errors
		4.4.6 Calibration Induced Errors
		4.4.7 Data Reduction and Analysis Errors
		4.4.8 Operator Errors
		4.4.9 Error Propagation
	4.5 Combining Errors
		4.5.1 Error Classifications
		4.5.2 Common Units and Confidence levels
		4.5.3 Establishing the Total Bias Estimate
		4.5.4 Establishing the Total Precision Estimate
		4.5.5 Establishing the Total Uncertainty Estimate
		4.5.6 Example—Budgeting Measurement Uncertainty in the Desig
		4.5.7 Example—Establishing Maximum Allowable Errors
	4.6 Constructing Error Models
		4.6.1 Measurement Uncertainty
		4.6.2 Measurement Error
	4.7 Example—Developing a Temperature Measurement System
		4.7.1 Temperature Measurement System Equipment Selection and
		4.7.2 Example Temperature Measurement System Error Model
	4.8 Consideration of Calibration Techniques to Reduce Predic
	4.9 Consideration of Uncertainty Growth in the Measurement S
	4.10 Consideration of Decision Risk in the Measurement Syste
		4.10.1 False Accepts
		4.10.2 False Rejects
5. MEASUREMENT TRACEABILITY
	5.1 General
		5.1.1 Components of a Measurement
		5.1.2 Definition of Tolerance, Uncertainty, and Accuracy Rat
		5.1.3 The Metric System
	5.2 Measurement Standards
		5.2.1 Intrinsic Standards
		5.2.2 Artifact Standards
		5.2.3 Ratio Standards
		5.2.4 Reference Materials
		5.2.5 Other Standards
	5.3 United States Standards
		5.3.1 NIST Physical Measurement Services Program
		5.3.2 NIST SRM Program
		5.3.3 NIST National Standard Reference Data Program (NSRDP)
	5.4 International Compatibility
		5.4.1 Reciprocal Recognition of National Standards
		5.4.2 BIPM Calibrations
		5.4.3 International Comparisons
		5.4.4 NIST Calibrations
	5.5 Calibration Transfer Techniques
		5.5.1 Traditional Calibration
		5.5.2 Measurement Assurance Program (MAP) Transfers
		5.5.3 Regional Measurement Assurance Program (RMAP) Transfer
		5.5.4 Round Robins
		5.5.5 Intrinsic Standards
		5.5.6 SMPC Methods Transfers
	5.6 Calibration Methods and Techniques
		5.6.1 Calibration of Reference Standards
		5.6.2 Calibration of TME
		5.6.3 Calibration of Systems
		5.6.4 Calibration Using SRMs
		5.6.5 Scaling
	5.7 Calibration Traceability vs. Error Propagation
		5.7.1 Evaluation of the Process Uncertainty
		5.7.2 Propagation of Uncertainty in the Calibration Chain
	5.8 Calibration Adjustment Strategies
		5.8.1 Reference Standards
		5.8.2 Direct Reading Apparatus
	5.9 Software Issues
		5.9.1 Software Documentation
		5.9.2 Software Configuration Management
		5.9.3 Software Standards
6. CALIBRATION INTERVALS
	6.1 General
		6.1.1 Purpose
		6.1.2 Scope
		6.1.3 Background
		6.1.4 Basic Concepts
	6.2 Management Considerations
		6.2.1 Establishing the Need for Calibration Interval Analysi
		6.2.2 Measurement Reliability Targets
		6.2.3 Calibration Interval Objectives
		6.2.4 Potential Spin-offs
		6.2.5 Calibration Interval Elements
		6.2.6 Extended Deployment Considerations
	6.3 Technical Considerations
		6.3.1 The Calibration Interval Problem
		6.3.2 Measurement Reliability
		6.3.3 Calibration Interval System Objectives
		6.3.4 The Out-of-Tolerance Process
		6.3.5 Measurement Reliability Modeling
		6.3.6 Calibration Interval Assignment and Adjustment
		6.3.7 Multiparameter TME
		6.3.8 Equipment Adjustment Considerations
		6.3.9 Establishing Measurement Reliability Targets
		6.3.10 The Interval Analysis Process
