Quality Alchemist (品質煉金術師): Metrology Symposium 2020 (SI Unit

The Government Laboratory (GL), Hong Kong Council for Testing and Certification (HKCTC), Open University of Hong Kong (OUHK) and Standards and Calibration Laboratory of Innovation and Technology Commission (SCL) jointly organized the Metrology Symposium 2020 on 10^th Jan 2020. The theme is “The International System of Units – Fundamentally Better”. Hong Kong Society for Quality (HKSQ) was one of supporting organizations. On May 20, 2019, the World Metrology Day (WMD) 2019, the International System of Units (SI) was revised so that all the seven base units, namely, the second, the metre, the kilogram, the ampere, the kelvin, the mole and the candela, were defined based on seven defining constants related to the fundamental laws of nature. Before the seminar, I met many friends in testing and certification industry and we took a photo for memory. Ir. Brenda Lam and I took a photo first.

I also took a photo with Dr. Dr. Eric Sze and Mr. Raymond Leung.

I met Mr. CM Tsui again and took a photo for memory.

Dr. Steven Yang, Ms. Brenda Lam and I were all gradated in CityU (EE, AP & BCH/AP/SEEM).

I am honor to meet Dr. Alex CK Tse (Programme Director, Directorate Office, OUHK).

Gilson HK Lab team (Nic, Sally & Ben) also joined this metrology symposium.

In the beginning, Prof. Yuk-Shan Wong (President, OUHK) gave welcoming address. He said he serviced as Chairman of Consumer Council for many years in which metrology is important in measurement. It is not only focused on Quality but Quantity is also critical. Finally, he expected metrology as foundation of science in Testing and Certification which could be a new economic development engine.

Then all speakers and guests took a group photo.

The first and keynote speaker was Mr. CM Tsui (Head of Laboratory, Standards and Calibration Laboratory) and his topic entitled “A 35-year History of Setting up Primary Standards of Physical Measurements for Hong Kong”. Firstly, Mr. Tsui reviewed the history of metrological infrastructure development since Mr. Gordon Bell (Director Royal Observatory) suggested to maintain and certify standards of measurement in 1977. In that time, the Governor of Hong Kong appointed the Advisory Committee on Diversification (ACD) to study the ways to facilitate diversification of industry and the report issued in 1979.

Then Mr. Tsui told us that HKG Standards and Calibration Laboratory (SCL) was established in 1984. He introduced their time and frequency standard and the first HP5061A caesium beam frequency standard was acquired in 1983. At that time LORAN-C timing receiver was used to synchronize the HP5061A to UTC(USNO) by receiving the LORAN-C signal from Gesashi, Okinawa, Japan. He also briefed the history of traceability for time synchronization such as 1989 using GPS Receivers, 2007 using Multi-Channel GPS Receivers and 2017 using Multi-Frequency GPS Receivers.

Finally, Mr. Tsui introduced that their Mass Laboratory and Length Laboratory were established in 1986. SCL acquired the International Prototype Kilogram (IPK) Copy No.75 for Hong Kong from BIPM in 1990. He said SCL is lucky to order IPK in the Third Periodic Verification (PV) that 1^st PV from 1899 to 1911, 2^nd PV from 1939 to 1953 and 3^rd PV from 1988 to 1992. In future, SCL planned to replace with silicon sphere as the reference standard mass for Hong Kong.

Ms. Brenda HS Lam (Senior Electronic Engineer, Standards and Calibration Laboratory) was the second speaker and her topic named “The Story of the Candela, the Eye and the Cryogenic Radiometer”. She firstly briefed the candle light in which the highest temperature zone is about upto 2000K.

And then Ms. Brenda Lam compared the different of radiometry and photometry. In Photometry, visual response of eye was mentioned and it found that human eye is more sensitive in sun light (at 555nm) rather than at night (at 507nm).

Therefore, we would use CIE 1931 in sunlight. The following equation showed how luminosity function transferred from radiometric quantity. The peak value of luminous efficacy for photopic vision, K_m, occurs at a wavelength of 555nm and has the value 683.002 lm/W (max).

Finally, she introduced SCL primary cryogenic radiometer system in which included laser stabilization system and cryogenic radiometer for alignment use.

Dr. Kelly WY Chan (Chemist, Government Laboratory) was the third speaker and her presentation topic was “Mole: The Fundamental of Metrology in Chemistry and Biology”. In the beginning, Dr. Chan briefed the history of the Mole since John Dalton developed the “Atomic Theory” in 1808. Avogadro said that the same volumes of all gases contain the same number of molecules in 1811 and Wilhelm Ostwald introduced the concept of the “mole” in 1902.

