A field sensor control mechanism for doors and the like has two or more insulated electrodes mounted at different levels in the leading edge of a door or the like. A first oscillating circuit is connected with one of these electrodes and a second oscillating circuit, separate from the first one and serving as a comparison circuit for the same, is connected to the other electrode. The two circuits have base oscillating frequencies which are either identical or differ only slightly from one another. The circuits are so coupled to one another that the oscillations of the first circuit vary as a function of capacitance changes taking place in the electrodes.
A capacitance sensing security system in which comparison/reference and sensing oscillator are coupled together to operate in substantial frequency synchronism, each of the oscillators includes an amplifier having input and output terminals and a feedback circuit including a capacitor connected to the input terminals, the feedback circuit connected to the sensing oscillator exhibiting a low capacitive reactance, the input terminals of the sensing oscillator being connected to one or more objects to be secured so that extraneous transient signals appearing at or on the objects do not affect the phase/frequency of the sensing oscillator, the resistive component being substantially greater than the resistance of the input terminals and is provided either by adjusting the value of the capacitive component in the feedback circuit and/or disposing a resistor in series therewith. An automatic tuner is provided to initially provide frequency synchronism between the reference/comparison and sensing amplifiers, and thereafter, a predetermined phase difference between the two amplifiers is provided by a suitable offset biasing supply for the sensing oscillator and the reference/comparison oscillator. Improved intruder detection includes controlled clocks and selectively operable registers to actuate an alarm condition indicator.
A proximity switch is described, specifically a capacitive proximity switch, with two signal transmitters (1, 2) and with one signal receiver (3), a first signal output (4, 5) of each of the two signal transmitters (1, 2) being connected to one another and to a first signal input (6) of the signal receiver (3), and a second signal output (7, 8) of each of the two signal transmitters (1, 2) being connected via a respective signal transmission path (9, 10) to a second signal input (11) of the signal receiver (3), and at least one of the two signal transmission paths (9, 10) can be influenceable by an actuating object.
An oscillator which produces a continuous wave output signal on an antenna having a preset frequency. A detection circuit detects changes in the preset frequency resulting from proximity between the antenna and an object and when such an object is detected, the detection circuit generates an output signal. A compensation circuit is also provided for compensating for changes of the preset frequency which are caused by factors other than proximity of the antenna with an object. Such other factors include radio frequency interference, long term component degradation, temperature, and the like.
In order to be able to reliably detect when an object is caught between two parts which move in relation to one another in a motor-driven closing mechanism, in particular in an electromotively driven window winder system, provision is made for the sensor system to have an optical pressure sensor as well as an electrical capacitive sensor in addition. The optical pressure sensor comprises a light-guiding element, a light source for injecting light into the light-guiding element and a light sensor for sensing the light which has been output. The electrical sensor comprises an electrode which is connected to a voltage source. Both sensors are each assigned to an evaluation unit for evaluating the respective signal.
A device and method for passively activating an inductive loop vehicle sensor. The sensor has an inductive loop in a roadway that produces an electro-magnetic field and utilizes the changes caused by the interaction of a detectable vehicle with the field to activate it. The device includes at least one metallic foil having sufficient area and thickness to cause changes sufficiently similar to changes caused by a detectable vehicle to activate the sensor when said foil is placed within the electro-magnetic field. The method includes providing such a device and deploying the device in a plane substantially parallel to the roadway and within the field of the loop.
