Abstract: A single chamber ionization-type fire detector. The ionization current is directly amplified to provide a usable analogue signal by means of an operational amplifier which has a minimal effect in the ionization current. The operational amplifier is simultaneously employed to maintain a constant potential difference in the chamber so that the ionization current is not subjected to a fluctuating voltage. The amplified analogue signal drives a recorder and through analysis of the recorder output genuine fire alarm conditions can be distinguished from false alarm conditions.

Abstract: A fire detector of the type including a smoke chamber and a grid supported in the chamber on an insulating element. In order to prevent the flow of leakage currents from the grid to the body of the chamber an electrically-conductive element is arranged around the insulating element in circumferential contact therewith. The electrically-conductive element is arranged to be at the same potential as the grid so that no leakage currents are able to flow from the grid to the body of the chamber.