Brookfield CAP2000 Viscometer - Manual (Page 14)

Brookfield Engineering Labs., Inc. Page 14 Manual No. M/94-310F
III.2 Repeatability
CAP 1000 and CAP 2000 Viscometers are repeatable to
±
0.5% of the full scale viscosity range
(FSR). Due to shear heating considerations which occur in high shear rate instrumentation, the
measurement of NIST Viscosity Standard Fluids at rotational speeds above 900 RPM will show
a decrease in viscosity with an increase in rotational speed (shear rate). When using Brookfield
CAPCALC software together with CAP 2000 Series Viscometers and knowing the thermal
conductivity of the test sample being measured, corrections to the viscosity measurements can
be made which compensate for the heat generated. Refer to the CAPCALC Operator Manual
for additional information.
Normal forces due to the shearing of a viscoelastic fluid (such as paint) are accounted for in the
CAP Series Viscometers by weight on the spindle column of 3.4 Newtons (340,000 Dynes)
total force. This is done to avoid having the cone lift off the plate, thereby changing the cone
plate geometry and producing incorrect viscosity readings. For normal forces greater than 3.4
Newtons (340,000 Dynes) total force, additional externally mounted weights are required. How-
ever, more weight means more wear on the cone and plate. Additional weights should only be
considered when definitely required and removed when not required.
Contact Brookfield Engineering Laboratories or your Brookfield Dealer/Distributor/Represen-
tative for details on the above information.
III.3 Making Viscosity Measurements
The following procedure is recommended for making a viscosity measurement.
With the viscometer on a clean, level surface, connect it to the proper power supply (Section
I.4).
1. Turn the power switch ON (Section II.1).
The procedure assumes that the following list has been done:
a) If the viscometer has been “off” for an extended period (i.e., overnight) a “warm up”
period of 30 minutes is suggested. The default temperature (25
°
C) is used for low
temperature instruments (i.e., CAP1000L/2000). The default temperature for high
temperature is 50
°
C (i.e., CAP1000H/2000H). If a cone calibration is to be done
immediately after the warm up period, temperature should be set to 60
°
C (calibra-
tion temperature for high temperature instruments) to save some time.
b) The cone calibration procedure (Appendix B) should have been done for all cones
which are used with the instrument. Cone calibration is only required when a new
cone (i.e., replacement for lost/damaged cone) is used, or when calibration check
fails.
c) When making measurements with low temperature instruments (CAP1000L/
CAP2000L) the solvent trap may not be required (for the containment of solvents
and/or prevention of sample “drying”). The trap should be used for all measure-
ments with high temperature instruments (CAP1000H/CAP2000H).