1965 to 2005 – 40 Years of DMA

In 1965, Hans Stabinger began to explore the use of oscillating tubes for determining density. He was set the task of measuring the smallest differences in density in solutions based on Prof. O. Kratky’s small angle X-ray scattering (SAXS). Together with H. Leopold, who provided the electronic part with the help of the—then still young—technology, he successfully completed a functional prototype one year later.

Anton Paar GmbH, which had successfully taken over the production of the small angle x-ray camera a few years before, also took over the production of the density meter, as a support device for the small angle x-ray camera so to speak, and the name DMA (Dichtemessapparatur) was born. The DMA 02 was already presented at the ACHEMA in Frankfurt, Germany, in 1967. Soon it turned out that this device could be used as a replacement for plummet measuring and pycnometers, far beyond the use in small-angle X-ray scattering investigation.

The uncomplicated handling, the low usage of preparations, and the measuring speed were so far unequalled advantages. From the vantage point of the present, the first DMA 02 device was downright primitive. It was very limited with regard to both mechanical build and electronic equipment. The success of even this simple device encouraged the developers to sound out the use of the new method into all directions.

The rapid development of electronics and better insight into the physics of the oscillating U-tube brought forth a number of devices. The devices that followed the DMA 02 were the DMA 02B, the DMA 02C, and the DMA 02D, which above all featured a more refined measuring system. The wish for a more economically priced device brought forth the DMA 10, a minimum version of the oscillating U-tube principle. Then, as from the 1970s the available electronic components became sophisticated enough, so that density could be directly displayed by a built-in calculator. Before, only a period duration value had been displayed, which had then been manually converted into a density value. Yet only for the low accuracy class so far because the difficulties for high accuracy seemed insurmountable. The first battery-operated hand-held device, the DMA 35, was also developed in that time.

Our cooperation with Siemens Erlangen introduced us into the world of process technology. It was our task to measure the concentration of a boric acid solution via density in the nuclear power plant of Stade, which was under construction at that time. The requirements for the measuring cell and the electronics were enormous, and so was also the challenge for the developers. It had to be measured with metal oscillators in the flow, and the electronics had to cope with the rough power plant environment. These devices worked without malfunctions until the nuclear power plant was closed down after 32 years.

A family of density meters was born—DPRs (Dichteprozessrechner). Due to the more complex tasks in the process measuring sector, we developed and built devices with different oscillator diameters, materials, and pressure and temperature ranges. The nuclear power plant was only the beginning. Above all in food production (beverages), the DPR systems became an essential part of our product range.

With introducing thermostatting by means of Peltier elements, we placed the first stand-alone measuring device on the market with the DMA 46. In parallel, H. Leopold developed an electronic thermometer which finally, integrated in the density meter, made the complete measuring setup possible.

Until 1978, we mainly worked on the structure of the devices and its perfection. In 1978, we successfully won over H. Deimel, an excellent physicist who has also always stayed up-to-date with applications in practice, to join our development team. He examined–-and still examines—the theory underlying the oscillating U-tube and pointed out serious flaws in the accuracy of our measuring devices.

Based on the theoretical insights and their confirmation in practice, we have developed measures which, ultimately, make it possible for us to push the limits of accuracy to the limit of detection. After the versions DMA 48 and DMA 80, we developed the DMA 5000/4500 devices step by step, which leave nothing to be desired anymore with regard to measurement results.

Along with the measurement of density, we also developed combinations with the measurement of other qualities of liquids. The combination with the sound velocity measuring devices DSA 48 and DSA 5000 allows for determining the concentration in three-components mixtures; the inclusion of the refractive index successfully followed up the well-known measuring routines in the beverages industry, and density measurement for the calculation of kinematic viscosity is also integrated in a newly developed rotational viscometer.

If one looks back on the 40 years, the development of the oscillating U-tube method, it seems that it has gone ahead smoothly. What has not been mentioned here are the many wrong tracks that we have taken, and the mistakes we have made because we simply had no previous knowledge of completely new things. We have never had the opportunity to orient ourselves towards demand because their is no demand for the unknown. We have rather tried to explore and further pursue what is just feasible.