Monitor for indirect measurement of cable vibration frequency and tension

A non-contact cable tension monitor was designed, constructed, and evaluated. Such a monitor could be used to warn machine operators of unsafe cable tension or to inform operators of current cable tension for more efficient operation. The vibration frequency of a cable between supports varies with tension. A scanning laser beam and optical sensors were used to monitor the instantaneous transverse position of a vibrating cable. The period of oscillation of the cable was then determined from the sequence of position measurements. Tests were conducted for simulated center-to-center cable displacements from 13 mm to 50 mm, at both 5 and 15 Hz. Monitor output was within 10% of the actual period value 79% of the time under the most ideal conditions of 50 mm displacement and 15 Hz frequency. Performance deteriorated as either displacement or frequency decreased. Only 23% of the results were within 10% of the actual period value under the least favorable conditions of 13 mm displacement and 5 Hz frequency.