Abstract: A magnetic field sensor coil wherein the coil is formed into a shape comprising two generally C-shaped limbs (2, 3) one within the other, one of these limbs being covered by a magnetic screening material (4). In operation an e.m.f. is induced in each turn of the unscreened part of the coil (3) while no e.m.f. is induced in the screened part (4) and so the total e.m.f. induced is approximately equal to the e.m.f. that would be induced in a simple concentrically wound coil of the same number of turns and of the same dimensions as the unscreened portion of the coil. The coil according to the invention is especially suitable for use with a system for monitoring an electric motor where the coil may be placed adjacent the motor end plate concentrically around the motor shaft without having to uncouple the motor from its load.

Abstract: A system for converting A-scan signals in r, .theta. co-ordinates into display data for x, y co-ordinate display locations, in which, for each A-scan signal, signal values for which the r co-ordinate is greater than a predetermined value contribute to the display data and values for which the r co-ordinate is less do not, and the predetermined values of r are different for different A-scans. FIG. 2 shows pixels, or display locations, close to the origin of an x, y rastor display. The lines radiating from the origin show the r, .theta. co-ordinates of A-scan signals derived from a radar antenna, superposed for purposes of illustration on the grid of pixels. The display data used to brighten an individual pixel is taken only from some, and not from all, of the A-scans which intercept that pixel. In particular, no data is taken from the portions of the A-scans which lie radially inwardly of the points 28 to 36, but data is taken from the portions of the A-scans that lie radially outwardly.

Abstract: Control apparatus for controlling a windscreen wiper in accordance with the mean moisture level on the windscreen includes a microprocessor 9 arranged to detect via input 22 the time a wiper motor 1 takes to sweep the windscreen. The microprocessor calculates an appropriate delay in dependence on the detected sweep time and then causes a subsequent sweep via transistor 4. The delay is varied automatically by the microprocessor so as to rapidly clear the windscreen and then stop the wiper.

Abstract: A magnetic field motor monitor comprises an analogue-to-digital converter arranged to provide digital representations of instantaneous values of a motor magnetic field to a digital processor. A source of clock pulses provides clock pulses for the processor. The source is synchronized to a cyclical external signal, e.g. line (mains), as follows. A timing pulse is generated after a fixed number of clock pulses and the frequency of the clock pulses provided by the source is controlled in dependence on the time difference between the occurrence of the timing pulse and a fixed phase of the cycle of the external signal.

Abstract: A signal analysis system for a magnetic field motor monitor utilizes an analog-to-digital converter for sampling the motor magnetic field at accurately determined and equally spaced times synchronized with the line frequency driving the motor. A plurality of separate memories are provided to accumulate the respective samples which are added to or subtracted from the contents of respective memories, depending on which of the samples is being processed as indicated by control bits in a status register. Signals indicative of the amplitudes of respective harmonically related frequency components of the motor magnetic field are provided from the contents of the memories by combining the respective in phase and quadrature values. A monitor provides an indication of when there has been a change in these combined signals.

Abstract: When addressing a store comprising a plurality of low speed memory blocks each of which can be accessed through a high speed buffer having a limited number of memory elements, in accordance with a pattern which is more flexible than sequential then conflicts can occur due to overloading of the memory elements. In order to avoid this, prior to storing data, the address parameters are calculated taking into account the read/write sequence, depth of buffer and access times and a check is made to see if there are any conflicts among the simulated addresses. If so then a number of alternative measures can be tried in order to resolve the conflicts. Such measures include the use of a small capacity, high speed vestigial memory, adding an offset to the addresses or skipping a number of addresses. Once acceptable address parameters have been calculated then a hardware address generator can be instructed to address data accordingly.