GB2149238A - Control apparatus for an electrical fence - Google Patents

Abstract

An energiser 10 applies short-duration D.C. pulses to an electric fence 11 and has a switching circuit 12 connected electrically in parallel therewith. This parallel connection minimises the risk of the unit 12 being damaged if lightning strikes the fence 11. The energiser 10 can be switched on and off from a remote location by engaging a probe 20 with the fence 11 and applying an A.C. signal to the latter by means of a control unit 13. This A.C. signal is detected by the circuit 12, which switches the energiser 10 on and off, as the case may be. When a switch 21 in unit 13 is closed, an oscillator 23 and transformer 24 apply the A.C control signal to the probe 20 via a voltage clamping circuit 24. In the unit 12 the A.C. control signals pass via a voltage clamping circuit 24, rectifier 25 and low pass filter 26 to a monostable 27 operating to switch a bistable 14 controlling a relay 15 having contacts 16 in the supply line to energiser 10. Filter 26 blocks the pulses from energiser 10. A pulse stretcher 31 and lamp 32 in unit 13 can be used to detect remotely that the energiser 10 is working. <IMAGE>

Description

SPECIFICATION Control apparatus for an electric fence This invention relates to control apparatus for an electric fence.

According to a first aspect of the present invention, there is provided control apparatus for an electric fence, comprising an energiser by means of which electrical power is supplied to the fence, a switching unit responsive to an alternating electrical signal on the fence to switch the energiser on and off, and a control unit operable to apply such an alternating signal to the fence at a location remote from the energiser.

The control unit preferably includes a probe which can be engaged with the fence and through which the alternating electrical signal can be applied to the latter.

Desirably, the apparatus also comprises a detector which can be connected to the fence at a location remote from the energiser to indicate whether or not the energiser is supplying electrical power to the fence. The detector advantageously forms part of the control unit.

According to a second aspect of the present invention, there is provided control apparatus for an electric fence, comprising an energiser by means of which electrical power is supplied to the fence, a control unit operable to apply control signals to the fence at a location remote from the energiser, and a switching unit responsive to said control signals on the fence to switch the energiser on and off, the switching unit being connected electrically in parallel with the energiser.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagram of control apparatus for an electric fence, according to the present invention; Figure 2 is a circuit diagram of a switching unit which forms part of the apparatus shown in Figure 1; and Figure 3 is a circuit diagram of a control/detection unit which also forms part of the apparatus shown in Figure 1.

Referring first to Figure 1, the illustrated apparatus enables an energiser 10 for an electric fence 11 to be controlled from a remote location, and includes a switching unit 1 2 which switches the energiser 10 on and off under the command of electric signals received from a control/ detection unit 13, this latter unit also being operable to detect whether or not the f ence 11 is energised at any particular time.The switching unit 1 2 includes a bistable circuit 1 4 which controls the energisation state of a relay coil 15, a movable contact 1 6 of the relay being connected between a socket 1 7 into which the energiser 10 is plugged and a mains electricity supply 1 8. When the energiser 10 is initially plugged into the socket 1 7 and is switched on, a reset circuit 1 9 operates the bistable circuit 1 4 to energise the relay coil 15, thereby closing the contact 1 6 and bringing the energiser 10 into operation. The energiser then supplies short duration d.c.

pulses to the fence 11.

When it is desired to switch off the energiser 10, a probe 20 of the control/detection unit 1 3 is engaged with the fence 11 and a push button switch 21 is operated so as to cause an oscillator circuit 22 to apply an a.c.

signal to the probe 20 by way of a transformer 23 and a voltage clamping circuit 24.

The a.c. signal on the fence 11 is converted to d. c. by a rectifier circuit 25 in the switching unit 12, and is passed through a low pass filter circuit 26 to trigger a monostable circuit 27. The circuit 27 in turn applies a signal to the bistable circuit 14 to change the state of the latter, thereby de-energising the relay coil 1 5 and opening the contact 1 6. To bring the energiser 10 back into operation once again, the push button switch 21 of the control/detection unit 1 3 is operated so that a further a.c. signal is applied to the fence 11 by way of the probe 20.This signal is processed by the switching unit 1 2 in the same manner as before, so that the bistable circuit 1 4 is restored to its original state and the relay contact 1 6 is closed once more.

