News and pictures are transmitted via satellites. This technology has many advantages and requires updated and modernized transmission antenna masts and towers. Mast-sections are hoisted onto towers by winch. It may happen, however, that a section being hoisted may snag and cause damage to the tower. Therefore overload guards shall be used, which monitors the load in the winch and interrupts the hoisting if and when necessary. Regular maintenance of sections and parts of installations such as masts or antenna sections may involve lowering antenna-sections to the ground. Again, it may happen that the sections being lowered snag on the stay wires and further lowering should be stopped.
Product
PIAB Dynamometer Type S, of 10 ton capacity, with built-in potentiometer, connected to PIAB Readout Instrument 6:64 with two relay functions: Relay No. 1 set to operate at Overload, and Relay No. 2 set for Slack Rope conditions.
Customer
Imatra-Voima OY, Finland, the contractor for erecting high masts for OY Yliesradio AB, (Finnish Broadcasting Company).
Solution
The same winch is used for different masts and towers. Since the winch will have different positions at different masts, it is unlikely that it will be placed in level with the base of the mast. Therefore the hoisting rope will have a different load-angle at different installations. As a consequence the force on the pulley-wheel will vary. Therefore the switch value of the overload guard system must be easily adjustable.
The procedure for setting the relay trip-levels is as simple as follows: Lift the load just clear off the ground and note the value shown on the Readout Instrument 6:64. The overload relay is now adjusted to a value slightly higher than the noted reading, by means of the adjustment knob on the PIAB 6:64 instrument. Further hoisting can take place. The same procedure applies to setting the low level relay, except that it is set with the load suspended at its highest point at a value just below the weight indicated on the PIAB 6:64 instrument.
Result
After a period of operation with the PIAB equipment the customer was satisfied, and further orders have been received to supply equipment for different winch sizes.
