Abstract :
In the early 1960´s the first ideas were developed by leading companies in Germany (Siemens, Wachtel, etc) to design an intrusion detection system following a capacitance measurement principle. The first detection electronics and set-ups were designed for indoor use (jewellery shops, museums, etc..) but in 1964 the first capacitive detectors for outdoor use i.e. perimeter security systems appeared on the market with very poor performance results. During the 1970´s and 80´s and sometimes over very long periods, several world wide electronic companies tried to create good working solutions using simple and inexpensive hardware for outdoor use. Sometimes excellent ideas were integrated in the electronic design but generally any investment in a innovative hardware design such as (Insulators, wiring, etc...) were poorly supported. In 1982 Siemens AG was the first company in this market which analysed all outdoor influences and who recognised the essential problems which cause any classic capacitive or electrostatic detector suffering from high unwanted false alarm rates. This was even if the newest sophisticated digital electronics and algorithms were used. The result was that already in 1984 a complete new peripheral hardware design, with a very high electrical and capacitive stability, was created and patented by Siemens AG which remains state of the art even now and which is making capacitive detectors work under most of all environmental conditions. Nevertheless even if this high-grade material is installed, it can happen in certain cases that apparently invisible peripheral influences are the cause of important electrical effects. These effects change the field, periodically generating very high false alarm rates which are extremely difficult to detect and to measure. The reason is that the false alarm rate is specific to a site and as such is difficult to identify. It is a fact that even well trained system engineers have difficulty in solving such problems. This paper describes a practical case experienced in 1999 where a coincidental combination of seaside conditions and a local desert wind strongly interfered in the physics of a capacitive i.e. electrostatic field detector and where trivial (but expensive) measures needed to be taken to finally solve the problem
