Photoelectric smoke detector with count based A/D and D/A conver

Details Photoelectric smoke detector with count based A/D and D/A conver Photoelectric smoke detector with count based A/D and D/A conver

1996-07-08

1998-01-06

Hofsass, Jeffery

Communications: electrical

Condition responsive indicating system

Specific condition

340530, 340630, G08B 1710

Patent

active

057059888

ABSTRACT:
A method and apparatus in a smoke detector for comparing an analog signal voltage to a digital alarm threshold and for converting a digital sensitivity value to an analog test voltage. The analog signal voltage is converted to a digital value by: a) charging a capacitor at a first linear rate directly proportional to the analog signal voltage, for a predetermined time period; b) discharging the capacitor at a second predetermined linear rate to a predetermined threshold; c) counting during the discharging of the capacitor to establish a digital count representing the signal voltage; and, d) comparing the digital count to a an alarm threshold stored in the detector prior to its installation. The digital sensitivity value is converted to the analog test voltage by: charging the capacitor from the first predetermined voltage, at a predetermined rate, for a time period based on the sensitivity and a calibrated conversion factor. This charges the capacitor to an analog voltage representing the sensitivity.

REFERENCES:
patent: 4123658 (1978-10-01), Kajii
patent: 5365223 (1994-11-01), Sigafus
patent: 5530433 (1996-06-01), Morita
patent: 5543777 (1996-08-01), Vane et al.
patent: 5546074 (1996-08-01), Bernal et al.
patent: 5552765 (1996-09-01), Vane et al.

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