In our last blog entry, we talked about the large measurement range (0.1~1,000,000mPa･s) of the EMS-1000S, as well as the φ4.7mm (diameter=4.7mm) probe and how it excels at measuring in the high range. This time, we would like to talk about how our low viscosity probe, explaining how its design improves performance in the low range (0.1~1000mPa･s).
Conventional viscometers find it extremely difficult to measure low viscosity samples, but thanks to our sample tube, low viscosity probe and the technology of the EMS, high precision analysis of these samples is easy! So, what is it about our low viscosity probe that allows it to successfully analyse these samples with high precision?
Well, the development team found that both making it from an Aluminium alloy, and making it smaller, improved performance. These are the 2 key factors in its design, so why don’t we dive deeper into each to see why this is so?
Key Factor 1:
Changing the composition of the probe changed its surface properties
Changing the composition of the probe from Aluminium to an Aluminium alloy, improved the evenness of its surface, which in turn reduced the friction that it generated with the test tube's inner surface during spinning.
These are magnified images of the surface of both probes, and on comparison you should see an obvious difference in their smoothness. To understand why smoothness is an advantage here, let's dip into the science behind the measurement technology of the EMS-1000S.
Inside the EMS-1000S is a magnet-loaded spinning rotor that generates a rotating magnetic field directed toward the set position of the probe (see figure). This rotating magnetic field induces a slight electric current (properly known as an “eddy current”) in and around the probe. In turn, the Lorentz force created by the interaction between the magnetic field and the electric current, applies a driving torque to the probe, rotating it in the same direction as the magnetic field.
The rotational speed of the probe is influenced by the resistive force borne of the sample’s composition (can simply think of this as “viscosity”), as well as the friction generated between the probe and the bottom of the sample tube. It is known the that the resistive force applied to a rotating sphere on a flat surface in a liquid is proportional to the sphere’s volume and the viscosity of the liquid plus the force caused by the friction between the sphere and the surface. The influence of friction in measuring high viscosity samples is so miniscule that it can be ignored, though it must be accounted for when working with low viscosity samples. Knowing this, we understand that reducing the friction between the probe and the test tube will result in even higher measurement precision. Therefore, it was desirable to produce a probe with a smoother surface.
Key Factor 2:
Changing the size of the probe changes the torque it applies to samples
When you reduce the size of the probe, you in turn reduce the torque it applies to the sample medium. Measuring with small torque minimizes disruption of the sample’s structural integrity enabling successful measurement of samples of very low viscosity. Development of the φ1.5mm probe involved striking a balance whereby the amount of torque acting on the sample is minimized to a level that still ensures that it achieves a stable spin in substances of its target viscosity measurement range. In achieving the creation of this probe, we have opened the doors of possibility for users wishing not only to find a way to measure samples with low viscosity, but to do so with incredible precision!
We hope that you enjoyed learning about our φ1.5mm probe for low viscosity samples!
If you would like to learn even more about the scientific background of our EMS technology, please check out the measurement principle found here.
In our next article we will present the results of our experiment comparing the measurement of water using our standard and low viscosity probes.
If you would like to know more about the EMS-1000S Viscometer, please feel free to contact us by clicking the yellow “contact” button at the top of the page. Thank you for reading!