RU2419159C2 - Resonant capacitance device for security alarm - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device includes in-series connected signal shaping assembly, detector, amplifier, threshold device and actuating mechanism. Actuating signal shaping assembly consists of input LC-loop parallel connected to antenna - transmitter and through resistance element to output of high-frequency (HF) generator; at that, resistance element and LC-loop form divider of high-frequency voltage between output of HF-generator and common wire, and LC-loop is pre-tuned to level of high-frequency voltage, which is 0.4 - 0.9 of maximum level of voltage of HF-generator.

EFFECT: simplifying the design, and improving sensitivity and interference immunity.

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Description

The invention relates to technical means of protection, and in particular to alarm devices that generate an alarm notification when the capacitance of the sensitive element changes.

A device is known for capacitive type alarm systems (USSR AS No. 372571, 1973), comprising antennas connected to the ends of the primary winding of a differential transformer, the tap of which is connected to one terminal of the generator, the other terminal of which is connected to the zero potential bus, a secondary the winding of the differential transformer through the amplifier is connected to the signal processing circuit, the primary winding of the differential transformer is asymmetrical.

The disadvantage of this device is the low reliability and noise immunity of the device, low resistance to weather and climate influences.

A device of a capacitive type for burglar alarm is known, containing two sensing elements in the form of capacitive antennas connected to the terminals of the primary winding of a differential transformer, a high-pass filter and an actuating unit in the form of a relay (RF Patent No. 2277263, 2006).

The disadvantage of this device is the presence of two antennas for mutual compensation for sensitive elements, which increases the size and cost of the device, the presence of a low sensitivity zone between the antennas with equal signal effects on both antennas, and limited immunity to radio interference.

The present invention is based on the solution of the problem, which allows to simplify the design of the device, increase sensitivity, as well as increase noise immunity and resistance to weather and climate influences.

The problem is solved in that in a capacitive-type device for burglar alarms, comprising a signal conditioning unit, a detector, an amplifier, a threshold device and an actuator, the signal conditioning unit consists of an input oscillating LC circuit, a high-frequency generator and an antenna sensor, in parallel interconnected via small capacitors, while the input oscillating LC circuit is in a partially detuned state with respect to the high-frequency and generator of the pre-set level on the high voltage constituting 0.4 ÷ 0.9 of the maximum voltage level of the high frequency generator.

The invention is illustrated in the drawing, where figure 1 shows a functional diagram of a capacitive device.

The proposed capacitive device comprises a signal conditioning unit 1, which includes a parallel LC circuit, an antenna sensor, and a high-frequency generator. The detector assembly 2 includes a high-resistance field-effect transistor detector and a two-link low-pass filter. The signal amplifier 3 consists of two amplification stages and a bandpass filter. The threshold device 4 is based on the CMOS logic elements. The nodes of the device are interconnected in series.

The proposed device operates as follows

The response signal is generated in a parallel oscillatory LC circuit, which is the input of the device and suppresses electromagnetic influences coming from the antenna sensor to the device: various kinds of interference and radio interference. Two signals are applied to the oscillating LC circuit. One is a high-frequency signal coming from an RF generator. The second signal is the impact signal following from the antenna sensor. Under the action of the RF signal from the generator, an RF voltage is generated on the LC circuit, which depends on the configuration of the circuit and the signal from the antenna sensor. An RF voltage is supplied to the circuit through a small capacitor from the generator, with respect to which the LC circuit is in a partially detuned state and tuned to a lower frequency. On the circuit, it is necessary to maintain the RF voltage in the range of 0.4-0.9 from the maximum level. Stabilization of the circuit is achieved by an appropriate selection of the temperature coefficient of capacitance (TKE) of the loop capacitor. The LC circuit is in a resonant state, as the level of the HF voltage of the circuit is influenced by the resonant phenomenon in the generator-LC circuit. A slight change in the loop tuning frequency causes a significant change in the LC loop in the circuit. The circuit setting depends on the capacity of the antenna, which is connected to it through a small capacitor. When the intruder approaches the protected object, the antenna capacity and, consequently, the RF voltage level on the LC circuit changes, which is a signal for the device to operate. In relation to interference, the parallel-type LC circuit has a lower electrical resistance and shunts them to the housing, providing a low noise level at the input of the device and, as a result, a high level of sensitivity and noise immunity. The optimal value of the capacitance of the isolation capacitor in the circuit between the generator and the LC circuit is determined depending on the operating frequency of the device and is at the level of several picofarads. This capacitor and LC circuit form a divider in the circuit.

