Vehicle security systems

Application

The internationally applicable ECE Regulation No. 28 specifies that acoustic signals produced by motor vehicles must maintain a uniform sound quality with no perceptible frequency fluctuations during operation. Operation is permitted only as a hazard warning function. In countries where this regulation does not apply, the acoustic signaling device is a wearing part subject to heavy use. The use of sirens, signal bells and the like is not permitted, nor is playing melodies by triggering sound generators in a given sequence. Signaling devices must be installed facing forward in the vehicle and must produce the signal at a sufficient loudness level at a distance of 2m. They are subjected to temperatures ranging from –40°C to +90°C and must be designed to be resistant to moisture, salt spray as well as mechanical shock and vibration. Elastic couplings must be used to decouple electric horns and fanfare horns from the vehicle body, as the horn would otherwise induce sympathetic oscillations in the adjacent bodywork. The resulting feedback would diminish both loudness level and tone quality. Both electric and electropneumatic horns and fanfare horns are sensitive to series resistors in their control circuits. When horns are installed in pairs, they should be triggered by relays. The warning produced by the impact horn is more conspicuous; therefore, it is the better choice for vehicles that are frequently used for long-distance overland truck traffic instead of fanfare horns. Alternatively, the fanfare horn is superior for city driving, as pedestrians often find the standard horn excessively loud and unpleasant. Both sets of requirements can be fulfilled by installing the two horn types together in a single system with a selector switch for city or overland traffic. Standard and fanfare horns both operate at standardized frequencies. High and low tones can be combined to produce a harmonious dualtone sound.