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Belt Tension Meter

In 1988 CLAVIS invented a new type of belt tension meter.  No longer was it necessary to rely on the thumb for a measure of belt tension.  Suddenly all force/displacement type tension gauges were shown to be clumsy, inaccurate and in many cases difficult to use.  The CLAVIS belt tension meter became the automotive industry standard for belt tension measurement.  It only took CLAVIS a small step to introduce equipment using the same principle for automated belt setting on high speed automotive engine production lines.

The CLAVIS Belt Tension Meter is a two-component system consisting of a hand-held meter attached to a sensor via an electronic cable.  The two differing types of sensor are used with the CLAVIS meter.  The first is the acoustic sensor which is available in a range of sizes and profiles.  The second is an optical sensor which uses an infrared beam to detect the vibration of a belt strand and sends a signal to the meter.  The detected belt vibration signal is compared with the vibration of a quartz crystal by the meter which then computes the natural frequency of the belt.  The result is shown in the display window as Hertz (oscillations per second).  The internal programming of the meter is also able to report the belt tension in units of force (either Newton, pounds-force, or KgF) provided the operator has entered the belt mass and span length using the manually operated key pad.

Need help selecting a Belt Tension Meter?

Principle of operation

The CLAVIS Belt Tension Meter measures the natural frequency of vibration of a belt span.  This frequency is directly related to the tension in the belt.  As the tension in the belt is increased the frequency of vibration also increases.  The belt is forced into vibration by gently tapping or plucking it.  The vibration is usually not visible and also inaudible.  As the belt tension is increased the frequency of vibration also increases.  This can be likened to the tuning of a musical stringed instrument such as a guitar.

The relationship between the measured frequency and the tension of the belt should be determined from a calibration test on the belt span.  A CLAVIS calibration rig is available for those users of this instrument who wish to perform their own calibrations, or we can undertake your calibration in our laboratory.  Alternatively the relationship between belt tension (T) and frequency of vibration (f) may be calculated from knowing the mass per unit length of the belt (m), and the belt span (l), using the expression;

Belt Frequency Calculation
  • T = Newtons
  • m = Kg/meter
  • l = Meters
  • f = Hertz

The belt does have some flexural stiffness so the predicted tension for a given frequency will be slightly greater than the actual tension.  This is most noticeable on short belt spans where the belt bending stiffness is the greatest.  For belt spans greater than 250mm a calculation based on the above expression will provide results within 10% of the actual values.

Need help determining the correct frequency or tension for a specific belt?  Click here to use our CLAVIS Belt Calculator.

Operational Use

Belt Tension Meter Sensor Head
  1. Connect the sensing head to the lower central socket, and turn on the unit by pressing the ON/OFF button.
  2. If using an acoustic sensor head hold the sensing head steady across the belt span as shown in the photograph.  If you are using an optical sensor head aim the sensor at the belt with a gap between 5mm and 25mm.
  3. Tap the belt gently near mid span using the handle of a small screwdriver or similar, to cause the belt span to vibrate.
  4. The meter will now display the frequency of vibration, and BLEEP to indicate that a valid reading has been taken.
  5. If a reading is not obtained check that the sensing head is not touching the belt, and try again.

Sensor Head Operation

Acoustic Sensor

The acoustic sensor uses a CLAVIS patented technique for detecting the belt vibration signal whilst minimising ambient noise.  The acoustic sensor is particularly suitable for belts which vibrate poorly or where the amplitude of belt vibration is very small.  The 'jaws' of the sensor should be positioned over the centre of the belt and placed mid length of the belt span.  The sensor should not be allowed to touch the belt as this will reduce the belt vibration signal.  A range of sensors is available to suit belts of differing widths.  The standard Type 3 sensor is suitable for all automotive applications.

When the belt vibrates upwards a positive pressure is exerted on the top microphone and negative pressure on the bottom microphone.  External ambient noise falls equally on both microphones.  When the microphone output signals are subtracted the background noise is eliminated and the belt vibration signal is doubled.