RF signal (capacitance of the capacitor and impedance of the circuit). An LC-circuit reacts to an outside signal coming from outsiders by changing its resistance. For the operation of the forming unit, it is necessary that this change in resistance affects the level of the HF voltage of the circuit. For this, the signal from the generator must be supplied through a resistance, the value of which must be comparable with the loop resistance at the operating frequency and selected depending on this frequency.

In order to reduce the influence of surrounding objects and weather and climate fluctuations on the circuit tuning, as well as the absence of parasitic capacitors in the circuit that reduce its quality factor, a small capacitor is installed between the antenna and the LC circuit.

From the output of the shaper unit, the signal is fed to the input of the detector. In order to obtain thermal stability and efficiency, a detector circuit was developed on a field-effect transistor with a low-pass filter in the source circuit. The transistor operates at a low drain current, therefore, in the non-linear portion of the characteristic, it acts as a detector. A two-link low-pass filter is included in the source circuit to smooth out the ripple of the RF voltage and isolate the useful signal having an infralow frequency.

From the output of the detector, the signal is fed to the input of the amplifier. In the present invention, a strip amplifier is used, amplifying only the useful infra-low frequency signal and providing a high degree of amplification for realizing the possibilities of low-noise generation of the input node response signal. In this case, the strip amplifier provides the ability to operate the device from battery. These advantages of the amplifier are realized in an amplifier based on CMOS logic elements operating in linear mode. Inverters with significant amplification in linear operation are used as amplification stages. The high input impedance of the CMOS elements allows the use of low-capacitance isolation capacitors, which have increased reliability and reduced noise compared to electrolytic capacitors.

From the output of the amplifier, the signal enters the threshold device. The threshold device is also made on the CMOS logic elements, which ensures its stability and efficiency. CMOS elements are thermostable and threshold and output voltage. In addition, the input elements of the threshold device and the output stage of the amplifier are located in the same housing of the microcircuit, which further increases the stability of the device and simplifies the setup - it allows not to select the resistance of the input divider resistors. When a signal sufficient to switch one of the input elements arrives at the input of the threshold device, a signal of a certain duration appears on the device output, which is formed by one of two single-vibrators. The presence of two single vibrators makes it possible to distinguish between the type of impact on the antenna - the movement of intruders (or metal objects) approaching or moving away with respect to the antenna. This ability significantly expands the capabilities of the device. The presence of diodes is designed to ensure the stable operation of the circuit and for the fast discharge of time-consuming capacitors when installing single-vibrators in the initial state after applying the output operation signal. From the output of the threshold device, a signal-pulse of a certain duration is fed to the input of the actuator.

The device has the versatility of operation at various frequencies. When operating at a low frequency, the device is economical, a low level of radio interference on the air, ease of manufacture and tuning of the circuit generator. The operation of the device at high frequency allows you to get high sensitivity and resistance to interference and radio interference.

The use of the proposed capacitive device for burglar alarms in comparison with the known one allows to increase sensitivity and noise immunity, increase resistance to weather and climatic influences, in addition, the device does not contain expensive materials, it is quite simple to set up and convenient to use.

Claims (1)

A resonant capacitive device for burglar alarms, comprising a series of triggered signal generating unit, detector, amplifier, threshold device and actuator, characterized in that the signal generating unit consists of an input LC circuit connected in parallel with the antenna - sensor and through a resistance element - with the output of a high-frequency (HF) generator, while the resistance element and the LC circuit form a high-frequency voltage divider between the output of the HF generator as well as a common wire, a LC circuit is pre-tuned to a high-frequency voltage level of 0.4-0.9 of the maximum voltage level of an RF generator.