Flame detector trapezoidal excitation generator output control circuit and method

A gas turbine engine, comprising:

• a compressor having an inlet and a compressed air outlet;
• a turbine having at least an inlet;
• a combustor having at least an air inlet, a fuel inlet, and a combustion gas outlet, the air inlet in fluid communication with the compressed air outlet, the fuel inlet adapted to receive a flow of fuel from a fuel source, and the combustion gas outlet in fluid communication with the turbine inlet;
• and
• a flame detector coupled to the combustor, the flame detector configured to detect the presence of a flame in the combustor and supply a signal representative of an intensity of the flame;
• an excitation circuit coupled to the flame detector and operable to supply an excitation signal thereto, the excitation circuit including:
• a controllable frequency source configured to generate a square wave having a frequency that, upon energization of the controllable frequency source, decreases from an initial frequency value to a substantially constant frequency value a time period after energization of the controllable frequency source;
• and
• a trapezoidal waveform generator coupled to receive the square wave and operable, in response thereto, to generate a trapezoidal waveform at least when the square wave frequency attains the substantially constant frequency value, the trapezoidal waveform generator comprising:
• an integrator circuit coupled to receive the square wave and operable, in response thereto, to supply an integrated waveform, the integrated waveform having peak positive and negative voltage amplitude values, and a wave shape that is a mathematical integral of the source waveform over time;
• and
• a clipper circuit coupled to receive the integrated waveform and operable, in response thereto, to limit the peak positive and negative voltage amplitude values to predetermined positive and negative values, respectively.

A method of generating a trapezoidal waveform, comprising:

• generating a square wave having a frequency that decreases from an initial frequency value to a substantially constant frequency value over a time period;
• integrating the square wave to thereby generate a triangular wave having a peak voltage magnitude that increases from an initial voltage value to a substantially constant voltage value over the time period;
• and
• limiting the peak voltage magnitude of the triangular wave to a predetermined value,
• wherein the trapezoidal waveform is generated when the triangular wave peak voltage magnitude exceeds the predetermined value.

A flame detector, comprising:

• a sensor configured to detect the presence of a flame and supply a signal representative of an intensity of the flame;
• an excitation circuit coupled to the sensor and operable to supply a sensor excitation signal thereto, the excitation circuit including:
• a controllable frequency source configured to generate a square wave having a frequency that, upon energization of the controllable frequency source, decreases from an initial frequency value to a substantially constant frequency value a time period after energization of the controllable frequency source;
• and
• a trapezoidal waveform generator coupled to receive the square wave and operable, in response thereto, to generate a trapezoidal waveform at least when the square wave frequency attains the substantially constant frequency value, the trapezoidal waveform generator comprising:
• an integrator circuit coupled to receive the square wave and operable, in response thereto, to supply an integrated waveform, the integrated waveform having peak positive and negative voltage amplitude values, and a wave shape that is a mathematical integral of the source waveform over time;
• and
• a clipper circuit coupled to receive the integrated waveform and operable, in response thereto, to limit the peak positive and negative voltage amplitude values to predetermined positive and negative values, respectively.