The AOI Series 3520 is a portable, battery-operated trace oxygen analyzer designed for industrial and commercial applications requiring spot measurements. Its durable polycarbonate enclosure is rated NEMA 1 for general purpose service. The analyzer is powered by rechargeable NICAD batteries and includes a universal AC charger for convenience .

The Series 3520 features an ambient-temperature electrochemical sensor. The enhanced mechanical design ensures longer life and virtually eliminates leakage of caustic electrolyte. The sealed sensor is not position-sensitive and does not require manual adjustment based on changes in the molecular weights of sample gases such as helium and hydrogen. The output from the sensor is both linear and temperature-compensated to provide optimum performance. An optional CO2-tolerant trace oxygen sensor is capable of providing accurate oxygen readings in gases containing up to 100% CO2 without shortening the life of the sensor .

Key specifications include a wide selection of eight measurement ranges from 0-10 ppm up to 0-20,000 ppm, allowing it to cover a variety of trace applications. It offers ±1% of full scale accuracy and a fast 90% of full scale response time of less than 10 seconds. The analyzer is equipped with 1/4" stainless steel compression fittings for reliable sample connections and features a 3-1/2 digit LCD. The electronics carry a 2-year warranty, and the sensor carries a 1-year warranty .