Brookfield R/S-SST Rheometer - Manual (Page 9)

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Vane Constants For The Soft Solids Tester
Stress Constant:
ττττ
Prom.
All standard vanes supplied for the Soft Solids Tester have a height (H) to diameter
(D) ratio of 2:1. A stress constant is required for each vane to convert torque in
Newton metres to shear stress in Pascals. This constant is calculated as follows:
τ
π
prom
D
H
D
= +




− −
10 1
3
4
3
1
The constants for our standard vanes are as follows:
Vane Diameter (m) Height (m)
ττττ
-prom
V30-15 0.015 0.030 4.043
V40-20 0.020 0.040 1.706
V80-40 0.040 0.080 0.2132
These are now pre-loaded in our software. If you do not have these vanes available in
Block Editor or on your instrument then please load them using Meas-Editor for
software driven setups, or Utilities
→
Measuring Systems for stand-alone setups.
Strain / Rate Constant: K-Gamma
The constant K-Gamma converts the rotational rate or position into shear rate / strain
values. It’s value is dependent upon the ratio of container-to-vane diameter. The
vanes pre-loaded into your software (eg V40-20-3to1) assume a ratio of 3:1. If you
use vane/container combinations that don’t match this you will need to set up a new
measuring system in Meas-Editor or Utilities
→
Measuring Systems. You can
calculate out the required value using:
K gamma
b
− =
−
0 2094
1
2
.
where b is the ratio of inner to outer diameters, or select an appropriate value from the
following table:
Container to Vane Diameter Ratio K-Gamma
1.5 to 1 0.3763
2 to 1 0.2792
3 to 1 0.2355
4 to 1 0.2234
5 to 1 0.2181
Infinite sea 0.2094