Abstract: An instrument for determining ozone concentration in a gaseous fluid includes a chamber, at least one filter adapted to remove particulates from gaseous fluid entering the chamber, and at least one filter adapted to remove ozone from gaseous fluid entering the chamber. At least one element is arranged to draw gaseous fluid into the chamber. An ultra-violet source located at one end of the chamber and configured to generate a substantially collimated beam of radiation having a wave length in the range 240 to 290 nm, and an ultra-violet sensor is arranged at the other end of the chamber and configured to receive the ultra-violet light emitted by the said ultra-violet source.

Abstract: Apparatus for detecting particulates (46) within a medium in a chamber (10) comprises a photo-detector (14) which is maintained at a stable low temperature by a Peltier type cooling device (42). Scattered light from the particulate (46) is focused by a spherical lens (34) onto the input face (30) of a rod lens (22). The latter has an optical pitch of 0.5 and transfers the image to its output face (25) whence it passes via a light pipe (18) to the sensitive area (16) of the photo-electric device (14). The rod lens (22) provides an inexpensive means for transferring the light and which provides a thermal barrier. Thus, although the photo-electric device (14) is held at a low temperature, the input face (30) of the rod lens (22) can be held at the temperature of the medium within the chamber (10) and is not subjected to the formation of mist or ice.

Abstract: An electrical quenching circuit for detecting, and quenching, avalanches in an avalanching device (5), comprises a TTL comparator (14) having one of its inputs (24) fed with a predetermined potential via a potential divider (18,20) and a voltage reference (22). When a switchable current source (6) is in its low impedance state, and when the device (5) is quiescent, diodes (10 and 16) conduct and input (12) is held at the potential of the voltage reference (22). Comparator (14) is in one stable state. Variations in the voltage reference affect both comparator inputs substantially equally. When the device (5) avalanches, the current from source (6) is diverted through the device and the diodes (10 and 16) cease to conduct. The potential at comparator input (12) falls and, at a critical value, switches the comparator to its other stable state. This is indicated by a pulse on line (34). The output on line (28) switches current source (6) into its high impedance state and quenches the avalanche in the device (5).