CZ35482U1 - Motion detection system for living and non-living objects by changing the electric charge - Google Patents

Description

Motion detection system for living and non-living objects by changing the electric charge

Field of technology

The proposed technical solution concerns the field of sensory and security technology - specifically spatial and object protection. The system is designed to detect the movement or contact of living objects (persons, animals) and contact with a moving electrically conductive or non-conductive inanimate object. The detector responds to short distances (tens of cm) and to direct mechanical contact.

State of the art

Today, active infrared detectors (PIR) and microwave detectors (MW) are mainly used to secure buildings. These systems are especially suitable for the protection of entire rooms. Both systems have some fundamental limitations - for example, PIR systems are prone to false alarms during thermal changes in the room (heating, ventilation, drafts, exposure to the sun ...). MW systems, on the other hand, must not be installed in rooms with large conductive objects (eg production facilities ...), they are affected by fluorescent lighting, etc. In general, however, PIR and MW methods cannot be used for localized protection in a geometrically precisely determined zone.

A number of principles (capacitive sensors, magnetic detectors, optical barriers) are used to protect specific objects and zones. The individual methods are specific, must be chosen appropriately according to the application and are often combined, which increases the cost of security.

Existing area sensors responding to a change in electrical capacity due to the presence of an object in the environment - or responding to a change in inductance - are not very suitable for security technology, because the size of the sensing electrodes cannot be easily adjusted without significantly affecting the functionality of the device.

The essence of the technical solution

The essence of the proposed solution is to detect the change in electric charge around the conductor. The change in electric charge is caused either primarily by direct transmission from the detected object, which has a different potential than the sensing electrode, or secondarily by friction of the sensing conductor against a non-conductive substrate, textile element, etc. in mechanical contact with a moving object. An electrical potential other than the ground electrical potential is set (periodically or as required) for the sensing conductor and the sensing conductor is connected to a very sensitive electroscope with a sufficiently large input impedance (minimum 10 ⁶ Ohms). The electroscope evaluates the change in potential to both positive and negative values (for example, liquid spillage and thus grounding of the sensor wire). The sensing wire can have almost any length (units mm - tens of m) and can be applied linearly or flat, for example under the carpet. The condition of the function is an electrically insulating layer between the sensing conductor and an object having an earth potential (for example a concrete floor). The application of a detection fabric / ribbon is very advantageous, when the conductor is woven in an electrically insulating textile substrate (polyamide, polyester ...). Such a ribbon can be applied directly to the concrete floor, under plaster or to metal objects (metal window sills, door frames ...). The sensitivity of the system decreases at high substrate humidity, the system cannot be used in permanently humid conditions.

At rest (no movement of objects in the vicinity), the established electrical potential of the sensor wire changes at a steady speed (due to ground leads and due to the final input impedance of the electroscope). When a certain set potential level is reached, the sensor wire is automatically recharged to the defined potential. Steady potential changes are not evaluated as an event. Only alternating changes in the range 1 to 50 Hz are evaluated as events. In this way, the influence of ground fault and possible influence of alternating interference is eliminated

- 1 CZ 35482 UI from motors, electric cables etc.

Clarification of drawings

Giant. 1 - Schematic of the motion detection system

Example of technical solution

A special textile ribbon 1 consisting of a polyester matrix and a woven stainless steel wire serves as a sensitive sensor. The conductor is in the fabric to be insulated by the matrix. Fabric 1 can be adjusted by cutting to the required length. One end of the fabric 1 with the detection wire is connected to the control unit 5. The electric charge captured by the detection wire accumulates on a capacitor 2, which typically has a capacitance of 10 nF and is connected to the sensing electrode of the control unit 5. The potential of the detection wire is reset to half of the supply voltage of the control unit 5. In this particular case it is a value of 2.5 V and is given by a resistance divider. This potential is established by switching transistor 3 of the JFET (Junction Field Effect Transistor) type, which is connected to its digital output on the control unit 5. It is important that transistor 3 does not reduce the input impedance of the whole device. The signal enters the operational amplifier 4, which ideally has an input impedance of up to 10 ¹² Ohms and is connected to the analog input of the control unit 5. The resulting voltage is evaluated by the control unit 5, where signal processing, capacitor discharge control 2 and device communication take place. The system is highly resistant to electromagnetic interference.

Industrial applicability

It is advantageous to use the system not only to protect large areas, but also to secure geometrically precisely defined locations. The use of the system is possible, for example, for the full-area security of rooms under the floor covering, detection floor elements under windows and at doors, the possibility of attachment to door frames to detect passage, security of specific objects and zones in the room (museum exhibits, showcases, inaccessible zones ...). The great advantage of the system is its versatility and wide range of uses. Another advantage is very simple installation and low price.

Claims (2)

PROTECTION REQUIREMENTS A system for detecting the movement of living and non-living objects by changing the electric charge, characterized in that it consists of a control unit (5) at the digital output of which a JFET transistor (3) is connected, mounted on the sensing electrode of the control unit (5). capacitor (2) and an operational amplifier (4) is connected to the analog input of the control unit (5), which is connected to the detection fabric (1) with a woven conductor at the non-inverting input. it System for detecting the movement of living and non-living objects by changing the electric charge according to claim 1, characterized in that the capacitor (2) is bridged by a transistor (3).