Brookfield DV-II+ Digital Viscometer - Manual (Page 38)

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Brookfield Viscosity Standards Fluids are accurate to (+/-) 1% of their stated value.
Example: Calculate the acceptable range of viscosity using RVDV-II+ with RV-3 Spindle at 2
RPM; Brookfield Standard Fluid 12,500 with a viscosity of 12,257 cP at 25
°
C:
1) Calculate full scale viscosity range using the equation:
Full Scale Viscosity Range [cP] = TK SMC
10,000
RPM
* *
Where: TK = 1.0 from Table D2
SMC = 10 from Table D1
Full Scale Viscosity Range = = 50, 000 cP
* * 1 10 10,000
2
The viscosity is accurate to (+/-) 500 cP (which is 1% of 50,000)
2) The viscosity standard fluid is 12,257 cP. Its accuracy is (+/-)1% of 12,257 or
(+/-)122.57 cP.
3) Total allowable error is (122.57 + 500) cP = (+/-) 622.57 cP.
4) Therefore, any viscosity reading between 11,634.4 and 12,879.6 cP indicates that the Viscometer
is operating correctly. Any reading outside these limits may indicate a Viscometer problem.
Contact the Brookfield technical sales department or your local Brookfield dealer/distributor with
test results to determine the nature of the problem.
The Brookfield Guardleg
The guard leg was originally designed to protect the spindle during use. The first applications of the Brookfield
Viscometer included hand held operation while measuring fluids in a 55-gallon drum. It is clear that under those
conditions the potential for damage to the spindle was great. Original construction included a sleeve that protected the
spindle from side impact. Early RV guard legs attached to the dial housing and LV guard legs attached to the bottom
of the pivot cup with a twist and lock mechanism.
The current guard leg is a band of metal in the shape of the letter U with a bracket at the top that attaches to the pivot
cup of a Brookfield Viscometer/Rheometer. Because it must attach to the pivot cup, the guard leg cannot be used with
a Cone/Plate instrument. A guard leg is supplied with all LV and RV series instruments, but not with the HA or HB series.
It’s shape (shown in Figure 1) is designed to accommodate the spindles of the appropriate spindle set; therefore, the RV
guard leg is wider than the LV due to the large diameter of the RV #1 spindle. They are not interchangeable.
The calibration of the Brookfield Viscometer/Rheometer is determined using a 600 ml Low Form Griffin Beaker. The
calibration of LV and RV series instruments includes the guard leg. The beaker wall (for HA/HB instruments) or the
guard leg (for LV/RV instruments) define what is called the "outer boundary" of the measurement. The spindle factors
for the LV, RV, and HA/HB spindles were developed with the above boundary conditions. The spindle factors are used
to convert the instrument torque (expressed as the dial reading or %Torque value) into centipoise. Theoretically, if
measurements are made with different boundary conditions, e.g., without the guard leg or in a container other than 600
ml beaker, then the spindle factors found on the Factor Finder cannot be used to accurately calculate an absolute viscosity.
Changing the boundary conditions does not change the viscosity of the fluid, but it does change how the instrument torque