GB1527517A - Aural monitor system - Google Patents

Abstract

1527517 Indicating apparatus; speedometers E DARZI 30 Nov 1976 [5 Dec 1975] 49980/75 Headings G1J and G1K The magnitude of a measured variable, e.g. a vehicle or shaft speed, is represented by the pitch of an audible tone, a reference tone or a series of different reference tones being sounded simultaneously with the variable tone or briefly interspersed with it. The variable tone may be produced by a siren mechanically driven, e.g. from a vehicle propellor shaft, with reference tones produced by horns, whistles, tuned reeds, or electronically when selected by the driver or operator. The variable may be displayed visually at the same time. In Fig. 1, a transducer such as a tacho-generator produces an A.C. electrical signal having a frequency proportional to the magnitude of the measured variable. An L.P. filter, e.g. cutting off frequencies above 300Hz, removes harmonics, and the filtered signal is passed to a frequency multiplier to increase the band width to e.g. 0-3000Hz, the signal being amplified and fed to a loud-speaker. An oscillator includes selector switches enabling a selected division or reference tone to be fed to the speaker, a repetitive contactor giving intermittent output of the selected tone. In a modification, Fig. 2 (not shown), a set of pass-band filters in parallel covers the range of input frequencies. Each filter has its own frequency modifier, comprising a subtracting unit and a frequency multiplier, to convert the respective frequency band into the full frequency range used by the speaker. Thus as the variable rises from zero to its maximum value, the audible tone rises across its full frequency range a number of times equal to the number of pass-band filters. A series of different variables to be monitored can be represented by signals, all connected to the same frequency range, which are sampled in turn by a time division multi-plexer and fed to a speaker. It can be arranged that the normal operating value of each variable is represented by the mid-range frequency of the speaker, the full range of the speaker representing e.g. Œ25% of the normal operating value of each variable.