Abstract: An improved incipient fire detector that employs a sub-micrometer size particle detector of the Wilson cloud chamber type in conjunction with a continuous on-the-fly sequential selector valve assembly and sample gas conduit system for monitoring a plurality of different enclosed spaces (zones). The sampling line for each zone can have up to ten heads, and delivers air or other gaseous atmosphere samples from the respective parts of the zone to the centrally located particle detector at a continuous flow rate of about 14 liters a minute. Each zone line is sampled sequentially by an electronically controlled selector valve assembly for a 15 second interval, once a minute. The cloud chamber particle detector operates at a cycling rate of about once per second and provides a continuous analog voltage corresponding to small particle concentration in the portions of the zone being sampled.

Abstract: An optical oil monitor that measures particle contamination in oil by passing light through an oil sample and picking up the light that is scattered at 90.degree. by the particle contaminaton and measures chemical breakdown by the attenuation of the light passing substantially straight through the oil with a second sensor. Alternately a sample and a reference are passed between the light responsive sensors for error correction and calibration so that each sensor will have an output signal alternating between a sample signal and a reference signal. A control signal of the same frequency is provided in combination with a plurality of gates to separate the sample and reference signals. The attenuation reference signal is compared to a standard signal to produce an error output for regulating the intensity of the light source to compensate for power source fluctuations, lamp characteristic changes, window soiling and the like.