Photoelectric smoke detector with count based A/D and D/A converter
US5705988A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 8, 1996 |
| Grant date | Jan 6, 1998 |
| Priority date | — |
| Expiry date | Jul 8, 2016 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B29/185
- WIPO fieldControl
- WIPO sectorInstruments
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.