The air in the dual chambers of the XP95 ionisation smoke detector is irradiated to produce ions that travel to the positive and negative electrodes and hence create a current flow in the chambers. Smoke entering the outer chamber causes a drop in the current flow and an increase in the voltage measured at the junction between the outer and inner chambers. The analogue voltage signal produced in the sensing chamber is converted to a digital signal by the electronic circuitry and transmitted to the control equipment on interrogation. The micro-processor in the control equipment then compares the signal with the stored data and initiates a pre-alarm or fire alarm as smoke density increases. When the equipment determines that a fire condition exists, it instructs the detector to switch on its indicator LED and the pre-planned alarm routine is initiated.
Protector Alarms (UK) Ltd.