The dGW21 signalling bell was designed to warn, call or signal in areas with explosive atmospheres in Group II. Protection type II 2G EEx de IIC T6 allows this signalling bell to be used without restriction in all Ex areas classified 1 and 2. The signalling bell produces a sound volume of approximately 105dB(A) at 1 meter distance. The emphasis of the ringing lies at approximately 1000 Hz, as a result of which the signal stands out clearly against low frequency ambient noises. The bell is available in the usual supply voltages. The version dRGW 21 emits signals in time with a connected telephone. Explosion protection is ensured by the airtight enclosure of the driver system and the terminal box. The enclosed chamber contains the electromagnetic driver of the system and for the dRGW 21, an addiional telephone relay. The enclosure is made completely of GRP (glass-fibre reinforced polyester) thus guaranteeing protection against corrosion. In addition, safety class II is realized and no equipotential bonding is necessary. The construction is very light and robust. All DC versions are equipped with an electronic contact breaker which considerably increases service life.