US 5,073,769 AGranted

Flame detector using a discrete fourier transform to process amplitude samples from a flame signal

AssigneeHoneywell Inc.

InventorArlon D. Kompelien

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Abstract

A circuit for detecting presence of a flame receives a flame signal from a standard photocell positioned to receive radiation from the flame and digitally processes the amplitude variations in the photocell's output to sense for the presence of frequencies near a frequency which is characteristic of a flame. The frequencies substantially higher than the characteristic frequency are filtered from the signal, and the remaining signal is sampled at a frequency which is preferably four times the characteristic frequency. The samples are converted to digital values and processed using a discrete Fourier transform. If the value resulting from the transform operation exceeds a preselected value, presence of a flame is essentially certain. Such digital processing allows use of a dedicated microcircuit or a microprocessor for the flame sensing function and avoids the need for many large discrete components.

Claims7

Dependent claims

A flame sensing system for providing a flame sense signal responsive to receiving a flame signal from a photocell receiving radiative energy from a flame having in its energy output intensity a flicker whose frequency is within a predetermined frequency range, said flame signal instantaneously representative of the intensity of the energy emanating from the flame, the system comprising

a) a low pass filter receiving the flame signal and providing a filtered flame signal from which a substantial percentage of the amplitude of frequencies above the predetermined frequency range has been removed;
b) a clock circuit providing a clock signal having individual pulses at four times the frequency of the midpoint of the predetermined frequency range;
c) an analog to digital converter receiving the filtered flame signal and the clock signal, sampling he filtered flame signal responsive to each clock signal pulse, and providing a digital flame signal having a plurality of successive discrete, ordinary designated, digital values each encoding the amplitude of the filtered flame signal at successive sampling instants;
d) a fist accumulator register receiving the digital flame signal and forming from the plurality of digital values in the flame signal, the sum of the difference of successive pairs of digital values having even oridinal designations, and providing after a sampling instant a first intermediate digital transform signal ascending he current contents o the fist accumulator register;
e) a second accumulator register receiving the digital flame signal and forming from the plurality of digital values in the flame signal, the sum of he difference of successive pairs of digital values having odd ordinal designations, and providing after a sampling instant a second intermediate digital transform signal encoding the current contents of the second accumulator register;
f) a calculator means receiving the first ad second intermediate digital transform signals, and providing a transform signal at lest approximately equal o the square root of the sum of the squares of the digital value encoded in each of the fist and second intermediate digital transform signals;
and
g) a comparator means receiving he transom signal for comparing the digital value encoded in the transform signal with a predetermined transform constant value, and if generator than the transform constant value, issuing a flame sense signal signifying presence of flame.

5 more elements

A flame sensing system for providing a flame sense signal responsive to receiving a flame signal from a photocell receiving radiative energy from a flame having a flicker in its energy intensity whose frequency is within a predetermined frequency range, said flame signal instantaneously representative of the intensity of the energy emanating from the flame, the system comprising

a) a low pass filter receiving the flame signal and providing a filtered flame signal from which a substantial percentage of the amplitude of frequencies above the predetermined frequency range has been removed;
b) a clock circuit providing a clock signal having individual pulses at four times the frequency of the midpoint of the predetermined frequency range;
c) an analog to digital converter receiving the filtered flame signal and the clock signal, sampling the filtered flame signal responsive to each clock signal pulse, and providing a digital flame signal having a plurality of successive discrete, ordinally designated, digital values each encoding the amplitude of the filtered flame signal at successive sampling instants;
and
d) a microprocessor for executing instructions and including data registers, an instruction memory containing a plurality of instructions, and a digital input channel, said microprocessor instruction memory including instructions for causing the microprocessor to function as:
i) a first accumulator register receiving through the input channel the digital flame signal from the analog to digital converter and forming from the plurality of digital values in the flame signal, the sum of the difference of successive pairs o f digital values having even ordinal designations, and providing at the end of each sampling interval a first intermediate digital transform signal encoding the current contents of the first accumulator register;
ii) a second accumulator register receiving through the input channel the digital flame signal from the analog to digital converter and forming from the plurality of digital values in the flame signal, the sum of the difference of successive pairs of digital values having odd ordinal designations, and providing at the end of each sampling interval a second intermediate digital transform signal encoding the current contents of the second accumulator register;
iii) a calculator means receiving the first and second intermediate digital transform signals and providing a transform signal approximating the square root of sum of the squares of the digital values encoded in each of the first and second intermediate digital transform signals;
and
iv) a comparator means receiving the transform signal for comparing the digital value encoded in the transform signal with a predetermined transform constant value, and if greater than the transform constant value, issuing a flame sense signal signifying presence of flame.

7 more elements

Dependencies are inferred from the claim text.