The CLAVIS Hand Held Belt Tension Meter - Instructions for use

Theory 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 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;

T=4ml²f²

Where T is in Newtons, f in Hertz, l in meters, and m in Kg/metre. However as the belt does have some flexural stiffness 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.

Operational Use

1. Connect the sensing head to the lower central socket, and turn on the unit by pressing the ON/OFF button.

2. Hold the sensing head steady across the belt span as shown in the photograph.

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.

4 AA size batteries provide 160 hours of continuous operation, whilst optional rechargeable batteries provide 80 hours of operation. The meter automatically switches off 10 minutes after the last reading is taken, to prolong battery life. A 'LO BAT' indicator on the display shows when the unit needs recharging. The charging socket is adjacent to the sensing head connector. An overnight charge will fully restore the batteries. During charging the 'LO BAT' indicator will flash. The meter may be powered directly from the charger if required.

Additional notes

The range of the meter is from 30 to 600Hz . Readings below 30Hz will cause the display to flash '030' and then clear to '000'. Readings above 600Hz will cause the display to flash '600' and likewise clear to '000'. In most applications the meter is used to make comparative tension checks. Often two or three spans may be available on which to take measurements. As the frequency depends upon the span length, the span to be used for measurement must be defined. Normally it is found that the longer spans are easier to vibrate than the very short span lengths. If the belt tension adjuster is on the measurement span, ensure that the variation in span length created by the adjuster will not be significant.

Calibration

The Clavis Belt Tension Meter is based upon a microprocessor using digital signal processing techniques. A 8.0000 MHz quartz crystal provides the fundamental frequency reference which should ensure, for the life of the instrument, an accuracy of;

+ or - 1 digit below 100Hz
+ or - 1% of reading above 100 Hz

However as with all gauging equipment a calibration check should be made periodically. A Clavis Belt Tension Meter Calibrator is available for this purpose, or the unit may be returned to the manufacturers for a calibration check and the issue of a certificate of calibration.