		6.3.11 Extended Deployment Considerations
	6.4 Statistical Measurement Process Control (SMPC) Methods
		6.4.1 Basic Concepts
		6.4.2 SMPC Methodology
	6.5 Analyzing Measurement Decision Risk
		6.5.1 Measurement Decision Risk Analysis—General Concepts
		6.5.2 Measurement Decision Risk Analysis—A Simple Example
		6.5.3 Measurement Decision Risk Analysis—Methodology
	6.6 Managing Measurement Decision Risk
		6.6.1 Management of Technical Parameters
		6.6.2 Applicability and Responsibility
		6.6.3 Benefits
		6.6.4 Investment
		6.6.5 Return on Investment
	6.7 Optimizing the Hierarchy—Cost Modeling
	6.8 Example—The Solar Experiment
7. OPERATIONAL REQUIREMENTS
	7.1 Measurement Quality
		7.1.1 Establishing Measurement Quality
		7.1.2 Preserving Measurement Quality
		7.1.3 Maintaining Traceability
	7.2 Maintenance and Repair
		7.2.1 General
		7.2.2 Procedures
		7.2.3 Designs for Maintenance
		7.2.4 Repair
8. RECOMMENDATIONS FOR WAIVER/DEVIATION REQUESTS
	8.1 General
	8.2 Classification of Waiver/Deviation Requests
	8.3 Independent Risk Assessment of Waiver/Deviation to Techn
Appendix A DEFINITIONS
Appendix B MATHEMATICAL METHODS FOR OPTIMAL RECALL SYSTEMS
	B.1 Measurement Reliability
	B.2 Optimal Calibration Intervals
	B.3 Consequences of Suboptimal Systems
	B.4 The Out-of-Tolerance Process
	B.5 The Out-of-Tolerance Time Series
	B.6 Analyzing the Out-of-Tolerance Time Series
	B.7 Measurement Reliability Modeling
		B.7.1 The Likelihood Function
		B.7.2 Steepest Descent Solutions
	B.8 Reliability Model Selection
		B.8.1 Reliability Model Confidence Testing
		B.8.2 Model Selection Criteria
		B.8.3 Variance in the Reliability Model
	B.9 Measurement Reliability Models
	B.10 Calibration Interval Determination
		B.10.1 Interval Computation
		B.10.2 Interval Confidence Limits
	B.11 Dog/Gem Identification
		B.11.1 Dog/Gem Identification—Method 1
		B.11.2 Dog/Gem Identification—Method 2
		B.11.3 Support-Cost Dog Identification
		B.11.4 Suspect Activity Identification
	B.12 Data Continuity Evaluation
	B.13 Data Truncation
	B.14 Calibration Interval Candidate Selection
	B.15 Establishing Measurement Reliability Targets
Appendix C   TEST AND CALIBRATION HIERARCHY MODELING
	C.1 Introduction
	C.2 The Test and Calibration Support Hierarchy
	C.3 BOP Measurement Reliability—Test Process Accuracy
	C.4 Interval Adjustment
		C.4.1 Interval Adjustment to Reliability Target Changes
		C.4.2 Interval Adjustment to Tolerance Limit Changes
	C.5 Measurement Decision Risk
		C.5.1 True Versus Reported Measurement Reliability
		C.5.2 False Alarms/Missed Faults
	C.6 Average-Over-Period Reliability
	C.7 Availability
	C.8 Cost Modeling
	C.9 Multiple Product Testing
		C.9.1 The General Multiple Testing Model
		C.9.2 Definitions and Notation
		C.9.3 Determination of f ( x )
		C.9.4 A Simplified Model
	C.10 Measurement Uncertainty Analysis
Appendix D SMPC METHODOLOGY DEVELOPMENT
	D.1 Introduction
	D.2 Computation of In-Tolerance Probabilities
		D.2.1 UUT In-Tolerance Probability
		D.2.2 TME In-Tolerance Probability
	D.3 Computation of Variances
		D.3.1 Variance in Instrument Bias
		D.3.2 Accounting for Bias Fluctuations
		D.3.3 Treatment of Multiple Measurements
	D.4  Example
	D.5 Derivation of Eq. (D.3)
	D.6 Estimation of Biases
	D.7 Bias Confidence Limits
Appendix E ERROR ANALYSIS METHODS
