IES63485B2 - A sense and display system for a remote load - Google Patents

Description

The present invention relates to a system for the remote sensing (and display) of a load , and in particular, to the electrical loads encountered by a high voltage pulse generator such as an electric fence unit.

Such electric fence units are generally used on farms , game reserves and the like to energise fences which confine animals to a particular area. A charge is delivered from the generator along the line of the fence, and an io animal coming into contact with it receives a shock not sufficient to injure the animal, but nonetheless sufficient to cause discomfort, thus keeping the animal away from the fence. It is important that the energy transferred along the line is at all times sufficient to cause discomfort to the animal. If it is not then the animal may damage the fence or escape from the safe area.

A common cause of insufficient energy on the line is excessive loading of the electric fence unit. This excess loading can be caused by a number of common effects such as :- (i) Vegetation growth against the live fence wires creating a low impedance path to Earth (ii) Insulator failure due to physical deterioration (iii) Excessive fence length (iv) Deterioration of energy storage capacitor in electric fence energiser.

There is therefore a need for a system which can reliably sense and indicate that there is sufficient energy on the line for animal containment.

The present invention is directed towards providing such an indication to the user of the system.

According to the invention , there is provided a high voltage pulse generator comprising a transformer having a secondary winding across which a high voltage output pulse is provided, and a primary winding, at least one primary capacitor connected across the primary winding of the transformer to store a charge for discharge through the primary winding, the primary capacitor and primary winding forming an oscillating circuit, and a switch means to close the circuit between the capacitor and the primary winding for discharging of the capacitor.

Preferably, a first timing circuit is provided to activate the switch at predetermined intervals.

Advantageously, a second timing circuit is provided to hold the switch means closed for a predetermined period , to allow the primary capacitor to discharge through the primary winding. During the discharge of the primary capacitor through the primary winding a high voltage pulse appears across the secondary winding of the transformer.

In one embodiment of the invention , the load is placed across the secondary winding and the voltage across the primary winding is sensed and analysed giving a measurement and indication of that load which is across tire secondary winding.

In another embodiment of the invention , the load is across the primary winding and the voltage across the secondary winding is sensed and analysed giving a measurement and indication of that load which is across the primary winding.

In another embodiment of the invention , the load is across the primary winding and the voltage across the primary winding is sensed and analysed giving a measurement and indication of that load which is across the primary winding.

In another embodiment of the invention , the load is across the secondary winding and the voltage across the secondary winding is sensed and analysed giving a measurement and indication of that load which is across the secondary winding.

The advantages and savings given by the system accrue mainly in that embodiment of the invention where the load is on the high voltage secondary and the sensing is on the low voltage primary.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only, with reference to the accompanying drawings , in which : Fig. 1 is a circuit diagram of a high voltage pulse generator with load sense and display according to the invention.

Fig. 2 is a graph of the output of the high voltage pulse generator of Fig. 1 into two different loads.

Fig. 3 is an graph of the input voltage to the sense circuit of Fig. 1.

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Fig, 4 is a graph of the input voltage to the display circuit of Fig. 1.

Referring to the drawings , and initially to Fig. 1 , there is provided a high voltage pulse generator with a system for sensing and displaying the load on this generator. This is indicated generally by the reference numeral 1. The generator comprises a transformer 2 having a secondary coil 3 and a primary coil 4 with 700 and 70 turns respectively. In use , the electric fence is connected across the secondary coil 3 and forms the load on the generator. The energy for the high voltage pulse generator is stored in the main energy storage capacitor 5. In this particular case capacitor 5 has a value of 60 micro-farads. A power source 6 charges this capacitor in the time interval between pulses. This time interval is controlled by a first timing circuit 7. The pulsed discharge is initiated by closure of a switch means 8 by a second timing circuit 9. The sequence of events in the generator is as follows :(i) The switch means 8 is open and the storage capacitor 5 is charged from the power source 6 for a time given by the first timing circuit 7. (ii) The switch means 8 is closed by the timing circuit 9 for a period long enough for the stored energy to appear as a high voltage pulse across the load connected to the secondary 3 of the transformer 2. (iii) The switch means 8 is opened again.

The design of the generator should be such that it has sufficient power delivery capability to maintain a minimum voltage level of 2,000 volts on the electric fence load. This is the pulsed voltage level considered to be on the threshold of animal containment. Typically, this voltage would be between 2,500 volts and 5,000 volts under normal running conditions.

A typical voltage waveform for two levels of load is shown in Fig. 2. Waveform 1 is for a lightly loaded system and has adequate voltage for animal containment. Waveform 2 is for a heavily loaded system where the peak voltage attained is only 2,000 volts. This is generally considered to be at the threshold of animal containment. The actual loads and timescales involved depend on the power and energy characteristics of the high voltage pulse generator but the principle detailed here-in remains the same at all relevant power levels.

