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 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 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 ac- curacy 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 : • 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) nega- tive 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 chronom- eters. 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 fluctua- tion and the frequency accuracy must be ten 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 : 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 in- terval 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 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 fre- quency 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 re- sult 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. 3. mula (5): Pulse Width Measurement of the Positive Pulse

∆T = T − T i 0 (5) The single positive electronic pulse signal is given by the time interval generator and at the same time is sent to the A and B input terminals 3 1 of the calibrated chronometer. The trigger slope T i = ∑Ti 3 i=1 of A channel (start-up channel) is set to be pos- itive; the trigger slope of B channel (stop chan- where: nel) is set to be negative.

Ti value which is measured every time.

Fig. 3 The instruments connection diagram of the time interval measure for the electric pulses ITTC – Recommended 7.6-02-07 Procedures and guidelines Page 8 of 14 Calibration of Chronometers with Dig- Effective Date Revision ital Indication 2002 00

Pulse Width Measurement of the Negative Pulse The trigger slopes of both channels are set to be negative. The time interval generator gives a single negative pulse signal. The trigger slopes of A Action Time Measurement of the mechanical and B input channels of the calibrated chronom- contacts eter are set to be negative and positive respec- tively. The connection of the instruments is shown in Fig. 4. Time interval measurement of two positive elec- tronic pulses Duration Measurement of the closing for one contact The time interval generator gives a single positive pulse signal in two traces. The start-up A single start signal (short circuit) given by signal is put on A channel of the calibrated chro- the time interval generator, connected to the rel- nometer. The stop signal is put on B channel. evant measurement input terminal of the chro- The trigger slopes of both channels are set to be nometer. positive. Duration of the opening for a single contact Time interval measurement of two negative The single turn-off signal (open circuit) electronic pulses given by the time interval generator is put onto The time interval generator gives a single the relevant measurement input terminal of the negative pulse signal in two lines. The start-up chronometer. signal is put on A channel of the calibrated chro- nometer. The stop signal is put on B channel.

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Fig. 4 The instruments connection diagram of the action time measurement of the mechanical contacts

Measurement of the time interval for closing between two contacts 6. TREATMENT OF THE CALIBRA- TION RESULTS AND CALIBRATION The time interval generator gives single PERIOD start signals as two outputs, one is the start-up signal and the other is the stop signal. Both of 6.1 Treatment of Calibration Results. them are connected to the relevant measure- ment input terminals of the chronometer re- For chronometers which meet the require- spectively. ment of this working instruction, a calibration certificate will be supplied: For the ones which Measurement of the time interval for the turn- do not meet the requirement, an advice note of off of two contacts the calibration result should be supplied with the items which do not comply being pointed Single turn-off signals given by the time in- out. terval generator one after another are con- nected to the relevant measurement input ter- 6.2 Calibration period minals of the chronometer respectively. The calibration period of the chronometer is one year

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CONTENTS AND FORMAT OF THE CALIBRATION CERTIFICATE a) Calibration of the internal crystal oscilla- 4. Time interval measurement between two tion negative pulses 5. Duration measurement for closing mechan- 1. Frequency fluctuation ical contacts 2. Accuracy of frequency 6. Duration measurement for opening of me- b) Calibration of the time interval measure- chanical contacts ment 7. Time interval measurement for closing of two contacts 1. Pulse width measurement of the positive 8. The time interval measurement for opening pulse of two contacts 2. Pulse width measurement of the negative pulse Each item of the calibrated data is given on 3. Time interval measurement between two the basis of the following table. positive pulses

Standard value Measured value Error

T0 T i ΔT

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CALIBRATION OF THE CRYSTAL OSCILLATOR STANDARD IF THE CHRONOMETER DOES NOT HAVE AN OUTPUT OF THE CRYSTAL OSCIL- LATOR FREQUENCY

The connection of the instruments is shown in the following Figure

The functions of the chronometer are meas- After the chronometer has warmed up ac- ured by use of the electronic pulse. The time in- cording to the working instruction the measure- terval generator gives the pulse width of the sin- ment can be started. One measurement is taken gle pulse or the interval between two single per hour, in total N times (N = 4, 8 or 24). The pulses. frequency fluctuation value can be calculated by use of formulae (1): The given time interval may be supposed to be T0. The time unit corresponding to the mini- S = (yi)max –(yi)min (1) mum display position of the chronometer is τ0. Then the value of T0 must meet the following TTi − 0 formula: yi = T0

τ 1 0 ≤ v where: T0 10 Ti measured value every time. where: Alignment of the frequency accuracy v frequency fluctuation of the internal If the result of the calculation using the data crystal oscillator of the chronometer. from the frequency fluctuation measurements Calibration of the frequency fluctuation satisfies the following formula, the alignment of the crystal oscillator frequency is not needed.

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If the crystal oscillator frequency cannot be 10Sy≥≥ S (2) i max adjusted or although it can be adjusted but the requirement of formula (2) cannot be met, else: open the cover of the chronometer, adjust |yi|max must be stated in the calibration report as the frequency of the crystal oscillation till it the frequency accuracy. meets the requirement of formula (2). This time the value of |yi|max need only be calculated for one measured value after the alignment.

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CALIBRATION OF THE CRYSTAL-OSCILLATOR STOPWATCH

generator must possess the corresponding func- A crystal-oscillator stopwatch belongs to the tion or a calibrator for this special use may be type of instruments for the time interval measur- used. ing with digital indication based on its working principle and display. Owing to the particularity If the crystal-oscillator stopwatch does not and uniqueness of its measuring principle, the have an output of the crystal oscillator fre- general-purpose items in the main body of this quency, the interior crystal oscillator need not be working instruction cannot completely meet the calibrated. Only the measuring error of the time requirements for the calibration of the crystal– interval and the daily difference should be cali- oscillator stopwatch. For this reason a stopwatch brated. fixture i.e. a mechanical hand that starts and stops the stopwatch by use of an electromag- The connection of the instruments is shown netic pulse should be used in the standard cali- in the following Figure: bration equipment. The standard time interval

The measuring error can be calculated by use D.1. Calibration of the measuring error of the formula (5) in the main body of this work- ing instruction. The calibration values are selected as 1s, 10s, 1min and 1h. D.2. Calibration of the daily difference Three measurements should be carried out for the first three measuring values. The arith- The daily difference means the measuring metic mean of their measurement values may be error when the time interval is taken as one day. taken. For the last case, two measurements can For the normal stopwatch no one will measure be performed. Take the arithmetic mean value such a long time interval. But the crystal-oscil- of its measurement value. lator stopwatch also possess the display function of hour, minute and second. So the requirement

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of the index of the travel-time – “daily differ- The daily difference can also be calibrated ence” similar as watch and crystal clock is re- by use of an instantaneous measuring device for quired. the daily difference.

The calibration of the daily difference is the same as that of the calibration of the measuring D.3. Format of the calibration certificate for error. The crystal-oscillator stopwatch measures crystal-oscillator stopwatch the time interval, the standard time interval gen- See the table below. erator gives only one time. The calculation of the error is the same as above.

Standard value Measuring value Error T0 Ti ∆T = Ti − T0 1s 10s 1min 1h