Determination Of The Massmoment Of Inertia - Thermo Scientific HAAKE RotoVisco 1 Instruction Manual

Hints on Measurement

14.4 Determination of the massmoment of inertia

(RheoStress1)
Oscillation measurements are influenced very much by the
mass moment of inertia of the sensor system at higher fre-
quencies. This is why an exact determination of this value is
very important.
Because the measurement of the mass moment of inertia by
the jump-answer-method is not precise enough, another
method was developed which is described here briefly.
If the mechanical system motor--sensor--Newtonian--oil is
excited periodically by Torque Md,0 with frequency f , the fol-
lowing formula results for the angle amplitude
: (1)

0
in which I represents the mass moment of inertia ,  the vis-
cosity of the Newtonian--oil, and  = 2  f. At
the oscillation in air,   0 is valid. This means that at fre-
quencies that are high enough the second term under the
root in (1) can be neglected towards the first term. Equation
(1) can be changed to: (2)
If you now measure the resulting angle amplitudes at differ-
ent torque amplitudes (OSC--Stress--Sweep) and the mea-
suring results are described as 0 = f(M ), from the as-
d,0
cending gradient
of this function the mass moment of inertia I can be deter-
mined.
(3) or (4)
This processing is implemented in the Thermo Fisher Scien-
tific rheometer software. For increasing the accuracy it is rec-
ommended to repeat the determination of the mass moment
of inertia for each rotor (once) five times and to enter the av-
erage value of the determined values of the mass moment
of inertia manually into the sensor file.
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