Timer Calibrations Stopwatch and - NIST

1 Stopwatch andTimer CalibrationsJeff C. GustRobert M. GrahamMichael A. LombardiMay 2004960-12 SpecialPublication960-12iDEPARTMENTOFCOM MERCEUNITEDSTATESOFAMERICANIST Recommended Practice GuideSpecial Publication 960-12 Stopwatch andTimer CalibrationsJeff C. GustQuametec CorporationRobert M. GrahamSandia National LaboratoriesMichael A. LombardiNational Institute of Standards and TechnologyPhysics LaboratoryMay Department of CommerceDonald L. Evans, SecretaryTechnology AdministrationPhillip J. Bond, Under Secretary for TechnologyNational Institute of Standards and TechnologyArden L. Bement, Jr., Directorii Stopwatch and Timer CalibrationsCertain commercial entities, equipment, or materials may be identified inthis document in order to describe an experimental procedure or conceptadequately. Such identification is not intended to imply recommendation orendorsement by the National Institute of Standards and Technology, nor is itintended to imply that the entities, materials, or equipment are necessarily thebest available for the Institute of Standards and TechnologySpecial Publication 960-12 Natl.

2 Inst. Stand. Publ. 960-1257 pages (May 2004)CODEN: GOVERNMENT PRINTING OFFICEWASHINGTON: 2004 For sale by the Superintendent of Government Printing OfficeInternet: Phone: (202) 512 1800 Fax: (202) 512 2250 Mail: Stop SSOP, Washington, DC 20402-0001iiiFOREWORDS topwatch and Timer Calibrations are perhaps the most common calibrationsperformed in the field of time and frequency metrology. Hundreds ofUnited States laboratories calibrate many thousands of timing devices annuallyto meet legal and organizational metrology requirements. However, untilnow, no definitive text has existed on the subject. This NIST RecommendedPractice Guide was created to a fill a gap in the metrology assists the working metrologist or calibration technician by describing thetypes of stopwatches and timers that require calibration, the specificationsand tolerances of these devices, the methods used to calibrate them, andthe estimated measurement uncertainties for each calibration also discusses the process of establishing measurement traceabilityback to national and international iv Stopwatch and Timer CalibrationsvAcknowledgments ACKNOWLEDGMENTSThe authors thank the following individuals for their extremely usefulsuggestions regarding this manuscript: Georgia Harris and David Smithof NIST, Ross Andersen of the New York Bureau of Weights and Measures,Jim Jenkins of Quametec Corporation, and Warren Lewis and Dick Pettitof Sandia National Laboratories.

3 **Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed MartinCompany, for the United States Department of Energy s National Nuclear SecurityAdministration under Contract Stopwatch and Timer CalibrationsviiTable of Contents TABLE OF CONTENTSList of ixList of Tables .. x1. Introduction to Stopwatch and Timer Calibrations .. The Units of Time Interval and Frequency .. A Brief Overview of Calibrations .. Traceability and Coordinated UniversalTime (UTC).. 52. Description of Timing Devices thatRequire Basic Theory of Operation .. Commercial Timing Devices .. 143. Specifications and Tolerances .. Interpreting Manufacturer's Specifications .. Tolerances Required for Legal Metrology .. 194. Calibration Direct Comparison References for DirectComparison Calibration Procedure forDirect Comparison Totalize Method.

4 Time Base Method .. 29viii Stopwatch and Timer Calibrations5. Measurement Uncertainties of Direct Comparison Method .. Uncertainty of the TraceableTime Interval Uncertainty Due to HumanReaction Device Under Test (DUT)Resolution Uncertainty Uncertainties of Totalize Method .. Uncertainty of the Frequency Input .. Uncertainty Due to HumanReaction Uncertainty Due to the Counter .. Device Under Test (DUT)Resolution Uncertainties of Time Base Method .. Uncertainty Analysis of Using a CalibratedStopwatch to Calibrate Another Adequacy of Calibration Method toMeet the Required Uncertainty .. 46 Appendix A: Calibration 49 References .. 51ixList of FiguresFigure 1. The calibration and traceability hierarchy .. 6 Figure 2. Type I digital Stopwatch .. 9 Figure 3. Type II mechanical Stopwatch .. 9 Figure 4. Interior of digital (Type I) Stopwatch .

5 11 Figure 5. Inner workings of mechanical (Type II) Stopwatch or Timer .. 12 Figure 6. A collection of timers .. 13 Figure 7. Sample specifications for Stopwatch (Example 1) .. 16 Figure 8. Sample specifications for Stopwatch (Example 2) .. 18 Figure 9. Typical performance of quartz wristwatches using32 768 Hz time base oscillators .. 19 Figure 10. Portable shortwave radio receiver for reception ofaudio time 23 Figure 11. Block diagram of the Totalize Method .. 28 Figure 12. Using the start-stop button of the Stopwatch to startthe counter .. 29 Figure 13. Time base measurement system for stopwatches and timers .. 30 Figure 14. Reaction time measurements (four operators, ten runs each)for the Direct Comparison Method .. 37 Figure 15. Averaging measurement results for four different operators .. 38 Figure 16. Reaction time measurements (four operators, ten runs each)for the Totalize Method.

