Wink of Knowledge: High Density Media – DLO Density Meter for Liquids

Volume 2 | Number 3

Why this test?

The measurements carried out show that our DLO measures very precisely even in media with a density far above the previously specified maximum value.

What is a wink of knowledge?

Do you know the need to have to sometimes measure, draw or do something quickly? The speed to the result counts more than the perfect (scientific) approach. For this reason, we have introduced a wink of knowledge. Science with a wink, so to speak. We don’t want to prove anything scientifically, but quickly demonstrate something pragmatically. If you are interested, we would be happy to discuss these results in more detail with you and your project.

What liquids were used?

• Tetrachloroethylene (Carl Roth, item no.: 4737.1)

Tetrachloroethylene, C2Cl4

  • Carl Roth, item no.: 4737.1
  • Molar mass: 165.83 g/mol
  • Density: 1.61 g/cm³

Density measurement

The density measurement was carried out with the DLO-M1 density sensors for liquids. For this purpose, the sensors were each flushed with tetrachloroethylene. Using the logging function, one measured value per second was recorded for density and temperature. As a reference, the density was measured with the laboratory measuring instrument DSA 5000 M (Anton Paar). The reference values measured at 20 °C and 30 °C were linearly interpolated to obtain the temperature-dependent density of tetrachloroethylene.

The TrueDyne sensor

The DLO-M1 sensor measures the density of liquids in a microelectromechanical system (MEMS system). Within the MEMS system, the liquid is directed to an omega-shaped microchannel, the so-called omega chip. This tiny silicon tube – it is hardly thicker than a hair – is set into oscillation for the measurement. The density of the medium can be derived from the natural frequency of this oscillation: the denser the medium, the lower the oscillation.

TrueDyne_DLO-M1_VLO-M1_right
DLO density sensor for liquids

The measuring system in submillimetre size enables the compact construction of the sensor. It measures just 80 x 30 x 15 mm and thus fits into even the tightest of spaces. The measured values reach the higher-level system via an RS232 interface and in the ASCII command protocol in the TrueDyne Sensors standard.

Procedure

  1. Reference density measurement with laboratory density meter DSA 5000 M (Anton Paar)
  2. Inserting the sensor into the measurement setup according to figure 1
  3. Pumping the tetrachloroethylene through the density sensor by means of syringes

Measurement setup

  1. Syringe with tetrachloroethylene
  2. Density sensor DLO-M1
  3. Data evaluation
  4. Return of the medium
  5. Syringe takes up the test fluid again
DLO Sensor - Tetrachloroethylene measurement setup
Figure 1 – Measurement setup

Results

The measurement results are shown in Figure 2. The black dashed line marks the temperature-dependent reference density, which was determined with the laboratory measuring instrument DSA 5000 M (Anton Paar). The solid black lines mark the reference density with a tolerance of ±0.5 kg/m³ (±0.0005 g/cm³). This corresponds to the maximum measurement deviation of the TrueDyne density sensor DLO-M1.

DLO Sensor - Tetrachloroethylene - Measurement results
Figure 2: Measurement results of TrueDyne DLO-M1 density sensors with tetrachloroethylene

The coloured dots mark the readings of three different TrueDyne DLO-M1 sensors. It should be noted that dynamic measurement deviations occur during the flow through the sensors: Due to the self-heating of the sensor, the sensor temperature deviates from the temperature of the incoming, colder fluid. At lower flow rates, these two temperatures converge so that in the static case the measurement deviations from the reference density values are less than ±0.1 kg/m³ (±0.0001 g/cm³).

Summary

The measurement results shown demonstrate that the TrueDyne DLO-M1 sensors achieve the specified accuracy of ±0.5 kg/m³ in density measurement even far beyond the specified density range (>1600 kg/m³ instead of ≤1000 kg/m³). By compensating for the self-heating of the sensor, even accuracies of ±0.1 kg/m³ are possible.

Do you have applications in this extended measuring range? Get in touch with us!

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