GB2253084A

GB2253084A - Burglar alarm

Info

Publication number: GB2253084A
Application number: GB9103425A
Authority: GB
Inventors: Yia-Kong Chiu
Original assignee: CHIU YIA KONG
Current assignee: CHIU YIA KONG
Priority date: 1991-02-19
Filing date: 1991-02-19
Publication date: 1992-08-26
Also published as: GB9103425D0

Abstract

The burglar alarm uses resistors 901-904 for distributing and adjusting the voltage to supply the input terminals of operational amplifiers 41, 51. The output voltages of operational amplifiers excite relays 10 and trigger an alarm 16 when the resistance value of the resistors are changed, due to opening of a window or door, (Figs. 2-4, not shown). <IMAGE>

Description

BURGLAR ALARM BACKGROUND OF THE INVENTION This invention relates to a balanced burglar alarm. The detecting switch of the conventional burglar alarm relates to use a short-circuit switch or a normal-open magneto switch installed at the door and window of house. When the intruder breaks the door or window, the detecting switch will change from open-circuit to short-circuit, or from shortcircuit to open-circuit to trigger the burglar alarm and alarm bell which will threaten the intruder. However, the above open-circuit or shortcircuit type of detecting switch will be broken easily by the intruder just to short or cut the detecting switch. in advance. The burglar alarm will be useless. The intruder will easily enter into the house'and steal everything he wants.

SUMMARY OF THE INVENTION The purpose of this invention is to improve the defect of burglar alarm being broken easily. The resistance value of detecting switch is controlled within a specific preset value so that the detecting switch can not be replaced after broken. The burglar alarm will still be effective for security.

A kind of balanced burglar alarm relates to control the resistance value of detector within a specific value so that the output voltages of two operational amplifiers will keep in balance. The output voltage of two operational amplifiers will change to excite the relay and the alarm bell when the resistance value of detector changes.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is the circuit diagram of this invention; Figure 2 is the structure of the detector in this invention; Figure 3 is the practical example 1 of the detector in this invention; Figure 4 is the practical example 2 of the detector in this invention; DETAILED DESCRIPTION OF THE INVENTION First, referring to Fig. 1, this invention uses an alternating current source and a direct current source for the power supply supporting to the system. The alternating current source is in series with a buzzer 16 through the normal-open contact 11 of relay 10. The alternating current source is rectified by a bridge rectifier 301 and filtered byacapacitor 311 to become a direct current source as the supply voltage of operational amplifiers 41, 42, 51, 52.The rectified and filtered voltage is stepped down by resistors 321, 322, 323 for supplying the proper working voltage of operational amplifier 41. In the same way, the voltage is stepped down by resistors 331, 332, 333 to supply operational amplifier 51, and by resistors 341, 342, 343 and variable resistors 344, 345 to supply operational amplifier 42. Moreover, the voltage is stepped down by resistors 351, 352, 353 and variable resistors 354, 355 to supply operational amplifier 52.

The input voltages of operational amplifiers 41, 42, 51, 52 are from the direct current stepped down by a group of resistors as reference voltages.

The direct current source after stepping down passes through three parallel circuits. Each parallel circuit has two resistors in series like as resistors 601, 602, resistors 701, 702, resistors 801, 802.

The tap of each cascaded resistor circuit connects to the input of operational amplifiers 42, 52. In the operational amplifiers 42, 52, the input voltages at the positive terminals are lower than those at the negative terminals by adjusting variable resistors 603, 803 so that the output voltages of operational amplifiers 42, 52 are zero. In the same way, the input voltages of operational amplifiers 41, 51 are distributed by a group of resistors 901, 902, 903, 904, 905, 906. In operational amplifiers 41, 51, the voltages at the positive terminals are lower than those at the negative terminals by adjusting variable resistor 907 so that the output voltages of operational amplifiers 41, 51 are zero. The resistors 901, 902, 903, 904 are used for detectors.

