Model NGN-2: Open-Air Integrating Nephelometer: Technical Manual for Theory of Operation and Operating Procedures

OPTEC, Inc.

The Model NGN-2 (Next Generation Nephelometer) uses a unique integrating open-air design that allows accurate measurement of the scattering extinction coefficient of ambient air. Because of the open-air design, relative humidity and temperature of the air sample are essentially unchanged, thus the aerosol is negligibly modified when brought into the optical measuring chamber. With improvements made to the prototype NGN-1, the production Model NGN-2 nephelometer alters the temperature of the air sample by less than 0.5° C. Extinction due to scatter can accurately be measured from Rayleigh to 100% saturated fog conditions. Using principals and techniques developed for the popular and successful Optec LPV transmissometer, the NGN-2 features low power consumption, solid compact design, and easy operation - all necessary parameters when installing and operating a measuring instrument in remote locations. Housed in a single environmentally sealed enclosure, the nephelometer contains all the necessary components for ambient standalone operation. The NGN-2 consists of a large inlet with motorized door, measuring chamber, clean air pump for calibration, blower, solenoid activated inlet for a span gas, temperature sensor, real time clock and rain detector for closing the inlet during wet conditions. See Figure 1-2 for a cross-sectional view of the NGN-2. A CMOS computer controls all operating functions and outputs data either in digital or analog format. External to the NGN-2 unit, a 13.8V DC, 5 amp power supply, compressed span gas and a data logger or printer are required.