The low pass filter circuit 26 in the switching unit 1 2 prevents the monostable circuit 27 from being triggered by the short duration current pulse on the fence 11 during normal operation of the latter. The switching unit 1 2 also includes a voltage clamping circuit 28 to protect the unit 1 2 from high voltages on the fence 11, such as a would occur if the fence were to be struck by lightning, and a power supply circuit 29 to provide inter alia the current for operating the relay coil 1 5.

In order to detect whether or not the energiser 10 is operating at any particular time, a push button switch 30 of the control/detection unit 1 3 is operated with the probe 20 engaged with the fence 11. If the energiser 10 is indeed operating, then the short duration current pulses on the fence will be picked up by the probe 20 and passed through the voltage clamping circuit 24 to a pulse stretching circuit 31 which energises an indicator lamp 32 accordingly. The various circuits in the unit 1 3 are all powered by one or more batteries 33.

The switching unit 1 2 will now be described in greater detail with ref erence to Figure 2. The socket 1 7 has three terminals which are connected respectively to the live, neutral and earth lines of the three phase mains supply 18, with the relay contact 1 6 being provided in the live connection. The live and neutral lines are also connected to opposite ends of a primary winding 34 of a trans former 35 forming part of the aforementioned power supply circuit 29. A secondary winding 36 of the transformer 35 has diodes 37 and 38 connected to its ends respectively and a centre tapping 39 which is connected to earth.The diodes 37, 38 and the tapping 39 together form a full wave rectifier producing raw d.c. at an output point 40 thereof, this raw d.c. being supplied to the relay coil 1 5. A diode 41 is connected in parallel with the coil 1 5, and provides protection from the back e.m.f. generated in the coil when the latter de-energises. The flow of current through the relay coil 1 5 is controlled by a transistor 42 whose base is connected by way of a resistor 43 to an output terminal 44 of the bistable circuit 14.

The output point 40 of the power supply circuit 29 is also connected by way of a diode 45, resistors 46 and 47 and a smoothing capacitor 48 to a subsidiary power supply unit comprising a resistor 49, a zener diode 50 and a capacitor 51 connected in parallel. This supply unit powers an integrated circuit 52, which is a c.m.o.s. hex Schmidt trigger having six gates.

The voltage clamping circuit 28 comprises five series-connected resistors 52 to 56, the resistor 52 being connected to the fence 11 while the resistor 56 is connected to earth via a zener diode 57. The rectifying circuit 25 is composed of a diode 58 whose anode is coupled to the connection point between the resistor 56 and the zener diode 57 and whose cathode is connected to earth via a resistor 59. The cathode of the diode 58 is also connected to one end of a resistor 60, the other end of the latter being connected to earth by way of a capacitor 61: the resistor 60 and the capacitor 61 together form the low pass filter circuit 26.

To the connection point between the resistor 60 and the capacitor 61, there is connected a first gate 62 of the integrated circuit 52. An output of this gate is connected to one side of a capacitor 63, the other side of the capacitor being connected to the power supply unit 29 by way inter alia of a resistor 64.

The gate 62, the capacitor 63 and the resistor 64 together form the monostable circuit 27, with the voltage at the output of the gate 62 dropping to OV for a short duration when d.c.

is detected on the fence 11. The said other side of the capacitor 63 is also connected to second and third gates 65, 66 of the integrated circuit 52 by way of respective diodes 67, 68 the outputs of these gates in turn being connected to fourth and fifth gates 69, 70 by way of respective further diodes 71, 72. Resistors 73 and 74 provide cross-coupled positive feedback between the gates 69 and 70, thereby forming the bistable circuit 14. The output of the gate 69 is coupled to the input of the gate 66 by way of a resistor 75 and a diode 76, the connection point between these latter components being earthed through a capacitor 77, while the connection point between the diode 76 and the gate 66 is connected to earth by way of a resistor 78.The output of the gate 70 is similarly coupled to the input of the gate 65 by a resistor 79 and a diode 80, with a capacitor 81 and a resistor 82 being provided in an analagous manner to the capacitor 77 and the resistor 78. This arrangement enables the bistable circuit 1 4 to change its state each time an output pulse is received from the monostable circuit 27. The output terminal 44 of the bistable circuit 14 is connected to the output of the gate 70.

