Patent ID: 8874377

Claim:
A method of detecting biological aerosols using a photon counting technique that processes both fluorescent and scattered photon data, comprising: receiving two channels of signals, a first channel indicative of a fluorescent photon count and a second channel indicative of a scattered photon count, wherein each photon count represents the number of photons detected in a time-based sampling bin; updating counting variables by calculating the sum and sum squared of the photon counts measured across multiple sampling bins for each channel and calculating the mean and standard deviation of photon counts across the sampling bins for each channel; calculating sigma values using the photon count, mean and standard deviation for each channel; performing a Schmitt trigger operation using the sigma value to produce a Schmitt trigger count for each channel; calculating the mean and standard deviation of the Schmitt trigger counts for each channel over a period of time; and triggering an alarm in a biological aerosol detector when a calculated alarm threshold is obtained using said fluorescent and scattered Schmitt trigger counts.