e State of Particle Counters in the 1970s“Particle counters are an essential tech-nology for cleanrooms,” says Dr. Shuji Fujii, professor emeritus at the Tokyo Institute of Technology and current chairman of the Japan Air Cleaning Association.As the name implies, a particle counter measures particles suspended in air or liquid. Airborne particle count-ers, which measure particles suspended in air, are primarily used for contami-nation control in cleanrooms. Liquid-borne particle counters, which measure particles suspended in liquids, are used by the electronics industry for particu-late control of pure water and reagents and for tests of parenteral solutions.Rion currently markets various air- and liquid-borne particle counters. e rst of such products was the KC-01, Japan’s rst domestically manufactured particle counter, which was developed in 1976 and launched the following year in 1977. Capable of simultaneously measuring particle diameters in five dierent ranges, the KC-01 sold for less than 1 million yen, a relatively low price at the time. Dr. Fujii was a key gure in the release of the KC-01 and in the sub-sequent development of particle count-ers at Rion.In the 1970s, Dr. Fujii was a gradu-ate student at the Tokyo Institute of Technology in Prof. Kazuya Hayakawa’s laboratory, where he studied energy through to his master’s program.“During my years in the doctorate program, I started to get interested in air purification and started doing research on the problem of particulates in indoor environments. At the time, I was mainly doing research on air puri-cation in hospitals. Air purication in cleanrooms for semiconductors was still a special eld.”He recalls how foreign-made parti-cle counters were imported and sold in Japan before the arrival of KC-01 on the market. “When I was a student, a parti-cle counter invented by the American company Royco was available. But it was expensive, and only a few units had been imported into Japan.”A technology for simple particle measurements based on the scattering phenomenon of light had been devel-oped in the US. In this method, light is projected onto particles, and the light scattered by the particles is measured. (Note 1) Dr. Fujii wondered if this simple method, which counted particles by size, might be applied to air purication in hospitals in Japan.In 1972, Rion began importing and selling particle counters manufactured by Climet.“At the time, Rion was importing and selling particle counters made by Climet, another US company. The Climet particle counters were consider-ably less expensive than Royco’s. Our laboratory managed to purchase two units.”Study of particle counter made overseas connected to a Rion pulse height analyzerClimet’s particle counter was design ed to measure particles in one range of particle size at a time by switch-ing channels and adjusting the voltage level for each size range. e user could select one of ve particle sizes (0.5 µm, 1 µm, 3 µm, 5 µm, and 10 µm or larger) for measurement. Aer the laboratory purchased the instrument, he looked at the specications and noticed it had an analog output terminal.“Could I use the analog output to measure ve particle sizes simultane-ously?” Dr. Fujii wondered.He decided to develop a new device and applied for the Grant-in-Aid for Scientic Research from what was the Ministry of Education at the time. What he originally intended to develop was a combination of the particle counter manufactured by Climet as the sensor, a pulse height analyzer capable of tak-ing particle counts of multiple particle sizes simultaneously using analog out-put and outputting the data aer con-verting the signal into five parallel pulses, and a memory device to digitally record the data.Climet’s particle counter was based on the light-scattering method. Data taken with this method could be sepa-rated into data based on particle size by analyzing the pulse height of the scat-tered light.“e original sensor part was made by Climet, so we decided to consult with its importer and distributor, Rion, about Shuji FujiiProfessor emeritus at the Tokyo Institute of Technology and Chairman of the Japan Air Cleaning Association. He spe-cializes in building environments and fa-cilities, air purication, and information environments. After graduating in 1973 from the Department of Architecture, Faculty of Engineering, Tokyo Institute of Technology, he spent his graduate years under Professor Kazuya Hayakawa at the Graduate School of Science and Engineering of the same university until 1978. After working as a research asso-ciate and associate professor at the uni-versity, he served as professor from 1994 to 2015.Conceptual diagram of the particle counter used by Dr. Fujii during his graduate school yearsA conceptual diagram of the in-strument used by Dr. Fujii and Prof. Hayakawa for particle measurements at a hospital in 1976. The device on top is a particle counter manufactured by Climet. The device in the center is a pulse height analyzer developed by Rion. The bottom device is a digital storage device. (“Studies on the Meth-ods to Estimate the Concentration of Fluctuating Airborn Particles - Surveys at Operation Rooms in Two Hospitals.” Shuji Fujii, 1977)(Note 1) During the production of atomic bombs during World War II, air lters were used to protect workers from airborne radioactive particles. A light-scattering particle counter was developed to mea-sure the performance of these filters. In 1973, Rion became the first to introduce this technology to Japan.Ad for the KC-01 at the time of its launchAn ad for the KC-01 particle counter placed in the September 1977 issue of the Japan Air Cleaning Association journal. The KC-01 proved very popular for its compact dimensions and for its price point below 1 million yen.3
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