Abstract: A system for detecting a flame or droplets of burning polypropylene in an area below an upper surface of a conventional wet bench used in semiconductor production includes at least one sensor, a threshold detector, a discrimination, a counter and a latch. The sensor detects radiation generated by activity in the area and for generating a sensor signal in response to the detected radiation. The threshold detector determines whether the activity has a cross-sectional area which exceeds a predetermined threshold area. The discriminator determines whether the activity displays a flicker rate or a droplet rate that is within the predetermined flicker rate range.

Abstract: An ionization detector unit for use in a smoke detector includes a housing wall enclosing an ionization chamber, the wall having openings for passage of air through the chamber, the frontal surface of the wall that is exposed to an oncoming air flow from a given direction being inclined relative to an intersecting second surface exposed to the flow. The frontal surface is shaped and positioned to deflect the air flow generally toward the second surface, and the second surface is shaped and positioned to deflect the air flow generally toward the frontal surface, the shape and position of the surfaces cooperatively arranged to cause the deflected air flows to converge and form a region of air in the vicinity of the intersection of the surfaces that is at higher pressure and slower velocity than the oncoming air flow.

Abstract: A radiation detector for use in hazardous locations, comprising an explosion proof housing with a viewing window and a detector element positioned inside the housing to receive radiation through the viewing window, and means within the housing to apply test radiation onto the external face of the viewing window directly. In one embodiment of the invention the viewing window is recessed in a housing cavity with a flared wall and the test radiation is applied from a housing portion that extends forwardly of the plane of the viewing window. In a preferred embodiment of the invention the housing is formed of front and rear portions which are rotatable in relation to each other, and the viewing window is mounted in a surface of the front portion which is inclined at a 45.degree. angle to the axis of rotation of the portions, and the rear portion has mounting means enabling mounting of the detector so that it can rotate about an axis disposed at a 45.degree.

Abstract: An ionization detector of the type having a housing with electrodes and a radiation source for causing ion current flow between the electrodes, collector means for detecting, by a change in voltage, a drop in ion current flow, and means responsive to a predetermined change in collector voltage to provide an output signal, in which a test electrode is provided in the housing and means is provided for applying to the test electrode a predetermined voltage of a value that causes said predetermined change in voltage at the collector, whereby said output signal is provided when said predetermined voltage is applied to the test electrode if said detector is operating satisfactorily.

Abstract: An ionization type smoke detector (10) includes a chamber having a measuring electrode (12), the voltage on the measuring electrode being a function of the concentration of smoke in the chamber, and further includes a comparison device (A3) for comparing the voltage measured on electrode (12) at two different times, and an output device (K) for producing an output signal if the voltages differ by a predetermined value.