ContiTech TensionRite User Manual

I am more comfortable using inches and pounds rather than
millimeters and newtons. Why SI units?
Belt tensioning became particularly critical with the advent of 2nd
generation synchronous belts. All such belts are of metric design
with the tooth pitch, width and length speciied in SI (System
International d’Unites) units. It follows that tools for use with such
belts should also utilize the SI system. While the TensionRite® Belt
Frequency Meter requires span and mass inputs to be made in
SI units, the output can be toggled to pounds-force if you wish.
Conversion factors for English to SI and SI to English are also
shown in the TensionRite® Belt Frequency Meter User Manual.
Which is the best span to use when tensioning a multi-span
drive (a dR with more than one dN)?
Best practice is to use the longest span that can be readily
accessed. Using too short a span can compromise accuracy. The
natural frequency of a span should be between 10Hz and 400Hz
to be properly read by the TensionRite® Belt Frequency Meter. It is
highly unlikely that your drive will be outside this window. However,
if the measured frequency is below 10Hz, choose a shorter span.
If the measured frequency is above 400Hz, chose a longer span.
What constitutes “too short a span” and why?
Let’s start with the “why” part of your question. Transverse vibration
of string theory (the science behind frequency based tension
measurement) overlooks the rigidity of the string. Although hard
to quantify, belts have considerable internal rigidity (stiness).
The shorter the span, the greater is the eect of this stiness in
dampening both the natural frequency and amplitude of strand
vibration. The eect is that belt tension in a short span is lower than
the vibration frequency would indicate (measured results are much
higher than actual belt conditions).
To limit such error there have evolved some informal guidelines
for the most common belt constructions. For synchronous belts
(toothed belts) the recommended minimum span length is
deined as greater than 20 times the tooth pitch. For example:
an 8mm pitch belt would require a minimum span of 160mm
(approximately 6.3 in.) to yield reliable frequency based tension
data. For V-belts the recommended minimum span length is about
30 times the belt top width.
These are guidelines or rules of thumb that have evolved over
time. It is the link between frequency and tension, as well as the
optical signal that degrades as these minimums are approached.
A practical test is to take several readings (from 3 to 5 repeats)
under identical conditions. If the results vary wildly or if frequency
exceeds 400Hz (top of meter range) you need to select a longer
span. If you have concerns about a speciic drive, you should
contact Continental ContiTech Customer Service or your local
Continental ContiTech Products Distributor. Telephone or e-mail
contact information for Technical Support is given in the
User Manual.
What if I cannot access the top surface of the belt
span selected?
If the lat face of the belt is not accessible it may be possible
to beam the sensor onto the edge of the belt to take your
measurement. The inside surface (toothed side of a synchronous
belt) is equally acceptable as a target for the sensor. Regardless
of the surface selected, the best readings are obtained with the
sensor held square to the target surface at a distance of 3/8 in. In
practice, valid readings have been taken at distances up to 2 in.
and at angles varying from vertical to plus/minus 45 degrees.
Does the sensor need to be aimed at the exact center of
the span?
Let speciic drive conditions be your guide. Best shop practice is
to take your reading as close to the span center as is practical. A
strummed belt vibrates with the same frequency everywhere along
the unsupported span. The amplitude of vibration is greatest in the
center of the span, degrading geometrically as the tangent points
(sprocket or pulley contacts) are approached. Bigger features are
generally the easiest to see (think eye chart). The TensionRite® Belt
Frequency Meter is an optical system so the best reading is taken
directly above the center of the span, although on most belts valid
and accurate readings can be achieved almost anywhere along the
belt span.
Sometimes I have trouble getting a reading on a narrow belt
such as a Torque Flex AX, any suggestions?
Best shop practice is to orient the sensor with the long edge of the
sensor parallel to the centerline of the belt. There may be a slight
dierence in focus between the aiming LED and the infrared beam
at the distance you happened to be holding the sensor. Orienting
with the long edge parallel to the belt centerline simply provides
a larger target area thus easing the need for very precise aiming.
This suggestion also applies when taking measurements from the
edge of a belt.
What are some of the advantages of the new TensionRite® Belt
Frequency Meter over the older sonic meter?
Accuracy, reliability and ease of use are the primary beneits of the
TensionRite® Belt Frequency Meter. The accuracy of measurement
is largely determined by the method of measurement. While both
sonic and optical tension meters rely upon the same transverse
vibration of string theory (think tuning a violin) to determine belt
strand tension, the two methods dier in how the frequency of
vibration (Hz) is actually determined.
A sonic meter (also known as an acoustic meter) indirectly measures
vibration. It predicts vibration frequency based upon sensing
disturbances in the pressure of the air (essentially noise) adjacent
to the belt. The sensor is really a specialized microphone. Ambient
conditions are a critical factor. Background noise and air currents can
and will aect the accuracy of this type of sensor. Some sonic meters
incorporate internal ilters in an attempt to counter stray inputs while
other units include a “gain” adjustment for the sensor.
17
3.0 Frequently Asked Questions (FAQs)
Appendix 3.0 Frequently Asked Questions

ContiTech TensionRite Specifications

General

Brand	ContiTech
Model	TensionRite
Category	Measuring Instruments
Language	English