Dr. Kelly Chan stated mole definition which was SI base unit that measure amount of substance. One mole contained a defined number of elementary entities (atoms/molecules) that is Avogadro constant (N_A) about 6.22 x10^23 mol^-1. Then she mentioned that one mole of grapefruit would have approximately the same volume as the Earth!

After that Dr. Chan said metrology in Chemistry and Biology focused on the study of comparability and traceability of those measurements to ensure the reliability results. The following diagram demonstrated how analytical measurement could be traceable to SI unit (unbroken chain) for comparison of their results.

Lastly, she explained the calibration hierarchy for protein which needed to decompose to small unit as amino acid which could be traceable to SI unit.

The fourth speaker was Dr. Steven SL Yang (Acting Senior Electronics Engineer, Standards and Calibration Laboratory) and his presentation title named “Let’s Count Elementary Charges”. Firstly, he explained how to count elementary charges. It was using conventional current (from +ve to -ve) or flow of electron (from -ve to +ve).

In 1860s, people determined the mass of the silver before and after to indicate the current passed through it. (1A generate ~ 1.118g silver per second or per coulomb). Another old method was oil drop experiment in 1909. Recently, SI definition of electric current that the ampere (A) is the SI unit and defined by taking the fixed numerical value of the elementary charge e to be 1.602 176 634 x10^-19 when expressed in the unit C, which is equal to A s, where the second is defined in terms of △V_Cs. (A = C/s)

The Quantum Metrological Triangle was introduced for practical realization of ampere that included Voltage, frequency and Current. He explained Single electron transport (SET) had technical limitations and larger relative uncertainties but it offered unique and elegant approaches to realizing SI units.

Finally, Dr. Steven Yang showed SCL equipment for practical realization the ampere. At the end, he asked us how much capacity of portable power bank and give three equal amount but different unit answers that 10,000mAh = 36,000C = 2.246 943 266 805 87 x10²³e.

During the tea break, there were some research posters demonstration. Poster for Transition from the IPK to a fundamental constant h.

Another poster showed the story of the candela.

The fifth speaker was Dr. Terry HW Lai (Electronics Engineer, Standards and Calibration Laboratory) and his topic entitled “From Ancient to Modern, the Development of Time Measurement Using Optics”. Dr. Lai briefed the history of timekeeping development in Ancient to now.

Since sunrise and sunset is periodical that is suitable for time measurement using Sundials in ancient. In Hong Kong, there were some place established Sundials and the most famous one was in HKUST. And then Crystal Oscillator developed for digital timekeeping based on the piezoelectric material to generate an electrical signal with a precise frequency (Typically 32,768 Hz per second).

And then Dr. Lai briefed the atomic time since 1960 that an atomic standard of time, based on a transition between two energy levels of an atom or molecule, could be realized and reproduced much more accurately. Caesium 133 atom was chosed in 1967.

Lastly, Dr. Lai showed the comparison between optical clock and Caesium Fountain Atomic clock. He concluded optical clocks had potential to realize the second in the future.

The sixth speaker was Dr. Eric TP Sze (Associate Professor, OUHK) and his presentation was “Reference Materials – Considerations to Maintain Metrological Traceability”. Dr. Sze briefed the metrological traceability that related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.

In order to give student experience the important of traceability, he ordered the Standard Reference Material 2582 powdered paint (nominal 200mg/kg Lead) for student use. It costs HK$6000 per 20g!

At the end, Dr. Eric Sze briefed the main steps in producing and maintaining CRM based on PD ISO Guide 35:2017 and explained how to assure the homogeneity and stability of this CRM.

Mr. Raymond Leung (Electrical and Mechanical Engineer, SCL) was the last speaker and his topic entitled “Optical Clocks and the Future of the Second”. In the beginning, Mr. Leung briefed the history of International Mass Prototype, The Grand K (1889-2019).

Then he briefed the new definition of kg by taking the fixed numerical value of the Planck constant h to be 6.606 070 15 x10^-34 when expressed in the unit Js, which is equal to kgm²s^-1, where the metre and the second are defined in terms of c and △V_Cs. And then practical realization for the definition of the kilogram were discussed.

After that Mr. Leung used Kibble balance calculation to derive the relationship of the Planck constant and the mass.

Lastly, Mr. Raymond Leung briefed how to use X-ray-crystal-density method (XRCD) and the single crystal of silicon sphere (high chemical purity and no dislocations) for practical realization for the definition of the kilogram. He told us that the Silicon Sphere cost 1 million Euro!

Q&A Session:

I questioned that we studied mole in Chemistry under university BSc level but we all used ppm working in laboratory; and why let student use very expensive CRM. Dr. Kelly Chan said it related to chemical reaction but both units were related to each other that ppm could be mg/l in which was able to calculate back to mole again. Dr. Sze said it could let student more understand the traceability and experience on how to handle CRM.