Abstract: An apparatus for displaying patterns of balls forming a Braille-sign or other symbol or picture, comprise a driven running belt carrying the balls with it. According to the invention the belt is smooth--instead of being perforated--whereby the balls may be grouped upon the belt in arbitrary mutual positions. The balls are kept in place by being clamped against said belt by means of a second belt and due to the spaces between the two belts being maintained at a reduced air pressure.

Abstract: The invention relates to a method and an apparatus for investigating a filling of liquid in a container, e.g. a fuel tank in respect of actual volume, density, temperature, opacity or other condition. From an emitter (19) at the bottom of the container there are emitted pulses of ultrasonic waves which are reflected by one or more horizontal border faces (17, 21) of the liquid and returned to the bottom of the container and detected by a receiver (20) there. The passage times of the reflected signals are compared with the passage times of direct and not-reflected signals that are detected by a plurality of receivers (1, 2, 3, 4, 5) placed above each other in fixed known positions. The result of said comparison is made the basis of a calculation of the sought quality. Measurement of the passage times, comparison, calculation and exposition of the result takes place by the use of electronic or data equipment (23).

Abstract: Readable Braille dot matrix formations are easily formed and utilized to print Braille books and the like. A belt forms an endless loop and has a number of small holes each for receiving a ball. An upper horizontal or slightly inclined path of the belt is supported by and drawn in contact with an underlying support. The belt has a smaller thickness than the diameter of the balls, and the uppermost parts of the balls extend above the upper face of the belt so that they may be tactilly perceived. Empty belt holes are filled with balls at a first area of the belt along its path, and some of the balls are selectively removed from the belt holes at another, second area along the looped path. Selective removal of the balls may be provided by disposing slots in the underlying support with piezoelectric bars providing movable obstacles in the slots. Alternatively electromagnets disposed above the balls may be provided.

Abstract: The power drawn by a load (R.sub.L) from an A.C. network is controlled by an operational amplifier (OP1) and a power transistor (TR2). The operational amplifier makes the transistor leading when the voltage of its inverting input which is derived from said network, is lower than a reference voltage supplied to its non-inverting input. The pulses through the load take a form corresponding to the first and last parts of a sinusoidal half-wave. Their time lengths are shortened according as the voltage of the feeding network increases, and vice versa. FIG. 1.