A novel optical instrument has been developed that estimates size segregated aerosol mass concentration (i.e., PM 10 , PM 4 , PM 2.5 , and PM 1 ) over a wide concentration range (0.001-150 mg/m 3 ) in real time. This instrument combines photometric measurement of the particle cloud and optical sizing of single particles in a single optical system. The photometric signal is calibrated to approximate the PM 2.5 fraction of the particulate mass, the size range over which the photometric signal is most sensitive. The electrical pulse heights generated by light scattering from particles larger than 1 micron are calibrated to approximate the aerodynamic diameter of an aerosol of given physical properties, from which the aerosol mass distribution can be inferred. By combining the photometric and optical pulse measurements, this instrument can estimate aerosol mass concentrations higher than typical single particle counting instruments while providing size information and more accurate mass concentration information than traditional photometers. Experiments have shown that this instrument can be calibrated to measure aerosols with very different properties and yet achieve reasonable accuracy.
Construction and performance of a printed circuit board is described that is built for phase measurement in a state-of-theart phase Doppler system. Special requirements in treating phase Doppler signals are highlighted and shown to be met satisfactorily by an innovative electronic design that involves signal burst detection, multi-bit sampling, frequency-band narrowing, and phase signal validation based on integrated amplitude and waveform recognition. Performance of the device is measured in terms of phase accuracy for various signal-to-noise ratios, signal frequencies and operating temperatures. The present device is also compared with some alternative techniques for phase measurement.
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