Dual/Redundant Self Check Ultraviolet Flame Sensor and Combustion Safeguard Control

Abstract

Two UV tubes are contained in one ultraviolet sensor to monitor one burner flame. Each UV tube is powered during a different time cycle to eliminate interference between the two UV tubes. This is made possible by two rectifier circuits being powered by two transformers that are 180° out of phase with each other. Self check is accomplished by the redundancy of two amplifiers providing output to two flame relays so that if one UV tube was to fail in the conducting mode, the combustion safeguard control will continue to safely monitor the flame by powering the fuel valve when the flame is present and removing power to the fuel valve when the flame goes out.

Description

BACKGROUND OF THE INVENTION

Industrial burners utilize a flame sensor with a combustion safeguard control to enable opening of the fuel valve(s) in the presence of a flame or conversely, to close the fuel valve(s) in the absence of a flame. The preferred optical flame detector is an ultraviolet sensitive, cold cathode, gas discharge tube, hereinafter generally referred to as a UV tube. When ultraviolet rays from a flame are incident upon the UV tube and sufficient voltage potential exists across the electrodes in the tube, the UV tube conducts. This current is an input to a combustion safeguard control, which amplifies this input and provides an output to the fuel valve(s). It is possible for a UV tube to fail in the conduction mode with no UV present. Self check UV tube sensors with mechanical shutters that intermittently shield the UV tube from the flame to identify a failed UV tube are subject to mechanical failure due to wear and temperature degradation on the moving parts.

BRIEF DESCRIPTION OF THE SEVERAL DRAWING VIEWS

FIG. 1 is a series of diagrams illustrating voltage waveforms;

FIG. 2 is a wiring diagram illustrating the interconnection of the dual/redundant self check ultraviolet sensor, the combustion safeguard control with transformer 180° phase differential, and burner fuel valve(s).

DESCRIPTION OF THE INVENTION

The purpose of this invention is to include two UV tubes in one ultraviolet sensor to monitor one burner flame. Since UV tubes produce UV rays when they conduct, two UV tubes in one sensor would not normally be suitable for sensing a burner flame, as one UV tube could be responding to the other tube and not the flame.

The Dual/Redundant self check ultraviolet flame sensor and combustion safeguard control features voltage supply to the UV tubes that are out of phase with each other. When one UV tube is powered and may respond to UV rays, the other UV tube is off. The two UV tubes are powered thru two rectifier circuits from two transformers that are out of phase with each other. The two UV tubes are powered and sense UV from the flame on alternating half cycles (See FIG. 1.) Each UV tube and rectifier circuit provides input to its own amplifier. Each amplifier provides input to its own flame relay (See FIG. 2.) Upon burner startup, before burner ignition, if either UV tube is in conduction, the safe start check circuit does not permit powering the fuel valve.

During the burner run cycle, if either UV tube fails in a conduction state, the cycle will safely continue with the other UV tube sensing the burner flame.

Claims

1. In a burner fuel valve control, a control circuit consists of two UV tubes in one sensor housing, the rectifier circuits, two transformers 180° out of phase with each other, two amplifiers, two flame relays (output from amplifier), a safe start circuit and an output circuit controlling said burner fuel valve in response to combined circuit.

2. The control circuit of claim 1 wherein output circuit opens fuel valve in response to said presence of UV rays.

3. The control circuit of claim 1 wherein output circuit closes fuel valve in response to said absence of UV rays.

4. The control circuit of claim 1 wherein output circuit closes fuel valve in response to said absence of UV rays even if a UV tube fails in a conducting mode.