	E.1 Measurement System Modeling
	E.2 Measurement Error Modeling
		E.2.1 Series Systems
		E.2.2 Series-Parallel Systems
		E.2.3 Nonlinear Responses
		E.2.4 Large Error Considerations
	E.3 Small Error Theory
	E.4 Example
Appendix F PRACTICAL METHOD FOR ANALYSIS OF UNCERTAINTY PROP
	F.1 Introduction
		F.1.1 Why Make Measurements?
		F.1.2 Why Estimate Uncertainties?
	F.2 Estimating Uncertainty — Conventional Methods
		F.2.1 Methodological Drawbacks
		F.2.2 Methodology Requirements
	F.3 Estimating Uncertainty — The Practical Method
		F.3.1 The Error Model
		F.3.2 Accounting for Process Error
		F.3.3 Accounting for Perception Error
		F.3.4 Measurement Uncertainty Estimation
	F.4 Construction of Component pdfs
		F.4.1 The Process Error Model
		F.4.2 The Perception Error Model
		F.4.3 Inferences Concerning Measurand Values
		F.4.4 Example — Normally Distributed s-Independent Sources
		F.4.5 Example — Mixed Error-Source Distributions
	F.5 Applications
		F.5.1 Estimating Measurement Confidence Limits
		F.5.2 Estimating Measurand Values
		F.5.3 Estimating Confidence Limits for x
		F.5.4 Estimating Measurement Decision Risk
		F.5.5 Example — Normally Distributed s-Independent Sources
		F.5.6 Example — s-independent Error Sources with Mixed Distr
	F.6 Nomenclature
Appendix G   DETERMINING UNCERTAINTY OF AN EXAMPLE DIGITAL T
	G.1 Introduction
	G.2 Identifying the Measurement System Errors
		G.2.1. Sensing (Thermocouple)
		G.2.2. Interfacing (Reference Junction—Low-Pass Filter)
		G.2.3. Filtering (Low-Pass Filter)
		G.2.4. Interfacing (Low-Pass Filter—Amplifier)
		G.2.5. Amplification (Amplifier)
		G.2.6. Interfacing (Amplifier—A/D Converter)
		G.2.7. Sampling (A/D Converter)
		G.2.8. Sensing (A/D Converter)
		G.2.9. Quantizing (A/D Converter)
		G.2.10. Data Reduction and Analysis (Data Processor)
		G.2.11. Decoding (Data Processor)
	G.3 Identifying the Measurement Process Errors
		G.3.1. Precision Error
		G.3.2. Ancillary Error
		G.3.3. Operator Error
	G.4 Methodology for Developing a Measurement System Error Mo
	G.5 Developing the System Error Model
	G.6 Methodology for Developing a Measurement System Uncertai
		G.6.1 Statistical Variance
		G.6.2 Relationship of Standard Deviation to System Uncertain
	G.7 Evaluating the Measurement Uncertainty
		G.7.1 Thermocouple
		G.7.2 Interface 1 (Reference Junction—Low-Pass Filter)
		G.7.3 Low-Pass Filter
		G.7.4 Interface 2 (Low-Pass Filter—Amplifier)
		G.7.5 Amplifier
		G.7.6 Interface 3 (Amplifier—A/D Converter)
		G.7.7 Sampling (A/D Converter)
		G.7.8 System Uncertainty
	G.8 Establishing the Standard Deviations for Uncertainty Com
		G.8.1 Thermocouple
		G.8.2 Interface 1 (Reference Junction—Low-Pass Filter)
		G.8.3 Low-Pass Filter
		G.8.4 Interface 2 (Low-Pass Filter—Amplifier)
		G.8.5 Amplifier
		G.8.6 Interface 3 (Amplifier—A/D Converter)
		G.8.7 Sampling (A/D Converter)
		G.8.8 System Uncertainty
	G.9 Estimating the Process Uncertainty
	G.10 Estimating the Total Uncertainty
Appendix H THE INTERNATIONAL SYSTEM OF UNITS (SI)
	H.1 The SI
	H.2 SI Units
		H.2.1 Base Units
		H.2.2 Supplementary Units
		H.2.3 Derived Units
		H.2.4  Other Units
	H.3 Units in Temporary Use
	H.4 Obsolete Units
	H.5  Rules for Writing and Using Symbols
	H.6 SI Prefixes
	H.7 Conversion to Metric
Bibliography
Index
                        
