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This time I would like to talk about the newly revised Japanese Industrial Standard JISZ8803: “Methods for Viscosity Measurement of Liquid”. The most significant change made this time was the addition of vibration-type viscometers as one of the standards. I would like to leave the details of the new standardization to the actual document itself or to published interpretations, and instead look at some of the background to its introduction.
The fundamental principles of the vibration viscometer were proposed a long time ago, but there were always many high technological hurdles that made its commercialization extremely difficult. As a consequence, it took around 20 years until it was finally commercialized. Meanwhile, the American car maker Ford Motors, which led the way in the mass production of car engines originally developed by a European manufacturer, first started viscosity control in its manufacturing processes more than 100 years ago. Since that time there have been various viscometers proposed and you could say the viscometer has a very long history in industrial production.
I’ll return to the new Japanese Industrial Standard. JIS standards on the measurement of viscosity were first enacted in 1959. The standards were supposed to be revised every five years, but the previous last revision occurred in 1991 so since that time more than 20 years passed without a rethink of the standards.
Naturally during this period there has been significant technological progress made around the world, and in Japan there have been major changes to society and the important industries that support it. In the field of viscosity measurement as well, the vibration viscometer has become well established as a new method of measuring viscosity during this period and its production has increased greatly. In today’s industries, many vibration viscometers can be found in use as an important tool for the management, control and analysis of liquids, in both research labs and on production lines.
Behind the development of this vibration viscometer were advances in electrical circuitry technology based on semiconductor (IC) technology, and the resulting advances in control technology, as well as the digitalization of measuring and use of computers for visualizing analysis results.
As a method for assessing the physical properties of liquids, viscosity is the most fundamental physical quantity assessed. For example, when liquids are being conveyed on a production line, flow rates, which are based upon kinetic viscosity, form an important aspect of production line control. Also, engine oil’s viscosity in response to very high and low temperatures clearly affects not only the engine’s characteristics but also the possibility of burnout. In the case of engine oil in particular, as its performance within an engine can have such a dramatic influence on reducing mechanical energy loss, and hence lead to significant improvements in fuel consumption, there is fierce competition between oil makers to develop the most efficient product.
Or when flying, consideration of the viscosity of the oil circulating in the many hydraulic cylinders of the plane’s drive-train under enormous changes of temperature is extremely important.
In applications away from the industrial uses mentioned above, the measurement and analysis of low viscosity beverages to improve their drinkability is progressing significantly. In the food sector, for such uses as developing liquid meals or barium sulfate for X-ray scanning, viscosity measurement is necessary to pursue the ease of consumption as well as the prevention of accidental swallowing. Furthermore, in the medical sector measurement of viscosity of bile or blood with a small sample quantity is required, and vibration viscometers are being regarded as particularly useful in such applications.
For the newly revised JIS, there have been two additions for vibration viscometers: the tuning fork type and the rotational-vibration type. The special characteristics of vibration viscometers are their high sensitivity and wide dynamic range, which allows them to measure a vast range of liquids, from those with viscosities lower than water to those with ten thousand times the viscosity of water. They can also measure viscosity with a sample of just a few milliliters and can perform consecutive measurements over a period of time to measure viscosity over a change of temperature. Finally, since the energy applied to the sample is minimized, the measurement can be completed in a few dozen seconds.
In the development of new materials, new methods of measurement must also accordingly be introduced. Viscosity measurement in many of the above mentioned situations was previously difficult until the development and use of the vibration viscometer. It is anticipated that the vibration viscometer will contribute to the development and improvement of substances in new fields and be further effectively used as a viscosity measurement method that sustains Japanese advanced materials technology in a variety of fields.
Lastly, I would like to add the following comments. To all those who have shared the task of completing a very wide range of JIS revisions on viscosity over a short period of approximately just one year, I’m sure you will feel a big load lifted from your shoulders. While the positioning of JIS is less clear these days, we have accomplished world-leading standardization and I would like to take this opportunity here to express my thanks and appreciation for all your hard work and efforts.
A tuning fork vibration viscometer is not the kind of product you hear of very often. This is not surprising since, while there are many viscometers available, A&D is the only company in the world making and selling viscometers based on our unique tuning fork vibration technology. Viscometers in labs and research facilities are typically capillary or rotational types. Several companies make vibratory viscometers for production lines, but these use a rotary reciprocating motion with a high frequency of several kHz. Only A&D makes a model that uses a low frequency reciprocating motion like a tuning fork.
