Specially engineered limit switch

Citation

(1998), "Specially engineered limit switch", Aircraft Engineering and Aerospace Technology, Vol. 70 No. 4. https://doi.org/10.1108/aeat.1998.12770dad.006

Specially engineered limit switch

Specially engineered limit switch

Keywords Aircraft, De-icing, Sigma

Sigma's ability to engineer special products is making a significant contribution to aircraft safety. The company has supplied a special adaption of its heavy duty Eurolock product to provide proximity sensing on a gantry system which de-ices the wings and fuselages of airplanes prior to take-off (Plate 1).

The gantry system is brought into operation as planes are readied for service after intervals where they may have been standing for long periods, often in sub-zero temperatures. Its operation is necessary because any excess weight, in the form of ice, on an aircraft's wings or fuselage, can cause it to abort on take-off or even crash. The de-icing process is totally computer controlled, and for maximum speed and flexibility, the computer has the dimensions of the majority of passenger jets programmed into it.

Plate 1 The gantry is equipped with Sigma's specially engineered limit switch

The gantry is a high structure out of necessity to cope with the varying heights of wings and fuselages of many different types of aircraft. Unfortunately, airports in many parts of the world are particularly exposed places and are often quite windy. Without adequate safeguards such blustery conditions could cause the gantry to impact on the body of the aircraft, resulting in expensive damage that might also put the aircraft out of service.

To overcome this problem the gantries are equipped with a version of Sigma's Eurolock limit switches, modified to accommodate a four foot long carbon rod. If a gust catches the gantry, causing the rod to touch the aircraft surface, a signal is sent from the Eurolock switch back to the control computer. The computer then steadies the gantry until no further contact signals are received.

The modified Eurolock units are said to be ideal for this rugged application as they are heavy duty, and water/oil/dust proof to IEC 144, Class IP65. Designed to meet the mechanical and electrical requirements of IEC337-1 and BS4794, the Eurolock switches are based on a single design of body which can accommodate a variety of turret heads for clockwise (CW) operation, counter clockwise (CCW) operation, or a combination of both.

Further details are available from Sigma Controls Ltd, UK. Tel: +44 (0) 1942 257112; Fax: +44 (0) 1942 523111.