Document Text Contents
Page 1

NASA
Reference
Publication
1342


1994




Metrology — Calibration and
Measurement Processes
Guidelines




NASA Metrology and Calibration Working Group

Page 182

Section 7— OPERATIONAL REQUIREMENTS 160


While maintenance can be an independent function, for convenience much of it is done during
calibration. Typically, maintenance intervals are longer than calibration intervals. Therefore, much
maintenance is scheduled to be done, for example, at every second or third scheduled calibration.

REF: NHB 4200. 1C, 2.209 A

A maintenance program shall be prescribed for all installation assigned equipment. The
basic goal of the maintenance program will be to assure maximum readiness of equipment
to perform assigned functions safely and efficiently and at the lowest cost.

Maintenance is a continuing activity that is done more effectively under uniformly pre-
scribed procedures and practices and with proper guidelines for the maintenance of each
category of equipment in use at the installation. For applicable categories of equipment,
these guidelines will identify maintenance requirements set forth in appropriate Federal
Regulations and existing NASA Management Directives. When no such guidelines have
otherwise been prescribed, maintenance will generally be done in accordance with the
manufacturer’s or design agency’s recommended procedures.

7.2.2 Procedures
REF: NHB 4200. 1C, 2.209 A

Maintenance programs will include procedures that ensure:

(1) Identification and estimation of maintenance requirements.

(2) Uniform scheduling of maintenance service.

(3) Correction of deficiencies detected during visual inspections of daily operations.

(4) Prompt repair and calibration of equipment in keeping with the user’s performance
requirements.

(5) Periodic scheduling of inspections to verify the effectiveness of the maintenance pro-
gram and general operating conditions of equipment.

(6) Use of manufacturer warranties or servicing agreements, as applicable.

(7) Establishment of a technical library of applicable maintenance instructions for each
category of equipment for which maintenance is provided.

(8) Appropriate preservation and protection of inactive equipment held in storage.

(9) Preprinted maintenance check lists when appropriate.

7.2.3 Designs for Maintenance
7.2.3.1 Defining Maintenance Requirements
The requirements for maintenance are usually defined in manufacturer manuals where specific
activities are directed to keep measuring systems operable. Other requirements are derived from
data taken during calibrations, during repairs, and from user complaints made to repair and/or
maintenance personnel. These requirements try to define the circuits, parts, mechanisms, and
devices whose failure could be avoided by detecting diminished capability, fluid loss, dirt and
grease accumulation, environmental stresses, and wear. Also, equipment use should be reviewed to
find out the experience level of users, their opinions regarding its functional reliability, the

Page 183

Section 7— OPERATIONAL REQUIREMENTS 161

environment in which it is used, and whether maintenance can be divided between the user and the
maintenance facility. Special attention should be paid to instruments in space applications where
maintenance considered routine on Earth will be difficult or impossible. The selection of
measuring systems should consider designs that minimize or eliminate maintenance needs.

7.2.3.2 Selection of Maintenance Equipment
Typically, maintenance during the calibration process uses much of the same equipment used for
calibration. Also, special facilities are needed for cleaning, lubricating, and stress testing for safety
hazards and imminent failures. Some items categorized as measuring devices or accessories may
need only maintenance and no calibration. They may also need special tests or actuations to
confirm operability of emergency circuits and actuator equipment for more complex tasks or
nonuncertainty related measurement capabilities, such as indications of presence or absence of
signal, pressure, and flow.

As with calibration equipment, the site where maintenance is to be done has an influence on the
equipment chosen. Design and selection of the measurement systems should include devices that
need little maintenance or that can be maintained by remote means wherever possible.

7.2.3.3 Designing Maintenance Procedures
Clearly written and logically sequenced procedures are essential to successful maintenance
operations. Where these procedures are scheduled in conjunction with calibration operations, they
should be integrated to follow the flow of the calibration process. However, many maintenance
operations should precede calibration to assure functional adequacy of the equipment before
subjecting it to the more time-consuming calibrations. Maintenance procedures should have the
same characteristics as those of well-designed calibration procedures. The better, more clearly
written these procedures are, the less costly the continued maintenance operations will be. A small
investment in well-prepared procedures will pay large dividends ultimately.

7.2.3.4 Defining Maintenance Servicing Intervals
One of the more difficult design problems is to develop a system that determines the most desirable
time to do maintenance. Done too frequently, maintenance is a waste of time, or it may even be
deleterious because of possible operator error; done too infrequently, it results in costly losses to
both the measuring instruments and the operations in which they are used. Many owners schedule
instrument maintenance at multiples of the calibration interval.

