Abstract: An A.C. power supply controller for a capacitive load such as an array of electroluminescent panels (1) having circuit elements (10 to 15) for producing a pulsed switching waveform (p) centered on the zero-crossing points (z) of an applied alternating voltage waveform, powerswitch (17) for connecting the applied voltage waveform or another voltage waveform to the load in response to the pulsed switching waveform (p), and control elements (5) for widening the pulse width of the switching waveform (p) symmetrically about the zero-crossing points (z) to vary the power applied to the load. The circuit elements (10 to 15) includes a rectifier (10) that rectifies the applied alternating voltage waveform, and a comparator (13) that compares the rectified waveform with a control D.C. input level (15) to produce an output level between adjacent crossing points of the two signals about the zero-crossing points (z). A linear potentiometer varies the D.C. input level (15).

Abstract: A gas supply apparatus (1) particularly for supplying oxygen comprises a gas separator (2) for separating oxygen from the other constituents of the air. The oxygen passes to a piston cavity (6) of a compressor unit (7) where it is compressed and passed to a storage means (12) from where it can be dispensed via a pressure regulator (13) to a number of emergency oxygen masks (14). The compressor unit (7) includes a number of moving parts lubricated by oil within a first cavity (8). Cavity (8) is separated from the piston cavity (6) by a purge cavity (9). In the event of an oil leak from the first cavity (8), the oil will gather in the purge cavity (9) where it is purged therefrom by the waste gas from the separator unit (2) after the oxygen has been removed. If any of the waste gas leaks from the purge cavity (9) into the piston cavity (6) it will mix with the oxygen compressed therein and form a safe mixture.