Addis, Desi Clynton (1/70 Motatau Road, Papatoetoe Manakau City, 1701, NZ)
Addis, Desi Clynton (1/70 Motatau Road, Papatoetoe Manakau City, 1701, NZ)
|1.||A farmer's test device comprising a combination support stick and test device adapted for service as a hand tool for general use about a farm, characterised in 410 that the stick further includes means for ascertaining the capability of an electric fence to provide an electric shock in the form of a train of electric pulses, the means including (a) connection means; an elongated shaft, electrically conductive over substantially the full length of the shaft, capable in use of making contact with an electrified wire of the electric fence, the shaft having an electrically 415 insulated handle at a first end and also having a conductive tip at a second end, insulated from the conductive shaft, and (b) testing means; an internal electric circuit connected between the shaft and the tip; the circuit including at least one visual display means responsive, by going through a reversible change of visual appearance, to a voltage applied between the shaft and the tip, and a window into 420 the interior of the stick to allow a view of the visual display means, so that in use the stick can be held by the insulated handle with the conductive tip in contact with the ground and with part of the shaft touching an electrified wire of an electric fence, whereupon inspection of the visual display means through the window will, without risk of shock to the user, indicate the present status of the 425 electric fence.|
|2.||A combination support stick and test device as claimed in claim 1, characterised in that the internal circuit derives operating power from each electric pulse carried by the electrified wire.|
|3.||A combination support stick and test device as claimed in claim 2, characterised 430 in that the visual display means employs more than one visual display unit, each capable of making a reversible change in appearance, within a circuit arranged so that more of the visual display units will change appearance in sequence as the pulse voltage increases, so that a user can determine the approximate peak voltage present on a wire of an electric fence.|
|5.||A combination support stick and test device as claimed in claim 3, characterised in that the visual display means employs two visual display units so that three states are indicated: ineffective fence pulse (no effect), effective pulse (one display means changed appearance), and high pulse (two display means changed appearance).|
|6.||A combination support stick and test device as claimed in claim 2, characterised in that the at least one visual display unit comprises a gas discharge lamp having an inherent voltage threshold for the conduction of current, so that a sub threshold excitation voltage produces no light from the lamp.|
|7.||A combination support stick and test device as claimed in claim 2, characterised in that the internal circuit employs a transformer having a turns ratio selected so that a pulse voltage present on the electrified wire of the electric fence is trans formed into a pulse having a lower voltage and a higher current thereby matching the requirements of the at least one visual display unit.|
|8.||A combination walking stick and test device as claimed in claim 6, characterised in that the transformer has a ferromagnetic core having a selected level of saturation and having a turns ratio selected so that a pulse voltage present on the electrified wire of the electric fence is transformed into a proportional current; subject to the proportional current having a maximum value substantially limited by saturation of the core.|
|9.||A combination support stick and test device as claimed in claim 6, characterised in that each visual display unit comprises a solidstate lamp (LED) having an inherent voltage threshold for the conduction of current, so that a subthreshold excitation voltage produces no light from the lamp.|
|10.||A combination support stick and test device as claimed in claim 6, characterised in that each visual display unit comprises an electrode of a liquid crystal display; the electrode being connected to a circuit having an inherent input voltage threshold for producing a change in output voltage, so that a subthreshold excitation voltage produces no visual indication.|
|11.||A combination support stick and test device as claimed in claim 6 characterised in that the visual display means employs a combination of types of visual display unit, so that a first type suitable for use in darkness, and a second type suitable for use in daylight are provided for viewing through the window.|
BACKGROUND Electric fences have been widely used in New Zealand particularly since Ruakura Agricultural Research Centre (Mr D S M Philips et an created an early electronic fence controller in the 1960s, which was subsequently developed further, and manufactured in large quantities by firms such as Gallaghers, Stafix, Speedrite, Tru-Test and others.
On the farm, electric fences allow for more efficient pasture control but farmers have to move the fences from time to time, locate faults, and sometimes climb through or past an active, energised fence. An energised fence is hard to recognise apart from one that is off, and safe to touch. Electric fence energisers generate pulses of the order of 5 kV, 2 mS (2-50A) with a repetition rate of 1 or 2 seconds, and comply with formal safety requirements such as in the energy (in Joules) per shock, determined so that inadvertent contact with the fence means only non-lethal shocks for most people. Many farmers have a phobia of electric shocks from electric fences (or inadvertent spread of current into other conductive structures) which is a great inconvenience. There is always a possibility, however remote, that a fence may come into contact with highly lethal mains electricity, such as during or after a gale.
