This invention relates to a method of electronic control.
In particular, the present invention will be discussed with respect
to fence systems having electric fence energisers, although it may be possible
that aspects of the present invention could be applied to other situations.
Electric fence energisers emit a high voltage pulse approximately
every second. The 'intensity' of the pulse is such that it acts to deter stock
from touching the electric fence.
Typically, an electric fence energiser supplies pulses to electric
fences covering a very broad area of a farm. If the farmer is moving stock, has
temporary electric fence lines or for some other reason wishes to turn off the
electric fence energiser, then he/she usually has to walk a considerable distance
to turn off the electric fence energiser or to turn the energiser back on.
A product was invented (which is the subject matter of US Patent No.
4270735) that applied a DC signal to the electric fence line by connecting a battery
from the fence to ground. The signal was received by a device that turned the energiser
off or on. Unfortunately, this device had many problems. For example, the operation
of the device was such that there was a large drain on the batteries used in the
device to send the signal.
Poor electrical connections commonly occur on an electric fence, e.g.
line clamps. Because of these poor connections, often the emitted signal would
not reach the energiser switching device.
A further problem was that once the power supply was disconnected
from the electric fence energiser, there was a significant start up time from when
the electric fence energiser was turned on and the energy storage capacitor becoming
sufficiently charged for normal energiser operation.
Further, the above device required a separate control device to the
electric fence energiser. This totally separate device connected and disconnected
the power supply to the energiser. The cost in labour required in producing the
separate device was also a detriment commercially.
There are also other problems associated with attempting to send
signals along an electric fence line. One such problem is that it is common for
an electric fence line to have induced on it signals from other electric fences,
power lines and the like. Often there is attenuation of a signal down the line
US-A-4270735 discloses a method of and an apparatus for electronically
controlling an electric fence energiser which emits energiser pulses to energise
an electric fence line in which a signal is sent along an electric fence line
to the electric fence energiser to cause the operative state of the electric fence
energiser to change.
EP-A-514222 discloses a communications device capable of sending
a coded signal down an electric sense line, the pulses of the coded signal being
separate from the normal pulses produced by an electric fence energiser. The communications
device may form part of the electric fence energiser and send signals which operate
machinery or send a trigger signal to an information station or responder to obtain
information. The responders may use a similar communications device to that used
in the electric fence energiser to send back the required information.
It is an object of the present invention to address the above problems,
or at least to provide the public with a useful choice.
Further objects and advantages of the present invention will become
apparent from the following description which is given by way of example only.
DISCLOSURE OF INVENTION
According to one aspect of the present invention there is provided
a method of electronically controlling an electric fence energiser which emits
energiser pulses to energise an electric fence line comprising the step of sending
a signal along an electric fence line to the electric fence energiser to cause
the operative state of the electric fence energiser to change, characterised in
that the signal is a coded signal and the method includes the step of applying
partial validating checking to the coded signal.
Generally the change in operative state of the energiser will be
on or off.
Use of a coded signal has a number of advantages. One advantage is
that the signal is readily distinguished from natural noise which occurs on electric
fence lines. Another advantage is that the production of a coded signal as opposed
to a straight DC signal as previously, means that there is potentially less drain
on the batteries of the device sending the signal.
The coded signal may come in a variety of forms, but in one embodiment
the coded signal may comprise of a number of short pulses sent at predetermined
times apart. Other types of coded signals may also be sent with variations in
amplitude and so forth. However, the applicant has found that there can be attenuation
in the amplitude of signals and therefore a coded signal which varies in the time
domain is preferred to one that varies in the voltage domain.
A second aspect of the present invention provides a receiver for
receiving a coded signal associated with an electric fence line, characterised
by checking means for applying partial validity checking to received signals to
determine if a coded signal specific to the receiver has been received.
A signalling device is provided in combination with the receiver
of the second aspect of the present invention, said device having a signal power
supply, signal producing means, and signal control means to control the signal
producing means, the arrangement and construction being such that in operation
the signal power supply can provide power to the signal producing means which
is then controlled by the control means so that a coded signal produced by the
signal producing means can be sent along the electric fence line.