Optical Sensor

The optical sensor uses an invisible infrared beam to detect vibrations of the belt.  A narrow angle orange LED generated beam is provided to guide the aiming of the sensor.

The best signal from the belt is seen when the sensor is held perpendicular to the belt at the centre of the span at 9,5 mm (3/8 in) distance.  When physical restrictions are present, it is possible to get useable readings with the sensor up to 50 mm (2 in) distance from the belt and/or tipped up to 45° from perpendicular.

It is possible to take measurements from the edge of the belt.  The toothed side of a belt is equally acceptable as a target for the sensor.  The sensor LEDs should be kept clean by wiping with a soft cotton cloth.  Solvents are never to be used.

When the emitter is 'ON' the detector sees both the reflected belt IR signal and the ambient IR signal.  When the emitter is 'OFF' only the ambient IR signal is detected.  Subtracting the two signals results in only the IR reflected belt signal.

Belt Tension Meter Sensor Head Operation
  • Rs = Reflective Belt IR Signal
  • As = Ambient IR Signal

A range of interchangeable sensing heads with differing dimensions are available upon request.  For more information about our sensor heads please click here.


Belt Meter Range

Type 3 (Optical) Belt Meter

Belt Tension Meter - Type 3

The Type 3 Optical Belt Meter has the capability to measure belt tension frequency from 7Hz to 300Hz and is supplied with an optical head, which is optimised for the best performance at low frequencies.

This belt meter is operated by a simple ON/OFF keypad button.

The optical sensor head uses an infrared beam to detect the vibration of the belt.  It is particularly suitable for small belts under low levels of tension.  Read more...

Type 4 Belt Meter

Belt Tension Meter - Type 4

The Type 4 Belt Meter is suitable for measuring tension in all types of power transmission belts, ranging from toothed timing belts, poly-vee belts, and simple vee belts.  This belt meter is available with an optical or an acoustic sensor head.  

The optical sensor has a frequency measurement range of 10Hz to 600Hz.  The acoustic sensor has a frequency measurement range of 30Hz to 600Hz.  Read more...

Type 5 Belt Meter

Belt Tension Meter - Type 5

The Type 5 Belt Meter is capable of measuring belt vibration frequencies between 10Hz and 600Hz.  This belt meter has the function to operate in kilogram-force (KGF) as well as Hertz (Hz).

This value is calculated from the belt span and belt mass data, which is entered into the meter.  Up to 3 sets of data may be stored in the meter for easy recall.  Read more...

Type 7 Belt Meter

Belt Tension Meter - Type 7

The Type 7 Belt Meter is capable of measuring belt vibration frequencies between 10Hz and 600Hz.  This belt meter has the function to operate in Newtons and pounds as well as Hz.

Depending on the type of belt you require to measure the Type 7 is available with either an optical or acoustic sensor head.

On multi-shaft (three or more shafts) it may be possible to get valid measurements by selecting a different belt span for measurement.  Read more...

Type 13 SR (Super Rugged) Belt Meter

Belt Tension Meter - Type 13

If your are cold climate testing in the Arctic Circle or maintaining a battalion of armoured fighting vehicles like some of our customers then the only meter to choose is the Type 13 SR.

Capable of operating between a temperature range of -40 to +80 degrees Centigrade and fully submersible down to a depth of 15 metres (50 feet) this meter will survive the most arduous of conditions.  Read more...

Type 14 Belt Meter

Belt Tension Meter - Type 14

The Type 14 Belt Meter is suitable for measuring tension in toothed timing belts, poly-vee belts, simple vee belts and cogged belts.  The frequency measurement range is from 30Hz to 600Hz which covers most automotive applications.

The Type 14 boasts high stability precision and easily validates calibration accuracy from its resonator.  Read more...

Need help selecting a Belt Tension Meter?



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