
Model 35 Viscometer Instruction Manual
208878
Revision N, February 2013
26
6.2
Fluid Calibration Check
This procedure describes the calibration check using only certified Newtonian
calibration fluids. Fann calibration fluids are available for separate purchase
(Table 9-1). All calibration standards are certified by methods traceable to the
United States National Institute of Standards and Technology (NIST).
1.
Make sure that the instrument is clean before immersing the rotor and bob into
the calibration fluid. If necessary, remove the rotor and thoroughly clean the
bob, bob shaft, and rotor. Make sure the bob shaft and rotor are straight and
have not been damaged.
The batch number on the label of the calibration fluid must match
the number on the viscosity/temperature chart.
2.
Fill the sample cup to the scribed line with calibration fluid and place it on the
instrument stage. Elevate the stage so that the rotor is immersed to the proper
immersion depth. Refer to Figure 3-2.
3.
Place a thermometer into the sample cup until it touches the bottom, and then
secure it to the side of the viscometer to prevent breakage.
4.
Operate the instrument at 100 rpm for approximately three minutes. This will
equalize the temperature of the bob, rotor, and the fluid.
5.
Read the dial at 300 rpm and 600 rpm. Record these numbers and the
temperature from the thermometer to the nearest 0.1° C (0.15° F).
The viscosity at the 300 rpm reading should be within ±1.5 cP of the viscosity from
the temperature chart at the recorded temperature.
Divide the 600 rpm reading by 1.98; compare this value to the value on the chart.
The viscosity at the 600 rpm reading should be within ±1.5 cP of this viscosity
value.
Plot the 300 rpm reading and the 600 rpm reading then draw a straight line from
zero through these two points. If the 300 and 600 points do not fall in a straight
line, it is possible that the either rotor, bob, or bob shaft is bent or that other
eccentricity exists.
Points at 100 rpm and 200 rpm can be plotted if verification is needed.