GB1228647A - - Google Patents

Abstract

1,228,647. Inductive control systems. SABA SCHWARZWALDER APPARATE - BAUANSTALT AUGUST SCHWER SOHNE G.m.b.H. 11 June, 1968, No. 27684/68. Heading H4U. In a control system, e.g. for automatic door opening, oscillations of different characteristic frequencies are produced by a plurality of oscillators and operating signals are produced by a detached passive element comprising a corresponding plurality of resonant circuits which are tuned respectively to the oscillator frequencies and are brought into inductive or capacitive coupling with the oscillators, a control signal being effective when all the operating signals are coincident. The passive element may be in the form of a key, and the resonant circuits may be embedded in moulded resin or the like and spaced by the distance between aerials connected to the oscillators. As shown, characteristic frequencies fa, fb are generated by oscillators 2, 2<SP>1</SP>, respectively, and frequency-swept by means of a low-frequency generator 3, e.g. at 2 c/s. When two resonant circuits tuned to frequencies fa, fb are brought into the vicinity of aerials 1, 1<SP>1</SP>, the output of the oscillators 2, 2<SP>1</SP> is briefly reduced, resulting in pulses of highfrequency oscillations which are detected at 4, 41. The aerials may be arranged in pairs for each oscillator so that the fields at a distance cancel. The low-frequency pulses from the detectors are fed via bandpass filters 7, 7<SP>1</SP> and amplifiers 8, 81 to rectifiers 9, 9<SP>1</SP>, the resulting voltage being smoothed and amplified at 10, 10<SP>1</SP> and supplied to an amplifier 11 controlling a relay 12 connected, for example, to a door opener. Only when the two signals coincide and exceed a theshold value will the relay be operated. If disturbance signals are present, which may be arranged to be produced by a burglar detector, they are separated from the signal pulses by high pass filters 13, 13<SP>1</SP>, ampli. fied at 14 and supplied to rectifier 15 which is oppositely poled to rectifiers 9, 9<SP>1</SP>; The rectified voltage from 15 is amplified and smoothed at 16 and causes the input to amplifier 11 to be shortcircuited so that the relay does not operate. An alarm may be operated at the same time. Low pass filters 5, 5<SP>1</SP> extract the D.C. component from the output of demodulators 4, 4<SP>1</SP> which via amplifiers 6, 6<SP>1</SP> controls the amplitude of the oscillations from oscillators 2, 2<SP>1</SP>, respectively. It is stated that, in a modification, a further frequency modulated oscillator is controlled to produce from the disturbance signals frequencymodulated oscillations distinguishable from the signals produced by the characteristic frequencies, which may be used as before to disable the output circuit.