Abstract: To measure the height of the surface of a fluent material, such as coal, in a bunker or container, pulsed radiation from a microwave source is beamed down on to said surface, and the return radiation reflected from the surface is processed to detect pulses in the waveform with time-varying amplitudes, and therefore denoting returns from the fluent material, and to reject fixed shape pulses denoting returns from the fixed structure of the bunker. To discriminate between returns of time-varying amplitude (i) from the fluent material surface and (ii) from material flowing in from an in-feed, the higher frequency components, denoting the material flowing in, are filtered out.

Abstract: To measure the contents of a bunker or silo a transmitter mounted over the bunker beams down on to the contents surface a very high frequency signal that is caused repeatedly to rise and fall in frequency with either a constant sweep time and a progressively varying amplitude of frequency change or a constant amplitude and a progressively varying sweep time. The reflected target return signals are mixed with the transmitted signal to obtain a beat frequency which is filtered and processed to derive a signal representative of the range of the target, i.e. the contents surface, below the transmitter. To discriminate against target returns from fixed parts of the bunker structure, such as support members, a control unit is provided with a memory store into which are preloaded signals representative of fixed structure returns. The target returns received when the apparatus is in operation are then compared with the stored signals and any that are the same as stored signals are rejected.