Abstract: A simple and mechanically-rugged calculation or monitoring of the density of fluids, particularly of fuels serving the purpose of driving an internal-combustion engine, provides that a buoyant member is immersed into the fluid under examination, the buoyancy thereof being balanced out via a load applied with a spring. A capacitor that is dependent on the buoyancy and, therefore, on the density of the fluid under examination is formed between the buoyant member and the housing that holds the spring and is filled with the fluid under examination, the capacitor being monitored via a circuit arrangement.

Abstract: To improve the measuring sensitivity of a measuring device to determine the istance between an electrically conducting part, which can be moved in a defined chamber, and a reference point, in particular to determine the upper dead point of the piston of an internal combustion engine, with an electronic evaluation circuit, in which a capacitive sensor can be positioned in a holding device, held in the wall of the chamber, and is connected to an evaluation circuit, the invention provides that the evaluation circuit has a measuring bridge, fed by an oscillator by means of output potential dependent switching elements, with at least two capacitors, that the sensor head of the sensor and the movable part, in particular the piston of the internal combustion engine form one of the two capacitors, and that there is a differential amplifier to which the transverse voltage, which can be picked off the measuring bridge, can be led, and that the outputs of the differential amplifier control the output potentials of the p

Abstract: A charge amplifier circuit for balancing drift between periodically occurring measured signals includes a drift-compensating device with a sample/hold unit which is triggered by a trigger device in accordance with the period of the measured signals. The trigger device is connected for supplying trigger pulses, so that the drift at an output of the charge amplifier, determined at the end of a compensation period, can be taken into account by the sample/hold unit to supply a compensating current to an input of the charge amplifier. The triggering of the sample/hold unit can be performed by external or internal triggering arrangements, so that simple measurements can be undertaken without a large outlay of equipment.

Abstract: An operational testing device for inlet valves and outlet valves of reciprocating engines which are separately driven for an operational test comprises at least one microphone arranged in the inlet pipe and at least one microphone arranged in the outlet pipe of the engine, a combined amplifier and electronic filter, and a gate circuit to which the signals of the microphones are supplied after passing the amplifier and electronic filter. To enable a clear identification of the microphone signals of a defective valve as compared to signals generated by valve noise and extraneous noise, a gate circuit is controlled according to the crank angle of the engine, at least one limit value switch is provided to which the signal is forwarded via the gate circuit in a predetermined crank angle area, and an interpretive circuit is controlled according to the crank angle, actuated by the output signal of the limit value switch and allocating the output signal to the particular valve causing the signal.