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: In a process control system for machines operating according to a repetitive cycle, with a number of machine events occurring in appropriate mutual phase relationship during the cycle, transducers are employed in association with rotating parts of the machine to generate reference pulses, one at the end of each complete cycle, and a large number of marker pulses equally between consecutive reference pulses. The marker pulses drive a counter which is reset to zero by each reference pulse; and at each count increment the count is compared with he whole contents of a memory in which is stored count numbers constituting data as to the points in the machine cycle at which particular events are to commence and terminate, with output stages responsive to the comparator and the memory addressing control giving output control signals when number identity is recognized.