10
Sonic Tension Meter Operating Theory
When an impulse is applied to a belt span, it first oscillates in all modes
of vibration, but the higher
frequency modes decay
faster than the fundamental
mode. This leaves a
continuous sinusoidal wave
that is related to a specific
belt tension; note diagram.
Using a microcomputer, a
data processing method
to capture a belt’s natural
oscillation frequency was
developed. Using this
method, the wave form
frequency can be
determined easily.
The new system uses special sensors to detect belt oscillation wave
forms. Data from these sensors is sent to the microcomputer inside
the Sonic Tension Meter for processing and conversion into the natural
frequency. To calculate belt tension, the Sonic Tension Meter system
uses the “transverse vibration of strings theory.” To operate the meter,
the belt mass, span length and width of the belt must be entered.
Formula:
T = 4 x M x W x S
2
x f
2
x 10
-9
Where:
T = Belt span tension (Newtons)
M* = Belt mass constant (g/m)
W = Belt width (mm) or number of belt strands
S = Length of the span to be measured (mm)
f = Natural frequency of the belt (Hz)
*Units of mass constant M for synchronous belts is g
/(m)(mm) or g
/10 cm
2
along the belt pitch line. Constant M for V-belts represents the
weight in grams of a 1 meter length of belting with a correction factor
applied to compensate for internal bending resistance.
Unlike a string, belts have cross-sectional rigidity. Therefore, tension
values measured by the meter may be higher than the actual belt
tension, depending on the operating conditions under which the effects
of rigidity arise. When the actual belt tension must be more precisely
measured, a simple calibration test may be necessary.
SonicTensionMeter_Manual_4_14.indd 10 4/26/14 9:09 AM
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