GB1467592A - Ionization fire alarm - Google Patents

Abstract

1467592 lonization detector GEBA GES FUR ELEKTRONISCHE BRANDMELDEANLAGEN mbH & CO 22 Jan 1975 [24 Jan 1974] 2788/75 Heading HID A compact smoke detector comprising measuring and reference ionization chambers in series consists of outer electrode 18 preferably earthed with annular orifice between rim 76 and depressed plate 80 allowing air entry into measuring chamber 10 in which cup-like second electrode 14 is pegged to double walled insulator 16, the central bore of which forms the reference chamber with electrode 14 and cuplike third electrode 22 recessed into but not touching the bore. In both chambers radioactive strip sources 24, 26, with at least strip 26 being concave to concentrate radiation, initiate ionization. The circuitry comprising FET 30 and resistor 32 is potted in the annular recess 44 with interconnections 34, 35 on the planar base 38, and with terminals 58 for external connection. An earthed screen may be fitted behind base 38. Insulator 16 has shoulders 20 providing a long leakage path. It carries mounting lugs (48, Fig. 2, not shown) covered by a decorative ring 32; alternatively the appliance may be recessed 54 with cover 56. Sensitivity may be adjusted by axial movement of electrode 18. In an alternative embodiment (Fig. 6, not shown) electrode 18 is extended below the insulator where it is clipped into a recessed base carrying terminals making connection to the circuitry via spring contacts.