Recommended Procedures and Guidelines ITTC Quality System

ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 1 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00 ITTC Quality System Manual Sample Work Instructions Work Instructions Calibration of Chronometers with Digital Indication 7.6 Control of Inspection, Measuring and Test Equipment 7.6-02 Sample Work Instructions 7.6-02-07 Calibration of Chronometers with Digital Indication Updated / Edited by Approved Quality Systems Group of the 28th ITTC 23rd ITTC 2002 Date: 07/2017 Date: 09/2002 ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 2 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00 Table of Contents 6.1 Treatment of Calibration Results. ... 9 1. PURPOSE .............................................. 3 6.2 Calibration period ............................. 9 2. INTRODUCTION ................................. 3 CONTENTS AND FORMAT 3. TECHNICAL REQUIREMENTS ....... 4 OF THE CALIBRATION 3.1 Interior Crystal Oscillator ................ 4 CERTIFICATE ................................... 10 3.2 Time Interval Measuring .................. 4 CALIBRATION OF THE CRYSTAL OSCILLATOR 4. CALIBRATION CONDITIONS .......... 4 STANDARD IF THE 4.1 Environmental Conditions ................ 4 CHRONOMETER DOES NOT HAVE 4.2 Standard equipment for calibration 4 AN OUTPUT OF THE CRYSTAL OSCILLATOR FREQUENCY .......... 11 5. SUBJECT AND METHOD OF THE CALIBRATION .................................... 5 CALIBRATION OF THE CRYSTAL-OSCILLATOR 5.1 Examination of the exterior and STOPWATCH ..................................... 13 during normal working ..................... 5 D.1. Calibration of the measuring error 13 5.2 Calibration of the interior crystal oscillation ............................................ 5 D.2. Calibration of the daily difference .. 13 5.3 Calibration of the measuring error .. 6 D.3. Format of the calibration certificate for crystal-oscillator stopwatch ...... 14 6. TREATMENT OF THE CALIBRATION RESULTS AND CALIBRATION PERIOD .................... 9 Source: Verification regulation of time interval measuring instrument with digital indication (trial usage) [Issued on May 31, 1995 and put into effect since May 1, 1996 by National Technical Bureau - JJG 238—95, National Measuring Verification Regulation of People’s Republic of China] ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 3 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00 Calibration of Chronometers with Digital Indication The fundamental principle of these chro- 1. PURPOSE nometers is that the unit time (time base), the accuracy of which is known, is used to measure the This working instruction can be applied to time interval. The measuring results are rec- the calibration of a time interval-measuring in- orded and displayed by an electronic counter. strument with digital indication with a measur- The selected time base is generated by division ing range larger than 10 ns on new products, also or doubling of the frequency of a quartz crystal for products in the use and after repair. oscillator. 2. INTRODUCTION The principle block-diagram is shown in Fig. 1. Chronometer with digital indication means a time interval measuring instrument with num- bers for indicating the time interval measuring value. Fig. 1 Fundamental diagram of the time interval measuring instrument with digital indication • time interval between closing and (or) open- These chronometers are used for the fol- ing of two mechanical contacts lowing measurements: • duration of closing or opening for a single • time interval between two electronic pulses mechanical contact (rising or falling edge) • time interval between the actions of a single • time of one single electronic pulse electronic pulse and a single mechanical contact ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 4 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00 3. TECHNICAL REQUIREMENTS o The interval of two positive and (or) negative electronic pulses 3.1 Interior Crystal Oscillator o single positive or negative electric pulse width -6 -10 Frequency fluctuation: 10 ~ 10 o the interval between the open circuit and (or) the short circuit of two output terminals Accuracy of frequency: 10-5 ~ 10 -9 o the duration of the open circuit or the short circuit of the single output terminal 3.2 Time Interval Measuring o The rise or fall time of the pulse must be • Time base: 10ns ~ 100ms less than one-fifth of the minimum resolu- • Measuring range: 10ns ~1d tion of the calibrated chronometer. o The range of the output time interval should The measuring error may be calculated by meet the measuring requirements of the cal- the following formula ibrated chronometers. o The error of the output time interval should Measuring error = T × accuracy of the fre- be less than or equal to one-tenth of the quency of crystal oscillation + trigger error +τ0 measuring error of the calibrated chronometers. Where: • Reference frequency standard: This can be a T measured time interval highly stable crystal oscillator or an atomic τ0 selected time base during measuring frequency standard. The frequency fluctuation and the frequency accuracy must be ten times higher than the relevant indexes of the 4. CALIBRATION CONDITIONS calibrated chronometer. • Frequency Standard Comparator: Able to compare the functions and the technical in- 4.1 Environmental Conditions dexes for realizing the calibration of the • Environmental temperature: can be between crystal oscillation index of the calibrated 10 ~30 . The temperature variation chronometer. should not exceed ±2 during the calibra- • Electronic counter: Able to measure the fre- tion.