Wink of knowledge: Ethylene Glycol-Water Mixture – VLO Density and Viscosity Meter for Liquids
Volume 2 | Number 1
Why this test?
The measurements carried out are intended to show, in a series of various quick tests, how the concentration of two liquids can be controlled in operation using the VLO density and viscosity sensor.
The present measurement results show the top performance of our small sensor.
What is a wink of knowledge?
Do you sometimes need to quickly measure, draw or tinker with something?
The speed with which you arrive at the result counts more than the perfect (scientific) approach.
For this reason, we’ve 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’re interested, we’d be happy to discuss these results in more detail with you and your project.
What liquids were used?
- Ethylene glycol
Carl Roth (art. no.: 2441.4) - Deionised water
Density measurement
The density was measured using the VLO density and viscosity sensor for liquids.
For this purpose, the listed mixtures were passed through the sensor at a constant flow rate.
By means of the logging function, one measured value per second was recorded for density, temperature, pressure and reference density.
Ethylene glycol (C2H6O2)
1,113.37 kg/m³ 2
at 20 °C, 1.01325 bar abs
Water (H2O)
998.21 kg/m³
at 20 °C, 1.01325 bar abs
The TrueDyne sensor
The VLO-M2 viscosity sensor measures the viscosity of a liquid in a microelectromechanical system (MEMS system).
The medium is guided in the sensor via a pressure gradient to the so-called omega chip, which contains an omega-shaped microchannel.
This vibronic measuring system generates the measured values by setting a silicon tube in the chip into resonant vibration and analysing this.
This is because the vibration quality depends on the viscosity of the liquid in the microchannel.
At the same time – and independent of the viscosity – the density of the medium can be determined via the frequency of the microchannel.
Since temperature influences both viscosity and density, the temperature of the medium is also recorded in the chip in real time.
In this way, the temperature effect can be compensated for.
The measuring system in the submillimetre range enables the compact construction of the sensor.
Measuring just 80 x 30 x 15 mm (36,000 mm³), there is room for it in 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.
VLO density and viscosity sensor for liquids
Procedure
- Purification of ethylene glycol and determination of purity through density measurement with a laboratory density meter DSA 5000 M (Anton Paar)
- Mixing of water on a laboratory scale (Kern, PCB 1000-2) to produce different target concentrations (w/w) as a reference.
- Inserting the viscosity sensor into the measurement setup according to the sketch
- Pumping the ethylene glycol-water mixture through the viscosity sensor
Measurement setup
- Ethylene glycol / water mixture
- Peristaltic pump (Ismatec, ISM930C)
- Temperature basin (Julabo, F 34)
- VLO density and viscosity sensor
- Evaluation calculator
- Hose (media supply)
- Hose (media removal)
Figure 1 – Measurement setup
Results
The following table shows the measured values obtained for ethylene glycol concentrations of between 0 and 60%.
Table 1 – Measured values for concentrations of between 0 and 60%
In the following graph, the measurement deviation is plotted against the reference ethylene glycol concentration.
Over the entire measuring range (0 to 60% ethylene glycol), the maximum concentration deviation is less than 0.4%.
In addition to the direct output of the ethylene glycol concentration, other applications are conceivable, such as the direct output of the freezing point of the ethylene glycol-water mixture.
Figure 2 – Measurement deviation in the tested measurement range between 0 and 60%
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