SPM T30 - Calculating the Correction Mass

Technical data are subject to change without notice.
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Calculating the correction mass
Choose a suitable scale on the SPM balancing form. Use the compasses to mark off V
0
(= 6.1) on
each of the three printed lines. This gives you three points at equal distance from the origin of the
figure, which are numbered counter clockwise 1, 2 and 3.
Compare the readings from the three runs with trial weight. In our example, V
3
and V
1
are both
larger than V
2
. The weight of the correction mass always depends on the two highest readings (the
third helps to define its position).
Draw an arc with radius V
3
, the highest value (= 10.3), from point 3 towards point 2. Then draw an
arc with radius V
1
, the second highest value (= 7.7), from point 1 so that it intersects the first arc.
Measure the distance (same scale) between the point of intersection and the origin of the figure.
This distance (= 4.6) is the divisor V
t
for the equation below.
The equation for the weight of the correction mass is:
M
t
x V
0
=M
b
V
t
In our example, the figures are 12.3 x 6.1 / 4.6 = 16.3 (grams). We need a correction mass weighing
16.3 grams.
Position of the Mass
Measure the angle between the lines V
1
and V
t
(always these two, and always measure from V
1
to V
t
counter clockwise). The correction mass is attached to the rotor at this angle (here 91°) measured
counter clockwise from trial point 1, and at the same radial distance from the shaft as the trial
weight.
To illustrate the procedure we use the
following values as an example:
Trial weight: M
t
= 12.3 grams
Vibration without weight: V
0
= 6.1 mm/s
Trial weight at point 1: V
1
= 7.7 mm/s
Trial weight at point 2: V
2
= 3.2 mm/s
Trial weight at point 3: V
3
= 10.3 mm/s
We are looking for the following values:
V
t
= dividing factor for the calculation
M
b
= correction mass in grams
αα
αα
α = angular position of the mass.
70 Balancing with T30