The reset circuit 1 9 is composed of a resistor 83 and a capacitor 84 connected in series between the power supply circuit 29 and earth. A sixth gate 85 of the integrated circuit 52 is coupled to the connection point between the resistor 83 and the capacitor 84, and has its output connected to the input of the gate 69 by way of a diode 86. These components force the bistable circuit 1 4 into a state wherein it energises the relay, coil 1 5 each time the power is switched on.

The control/detection unit 1 3 is shown in detail in Figure 3. When the push button switch 21 is operated, the battery or batteries 33 become connected to an input point 87 of a control circuit 88 for the oscillator 22. The input point 87 is connected to earth by way of a resistor 89 and to a first gate 90 of an integrated circuit 91 by way of a resistor 92.

the connection point between the resistor 92 and the gate 90 being coupled to earth through a capacitor 93. The output of the gate 90 is connected by way of a diode 94 to an input of the oscillator 22. The control circuit 88 functions to allow the oscillator 22 to produce a square-wave output when the switch 21 is closed, and to stop the oscillator when the switch 21 is opened.

The oscillator 22 is composed of a second gate 95 of the integrated circuit 91 whose input is connected to the diode 94 in the control circuit 88. A resistor 96 is connected across the gate 95, and the input of the gate is connected to earth through a capacitor 97.

The output of the gate 95 is connected by way of a resistor 98 to the base of a transistor 99, the main conduction path of this transistor being connected in series with one winding 100 of the transformer 23. When the output of the oscillator 22 is at a high level, the transistor 99 is rendered conductive to allow current to flow through the winding 100 via the switch 21, a diode 101 and a current limiting resistor 102. When the output of the oscillator 22 is at a low level, the transistor 99 does not conduct and therefore the winding 100 becomes de-energised. A diode 103 connected across the winding 100 provides a current path for the back e.m.f.

generated when the latter is deenergised. A capacitor 104 connected to the base of the transistor 99 controls the switching time of the latter, while a zener diode 105 connected in parallel with the main conduction path of the transistor 99 provides protection against high voltage spikes.

The square wave voltage thus applied to the winding 100 is stepped up in a further winding 106 of the transformer 23 to about 50 volts peak-to-peak. The stepped-up voltage is then applied to the probe 20 of the unit 1 3 through a series connection of five resistors 107 to 111. The alternating signal thus applied by the probe to the fence 11 is detected by the switching circuit 12, which then switches the energiser 10 on or off in the manner described previously.

In order to detect whether or not the fence 11 is energised at any particular time, the push button switch 30 of the unit 1 3 is operated. This allows current from the battery or batteries 33 to flow via a diode 11 2 to the indicator lamp 32 when a transistor 11 3 is rendered conductive. If the fence 11 is indeed energised, then the fence pulses will be picked up by the probe 20 and will pass through the current limiting resistors 107 to 111 of the voltage clamping circuit 24 to the input of a third gate 114 of the integrated circuit 91 by way of a resistor 115.The high voltage pulse from the fence is clamped by an impedance element 11 6 connected between the resistor 107 and earth, with further voltage clamping being perf ormed by a resistor 11 7 connected between the resistors 107 and 11 5 and a zener diode 11 8 coupled between the resistor 11 7 and earth.

