Abstract: The invention is directed to a double refracting planar plate arrangement and a .lambda./4 plate suitable for deep ultraviolet light. The .lambda./4 plate or the like is configured as a planar plate with stress-induced birefringence. The planar plate 1 is made of high quality quartz glass and is torsion-free and uniformly loaded in tension via suitable construction having several parallel tension devices (3, 7).

Abstract: The invention is directed to an ignition circuit for an internal combustion engine in a portable handheld work apparatus wherein a work tool is driven via a clutch. The ignition circuit includes an ignition time point control which connects a spark plug via a switch to a voltage source in order to trigger an ignition spark. The spark plug is mounted in the combustion chamber of the engine. This connection takes place in dependence upon the crankshaft angle and the rpm of the engine. In order to prevent damage to the clutch because of a blocked work tool, a test value counter driven via a rpm gate circuit is provided. The test value counter increments its value in the pregiven rpm window of the gate circuit with each rotation of the crankshaft and the content of the test value counter is compared to a pregiven limit value by a comparator. The output of the comparator activates a rpm-reducing protective circuit and the output of the comparator indicates reaching or exceeding the limit value.

Abstract: A power-assisted steering system for a vehicle such as an automobile or truck and having an electro-mechanical servo drive. The servo drive directs the wheels to be steered which are journalled on a wheel carrier assembly and coacts with a steering wheel of the vehicle. The steering system includes a controller to which a steering wheel torque and a steering torque are supplied for forming a control difference with the steering wheel torque being generated by the driver when steering. The steering torque is the actuating torque occurring between the servo drive and the wheel carrier and the forces developed on the steering wheel are controlled to pregiven values while considering the mechanical reaction.

Abstract: For generating several interferograms which differ from each other in the relative phase position between the interfering partial beams, a light source is utilized having a coherence length less than the optical path difference between the two component beams in the measuring path of the interferometer. Furthermore, at least one optical delay device is provided which splits the beam into two component beams and which generates an optical path difference between these component beams which is approximately the same as the optical path difference of the partial beams in the measuring path of the interferometer. Thereafter, the delay device again unites the component beams congruently.

Abstract: A switch actuator in the form of a bifurcated elongated member has a pair of legs pivoted relative to each other. In the "off" position of the switch, the legs may be pivoted relative to each other, and the actuator may be withdrawn from the switch. This precludes an unauthorized operation of the switch and the equipment controlled thereby. In the "on" position of the switch, an interlocking means precludes the relative pivotal movement of the legs, and the actuator may not be withdrawn from the switch. In the preferred embodiment, the legs of the actuator automatically engage an operating element of the switch, upon the insertion of the actuator into the switch. Thereafter, the actuator has a limited sliding movement to alternately move the switch into its "on" and "off" positions. Preferably, the switch is of the "pull on/push off" type; and the sliding movement of the actuator is in a plane which is substantially parallel to the linear movement of the switch operating element.