Methods and systems for signal processing in particle detection systems

A method of deciding whether a particle-containing sample of an air stream, which air stream may contain particles of interest and background particles, is a sample of interest, comprising:

• detecting a measurement set of particles in the air stream;
• defining a numerical characterization scheme for characterizing particles in the measurement set;
• individually assigning a numerical characterization to each detected particle in the measurement set;
• defining a grey-scale weighting function, with a range of more than two weights, capable of associating a weight with a numerical characterization;
• using the weighting function in assigning weights to particles in the measurement set, based on the numerical characterization of a particle and the weight associated with that characterization;
• processing the assigned weights for detected particles in a sample;
• and
• producing an indication, based on the processing of the assigned weights, whether the measurement set contains some particles of interest or background particles.

A device for analyzing samples of an air stream containing particles, comprising:

• an excitation wavelength;
• an emission wavelength that is different from the excitation wavelength;
• an illumination area through which the air stream passes;
• a light source, comprising light at the excitation wavelength, that illuminates, in the illumination area, the particles contained in the air stream;
• an excitation light detector that detects light from the particles at the excitation wavelength;
• a fluorescence detector that detects light at the emission wavelength;
• a memory that accumulates particle information, including (a) data representing a count of a number of particles that has passed through the illumination area and (b) data representing light detected by the fluorescence detector;
• a sample-size criterion comprising data representing a maximum number of particles to be included in a complete sample, the complete sample comprising a plurality of particles;
• and
• a sample-completion testing module that applies the sample-size criterion to determine when the memory has accumulated particle data from a complete sample.

A system for reducing the false positives in a particle detection system, comprising:

• a laser that irradiates a particle-containing airstream containing unknown particles which may be particles of interest or background particles;
• a fluorescence detector that detects fluorescence emitted by the particles in the airstream in response to irradiation by the laser;
• a non-fluorescence detector that detects particles in the airstream regardless of fluorescence;
• a computer-readable medium for storing:
• a sample size, expressible or convertible into in time, to determine a size of a sample of detected particles a sample volume rate expressible in liters per second;
• a sensitivity expressible by a number of Bacillus globigii particles amid a number of total particles per volume;
• a mean time between false positives;
• and
• a true positive confidence level;
• where a common log of the mean time in seconds between false positives is greater than 4 for a true positive confidence level of 90% and a sample time, sensitivity, and true positive confidence level for conditions with ratios of:
• (a) 10 seconds, to (b) a ratio of 42 Bacillus globigii particles per 2500 total particles per liter.