Abstract: An electronic ballast circuit for operating high intensity gas discharge tubes such as high pressure sodium, high pressure mercury and metal halide tubes, as well as ordinary fluorescent tubes. In the preferred embodiment, an inductance and a capacitance are connected in series with the load across the dc supply, with a solid state switch between the junction of the inductance and capacitance and the other side of the load, and a control circuit for the switch to operate the switch at a high frequency such as 20,000 hertz. Alternative embodiments omitting the capacitance and utilizing a transformer for the inductance are especially suited for less expensive units and for emergency lighting use. Power supply circuits with switching operated in conjunction with the previously mentioned switch provide for regulation of lamp output during start-up and for compensating changes in supply voltage coordinated with lamp aging.

Abstract: A pressure gauge having two coaxial helical bourdon tubes interconnected at the pointer ends and coupled to the pointer, with an inlet line for each tube permitting fluid flow through both tubes. A valving arrangement for operation as a pressure gauge by blocking one inlet line retaining the fluid under pressure in the tubes, and for flushing the tubes by opening both inlet lines and moving a fluid through the tubes.