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Brookeld Engineering Labs., Inc. Page 17 Manual No. M09-352-B0411

Appendix B - Calibration of the Ball Constants

Re-calibration of the ball constants is required if:

1. changes in the sample tube or water jacket were made

2. one or more balls were replaced

The calibration requires the use of a Newtonian viscosity standard.

Choice of the viscosity standard is according to the ball; the standards are provided in 100 mL

bottles and can be obtained from your Brookeld dealer.

BALL NO. 1 2 3 4 5

N44 Viscosity Fluid

(Nominal Value of 92cP @

20ºC) [mPa•s}

4 20 250 1000 3000

The calibration is made according to the method in DIN 53015 at 20°C ± .05 C. A suitably

calibrated thermometer can be obtained from your Brookeld dealer, on request.

The ball constants are determined from (5) running times, in both forward and reverse direc-

tion.

The ball constant is calculated according to the following equation:

Equation 3:

K =

(ρ

-ρ

)

• t

t Mean value from 5 running times [s]

η Dynamic viscosity of the calibrating uid [mPa•s] at 20°C ± .05 C

Density of ball [g/cm

]

Density of calibrating uid [g/cm

]

Note: Be sure to measure the sample density at the same temperature at which the viscosity

will be measured.

The expected value of the constant should be similar to the constant stated in the test certi-

cate.

For Ball No. 6, the ball constant changes signicantly as a function of the falling tube diam-

eter and diameter of the ball, so that the ball constant is calculated according to the following

equation:

Equation 4:

= 1.4057(D-d

)

(0.75042+1.82637 )

D Falling tube diameter (see calibration certicate)

Diameter of Ball No. 6 (see calibration certicate)

Ball constant of Ball No. 6

1 2 ... 12 13 14 15 16 17 18

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