The signal producing means may come in a variety of forms, however
in preferred embodiments this is a capacitor. The power supply may again be any
type of power supply, but in preferred embodiments shall be a battery. The control
means may also come in variety of forms, but in preferred embodiments is a programmed
Reference throughout this specification shall now be made to the
power supply as being a battery, the signal producing means being a capacitor and
the control means as being a microprocessor. Other componentry may of course be
In previous devices, the batteries of the signalling device were connected
between the electric fence line and ground, and therefore the supply of the DC
signal throughout the electric fence line placed a heavy load on the battery -
tending to drain same. With a send device in accordance with the present invention,
the battery need only charge a capacitor (or some other pulse/signal producing
device) which is then discharged into the electric fence line. Therefore, there
is no direct link between the battery and the electric fence line, and the capacitor
is only charged for a short period of time - thus less drain on the battery.
In preferred embodiments, a high voltage is used (say 100V to 20kV),
and in preferred embodiments in the order of kilovolts - which is a similar magnitude
to that of electric fence energiser pulses. If a high voltage is used, then a signal
is more likely to cross air gaps created by poor electrical connections (for example
improperly connected fence wires) on the electric fence line.
In preferred embodiments of the present invention the signal sent
along the electric fence line may have a voltage lower than that typically produced
by an electric fence energiser, but still sufficiently high to be read by a suitable
receiving device and cross typical poor electrical connections found in electric
For example with a load of 500 ohms, a low energy electric fence energiser
may product a typical pulse every second in the order of 3 kilovolts having a duration
of approximately 30 microseconds. A high energy energiser with a load of 500 ohms
may produce pulses having a peak voltage in the order of 4.7 kilovolts and the
duration in the order of 300 microseconds. In comparison, the signal pulse may
have a peak voltage of between 800 to 3kV and a duration in the order of 6 microseconds.
Due to the high voltage of the signalling device pulses, these pulses
could appear on adjacent or nearby fence lines (by capacitor or inductive pick-up,
or a direct connection etc), and turn an energiser on or off. To overcome this
problem, the receiving and sending devices could have a matching selectable pulse
interval or an identity code. This selectable pulse interval could be stored via
a series of switches, or EPROM, or in some similar manner. The selectable pulse
interval may alter the signalling device pulse interval so the units are distinguishable,
and will not turn off an adjacent fence line.
A significant feature of the present invention is the ability for
the receiver to not just react when it received a signal of any type, but only
react when it receives a signal having the appropriate code/characteristics. Therefore,
if the signals sent along one fence system are induced onto another fence system,
they would not necessarily match the signal expected to be received and therefore
are not affected by same. This is described in greater detail below.
For example, a user may control the code in the send or signalling
device with user selectable code circuitry. This may be DIP switches or header
pins or some other method. This can be used to change the timing of the signal
pulse train which allows the signalling device to only act on the desired energiser.
For example, consider four neighbouring farms having each electric
fence energiser all set at code 1.
If farmer 1 turns his/her system off on the fence, the signals may
be induced onto the other farms fences. This is caused by the nature of the signals
and the nature of the electric fences. This is because the signals are high voltage
pulses and the fences are large conducting networks. Therefore systems on the neighbouring
farms may be switched on or off.
If user selectable codes are used then the four systems can be set
so that they are all different as illustrated below. No signal will therefore interfere
with the neighbouring system.
The number of pulses sent in a typical coded signal may vary but in
a preferred embodiment five coded pulses will be sent:
A further advantage of having a coded signal means that a signal can
be validity checked and distinguished by a control circuit within the electric
fence energiser over other signals which may appear on the electric fence line.
As one of the functions of an electric fence energiser is to produce
pulses, it is highly probable that a pulse could be produced by the energiser while
the coded signal is being received. If only the exact coded signal was required
to change the state of the electric fence energiser, then it is possible that the
natural function of the electric fence energiser may interfere with same and multiple
coded signals may have to be sent before they are received and acted on.
The present invention therefore includes the feature of partial validity
checking. For example, if the coded signal has five pulses and four corresponding
pulse intervals, then the control means within the energiser need only detect say
four of these pulses and three of the pulse intervals. As an example, the coded
signal may comprise of five pulses which are sent at equal times apart. The partial
validity checking means need only determine whether four pulses have been received
and that three valid pulse intervals were detected.