In this embodiment of the invention , a means not known heretofore is demonstrated for the measurement and display of this voltage. This means Page 4 IX is simple and accurate and offers economic and safety advantages over presently known systems.

This means accomplishes the measurement in the primary circuit of the high voltage generator. In the manufacture of electric fence units it will be understood that for safety reasons there can be no connection allowed between the power source and the load. The power source is often line mains which must at all times must be isolated from any electric fence connected to the electric fence unit.

A further economic advantage is accomplished by this means. By making the measurement on the lower voltage primary side of the transformer 2 , the use of expensive and unreliable components is avoided. General physical layout is also simplified and units may be manufactured at a lower cost than presently known systems.

The sense and display system is accomplished as follows. Referring again to Fig. 1 , the voltage appearing across the transformer primary 4 is sampled and divided by the two resistors 10 and 11. In this particular case , resistor 10 has a value of 330 ohms and resistor 11 has a value of 10 ohms. The voltage appearing across resistor 11 is shown in Fig. 3. The essential problem of sensing peak secondary voltage on the primary is illustrated by this waveform i.e. the waveform is similar for both loads.

This voltage is fed by capacitor 12 to resistor 13 and capacitor 14. Across resistor 13 and capacitor 14 , is connected switch means 15. By holding switch means 15 closed for a time controlled by a third timing circuit 16 , the combination of resistor 13 and capacitor 14 perform voltage integration only on the tail of the waveforms shown in Fig. 3. In this way, it is possible to easily and accurately discriminate between lightly loaded and heavily loaded systems. The duration of the third timing circuit is marked on Fig. 3. (From time zero to the vertical dotted line.) It can be seen that after this time there is a large difference in the area under the lightly loaded curve (shown as a solid line) and the heavily loaded curve (shown as a dashed line). The result of the voltage integration (i.e. the peak voltage appearing on the capacitor 14 ) reflects this difference and is shown Fig. 4.

In this particular case, capacitor 12 has a value of 470 nanofarads, resistor 13 has a value of 100 ohms and capacitor 14 has a value of 100 nanofarads. 19L Resistors 17,18 and 19 discharge capacitor 14 , in a time set at approximately 30 milliseconds. As the time between pulses in the high voltage pulse generator ( as set by the first timing circuit 7 ) is typically 1.2 seconds , capacitor 14 is totally discharged in this time. Resistors 17,18 and 19 also form a voltage divider to drive the three Schmitt-Trigger Invertor Gates 20,21 and 22. The outputs of these gates are used to drive three Light Emitting Diodes 23,24 and 25. This forms the display system used to indicate the load being applied across the secondary 3 of the transformer 2.

In this particular case, resistors 17 and 18 each have a value of 47 kiloohms and resistor 19 has a value of 470 kilo-ohms.

As Schmitt-Trigger Invertor Gates have upper and lower threshold levels , two effects are accomplished by their use in the display system. Firstly , the Light Emitting Diode connected to their output will only light if the upper threshold voltage is exceeded and secondly , will remain lit until the input voltage falls below the lower threshold. The 30 millisecond voltage fall time shown in Fig. 4 is equivalent to the integration time for human vision and allows the most visible display pulse to be used with minimum energy consumption.

The use of three lamps allows three threshold levels of load to be indicated. This is generally adequate for use in electric fencing applications. Of course , with the use of more resistors and SchmittTrigger Invertor Gates many more levels could be displayed.

It will be appreciated that the method described is one simple means of implementing the technique. For instance, a different configuration of resistors (10 & 11), capacitor (12) and switch means (15) could be used to produce a time-gated sample of primary voltage or current which would be sensitive to the load on the transformer secondary (3). Equally, inductors and transistors could be incorporated to accomplish the same result. Equally, the integration could be accomplished by another configuration of resistors , capacitors , inductors and transistors. Equally , the result of the analysis of the time-gated signal could be displayed by other means than shown in this embodiment of the invention. Other optical devices could be used. Equally, acoustic sounders or alarms could be used to indicate different load levels.

It will be appreciated that while the various capacitors and resistors have been described as being of particular values that any other suitable values may be chosen. Additionally, the numbers of turns in the primary and secondary coils of the transformer could also be varied as desired.

Claims (5)

1. CLAIMS 5 1. A means for sensing and displaying the load connected to the output of a voltage pulse generator either on the primary or secondary of the output transformer where the voltage or current waveform is passed through a time gate. 10
2. 2. As per claim 1, where the result of the load sensing is given acoustically.
3. 3. As per claim 1, where the result of the load sensing is feed to 15 an external apparatus.
4. 4. As per claim 1, where the result after passing through the time gate is used without integration. 20
5. 5. An electric fence incorporating the sense and / or display system of any of die preceding claims.