Abstract: In a exhaust smoke sensor a light emitter generates a light beam which passes through a region containing the exhaust gas to a first light sensor. To reduce interference the light emitter is driven by a near square wave signal produced by passing a square wave through a low pass filter.

Abstract: An exhaust gas particle sensor has an inlet tube and a sensing region having different cross sections and linked by a transition region including a number of baffles arranged so that the time taken for gas to travel from the inlet tube to the sensing region is substantially independent of the position of the gas across the inlet tube. The sensor operates by measuring the opacity of the exhaust gas using a light beam which passes in and out of the sensing region through windows, the exhaust gas being prevented from impinging on each window by a double air curtain.

Abstract: Communication networks, specifically network topologies and apparatus therefor suitable for data communication between computers, tend to be of three main types--those with a star topology (the older sort), those with a bus topology, and those with a ring topology. The ring topology networks have many advantages, but their simpler forms are highly vulnerable to link or repeater failure.