In other embodiments, the times between pulses may not be equal but
In a further embodiment of the present invention, the control means
may not act to connect or disconnect the power supply from the electric fence energiser
as with previous devices, but may control directly the main pulse switching devices
(generally an SCR) that discharges the main energy storage capacitor within the
electric fence energiser. There is now no need to wait before an electric fence
energiser can be operated as the main storage capacitor remains charged. It is
only the pulse switching device that discharges the capacitor which is disabled.
A further advantage of having an embodiment as described above is
that the receiving unit may be placed within the energiser rather than being a
In a preferred embodiment a capacitor divider network is used (at
the energiser) to detect pulses on the fence while still providing mains isolation.
The capacitor divider is also a high pass filter which removes any 50 Hz mains
components (and any other low frequencies). This high pass filter enables the pulse
detection level to be set as low as 200 mV (which increases the sensitivity of
the receiving means to detect the sending device), while avoiding false pulse detection
due to mains on the fence line.
BRIEF DESCRIPTION OF DRAWINGS
Aspects of the present invention will now be discussed by way of example
only and with reference to the accompanying drawings in which:
BEST MODES FOR CARRYING OUT THE INVENTION
- Figure 1a:
- is a diagram of a possible coded signal for use with the present invention,
- Figure 1b:
- is a diagram of a possible coded signal for use with the present invention
with an energiser output signal shown and
- Figure 2a, 2b:
- illustrate the proportional sizes between typical electric fence pulses and
signal pulses in accordance with one embodiment of the present invention, and
- Figure 3:
- is a block diagram of possible circuitry to be used with a signalling device
in accordance with the present invention.
Figure 1a is a voltage verses time graph in which a possible coded
signal 1a in accordance with one possible embodiment of the present invention is
It should be appreciated that Figures 1a and 1b are not intended to
show the relative sizes of the electric fence pulses and the coded pulses with
respect to each other but merely illustrate the overall operation of the present
invention. Figures 2a and 2b however are representative and show more clearly the
relative sizes of the electric fence energiser pulse and the signal pulses.
Referring back to Figure 1a, there are five pulses 2, all of which
are of equal height and width and are spaced at predetermined intervals.
In this particular embodiment of the present invention, the height
and width of the pulses 2 which make up the coded signal are immaterial. All that
really matters is the length of time 3 between the leading edges 4 of the pulses
2. The fact that the pulses 2 are identical in height and width can be attributed
to the electronic control means in the signal device.
Figure 1b illustrates the signal shown in Figure 1a, but with an electric
fence pulse 5 appearing in the middle of the signal 16. The pulses 2 are still
the same periods of time 3 apart as previously. However, the receiving means in
the electric fence energiser will read the pulse 5.
In addition to the expected time differences 3 between leading edges,
there are also time distances 6 and 7 between the leading edges caused by the unexpected
arrival of the electric fence pulse 5.
If partial validity checking is used, then the receiving means only
requires three valid time periods 3. Thus the existence of the electric fence pulse
5 enables the energiser to be controlled despite the receiving means receiving
a corrupted signal. The interval between coded pulses is significantly longer than
an energiser pulse width so that only one of the code pulse intervals could be
It is thought that the controlling circuitry can be incorporated into
the usual energiser control. In other embodiments the control may come from a microprocessor
or microcontroller device. This control means can disable the SCR so that it cannot
fire in response from other signals from within the control means of the electric
Referring now to Figure 3, there is illustrated a block diagram which
shows one possible construction of a signalling device in accordance with one embodiment
of the present invention.
The power supply in this embodiment is either a 9 or 12 volt battery
The battery 10 is connected to a DC to DC converter 11 which converts
the battery voltage so that the capacitor 12 can be charged to a few hundred volts.
The capacitor 12 can be discharged through the transformer 13 via
a controllable switch in the form of a SCR 14. The discharge of the capacitor 12
produces the signal pulse.
The timing of the signal pulses or discharge of the capacitor 12 is
controlled by the control circuitry 15 which is governed by the user selectable
code circuitry 16. The control circuitry 15 may come in a variety of forms and
in some embodiments may be a microprocessor or micro controller. The user selectable
code circuitry may also come in a variety of forms and may in some embodiments
DIP switches or header pins.
Aspects of the present invention have been described by way of example
only and it should be appreciated that modifications and additions may be made
thereto without departing from the scope thereof as defined in the appended claims.