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1. INTRODUCTION
The FIRST PLUS is a device able to measure the viscosity, which is the capacity of a product
to resist to the flow.
The fluid is forced to a shear rate (rotational speed) and the shear stress (motor torque) is
measured. The values of shear rate and shear stress then make it possible to calculate the
viscosity using the Newton equation and the constants associated with the mobile used.
Equation of Newton is:
With for viscosity in Pa.s, for shear stress in Pa and for shear rate in s-1.
Shear stress and shear rate are calculated by using constants of each measuring system as:
M x KTau with M for motor torque in mNm and KTau in Pa/mNm.
= n x KDwith n for rotational speed in rpm and KDin s-1/ rpm.
The viscometer calculates the viscosity by dividing the shear stress by the shear rate for each
measuring point. The KTau and KDconstants used depend on the measuring system selected
for the measurement.
Viscosity depends on the temperature, then it must be essential that all viscosity values are
associated to a reading of the sample temperature, in order to compare viscosity for different
samples.
There are some products for which the viscosity, to a constant temperature, stay unchanged,
even if we change the shear rate. Those samples are named Newtonian fluids, i.e. : Oils,
Water, Glycerol, etc…However, many substances have a variation of viscosity in function of
speed of shearing, and the Flow Behaviour of those samples could be determined with
measuring instruments able to set many speeds of rotation.
The viscometer is constituted with a continuous current motor and an optical encoder, in order
to warranty a great accuracy of rotational speed of bob, on all torque range.
The viscometer has an easy touch screen display, on which you could read the speed, shear
rate (according to spindle), measuring spindle reference, the measured torque and the
dynamic viscosity in mPa.s (=cPoises) or Pa.s.
The Viscometer FIRST PLUS can be used with different measuring system. You will find below
a list of compatible measuring system with this viscometer.
-MS ASTM: Measuring spindles according to ASTM / ISO 2555 (316L stainless
steel).These systems are ideally suited for simple viscosity measurement at controlled
rotational speed in all areas of activity. The standard recommends use of 600ml beaker for
measurement.
-MS ULV: Measuring system (Aluminium) for low viscosities usable with
instruments LR version. This system, unlike the MS-ASTM or MS-DIN systems, makes it
possible to measure low viscosity products in control by applying a shear rate. Its advantage
is to be compatible with instruments in LR version unlike all other measuring systems.