6 42 Figure 17. Mean reaction times (four operators, ten runs each) for theTotalize 43 Figure A1. Sample calibration certificate, page 1 .. 49 Figure A2. Sample calibration certificate, page 2 .. 50 Table of Contents x Stopwatch and Timer CalibrationsList of TablesTable 1:Prefixes (May Be Applied to All SI Units).. 2 Table 2:Unit Values, Unit Less Values, and Percentages .. 4 Table 3: Type I and Type II 10 Table 4: Comparison of Calibration Methods .. 21 Table 5: Traceable Audio Time Signals .. 22 Table 6:The Contribution of 300 ms Variation in Reaction Time tothe Measurement 26 Table 7: The Effect of Averaging Time on 31 Table 8:Uncertainty Analysis for Direct Comparison Method(Digital DUT) Using Land Line .. 40 Table 9:Uncertainty Analysis for Direct Comparison Method(Digital DUT) Using Cell Phone .. 40 Table 10:Uncertainty Analysis for Direct Comparison Method(Analog DUT) Using Land Line.

7 41 Table 11:Uncertainty Analysis for Totalize 44 Table 12:Uncertainty Analysis of Using a Calibrated Stopwatchto Calibrate Another 4611. INTRODUCTION TO Stopwatch ANDTIMER CALIBRATIONSThis document is a recommended practice guide for Stopwatch and timercalibrations. It discusses the types of stopwatches and timers that requirecalibration, the specifications and tolerances of these devices, and themethods used to calibrate them. It also discusses measurement uncertaintiesand the process of establishing measurement traceability back to nationaland international guide is intended as a reference for the metrologist or calibrationtechnician. It attempts to provide a complete technical discussion ofstopwatch and Timer Calibrations by presenting practical, real worldexamples of how these Calibrations are guide is divided into five sections. Section 1 provides an overview,Section 2 describes the types of timing devices that require calibration,Section 3 discusses specifications and tolerances, Section 4 discussescalibration methods, and Section 5 discusses measurement sample calibration report and references are provided in the ll begin Section 1 by introducing and defining the terminology usedthroughout the rest of this The Units of Time Interval and FrequencyStopwatches and timers are instruments used to measure time interval,which is defined as the elapsed time between two events.

8 One commonexample of a time interval is our age, which is simply the elapsed timesince our birth. Unlike a conventional clock that displays time-of-dayas hours, minutes, and seconds from an absolute epoch or starting point(such as the beginning of the day or year), a Stopwatch or Timer simplymeasures and displays the time interval from an arbitrary starting pointthat began at the instant the Stopwatch was standard unit of time interval is the second (s). Seconds can beaccumulated to form longer time intervals, such as minutes, hours, anddays; or they can be sliced into fractions of a second such as milliseconds(10 3 s, abbreviated as ms) or microseconds (10 6 s, abbreviated as s).Table 1 lists these and other prefixes that can be used with seconds, aswell as the multipliers and symbols used to represent them. The secondis one of the seven base units in the International System of Units (SI).

9 Other units (most notably the meter and the volt) have definitions thatdepend upon the definition of the Stopwatch and Timer Calibrations2 The SI defines the second based on a property of the cesium atom, andfor this reason, cesium oscillators are regarded as primary standards forboth time interval and frequency. A second is defined as the time intervalrequired for 9 192 631 770 transitions between two energy states of thecesium atom to take place. The atomic definition of the second, togetherwith current technology, allows it to be measured with much smalleruncertainties than any other SI unit. In fact, NIST can currently measurea second with an uncertainty of about 1 part in 1015, or about 1 billion(109) times smaller than the uncertainties required for the calibrationsdescribed in this guide!The resolution of a Stopwatch or Timer represents the smallest timeinterval that the device can measure or display.

10 Resolution is related tothe number of digits on the device s display for a digital Stopwatch orthe smallest increment or graduation on the face of an analog example, if a Stopwatch display shows two digits to the right of thedecimal point, it has a resolution of s (10 ms, or 1/100 of a second).This means, for example, that it can display a value of s or sbut that it lacks the resolution to display s. Resolution of 10 ms isTable 1: Prefixes (May Be Applied to All SI Units)Multiples and SubmultiplesPrefixSymbol1 000 000 000 000 = 1012teraT1 000 000 000 = 109gigaG1 000 000 = 106megaM1 000 = 103kilo k1= = 10 001 = 10 6micro 000 001 = 10 000 000 001 = 10 000 000 000 001 = 10 15femtof3common for digital stopwatches, but some devices might have 1 msresolution ( s), or even smaller. For analog stopwatches, a commonresolution is 1/5 of a second, or stopwatches and timers measure time interval, they do so byusing a frequency source.