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Density measurement redefined

New Developments in the Field of Density Measurement

| Author / Editor: Barbara Klug-Santner & Siegfried Hold* / Marc Platthaus

Correct results require correct sample filling

The Filling Check function, a means of recognizing inhomogeneities and gas bubbles in the measuring cell, has also been noticeably improved and is now able to react even more reliably thanks to the “Pulsed Excitation Method”. Also the correct functioning and immaculate state of the glass measuring cell can be monitored continuously due to this new method. Thus, on top of their robust and reliable construction and design, Anton Paar density meters score with a unique repeatability of better than 1*10-6 g/cm³.

The DMA 4200 M density meter with its measuring cell made of metal is especially suitable for the petroleum industry. DMA 4200 M was developed to cope with samples such as asphalt and waxes that have to be liquefied by elevated temperatures prior to being in a suitable aggregate state for density measurement. The “Pulsed Excitation Method” makes it possible for the first time to also use the Filling Check function for metallic measuring cells which have operating conditions in a temperature range up to 200 °C and pressures up to 500 bar.

DMA 4200 M is factory-adjusted prior to delivery. This so-called Temperfect adjustment is stored in the instrument together with the temperature coefficients. In this way, as soon as the desired measuring temperature between 0 °C and 150 °C has been defined, the instrument is ready for use at the selected temperature.

It’s the oscillation that matters

Today, all new Anton Paar benchtop density meters are equipped with a so-called Y-oscillator which can be seen in Figure 3 (left). This design eliminates viscosity constraints over the entire measuring range, allows the reliable detection of particles and gas bubbles, and achieves an accuracy of up to 0.000007 g/cm³.

Some other density meters that are available on the market contain U-tubes that oscillate in the X-direction, as is shown in Figure 3 (right). In the course of time it could be recognized that these X-oscillators are subject to technical limitations. These limitations manifest themselves in limited accuracy in the case of viscous samples and in a high error probability in the case of inhomogeneous samples or if there are particles and gas bubbles in the sample. For that reason, X-oscillators made from glass can only achieve accuracies of 0.001 g/cm³.

Additional Information
 
Pulsed Excitation

In order to develop a measuring instrument that was accurate to the fourth decimal place and affordable at the same time, the Anton Paar engineering team developed the Y-oscillator for the DMA 1001 density meter. Thanks to this oscillator and its option for a one-point adjustment, the reference oscillator became obsolete. The measured oscillation period of the water-filled measuring cell is compared to the obtained result of the prior adjustment and, based on the obtained data, a possible drift is compensated automatically. This means that the instrument is adjusted twice as fast and it takes only half the time that other density meters require to achieve full operational status. The density meters DMA 501 and DMA 1001 even point out insufficient ambient conditions such as humidity and temperature to the operators and give recommendations how to achieve optimum life expectancy of the instrument.

Finally, the portable density meter DMA 35 shall be mentioned. This density meter is also available in the versions DMA 35 Ex and DMA 35 Ex Petrol that are both intrinsically safe and thus fit for use in hazardous areas — a unique feature on the market. On top of its robustness and high accuracy, DMA 35 offers the patented feature of an exchangeable glass measuring cell (AT 516421 (B1)). Thus, a broken glass cell does not represent a huge problem anymore; the exchange of the measuring cell can be carried out by the user directly on-site. Additionally, the gesture control enables measurements to be initiated or stopped by defined movements of the instrument. This is especially useful as one hand remains free and represents an additional safety aspect if measurements have to be carried out in places that are difficult to access.

Table 1 indicates to what extent the technical configuration of Anton Paar’s individual density meters meets the needs of a vast number of customer applications. The ISO 17025 accreditation certifies that Anton Paar density meters are not only produced according to the highest quality standards, they can also be traceably calibrated with certified reference materials. n

Please note: The name DMA for all Anton Paar density meters as well as the instrument features Filling Check, U-View, and Temperfect are trademarks protected by Anton Paar. For better readability, the annex “TM” after the protected instrument features was omitted in the text.

* Dr. B. Klug-Santner, S. Hold, Anton Paar GmbH, 8054 Graz/Austria

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