Various test methods are widely used, such as the blade of grass (erratic), bravely touching the fence, listening for sparks, using a transistor radio to detect spark noise in the AM band, observing animal behaviour, or using electronic devices specifically adapted for detecting and measuring this type of pulse. Most methods require that the farmer has to carry some equipment about.
The inventors believe that development of a combination tool ; one that serves more than one purpose, would enhance the chance of a fence tester being to hand whenever needed.
PRIOR PUBLICATIONS Battery-free (passive) fence testers designed to be used at fixed positions include the simple signal light of Partikny (US 4171523) which comprises a resistor in series with a neon lamp, visible inside a fitting that resembles and may replace an insulator on an electric fence.
Current flows from the fence wire through the display device and to a conductive metal fence post. This device produces a flash. McKean's more elaborate indicator (US 4725825) converts the fence pulses into DC which then causes an xenon flash or strobe tube to flash at a rate indicating the mean peak voltage, not at the time of each flash. This involves energy storage. Neither device is adapted to be moved around; both are fixed onto posts.
Battery-free portable electric fence testers includes GB 683997 Korsgaard ; describing a walking stick shape with a bent handle including a restricted metallic contact section near the handle which is connected through a voltage-sensing device-a neon-filled lamp or the like-to an internal wire leading to a metal ferrule at the end. This is an attempt to integrate a fence tester into a farmer's stick in order to make a dual-purpose device. It appears to be built into a standard wooden walking stick (one that is described as a poorly conductive stick) so it would be prone to carrying high levels of current to the user's hand if wet and this may be dangerous. Water, or rain, or other liquids are very commonly experienced on farms. Later, US 2920273 Chruszch provided a less convenient arrangement wherein a metal stake having an insulated handle is fitted with an external side contact, separated from the metal stake by a voltage-sensing device-a neon lamp or the like. The side contact is elongated in order to contact energised fence wires at various heights. Then, Berg et al in US 3364424 provided a metal stake having an insulated handle and an external side contact within a downwards-facing groove for contacting the electrified wire. Use of a hand operated, insulated screw to vary the length of a spark gap will indicate the voltage and energy available at the fence. The side contact is poorly suited for contact with energised fence wires at various heights. These latter inventions are not good for general use as a walking or stock-handling stick. Way et al (US 5285195) describe a metal rod with a groundable tip, containing a short fluorescent lighting tube (mercury and inert gas filling) which can be directly connected by a flying lead and alligator clip to an electrified fence. No series resistor is described. This is not very convenient as either a stick or as a fence tester.
OBJECT It is an object of this invention to provide an improved electric fence tester as part of a multi-purpose tool, or at least to provide the public with a useful choice.
STATEMENT OF INVENTION In a first broad aspect, this invention provides a farmer's test device comprising a combi- nation support stick and test device adapted for service as a hand tool for general use about a farm, wherein the test device aspect of the stick comprises means for ascertaining the capability of an electric fence to provide an electric shock in the form of a train of electric pulses, the means including (a) connection means; an elongated shaft, electrically conductive over substantially the full length of the shaft, capable in use of making contact with an electrified wire of the electric fence, the shaft having an electrically insulated handle at a first end and also having a conductive tip at a second end, insulated from the conductive shaft, and (b) testing means; an internal electric circuit connected between the shaft and the tip; the circuit including at least one visual display means responsive, by going through a change of visual appearance to a voltage applied between the shaft and the tip, and a window into the interior of the stick to allow a view of the visual display means, so that in use the stick can be held by the insulated handle with the conductive tip in contact with the ground and with part of the shaft touching an electrified wire of an electric fence, whereupon inspection of the visual display means through the window will, without risk of shock to the user, indicate to the user the present status of the electric fence.
In a first related aspect, the internal circuit derives operating power from each electric pulse carried by the electrified wire. Preferably the internal circuit does not store power during the period from one pulse to the next.
In a second related aspect, the visual display means employs more than one visual display unit, each capable of making a reversible change in appearance, within a circuit arranged so that more of the visual display units will change appearance in sequence as the pulse voltage increases, so that a user can determine the approximate peak voltage present on a wire of an electric fence.
