Brookfield DV2+Pro Viscometer - Manual (Page 72)

Brookfield Engineering Labs., Inc. Page 72 Manual No. M03-165-F0612
Special Considerations
In taking viscosity measurements with the DV-II+Pro Viscometer there are two considerations
which pertain to the low viscosity limit of effective measurement.
1) Viscosity measurements should be accepted within the equivalent % Torque Range from
10% to 100% for any combination of spindle/speed rotation.
2) Viscosity measurements should be taken under laminar flow conditions, not under
turbulent flow conditions.
The first consideration has to do with the precision of the instrument. All DV-II+Pro Viscometers
have an accuracy of +/- 1% of the range in use for any standard spindle or cone/plate spindle.
(Note that accuracy values may be higher than 1% when using accessory devices with the DV-
II+Pro). We discourage taking readings below 10% of range because the potential viscosity error
of +/- 1% is a relatively high number compared to the instrument reading.
The second consideration involves the mechanics of fluid flow. All rheological measurements
of fluid flow properties should be made under laminar flow conditions. Laminar flow is flow
wherein all particle movement is in layers directed by the shearing force. For rotational systems,
this means all fluid movement must be circumferential. When the inertial forces on the fluid
become too great, the fluid can break into turbulent flow wherein the movement of fluid particles
becomes random and the flow can not be analyzed with standard math models. This turbulence
creates a falsely high Viscometer reading with the degree of non-linear increase in reading being
directly related to the degree of turbulence in the fluid.
For the following geometries, we have found that an approximate transition point to turbulent
flow occurs:
1) No. 1 LV Spindle: 15 cP at 60 RPM
2) No. 2 LV Spindle: 100 cP at 200 RPM
3) No. 1 RV Spindle: 100 cP at 50 RPM
4) UL Adapter: 0.85 cP at 60 RPM
Turbulent conditions will exist in these situations whenever the RPM/cP ratio exceeds the values
listed above.
Effect on accuracy when using accessory devices
The Brookfield viscometer has a stated accuracy of +/- 1% of the range in use. This stated accuracy
applies when the viscometer is used in accordance with the operating instructions detailed in
the instrument instruction manual and the calibration test fluid is used in accordance with the
instructions provided by the fluid supplier (including the critical parameters of temperature control
and stated fluid accuracy). Brookfield’s accuracy statement of +/- 1% of the range in use applies
to the Brookfield rotational viscometer when used with the standard spindles supplied with the
instrument, including LV spindles 1 through 4 (supplied with LV series viscometers), RV spindles
2 through 7 (supplied with RV series viscometers), and HV series spindles 2 through 7 (supplied
with HA series viscometers and HB series viscometers) in a 600 ML low form Griffin beaker.
Brookfield offers a range of accessories for use with the Brookfield viscometer to accommodate
special measurement circumstances. These accessories, while offering added capability to the
user, also contribute to an expanded measurement tolerance beyond the instrument accuracy of +/-
1% of the range in use. This expanded measurement tolerance is a function of many parameters
including spindle geometry, accessory alignment accuracy, sample volume requirement, and