Model 35 Viscometer Instruction Manual
208878 Revision N, February 2013 25
1. Remove rotor and bob. Refer to Section 6. Be sure that the tapered end of the
bob shaft is clean, and then install the calibrating spool.
2. Install the DW3 calibrating fixture by clamping it onto the upper portion of the
viscometer support legs.
3. Select a weight according to Table 6-1. Insert the bead at the end of the thread
into the recess in the top of the calibrating spool. Wrap the thread a little more
than once around the spool and then drape the thread over the pulley.
4. Hang the selected weight on the thread, and then adjust the calibrating fixture
up or down until the thread from the spool to the pulley is horizontal. Compare
the dial reading with the reading on Table 6-1.
5. If necessary, adjust the torsion spring as specified in Section 6.3.
From Table 6-1, the factory tolerances for F1 spring only are 127 ± 1/2° for
50 grams and 254 ± 1/2° for 100 grams. A movement of ± 1/2° is permissible when
the main shaft is turning. This movement will generally be dampened out when a
fluid is being tested.
Check the linearity of the dial reading with at least three weights. If the spring
appears to be non-linear, then bob shaft is probably bent. An instrument with these
characteristics needs additional service and/or repair.
Table 6-1 Dial Deflection for Calibration Weights and Torsion Spring Assemblies
Torsion Spring
Assembly (with R1-
B1 combination)
Torsion Spring
Constant, k
1
Dynes/cm/degree
deflection
Weight in Grams
10 20 50 100 200
Dial Reading
F-0.2 77.2 127.0 254.0 - - -
F-0.5 193.0 50.8 101.6 254.0 - -
F-1 386.0 25.4 50.8 127.0 254.0 -
F-2 772.0 - 25.4 63.5 127.0 254.0
F-3 1158.0 - - 43.0 84.7 169.4
F-4 1544.0 - - - 63.5 127.0
F-5 1930.0 - - - 50.8 101.6
F-10 3860.0 - - - - 50.8
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