M19-354
Page 13
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2019 AMETEK Brookfield Inc. All rights reserved.
II.4 Measuring the Falling Time
Before beginning the measurement, the upper cap must be loosened (unscrewed) again to let
off possible pressure.
The time which the balls take to run between the top and bottom ring marks in the sample tube
is determined with a stop watch (resolution 0.01s).
It is recommended that you record the passage of the lower ball point using the ring marks as
follows. Position your eyes at the same height as the ring marks so that these appear as a line.
A dark paper, placed behind the viscometer with its edge at the same height as the ring mark,
shows the ball periphery more distinctly.
With dark liquids, you can better observe the ball in the sample tube by looking from behind
the instrument.
Possible variations in the measuring times may be due to impurities in the sample, air bubbles
or the fact that it has not been brought to the right temperature (insufficient temperature control).
Even 0.1°C change in temperature is clearly measurable. The first forward and return passage
of the ball can be used to achieve a thorough mixing (temperature equalization) of the sample
before running the viscosity test.
BALL BEGINS
DESCENT
START STOP-
WATCH WHEN
BOTTOM OF
BALL CROSS-
ES OVER THE
RING MARK
BALL
BALL IN
TRANSIT
AT
MIDPOINT
BALL
FINISHES
DESCENT
STOP STOP-
WATCH WHEN
BOTTOM OF
BALL CROSSES
OVER RING
MARK
RING MARK
