LEVEL SENSOR

Abstract: An anti-jacking sensor comprising a Hall-effect device (1), a permanent magnet (3) mounted in the manner of a pendulum within a container (2) containing damping oil (5), the output of the Hall-effect device (1) being connected to the inputs of two integrators (11, 12) having different time constants, the time constants of one integrator (11) being approximately five time the periodicity of the vehicle suspension resonance and the time constants of the other integrator (12) being approximately five times the time constants of the first integrator, the output from said integrator (11, 12) being applied to the inputs of a differential amplifier (13), the output from the amplifier (13) being applied to a voltage window detector (14) connected to a monostable multivibrator (15) having its output connected to an alarm activating switch. The sensor according to the invention may also be used to detect the levelness or otherwise of a body such as for example, in survey work.

Description: LEVEL SENSOR F eld ot the Inventi on This invention rela.tes to devices for detecting whe body is level or other than level, or for detecting a cha in the angle of a body relative to a fixed point reference. More particularl , but not exclusively, invention relates to a device for detecting when a vehi is in a jacked or non-level condition. Background of the Invent on Anti -jacking sensors have in the past consis primarily of pendulum switches, mercury switches and iner switches. The first two switches rely upon tilting of vehicle body beyond a maximum angle off vertical whereupo contact closure is effected and used to trigger an al device. The third switch relies upon the detection sounds or vibrations which usually occur when a vehicle jacked and wheels removed. The above devi ces, although very s pl e construct on, suffer from many problems in the r environment. In the case of pendulum switches and merc switches, a vehicle body at rest at some nominal angle be subjected to oscillatory motion caused by passing traf or high winds and these oscillatory motions may sufficient to clause false alarms to be generated. Whil reduction in the sens tiv ty of this type of switch vercome such problems, the effectiveness of the device adjusted must remain in question. In the case of the th switch, the sounds or vibrations detected may not h resulted from jacking or wheel removal and the device also likely to pick up acoustic vibrations from numer other noise sources that exist in a busy urban environme Thus, the likelihood of false alarms is quite high. Brief Summary of the Invention It is one object of the present invention to provid device by means of which the above shortcomings are at le substantially reduced in a simple and economic manner. I broader sense, it is an object of the invention to provid device by means of which the levelness or otherwise o body may be simply and conveniently detected. In its broadest form, the invention provides a dev or detecting when a body is level or not level, compris eans generating -a magn.etic field of a predeter i intensity, means for suspend ng said magnetic fi generating means in the manner of a pendulum, magnetic fi detecting means mounted adjacent said magnetic fi generating means and having an output which varies accor to the proximity of the magnetic field generating means said detecting means, and means utilizing said output. In one application, the device is mounted on a vehi and is arranged to generate a pre-determined output when vehicle is in a jacked condition. In other applicatio the device may be used as a levelling device in whic maximum output from the device determines when the body which the device is attached is level. For example,, electrical output from the detecting device may be used provide an output in degrees off level or the output provide an audio pitch signal which peaks in frequency w the body is level. In one form of the invention, the magnetic field dev is a ferrite magnet or other permanent magnet havin magnetic f eld of suitable intensity, and the detect device s " a Hall-effect device or a Suhl-effect dev having an output which is a function of the detec magnetic flux density. Where the device is used as. an anti-jacking sensor, output from the Hall-effect device is applied to integration networks ' ha vi ng differing time constants, outputs of which are applied to a differential amplifi The input common mode rejection ratio of the different amplifier is selected to be large so that the long t output of the amplifier is stable for varying voltag Similarly, the shorter integration time constant of integration networks is preferably selected to approximately five times the periodicity of the vehi suspension resonance to effectively average the natu oscillatory motion of the vehicle under most circumstan The longer time constant is selected to be approximat five times the shorter time constant to provide long t stability for vari ations . i n vehicle parking angle. Bri ef Descrip ion of the Drawings One embodiment of the invention, as applied to an an jacking sensor, will now be described with reference to accompanying drawings in which: Fig. 1 is a block diagram of an anti-jacking sen embodying the invention; Fig. 2 shows typical wave forms produced at indicated positions of the sensor of Fig. 1; Fig. 3 is a detailed circuit diagram of one embodim of the anti-jacking sensor of Fig. 1, and Fig. 4 is a sectional elevation of one embodiment the container for housing the anti-jacking sensor of Fig. Description of Preferred Embodiments A typical circuit suitable for an anti-jacking sen is shown schematically in Fig. 1 of the drawings. In t embodiment, the Hall-effect sensor 1 is a Honeywell 634-S which has a sensitivity of 0.9 mV/Gauss, a range of -400 +400 Gauss and an output voltage range of from 0.6 t volt. Although this device is a differential output devi only one output is used in the present embodiment. As shown in Fig. 4; the Hall-effect device 1, mounted on a printed circuit board 8 housed withi generally cylindrical container 2 in which an Alnico mag 3 swings from a pendulum arrangement 4 in a bath of sili oil 5. The magnet 3 is in the form of a rod about 5 mm. diameter, 19 mm. long and has a magnetic flux density approximatel 1000 Gauss at the poles. The container 2 which the magnet is supported on the pendulu device 4 such as to allow a maximum movement of about + 20° and this end the container is approximately 45 mm. in diame and 70 mm. tall. The pendulum arrangement is preferabl ball chain 6 to which the magnet is attached, the chai being supported by a spacer bar 7 attached to the prin circuit board assembly 8 containing the circuitry shown Fig. 3. The board 8 is connected to an ' output prin circuit board 8a carrying output terminals 8b and clos the open end of the container 2 with the aid of exp sealant. A screw threaded projection at the bottom -of container 2 enables the container to be secured t mounting bracket by means of a nut as shown in Fig. 4. should of course be appreciated that the preferred mag and suspension arrangement is by no means essential as m other magnets and suspension means would be equa effective. Referring again to Fig. 1, the Hall-effect device 1 connected to a regulated supply 10 of approximately 4 V. Zener diode Z is connected to the output to protect aga undesirable transient voltages from the voltage suppl the vehicle to which the sensor is fitted. The outpu the Hall-effect device 1 is connected to the inputs of integrators 11 and 12 having different time constants. supply 10 also provides a fully regulated rail of 9 V the remainder of the circuit described below. In present embodiment, the time constant T- j of integrator 1 chosen to be approximately five times the periodicity of vehicle suspension resonance while the time constant T the other integrator 12 is chosen to be approximately times the shorter time constant T***. The output from integrator 11,12 is applied to the inputs of a differen amplifier 13 having a large input common mode rejec ratio to ensure-that the output from the amplifier 13 be stable for varying input voltages. The output from amplifier 13 is applied to a voltage window detecto which is in turn connected to a onostable multivibrato having its output connected to an alarm activating swit Referring now to Fig. 2 of the ' drawings, typ voltage outputs at the positions A to E in Fig. 1 of drawings are shown. As can be seen from the graphs, a s change in the voltage input caused by altering the veh angle produces an output pulse, the duration of whic determined by the longer ti e constant T- j of integrato This pulse is applied to. the window detector 14 and i window threshold levels are exceeded, (Fig. 2, D) an o pulse is generated by the monostable 15 to activate pulse is generated by the monostable 15 to activate alarm system (not shown).. The output pulse also actuates switching circuit 16 which provides the switches S- j and across the integrators 11,12. Closure of these switc S*- . , S 2 connects a low resistance (Fig. 3) across t integrators 11,12 which operates to greatly reduce integration time constants and effectively resets integrators 11,12. This switch action is also effected "turn-on" to provide a means of stabilizing the integrat il,1 quickly. The switch 16 is associated with a visu indicator in the form of an LED (Fig. 3) to enable easy s up and testing of the unit. A detailed circuit diagram is shown in Fig. 3 of t drawings and since the circuitry used is standard in fo further detai led description is not required. In th circuit the output consists of two open collect transistors providing alternate outputs so that the unit be interfaced easily with any existing alarm syst Similarly, the switch 16 is effected by the use of the sol state quad switch shown, the two spare poles S3, S of whi are used to drive the LED indicator 19. In use, the Hall-effect device 1 is preferably arran so as to be* parallel to the longitudinal a is of t vehicle. Other orientations of the device may be desirab for example, where the vehicle is of the centre jacki type. It will be appreciated that the electronic functi performed by the preferred circuit are not difficult achieve in a variety of different ways and accordingly invention is not restricted to the specific electro solution shown in greater detail in Fig. 3 of the drawing It should also be appreciated that while the prefer embodiment has been described in relation to an anti-jack sensor, the invention is clearly applicable to other devi for determining the levelness or otherwise of a particu body. UTE SHEET