In one option, the visual display means employs two visual display units so that three states are indicated: ineffective fence pulse (no effect), effective pulse (one display means changed appearance), and high pulse (two display means changed appearance).
In a third related aspect, the at least one visual display unit comprises a gas discharge lamp (such as a pigtail neon lamp) having an inherent voltage threshold for the conduction of current, so that a sub-threshold excitation voltage produces no light from the lamp.
In a fourth related aspect the internal circuit employs a transformer having a turns ratio selected so that a pulse voltage present on the electrified wire of the electric fence is trans- 95 formed into a pulse having a lower voltage and a higher current thereby better matching the requirements of the at least one visual display unit.
In a subsidiary aspect, the transformer has a ferromagnetic core having a selected level of saturation and having a turns ratio selected so that a pulse voltage present on the electrified wire of the electric fence is transformed into a proportional current; subject to the propor- 100 tional current having a maximum value substantially limited by saturation of the core.
In yet another aspect, the or each visual display unit comprises a solid-state lamp (LED) having an inherent voltage threshold for the conduction of current, so that a sub-threshold excitation voltage produces no light from the lamp.
In a yet further aspect, the or each visual display unit comprises an electrode of a liquid 105 crystal display; the electrode being connected to a circuit having an inherent input voltage threshold for producing a change in output voltage, so that a sub-threshold excitation voltage produces no visual indication.
Optionally the visual display means employs a combination of types of visual display unit, so that for example the farmer's test stick can be used in daylight or in darkness.
110 Optionally the visual display means employs passive pulse stretching means so that the apparent brightness of flashes of light from the or each solid-state lamp is increased, when used to test an electric fence.
PREFERRED EMBODIMENT The description of the invention to be provided herein is given purely by way of example 115 and is not to be taken in any way as limiting the scope or extent of the invention.
DRAWINGS Fig 1: as Figs 1A, 1B and 1C are diagrams showing the test stick in sectional view (1A) and ways to enhance lamp brightness (1B and 1C).
Fig 2: is a circuit diagram (Example 2) showing an electronic circuit for detecting electric 120 fence capability.
Fig 3: shows the fence tester in use.
Fig 4: including options Fig 4A, 4B and 4C, shows further circuit diagrams (Example 3).
Fig 5: is a schematic of the test stick and a preferred LED circuit diagram (Example 4).
Fig 6: is a schematic of a preferred LCD circuit diagram (Example 5).
The invention comprises a robust metal tube with an insulated handle at one end and a conductive tip at the other (insulated from the tube), forming a stick-shaped test device. A variety of circuits for indicating the presence of an electric pulse is provided for use inside or close to the handle. The inventors have chosen to avoid energy storage means (such as an internal battery or a device which parasitises earlier pulses of the fence power in order to provide power to an active circuit) in order to retain simplicity and accuracy, even for the first pulse.
EXAMPLE 1 In its preferred embodiment, the invention comprises a robust metal tube with an insulated handle at one end and a conductive tip at the other (insulated from the tube), forming a stick-shaped test device. This device 100 (see Fig 1) contains a voltage-sensitive indicator within the handle 104, suitable for testing electric fences. As shown in Fig 3, first the tip 101 is placed on the ground, and then the conductive tube or outer sheath 102 is brought against a fence wire to be tested; moving the stick by means of the insulated handle 104 in order to touch a selected wire on the fence and complete the circuit between the conductive tubular sheath and the conductive, earthed tip. The circuit passes through the internal electronic device 205 that serves as a visual indicator of fence pulse voltage; an electric fence tester. See Example 2,2A, 3,4, or 5 for details of other circuits. If sufficient voltage to shock is present, one or more indicators 203,204 (typically pigtail neon lamps) built into the handle may be seen to flash. The amplitude can be checked in relation to position along a fence, in case there is a short or a poor contact. Fig 3 demonstrates the manner of connection, with an electrified fence including wires 301,302, and 303, and the invention 100 being held with the tip touching the ground 304, and in a position contacting a fence wire at point 305, giving an indication 306 of fence pulses present in the wire 301. The about 1.3 metre long stick is intended for general hand support as well, so that it is more likely to be carried about, and be ready for use at any time, than a single-purpose fence tester.