This is a practical approach because typical calibration intervals are shorter than maintenance inter-
vals. As more knowledge accrues about calibration interval systems and calibration risk targets,
basing maintenance intervals on calibration intervals may not prove to be a safe relationship.
Calibration intervals have been getting longer and longer over the past few years because of
improved stability of electronic circuitry, accumulation of statistically significant historical data,
and improved interval adjustment systems. This could push maintenance intervals beyond prudent
limits, unless current practices are changed accordingly.

Maintenance interval analysis should stand alone and be based on mathematical and statistical
correlation of historical failure data that focus on types of maintenance done, time between
maintenance, failed components/parts, and time between failures. From these data, MTBF figures
should be developed for each family or model-numbered measuring instrument, sensor, or
transducer. These figures reflect reliability index and should be related to an MTBF target for a

Page 363

Index 341

standards, 23, 83

Technical Note 1297, 2, 4, 294, 316

traceability, 5, 24, 72, 73, 86, 209

NORMAL APPROXIMATION TO THE BINOMIAL, 195

NORMAL DISTRIBUTION, 188, 195

OBSERVED RELIABILITY, 202

OOTR, 199, 200, 201

OUT-OF-TOLERANCE RATE, 199

PERFORMANCE

objectives, 34, 35, 92, 95, 104, 156, 163, 207

PREDICTED RELIABILITY, 190

PROBABILITY DISTRIBUTION FUNCTION

construction, 274

PURE ERROR, 189

PURE ERROR SUM OF SQUARES, 188

QUALITY

control, 8, 28, 31, 77, 95, 157

establishing, 3, 11, 16, 72, 77, 87, 91, 141, 213,
222, 225, 226, 285

management, 1, 2, 262, 267

operational, 48, 75, 81, 86, 121, 157

recommendations, 1

TQM, 2

REGRESSION ANALYSIS, 202

REJECTION CONFIDENCE, 190

RELIABILITY

end-of-period (EOP), 18, 98, 215

RELIABILITY MODEL, 190

RELIABILITY MODEL FIGURE OF MERIT, 190

RELIABILITY MODELING, 195

RELIABILITY MODELS, 191

RELIABILITY TARGET, 190, 191, 194, 200

REQUIREMENTS

accuracy, 5, 6, 22, 28, 35, 49, 59, 98, 127, 134,
147, 207, 263

calibration, 29

contractual, 5, 163

customer, 6, 7, 85, 89, 90, 95, 137, 139, 158, 160,
211, 221, 222, 248, 261, 262

defining, 6, 58, 95

maintenance, 92, 102

mission, 9, 15, 21, 105, 134

NHB, 2, 8, 16, 20, 39, 158, 160

personnel, 100, 146, 158

traceability, 6

waiver, 33

RESIDUAL SUM OF SQUARES, 189

RESUBMISSION TIMES, 197, 201, 202

REVIEW, 7, 31, 58, 66, 107, 109, 157, 164

RSS, 189

SAFETY, 5, 14, 32, 163

SAMPLING INTERVALS, 188

SCALING, 37, 76

SERIAL NUMBER DOGS, 197

SERIAL NUMBER GEMS, 197

SI

conversion, 334

prefixes, 327

SMALL ERROR THEORY, 259

SMPC

rationale, 3

versus SPC, 3

SPACE-BASED

calibration, 28, 71, 77, 83, 95, 117, 127, 205

SMPC, 30

system, 9

system implications, 16, 25, 75, 95, 117, 205

uncertainty growth, 30

SPECIFICATIONS

interpretation, 133

STANDARD DEVIATION

establishing, 211, 294

Page 364

Index 342

relationship to uncertainty, 243, 293

STANDARDS

artifact, 76

ratio, 76

reference materials, 76

STOCHASTIC PROCESS, 190

SUPPORT COST OUTLIER IDENTIFICATION, 198

SUPPORT COST OUTLIERS, 198, 199

SUSPECT ACTIVITIES, 199

TIME LIMIT, 10, 13, 20, 36, 37, 38, 50

UNCERTAINTY

budget, 7, 73

control, 8, 9, 13, 30, 139

expanded, 58

identification, 7

limits, 97, 118

propagation, 139, 207, 263

system, 17, 39

Why estimate?, 264

WAIVER

assessment, 13, 33, 164

request, 22

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