Open path gas detector with synchronous flash detection

An open path gas detector for detecting the presence of a target hydrocarbon gas with improved uptime in the presence of adverse environmental conditions including fog, comprising:

• a transmitter unit comprising a flash lamp configured to transmit flashes of broadband optical energy along a path in an area under surveillance, the transmitter configured to generate energy at a sample wavelength in a sample spectrum at which optical energy is absorbed by the target gas along the path, at a reference wavelength in a reference spectrum not significantly absorbed by the target gas, and at a synchronization wavelength in a synchronization spectral region different from the sample and reference spectrums;
• wherein the synchronization spectrum is selected such that the flash lamp intensity is greater at the synchronization wavelength than at the sample wavelength;
• and
• a receiver for receiving the transmitted energy, comprising:
• an optical module including a main objective lens for capturing and focusing the received energy onto a beam splitter, the beam splitter splitting the received energy from the main objective lens into a sample path and a reference path, sample optics in the sample path for blocking out all but the sample spectrum for a sample photodiode, reference optics in the reference path for blocking out all but the reference spectrum for a reference photodiode, a synchronization objective lens for capturing and focusing the received energy onto a synchronization photodiode,
• receiver circuitry responsive to signals from the sample, reference and synchronization photodiodes to amplify and digitize the respective signals;
• a flash detection and waveform capture circuitry responsive to the respective sample, reference and synchronization signals, wherein the synchronization signal is used to detect the transmitter flashes and to capture waveforms representative of sample and reference photodiode signals;
• a processor responsive to the captured waveforms to detect the presence of the target gas;
• and
• wherein the receiver is configured to synchronize operation of the receiver to the transmitter flashes using the synchronization signal.

An open path gas detector for detecting the presence of a target gas with improved uptime, comprising:

• a transmitter unit comprising an optical source configured to transmit flashes of optical energy along a path in an area under surveillance, the transmitter configured to generate energy at detection spectral regions employed to detect the presence of the target gas including a sample spectral region at which optical energy absorbed by the target gas along the path and a reference spectral region at which optical energy is not absorbed by the target gas, and a synchronization spectral region unused by the detection;
• and
• a receiver for receiving the transmitted energy, comprising
• sample and reference channels responsive respectively only to received energy within the detection spectral regions and to provide a sample signal and a reference signal, and a synchronization channel responsive to the energy within the synchronization spectral region to provide a synchronization signal, wherein the synchronization spectral region is selected such that the synchronization signal is larger than the sample and reference signals;
• and
• the receiver configured to detect the presence of the target gas in response to the sample and reference signals, and wherein the receiver is configured to synchronize operation of the receiver to the transmitter flashes using the synchronization signal.