Hence, in the operational amplifier 41, or 51, when the resistance value of any resistor 901, 902, 903, or 904 is changed beyond the tolerance value, the input voltage at the positive terminal is higher than that at the negative terminal. The output voltage of operational amplifier 41 or 51 will excite are relay 43 or 53 whose normal-open contact 44 or 54 will close to excite the relays 10 and 12. The relays 10 and 12 will keep excited by closing the normalopen contact 13 of relay 12 whether the output voltage of operational amplifier 41 or 51 is termporarily or permanently or not. The normal-open contact 11 of relay 10 will close to let buzzer 16 send out the alarm sound.

The button switch 14 not only lights indicating lamp 15 for power indication but also cuts the circuit of relays 10, 12 for releasing the alarm sound.

Referring to Figs. 1 and 2, in this invention, the resistors 901, 902, 903, 904 are used for detectors as shown in Fig. 2. It relates to having a resistor 3 joined with the bottom of two legs 2 inside a box 1. The front end of box 1 has a hole 4 for inserting a plug 5 whose connecting line 6 is chosen for proper length according to its wire size and resistivity. Then the join resistance of connecting line 6 and resistor 3 is equal to the resistor 901, 902, 903, or 904. That is the practical example of resistors 901, 902, 903, 904 work as detectors.

Referring to Figs. 3 and 4, the detectors can be installed at the doors, windows, or something else. The connecting line 6 connects to the circuit of alarm to form a burglar alarm. The intruder did not know the true resistance value of detector so that the intruder can not ruin the burglar alarm and let it useless.

Claims

CLAIMS:

l. A burglar alarm comprising a detector having a predetermined finite impedance and positionable so as to prevent a means of access without a change of said impedance, and means responsive to a change in said impedance to produce an alarm signal.
2. A burglar alarm as claimed in claim 1, including a plurality of said detectors connected in an impedance network, said alarm signal producing means being responsive to a change in voltage at at least one point in the network for producing said alarm signal.
3. A burglar alarm as claimed in claim 2, wherein the alarm signal producing means is arranged to produce said alarm signal in response to either an increase or a decrease in voltage at said point.
4. A burglar alarm as claimed in claim 2 or claim 3, wherein said alarm signal producing means comprises four operational amplifiers having their positive and negative input terminals connected to said network such that their output voltages are zero, and such that a change of an impedance in the network will cause the output voltage of at least one operational amplifier to change and thus generate the alarm signal.
5. A balanced burglar alarm comprising circuit means in which, in use: an alternating current is rectified by a bridge rectifier, filtered by a capacitor, and stepped down by resistors to supply the voltage of four operational amplifiers; a direct current is distributed by three parallel circuits as reference voltages to the positive and negative terminals of two said operational amplifiers, each said parallel circuit having two resistors in series, two cascaded resistor circuits being connected in series with said three parallel circuits for distributing and adjusting the direct current to supply the positive and negative terminals of another two said operational amplifiers;; wherein the input voltages at the positive terminals are normally lower than those at the negative terminals in said operational amplifiers so that the output voltages are zero, whereby, when the resistance value of any said resistor in said circuits is changed beyond a tolerance value, the input voltage at the positive terminal becomes higher than that at the negative terminal in at least one said operational amplifier so that the output voltage of that said operational amplifier will excite at least one relay which connects with the outputs of a pair of said operational amplifiers, a normally-open contact of said relay thereby exciting another two cascaded relays and trigging an alarm bell.
6. A balanced burglar alarm as claimed in claim 5, wherein said operational amplifiers and said resistors can increase unlimitedly, at least some of said resistors being used as detectors, each said detector comprising a box which has its resistors inside joined with the bottom of two legs and which enables the insertion of a plug.
7. A balanced burglar alarm as claimed in claim 6, wherein said boxes are installed at suitable places such as doors, windows, or movable structures, said plug combining with said legs of said box, said resistor inside said box and a connecting line to form a detector circuit which in use is not separable from said main circuit means of the burglar alarm without generating an alarm.
8. A method of installing a burglar alarm having at least one detector of predetermined finite impedance and means for monitoring the detector impedance and producing an alarm signal upon detection of a change in that impedance, the method including the step of positioning the detector so as to prevent a means of access without a change of said impedance, selecting a wire in accordance with its resistance value and connecting the detector to the monitoring circuit by means of said selected wire.
9. A burglar alarm substantially as herein described with reference to the accompanying drawings.