Each time the fence pulse goes positive, a short negative voltage pulse is emitted from the output of the gate 1 1 4 and is stretched by the pulse stretching circuit 31. This latter circuit is composed of a reversed diode 11 9 whose anode is coupled to battery positive inter alia by a capacitor 1 20 and a resistor 121. The stretched voltage pulse is then fed to a fourth gate 1 22 of the integrated circuit 91, which produces at its output a positive voltage pulse of approximately 3 ms durations.A capacitor 1 23 connected to the output of the gate 11 2 and a resistor 1 24 connecting the capacitor 1 23 to battery positive serve to prolong the pulse still further, to about 200 ms duration. A series connection of a resistor 1 25 and a diode 1 26 provided in parallel with the resistor 1 24 ensure that the capacitor 1 23 discharges rapidly between pulses.The voltage pulse is then fed to the base of the transistor 1 1 3 through a fifth gate 127 of the integrated circuit 91 and a resistor 128, causing the transistor 11 3 to conduct (and therefore the lamp 32 to be illuminated) for about 200 ms each time a fence pulse is present.

A power supply for the integrated circuit 91 (which is a c.m.o.s. hex Schmidt trigger) is provided by a capacitor 129, two resistors 130 and 131, a further capacitor 132 and a zener diode 1 33. The two diodes 101 and 11 2 provide an OR function to ensure that power reaches the integrated circuit whichever of the switches 21 and 30 is operated.

In the arrangement described above, the switching unit 1 2 is connected in parallel with the fence energiser 10. Accordingly, the risk is minimised of the unit 1 2 being damaged in the event that the fence 11 is struck by lightning This is to be contrasted with conventional systems of this kind (for example, the arrangement disclosed in published UK Patent Application No. 2062375) where the switching circuit is in series with the fence energiser and therefore subject to the whole of the current present in the lightning stroke.

Claims (11)

1. Control apparatus for an electic fence, comprising an energiser by means of which electrical power is supplied to the fence, a control unit operable to apply control signals to the fence at a location remote from the energiser, and a switching unit responsive to said control signals on the fence to switch the energiser on and off, the switching unit being connected electrically in parallel with the energiser.

2. Control apparatus as claimed in Claim 1, wherein the control unit includes a probe which can be engaged with the fence and through which the control signals can be applied to the latter.

3. Control apparatus as claimed in Claim 1 or 2, further comprising a detector which can be connected to the fence at a location remote from the energiser to indicate whether or not the energiser is supplying electrical power to the fence.

4. Control apparatus as claimed in Claim 3, wherein the detector and the control unit are housed together in a common module, switch means being operable to enable the detector and the control unit to be brought selectively into operation.

5. Control apparatus as claimed in any preceding claim, wherein the control signals are alternating electrical signals.

6. Control apparatus as claimed in Claim 5, wherein the control unit includes an oscillator to generate said alternating signals and a switch whereby the oscillator may be turned on and off.

7. Control apparatus as claimed in claim 6, wherein the switch is a push-button switch.

8. Control apparatus as claimed in Claim 5 when appended to Claim 3, wherein the energiser applies short-duration electrical pulses to the fence, and the detector includes a pulse stretching circuit to prolong said short-duration electrical pulses and an indicator which is energised by the prolonged pulses.

9. Control apparatus as claimed in Claim 8, wherein the indicator takes the form of a lamp.

10. Control apparatus as claimed in any one of claims 5 to 9, wherein the switching circuit includes a bistable circuit whose state determines the on/off condition of the energiser, and also inludes a rectifier to rectify the alternating signal applied to the fence by the control unit, the rectified signal being applied to the bistable circuit.

11. Control apparatus as claimed in Claim 10, wherein the energiser is operative to apply short-duration electrical pulses to the fence, and the switching circuit includes an electrical filter to block said short-duration electrical pulses from reaching the bistable circuit.

1 2. Control apparatus for an electric fence, comprising an energiser by means of which electrical power is supplied to the fence, a switching unit responsive to an alternating electrical signal on the fence to switch the energiser on and off, and a control unit operable to apply such an alternating signal to the fence at a location remote from the energiser.

1 3. Control apparatus for an electric fence, substantially as hereinbefore described with reference to the accompanying drawings.