A tuning fork generates sound using the phenomenon of resonance at the same frequency. A tuning fork-type viscometer resonates its sensor plates at a natural frequency like a tuning fork and determines viscosity from the drive force (electromagnetic force) required to maintain constant amplitude. This method gains its high sensitivity from its tuning fork structure.
Technology to resonate an oscillator at the relatively low frequency range of 30 Hz was difficult to develop and had never been used in a product, even more than 50 years after the theory was developed. About 20 years ago, a cement company proposed a viscometer using this method and then about 15 years ago joined with A&D. By that time, however, the person responsible for the development was no longer with the company and work on the technology had stalled.
At that time, the product was still in its early stages so its viscosity measurement range was narrow and its cost was high. As a result, only about 10 units were sold a year. Later, another section within the company spent about 5 years trying to redevelop the technology but failed to complete a finished product. Then one day, the company president came and asked me to complete the vibration-type viscometer and so our section took up development of the viscometer.
Over five years of development had already been done in-house and the product had reached the pre-production stage. However, the development team that had worked on the project up to that point had broken up before the product was completed. It was surmised that pressure of product development might have been too mentally stressful for the development team.
When we first started development, things were a bit like a scavenger hunt. In the remains of the troubled project, we found a few completed items, like die assemblies. In the end though, most of the non-structural, technical elements had to be newly developed. Thankfully, our department was able to apply the technical expertise it had gained from developing digital balances. We were able to adapt the fulcrum used with digital balances and reused balance technology for the voice coil elements of the electromagnetic drive member. One particularly difficult area was the electronics. Even here, we were able to adapt the high resolution A/D converter technology of our electronic balances to achieve a high level of sensitivity. In the mass production stage, we struggled with issues such as getting a resonance point of 30±0.02 Hz, but ultimately we leveraged our electronic balance production technology to produce a new viscometer that had the same high accuracy and low cost as our balances.
The target viscosity measurement range was 0.30 to 10,000 mPas, with a minimum and maximum display of 0.01 mPas and 10,000 mPas, respectively. Technically speaking, the resolution was 1/1,000,000. There had never been a viscometer with such a high resolution, nor one that maintained a low viscosity sensitivity of 0.3 mPas and yet whose measurement was easy and stable.
To put a viscosity of 0.3 mPas in more concrete terms, water at 20 °C has a viscosity of approximately 1.0 mPas, meaning a viscosity of 0.3 is about 1/3 the viscosity of water. This is close to the viscosity of acetone, the liquid with the lowest viscosity. This excellent sensitivity made it possible to measure viscosity at a level that had been impossible up until that point.
After we completed the development described above about 6 years ago, we started selling the SV Series of tuning fork vibro viscometers as a new type of viscometer. There was quite a bit of skepticism toward this new type of viscometer as a general-purpose viscometer and the series did not sell well in the Japanese market early on. However, there were researchers who were unhappy with existing products and they quickly accepted the new viscometer, thanks to its ability to measure a lower level of viscosity and perform consecutive viscosity measurements over temperature changes and state changes from liquid to solid, which other viscometers had been unable to do up until that time.
The series was also well received in the European and other foreign markets. A manufacturer famous for measurement devices for particle size distribution found them excellent as a viscosity measurement method for base materials that determine Brownian motion, and SV was quickly set up as an optional device. As a result, the SV Series gradually gained acceptance as a viscometer. In the last few years, the SV Series has been recognized as part of the viscometer market, which is attested by the fact that, for example, the series is a recommended measurement instrument for oil viscosity at a leading oil company in Japan.
Our tuning fork vibro viscometer is already listed as a measurement instrument compliant with Japan Calibration Service System (JCSS) viscosity standards and the process for Japanese Industrial Standards (JIS) standardization is underway. Furthermore, we have proposed that the physical value measured by vibratory viscometers (viscosity x density) be described as “static viscosity” to distinguish it as a new concept separate from the established values of kinetic viscosity and viscosity.
A&D has considerable experience pioneering and expanding Japanese technology overseas. Considering that this tuning fork vibro viscometer was developed from unique technology developed in Japan and that the vibration method can measure a new physical quantity (static viscosity), we believe it best to quickly establish standards in Japan first. After that, we would like to proactively promote this new method to the rest of the world and let people know about the measurement abilities of our tuning-fork vibro viscometer.