Editing Viscometer (section)

===Electromagnetically spinning-sphere viscometer (EMS viscometer)===
[[File:EMS viscometer measuring principle.png|thumb|Measuring principle of the electromagnetically spinning-sphere viscometer]]

The EMS viscometer measures the viscosity of liquids through observation of the rotation of a sphere driven by electromagnetic interaction: Two magnets attached to a rotor create a rotating magnetic field. The sample ③ to be measured is in a small test tube ②. Inside the tube is an aluminium sphere ④. The tube is located in a temperature-controlled chamber ① and set such that the sphere is situated in the centre of the two magnets.

The rotating magnetic field induces eddy currents in the sphere. The resulting Lorentz interaction between the magnetic field and these eddy currents generate torque that rotates the sphere. The rotational speed of the sphere depends on the rotational velocity of the magnetic field, the magnitude of the magnetic field and the viscosity of the sample around the sphere. The motion of the sphere is monitored by a video camera ⑤ located below the cell. The torque applied to the sphere is proportional to the difference in the angular velocity of the magnetic field {{math|''Ω''<sub>B</sub>}} and that of the sphere {{math|''Ω''<sub>S</sub>}}. There is thus a linear relationship between {{math|(''Ω''<sub>B</sub> − ''Ω''<sub>S</sub>)/''Ω''<sub>S</sub>}} and the viscosity of the liquid.

This new measuring principle was developed by Sakai et al. at the University of Tokyo. The EMS viscometer distinguishes itself from other rotational viscometers by three main characteristics: 
* All parts of the viscometer that come in direct contact with the sample are disposable and inexpensive.
* The measurements are performed in a sealed sample vessel.
* The EMS viscometer requires only very small sample quantities (0.3&nbsp;mL).