Details For A Better Spindle Selection - Selecta ST-2020-L Manual De Instrucciones

INSTRUCTION MANUAL CODE 80239 REV C
J
.P. SELECTA s.a.u.
Sep2016

7.4 Details for a better spindle selection

There are more criterions to follow to select the appropriate combination spindle/
speed, besides what we have explained on chapter 7.2.
There are two starting criterions:
Measure it with the slightest measurement error possible.
Measure to be able to compare with other measures.
7.4.1 Measure it with the slightest measurement error
possible
We have to find a suitable combination spindle/speed that comply the following
requirements (in order of importance):
1. The average value (shown in the display) would be as close as possible to the Full
Scale. That is, that the percentage will be the highest possible.
2. The speed would be the highest possible.
For instance:
- We work with ST-2020-L, and apply table 7.3.1
- We want to measure a sample of about 5000cP.
- From table 7.3.1, we could use one of the following combinations:
- Spindle no 1; speed 1 rpm
- Spindle no 2; speed 5 rpm (it does not appear on the table)
- Spindle no 3; speed 20 rpm
- Spindle no 4; speed 50 rpm
- Spindle no 4; speed 60 rpm
and others.
In this case, we will use the next combination:
Spindle no 3; speed 20 rpm
As it is the higher speed (rpm) and higher FS percentage.
7.4.2 Measure to be able to compare among other equip-
ments
In many occasions (for instance, in quality control), the measurements made must
be compared to the ones made in other laboratories.
When indicating a measurement result, we must indicate all the conditions such as:
viscosity, temperature and spindle number.
«Newtonian» and «Non-newtonian» fluids:
There are two kinds of fluids:
- «Newtonian»: The dynamic viscosity measurement is not affected when changing
the average speed or the spindle.
- «Non-newtonian»: The dynamic viscosity measurement do affect when changing
the average speed or the spindle.
For instance: A «Newtonian» liquid of 5000cP provides the same reading in the vis-
cosimeter if measured under the following two conditions:
- Spindle no 3; speed 20 rpm
- Spindle no 4; speed 50 rpm
If the liquid would be «Non-newtonian», the reading would be different.
In practice, most of the liquids are «Non-newtonian». Only some silicone oils
are «Newtonian». That's why you have to enter the spindle number and the
speed used.
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