The Evolution of Density Measurement

Learn how glass has been used for thousands of years to measure density with ever more precise methods and how it finally made its way to the U-tube, one of Anton Paar’s core technologies. We also provide a comparison of three different types of density meters.

For thousands of years the demand for accurate density measurements has been increasing. Science went on a journey from the hydrometer over the pycnometer to digital U-tube technology. All these methods have some things in common: they all make use of glass for their sensor technology. The more accurate a result has to be, the longer a measurement takes and the more side effects have to be considered (e.g. accurate temperature regulation and measurement).

In U-tube technology’s much shorter history of only 50 years, a variety of different measurement setups has been developed.

  • Archimedes found out that any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. This realization is commonly known as Archimedes’ principle.

  • An early description of a hydrometer can be found in a letter from the Greek philosopher Synesius of Cyrene to the Greek scholar Hypatia of Alexandria asking her to make a hydrometer for him. Hypatia is given credit for inventing the hydrometer, a device made of glass, which immerses deeper into liquids of low density than into liquids of higher density.

  • Abu ‘r-Raihan Muhammad al-Biruni, an important Chorasmian (western central Asian) universal scholar constructed the first pycnometer. A pycnometer is also made of glass. The volume is described with a liquid of well-known density by simply weighing it when it is empty and then weighing it when it is filled with the liquid. An unknown sample is then filled and its density calculated thanks to the known volume and another weighing.

  • The master locksmith Anton Paar started a one-man machine repair workshop on Heinrichstraße in Graz, became his own boss, and thus laid the foundation for future generations. The company Anton Paar, today’s market leader in digital density measurement, was born.

  • The idea was born to carry out density measurements by using the principles of oscillation.

    A U-tube made of glass is excited to oscillate in its basic oscillation. If the U-tube is filled with a light sample (e.g. air), it oscillates with a high frequency. If the sample is heavier, i.e. its density is higher (e.g. water), the oscillation frequency is lower.

  • The digital density meter DMA 02 C by Anton Paar KG, based on the principle of an oscillating U-tube as indicator of a liquid’s density, was presented at ACHEMA.

    The apparatus for density measurement DMA 02 C with an accuracy of 10-6 g/cm³ revolutionized density measurement. However, only the period of oscillation was evaluated and the density had to be calculated manually.

  • The lighter and cheaper density meter DMA 10 was launched. The period of oscillation was still the primary output, further results were calculated manually.

  • The DMA 46 density meter was the first density meter that was equipped with a Peltier thermostat. This way, the sample’s highly temperature-dependent density could be measured at a defined constant temperature between 15 °C and 40 °C.

    DMA 46 was also the first calculation device with an integrated computer.

  • DMA 55 with its implemented oscillation constants directly displayed the density value which did not have to be calculated from the oscillation characteristics any more.

  • The first version of the handheld density meter DMA 35 was developed.

    This digital battery-operated compact density measuring device provided exact measurement results in a few seconds at any measuring location.

    Anton Paar received the Austrian National Award for Innovation for this product in 1982.

  • DMA 48 and DMA 58 were equipped with a microcontroller that delivered, in addition to the density result, also the solution’s concentration as it was the concentration the users were usually interested in. Also the temperature range was increased up to 70 °C. Today, DMA M density meters allow measurements at temperatures of up to 100 °C, specially designed instruments even at temperatures of up to 200 °C.

  • The reference oscillator (ThermoBalance™)  correcting the elastic behaviour of the glass U-tube and providing long term stability was implemented into DMA benchtop density meters along with the first full range viscosity correction.

  • 2004 marks the beginning of modularity and multiparameter systems. Today, a selection of the following measuring parameters can be combined to create any of several hundreds of custom-specific solutions: density, sound velocity, CO2, O2, alcohol content, pH, refractive index, optical rotation, viscosity, color and turbidity .

  • The new generation of benchtop density meters „DMA Generation M” in contemporary design used an embedded PC and represented an important milestone with its touchscreen display, an integrated camera (U-View™), automatic bubble detection (FillingCheck™), and considerably improved user-friendliness thanks to state-of-the-art GUI-design (Graphic User Interface design). The high-end model of this family – DMA 5000 M – is the world’s most accurate digital density meter.

  • DMA Generation M density meters are equipped with an even bigger touchscreen of 10.4”. Along with the bigger screen, these instruments were the first to be equipped with modern PCAP-touchscreen technology which is far more precise and robust compared to resistive touchscreens.

  • EasyDens, the world’s smallest digital density meter, is launched.

  • Happy Birthday DMA!

Modern digital density meters range from quick and mobile devices to highly precise lab instruments. There is a tendency to include more and more sophisticated technology and features to make the measurement process safer and more reliable than ever before. As soon as gases or liquids are produced, consumed, processed, or sold in any industry imaginable, these devices are found to ensure stable quality and save money. Quick and reliable digital density measurement has thus long become the standard for incoming control of raw materials and for process control as well as quality control on finished products in many industries.

Our guideline Good Density Measurement™ provides everything you need to know.

Pros and Cons of the three best known density meter types

Have a look at both the advantages and disadvantages of the three types of density meters introduced in the timeline.

Hydrometers

Advantages

  • fast results
  • affordable

Disadvantages

  • fairly large sample volumes needed
  • difficult to hold at a constant temperature during the measurement
  • result may depend on the operator due to a parallax error
  • glass is likely to break
  • different hydrometers for different samples needed (lactometer, alcoholmeter, saccharometer, etc.)

Pycnometers

Advantages

  • affordable
  • precise

Disadvantages

  • fairly large sample volumes needed
  • requires skilled operators
  • difficult to clean
  • fragile and breakable
  • additional equipment required (e.g. balance)
  • numerous errors possible (e.g. droplet on the outside, capillary not completely full, error when reading the balance, etc.)

Digital density meters

Advantages

  • fast
  • small sample volumes
  • user-friendly and easy to operate
  • operator-independent
  • precise and quick temperature regulation

Disadvantage

  • one-time higher investment required
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