Abstract: A glow plug for rotary piston engines adapted to be mounted in an engine plug hole so as not to project from the plug hole and to be traversed by a flow of fuel-air mixture temporarily trapped in the plug hole. The plug includes an elongated protective tube providing a straight root portion by which it is supported from a plug housing adapted to be inserted in a plug hole. The tube terminates in a closed end hook-shaped free tip portion spaced from the root portion and plug housing and lying in the same plane as the root portion. A helical heater coil is disposed in the protective tube with the pitch of the coil being smaller at the free tip portion than at the root portion so that greater heat is generated in the free tip portion than in the root portion.

Abstract: The heating element is made of a plurality of silicon carbide rods, at least four rods being employed in the heating element. The hot ends of all the rods are connected together by a single silicon carbide bridge member. The other (cold) ends of the rods are arranged so that at the current input side two rods are in parallel and on the output side the other two rods are also in parallel and the two pairs of electrically parallel rods are connected in series electrically at the silicon carbide bridge member. The rods are preferably arranged in a square configuration and preferably extend perpendicular to the bridge member. Accordingly the rods can be inserted in a silicon carbide tube closed at the hot end. The interior heating rods are electrically insulated from the silicon carbide tube.

Abstract: An air heating unit comprises a blower casing, a centrifugal impeller and a heating element in the shape of a cylindrical cage of longitudinal guide vanes fastened to the wall of the casing. The guide vanes are made from an electric resistance alloy in sheet form in the shape of uniform strips of a length conforming to the width of the impeller, all vanes being connected at their ends by conductive bridging pieces jointing the alternate ends of each two proximate vanes, thus forming a resister in zigzag pattern provided with terminals for energizing it. The vanes and the bridging pieces may form part of a single rectangular sheet rolled up to form the cylindrical casing and provided with alternate transverse cuts along both edges which stop short of the bridging pieces. The strips between the bridging pieces are bent or curved outwardly from the sheet at a desired angle.

Abstract: A high temperature electrical resistance heater for use within a high temperature furnace. The heater is composed of an elongated tubular element having first and second tubular sections contiguous with one another, the first section being of a high resistivity silicon carbide and disposable within a furnace chamber, the second section being of a low resistivity silicon carbide and disposable external to the furnace chamber. An elongated rod of silicon carbide of low resistivity is disposed coaxially within the tubular element and in electrical connection with an end of the first tubular section. The coaxial ends of the second tubular section and of the rod include contact areas for electrical connection to an external power source. The high resistivity tubular section provides efficient heating, while the low resistivity tubular section and coaxial rod provide a conductive electrical path to the heating section while minimizing the heating thereof.

Abstract: Microphone including an electrostatic microphone cartridge at least one of the electrodes of which is connected to a large resistor which forms part of an electronic circuit. The circuit may be the supply part or the input of the associated microphone amplifier which generally is incorporated in the cartridge. The large resistor is constituted by a structural component of the cartridge, which component is made of a weakly conductive synthetic material. The conductive synthetic material may be a conductive silicone rubber or a conductive polypropylene.

Abstract: An electrical resistance package comprises:A. an insulative substrate,B. a network in film form on the substrate, the network including resistance branches,C. there being terminals on the substrate and associated with the respective branches for registration with contact pins, whereby the resistance branch may be selectively electrically connected via said terminals with the pins in registration therewith.

Abstract: A metal bar with a metal felt covering on each side or therearound and sized externally to be a snug slip fit into slot means provided in a conductive surface monolithic refractory ceramic heater element provide for a convenient and desirable means for distributing current to the conductive surface of the element. As the felt covered electrode means heats up with electric current input to the element and under heat generating conditions, there will be a still tighter bond between the metal felt surfaces of the electrode and the slotted opening in the ceramic element to result in the desired tight contact and an efficient current distribution therefrom.