The TDD (true duct smoke detector) is able to detect smoke early on in a ventilation duct without giving false alarms. It checks for optical obscuration. The sensing part of the detector covers as much as possible of the duct. An infrared beam is transmitted through the sensing tube in the duct. If smoke is present, the beam is obscured to some extent and an alarm signal is given. The detector has an adjustable level of sensitivity that goes from 3 to 25 percent obscurity for all environments that can exist in a duct. According to the manufacturer, neither dust nor the velocity of the air in the duct cause the unit to give a false alarm. The signal is adjusted to compensate for a buildup of dust. However, should the obscuration change rapidly (within seconds) this will cause an alarm after an initial delay to compensate for drops of water or dust that have been disturbed from the duct wall, etc. The TDD is designed to be connected to all existing fire alarm and building management systems (BMS), both digital and analog. The internal calibration of the detector is provided at an outgoing terminal in order that the level may be seen if connected, for example, to a BMS. Without special training, the unit can be cleaned by maintenance staff.
Automatikprodukter AB, Gåsmossen 43, SE-436 39 ASKIM, Sweden; +46 (0)31-28 72 02; +46 (0)31-68 34 36 (fax); www.automatikprodukter.se