℃ ℃ quency in the range from 1 Hz to 10 MHz. • Relative humidity: (65℃±15)% • Power supply: ~Voltage(1±10%)V • No strong electro-magnetic interference 4.2 Standard equipment for calibration • Standard time interval generator. It has two outputs. The signal pattern should be: ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 5 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00 5. SUBJECT AND METHOD OF THE Switch the current on. A standard time inter- CALIBRATION val is deliberately given by a standard time interval generator for checking the variety of func- 5.1 Examination of the exterior and dur- tions in the measuring range of the calibrated ing normal working chronometer. The calibrated chronometer should not have 5.2 Calibration of the interior crystal os- any mechanical damages, which could affect the cillation normal use of the instrument. All the control switches should work easily and reliably. The connection of the instruments is shown in Fig. 2. Fig. 2 Connection diagram of the instruments for calibrating the interior crystal oscillation can be started. One measurement per hour, to- If the accuracy of the frequency measure- tally N times (N = 4, 8 or 24). The measuring ment can meet the calibration requirement when sample time can be taken as 10s. the gate time of the electronic counter is 10s, the version shown in Fig. 2 (b) may be selected for Three values each time. The frequency fluc- the calibration. The reference frequency stand- tuation value can be calculated the formulae (1) ard can be used as the input of the external or (2). standard for the electronic counter. ff− Calibration of the frequency fluctuation S = max min (1) f0 After the chronometer has been warmed up according to its specification the measurements ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 6 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00 3 If the result of the calculation is better than f 1 = ∑ fi the required accuracy, the crystal oscillating fre- 3 = i 1 quency need not be adjusted. Otherwise it must be aligned. where: When being adjusted the sampling time can fi measured value of each sample by use of the electronic counter. be taken as 10s and only one measurement is sufficient. The frequency accuracy may be cal- f0 nominal value of the output frequency for the calibrated crystal oscillation. culated by formula (4): ff− 0 S = ymax (τ ) - ymin (τ ) (2) A = (4) f0 3 y(τ ) = 1 The crystal oscillation frequency must be ∑ yi (τ ) 3 i=1 aligned to the same order as that of the frequency fluctuation. However, the accuracy where: ought to be noted on the calibration certificate. yi(τ) average relative frequency deviation di- If the calibrated chronometer does not have rectly measured using a comparator of an output of the crystal oscillation, the calibra- the frequency standard. tion of the crystal oscillation norm can be car- ried out on the basis of the method given in the Alignment of the frequency accuracy Appendix B. To ensure the reliability of the calibration result during the process the accuracy of the crys- 5.3 Calibration of the measuring error tal oscillation must be restricted to a value less Selection of the calibration values and the er- than one-tenth of the frequency fluctuation ror calculation. value. The measurement begins at the minimum The frequency accuracy may be calculated value, followed by a series of values ten times by formula (3) using the data of the frequency greater each time and then ends with the maxi- fluctuation calibration. mum value. − ff0 If the measuring range of the chronometer is A = max (3) f0 divided into sub-ranges, the calibration value at the lowest sub-range can be selected according ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 7 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00 to the above mentioned method. For the calibra- T0 given value of the standard time interval tion only the maximum values of the other sub- generator. ranges need to be taken. Measuring of the time interval of the electronic The measurement must be done three times pulse for each calibration value. The arithmetic mean value will be taken as the measuring value. The connection of the instruments is shown The measuring error can be calculated by for- in Fig.

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