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Question 12.45: During the field balancing of a cooling tower fan, the measu...

During the field balancing of a cooling tower fan, the measurement taken are: A_{1}=0.7 mm , A_{2}=1.06 mm, A_{3}=1.18 mm \text { and } A_{4}=0.5 mm . The trial mass used is 250 g. Determine the necessary balancing mass (to be placed at the same radius as the trial mass) and its angular location with respect to the position of the trial mass during the second run when the vibration amplitude is 1.06 mm.

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Refer to Fig.12.61

\text { Draw a triangle } O B E \text { by taking } O E=2 A_{1}, O B=A_{2} \text { and } B E=A_{4} . Mark the mid-point A of OE. Join AB.
Then AB = 0.46 mm and \theta=135^{\circ} .

\text { Correction mass, } m_{c}= m \cdot \frac{O A}{A B}=250 \times \frac{0.7}{0.46}=380.4 gm .

The balancing mass is attached 135° in the clockwise direction from that of the trial mass during the second run.

12.61
12.67

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