Claims: - £ - Claims: 1. A device for detecting when a body is level OΎ level, comprising means generating a magnetic field . o predetermines intensity, means for suspending said magne field generating means in the manner of a pendulum, magne field detecting means mounted adjacent said magnetic fi generating means and having an output which varies accord to the proximity of the magnetic field generating means said detecting means, and means utilizing said output. 2. A device for detecting when a motor vehicle is i jacked state, said device comprising means generatin magnetic field of a predetermined intensity, means suspending said magnetic field generating means in m anner of a pendulum, magnetic field detecting means moun adjacent said magnetic field generating means having output which varies, according to the. proximity of magnetic field generating means to said detecting mea said device being adapted for attachment to the body of vehicle so that jacking of the vehicle varies said outp said output being adapted for connection to an ala controlling circuit. 3. The device of Claim 1 or 2, wherein said magnetic fi generating means is a ' permanent magnet having a magne field of predetermined intensity, said field detecting me comprising a Hall-effect device having an output which i function of the detected magnetic flux density. 4. The device of Claim 3, wherein the output of the Ha effect device is connected to two integrator networks hav differing time constants, the outputs of which are connec to a differential amplifier, a voltage window detec connected to the output of said amplifier and drivin monostable for producing an output pulse when the thresh of said window detector is exceeded. 5. The device of Claim 4, wherein said different amplifier has its input common mode rejection ratio selec so as to be larger to ensure that the long term output the amplifier is stable for varying input voltages.' 6. The device of Claim 4, wherein the shorter integrat time constant is selected to be approximately five times t periodicity of the vehicle suspension resonance- effectively average * the natural oscillating motion of t vehicle under most circumstances, the longer time consta being selected to be approximately five times said short time constant to provide long term stability for variatio in vehicle parking angle. 7. The device of Claim 6, further comprising switch mea for connecting a resistor across each integration networ each resistor having a resistance valve lower than t resistance in the corresponding integration network, sa switch means being activated when said monostable produc an output pulse and when the device is first turned on.

Inventors: STAPLEHURST JOHN STUART, STAPLEHURST, JOHN, STUART
Applicants: CLIFT ELECTRONICS PTY LTD, CLIFT ELECTRONICS PTY. LTD.
Application year: 1985
Main classification: G01C9
IPC codes: G01C9