Ionisation chamber fire detector - with threshold cct. monitoring ionisation current connected to switch cct. for further chamber

摘要

The fire detector has an ionisation chamber (CH2) which is open to the atmosphere and which contains at least two electrodes (2, 3, 4) and one or more radioactive sources (d1, d2). The electrodes are connected to a threshold circuit (FET2ZD) for monitoring the ionisation current between the electrodes, with the threshold circuit connected to a switching device (A), which is operated in response to the ionisation current being below a given threshold, to switch in a further electrode (3) and ionisation chamber (CH2') and/or to move a sliding screen for a further ionisation source into an inoperative position, so as to provide an increase in the ionisation current.