Self-diagnostic flame rectification sensing circuit and method therefor
US5506569A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 31, 1994 |
| Grant date | Apr 9, 1996 |
| Priority date | — |
| Expiry date | May 31, 2014 |
Classification
- Technology area (CPC F)Mechanical Engineering; Lighting; Heating
- CPC primaryF23N2233/06
- WIPO fieldThermal processes and apparatus
- WIPO sectorMechanical engineering
Abstract
An electric control is shown for gas furnaces which controls fan motors and ignition controls based on inputs from a room thermostat (32), a high limit control and an ignition control (14) including a gas valve. A flame sense circuit (42, 42') is coupled to a microprocessor (U2) and includes a flameprobe (P1) energized by line power through a capacitor (C3) via a quick connect (QC31). A capacitor (C4) is charged by a 5 volt DC source through resistor (R12) and inputted to an inverter (U3, S2) which provides a low signal to the microprocessor when no flame is present. When a flame is present the capacitor (C4) discharges through the flame causing the inverter to change state providing a high to the microprocessor indicating that a flame is present. A diagnostic network comprising a low leakage diode (CR10) and serially connected resistor (R11) is coupled between the microprocessor (pin 8) and the input of the inverter (U3) so that the operation of the flame sense circuit can be tested. In an alternate embodiment CMOS switches (S1, S2) are used both to verify that the flame sense circuit is properly wired and to simulate a no-flame condition.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.