Electromagnetic instrument for determining the flow speed of electrically conductive substances, using a semiconductor preamplifier with an upstream-connected input transformer

摘要

A flow meter using the electromagnetic method, in which the effective input noise impedance of the measurement amplifier is reduced by means of a transformer. In the case of electrically highly conductive fluids, this results in a considerable improvement in the product from the required magnetic field strength (and hence the required auxiliary energy), time resolution and the lower measurement limit which can be reached. In order to keep interference in the transformers low, they can be constructed as annular-core transformers and can be accommodated in a screened housing. In order to simplify the handling of the transformers, the magnetic alternating field can be given a sinusoidal response with time in order to produce the measurement voltage, and the measurement amplifier can be provided with band limiting (for example a harmonic filter). Further optimisation of the totality of the above-mentioned properties can be achieved by adding a low-pass filter having a flow-speed-dependent limiting frequency to the sensor output (increasing the limiting frequency with increase in flow speed).