Frequently Asked Questions - Viscometers

1. Which IKA rotational viscometer is the most suitable for my sample?
lo-vi: for juices, solvents, edible oils, inks, liquid soap.
me-vi: for paints / varnishes, mayonnaise, dairy products, ketchup.
hi-vi I & hi-vi II: for pastes, ointments, molasses, gels.

2. How can the accuracy of the ROTAVISC be checked?
IKA sells standard liquids with a viscosity determined at 25 °C. The user can check his or her device using these fluids.

3. How is the spindle mounted on the device?
The delivery includes three different adaptations.
1. The spindle is screwed onto the device.
2. The spindle is attached to the device by means of a quick-fitting adapter.
3. The spindle is attached to the device by means of a hook adapter.

4. How long does a measurement take?
To obtain a stable viscosity value, the spindle should have completed 3 to 4 full revolutions in the medium. The lower the speed, the longer a measurement takes.

5. How deep does the spindle have to be immersed into the test medium?
Each spindle has a mark on the shaft. The spindle must be immersed into the medium up to this point.

6. What is the smallest viscosity that can be measured using ROTAVISC?
1 mPas with lo-vi and ELVAS-1 at 60 rpm.

7. How exactly does the IKA ROTAVISC work?
The rotational viscometer measures the torque required to turn a spindle immersed in a medium. The spindle is driven by a motor that uses a calibrated spring. The deflection serves as a measurement of the torque and is shown in the display as M%.

8. How much sample volume is needed?
The standard spindles in the scope of delivery are suitable for a volume of approx. 500 ml in the 600 ml beaker (low form). Smaller sample volumes can be measured with the absolute measuring systems (coaxial measuring system), such as with the VOLS-1 adapter.

9. Why does ROTAVISC measure different viscosities for the same sample?
Generally, viscosity is not a substance-specific constant. The viscosity describes a substance in a well-defined state, for instance at temperature X and speed Y. There are samples which reduce their viscosity with increasing speed, for example ketchup (shear thinning / pseudoplastic). For other samples, the viscosity increases with increasing speed, for example starch solutions (shear thickening / dilatant). Also there are samples that do not change their viscosity either as the speed increases or decreases, such as silicone oil (Newtonian fluid).

10. Which measured values does ROTAVISC output?
Temperature: °C or °F
Speed: rpm
Measuring time: hh:mm:ss
Torque: M%
Viscosity: mPas, cP, m²/s, cSt
Stop conditions: Time, torque, temperature, viscosity spindle
Density: g/cm³
Shear rate: 1/s (when using a coaxial measuring system)
Shear stress: PA (when using a coaxial measuring system)

11. How high should the maximum speed be?
Here it is important that the speed and the spindle are chosen so that the laminar flow range is not deviated from. Otherwise, the viscosity values will be too high. For the geometries SP-1, SP-2, SP-6 and ELVAS-SP, the following transition points to a turbulent flow were determined.
1. SP-1 lo-vi,15 mPas at 60 rpm > rpm / mPas = 4
2. SP-2 lo-vi 100 mPas at 200 rpm > rpm / mPas = 2
3. SP-6 me-vi 100 mPas at 50 rpm > rpm / mPas = 0.5
4. ELVAS-SP 0.85 mPas at 60 rpm > rpm / mPas = 70.6
If the ratio of rpm / mPas exceeds these values, turbulent conditions can occur with the spindles listed. Artificially higher viscosity values can occur with the geometries VAN-SP-1 to VAN-SP-4, due to turbulence at speeds of more than 10 rpm.

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