Brookfield DV-II+ Digital Viscometer - Manual (Page 39)

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is converted to centipoise. Without changing the spindle factor to suit the new boundary conditions, the calculation from
instrument torque to viscosity will be incorrect.
Practically speaking, the guard leg has the greatest effect when used with the #1 & #2 spindles of the LV and RV spindle
sets. Any other LV (#3 & #4) or RV (#3 - #7) spindle can be used in a 600 ml beaker with or without the guard leg to
produce correct results. The HA and HB series Viscometers/Rheometers are not supplied with guard legs in order to
reduce the potential problems when measuring high viscosity materials. HA/HB spindles #3 through #7 are identical
to those spindle numbers in the RV spindle set. The HA/HB #1 & #2 have slightly different dimensions than the
corresponding RV spindles. This dimensional difference allows the factors between the RV and HA/HB #1&#2 spindles
to follow the same ratios as the instrument torque even though the boundary conditions are different.
The recommended procedures of using a 600 ml beaker and the guard leg are difficult for some customers to follow. The
guard leg is one more item to clean. In some applications the 500 ml of test fluid required to immerse the spindles in
a 600 ml beaker is not available. In practice, a smaller vessel may be used and the guard leg is removed. The Brookfield
Viscometer/Rheometer will produce an accurate and repeatable torque reading under any measurement circumstance.
However, the conversion of this torque reading to centipoise will only be correct if the factor used was developed for
those specific conditions. Brookfield has outlined a method for recalibrating a Brookfield Viscometer/Rheometer to any
measurement circumstance in More Solutions to Sticky Problems, Section 3.3.10. It is important to note that for many
viscometer users the true viscosity is not as important as a repeatable day to day value. This repeatable value can be
obtained without any special effort for any measurement circumstance. But, it should be known that this type of torque
reading will not convert into a correct centipoise value when using a Brookfield factor if the boundary conditions are
not those specified by Brookfield.
The guard leg is a part of the calibration check of the Brookfield LV and RV series Viscometer/Rheometer. Our
customers should be aware of its existence, its purpose and the effect that it may have on data. With this knowledge,
the viscometer user may make modifications to the recommended method of operation to suit their needs.
RV Guardleg
LV Guardleg