This is a schematic view of the electro-optics in the CPI. The particle detection system (PDS) consists of two continuous-wave laser diodes with beams that are shaped into ribbons 2.4 mm wide and 0.5 mm thick. The intersection of the two PDS beams defines the sample volume of the instrument. The PDS performs two functions:

1. When a particle passes through the intersection of the two laser beams, the imaging laser is pulsed and an image of the particle is cast on the CCD of the digital camera.

2. The PDS counts particles that are transit-time qualified and particle concentration is determined by dividing particle counts by the sample area times true airspeed.

The data system and electronics in the sensor head perform three primary functions:

• The data system computer with the NT operating system orchestrates sensor-head control, data collection, and data display and recording. The data system has an extensive graphical user interface (GUI).

• Particle images are extracted in real time from the million-pixel digital camera and sent to the data system host processor for display and storage.

• A DSP controls functions in the sensor head, including: setting PDS laser power, conditioning and digitizing PDS detector signals, setting imaging laser power, acquiring and digitizing housekeeping signals, and controlling heaters.