The lower end of the stick is a tip comprising a metal rod 101, typically about 7 mm in diameter. (Preferred metals include stainless steel and brass). The tip is connected by an internal insulated wire 109 to the earth point 202 of the circuit. The tip is held within a hole drilled in a closely fitting rod of a non-conductive plastics material 105 (preferably acetal- Ertacetal (R)) which is pressed into the outer sheath 102. Another machined tube of acetal (106) at the top of the stick surrounds the electronic circuit and supports part 104, a moulded hand-hold of plastic, used to enhance the user's grip. The handle may be at an angle to the main body of the stick, for convenience. The indicator (s) are visible at the end 160 of the moulded handle. A preferred collar 108 may be included at the base of the handle to catch a slipping wire, for example before it touches the farmer's hand. The conductive outer sheath 102 is tubular and in our example we used a 1.3 metre length of 12.7 mm OD, 0.9 mm thickness stainless steel. This is reasonably strong. The circuit board 205 is connected electrically to the outer sheath by means of spring connectors 201. A clear 165 window 103 at the user's end of the stick allows the user to see flashes (306) within the neon tubes 203,204 (or other visual indicators such as 502,503, or 600).
Stick length is usually determined by typical fence height. It is desirable that the device can touch the ground with the tip and also reach past the top fence wire without being too close to the user's hand. (In a farm-bike version, a longer stick may be preferred, having a claw 170 107 or some other wire-engagement means near the far end so that the rider can engage a live fence wire tape or gate, lift it with the hook, and drive underneath).
EXAMPLE 2 This is the first of several circuits for the passive (i. e. without an additional source of energy such as from battery storage) display of pulse presence. Fig 2 is a simple circuit for 175 converting high voltage pulses into visible flashes based on two neon lamps 203 and 204 wherein lighting of none, one, or both provides some amplitude discrimination. The assembly of lamps is herein called a visual display means; each lamp is a visual display unit.
One preferred type of neon lamp emits 1.4 millicandelas (mcd) at 0.5 mA and has a breakdown (strike) voltage of between 95 and 135 V. Current limiting is provided by means 180 of a series resistor. A high-brightness type of neon lamp emits about 5 mcd at 1 mA current. Incoming pulses at 201 are passed through resistor 205 which forms part of a voltage divider chain, together with resistors 208-211. Device 206 is preferably a zinc oxide varistor or equivalent, for protecting the rectifying bridge 207 from high voltage transients.
The bridge rectifier 207 is comprised of diodes Dl, D2, D3 and D4. Values of resistors 207 185-211 are chosen so that both neon lamps 203 and 204 are lit at higher applied voltages but only one is lit at low voltages. Resistor 210 can be used to set the voltage gap between high and low. The neon pigtail lamps (203 and 204) have a typical strike (ignition) voltage of 180V though this is somewhat dependent on pulse rise times. Current from the visible display circuit is returned through the rectifying bridge 207 and to earth through a connector 190 to the metal rod comprising the tip of the stick, at 202. The circuit is constructed on a glass- fibre printed-circuit board (see 205 in Fig 1). Note the absence of any battery or means to "hold over"power from one pulse to the next (which tends to provide erroneous results until the hold-over device is filled).
Parts values: 195 203,204 pigtail (solder-in) high-brightness neon lamps.
205 two 47K 2W carbon resistors in series (for a high voltage rating) 206 ZnO varistor 207 4 x 400 mA diodes; 1 kV inverse voltage rated. 1N4007 or equiv.
208 7,200 ohms 200 209 5400 ohms 210 zero ohms (for this Example); could be 470 to 10,000 ohms.
211 8200 ohms One problem with Example 2 is that generic neon pigtail lamps have been found by some users to be of inadequate brightness when used under a summer sun. The inventors prefer 205 to avoid a battery-supported circuit with active components in order to solve brightness problem by (for example) pulse stretching. A battery supply adds to the cost and requires battery servicing from time to time, and access to a battery compromises the sealing of the interior circuitry from external water. A flat battery results in"false negative"test results.
EXAMPLE 2a 210 Weak flashes are hard to see in outdoors lighting. The perceived brightness of each flash can be improved by several methods, separately or in combination: 1. Use of a magnifying lens (shown here as part 103A (Fig 1B) placed between a selected pigtail neon lamp 203 or lamps and the user in order to enhance the apparent brightness of the flash. The magnifying lens gives an appearance, as seen by a user, of a broader, 215 bright area 306 of orange-red light during the flash. The focal length of the lens is about 15-30 mm and the lens may be a Fresnel type. The lens works by directing light in an approximate beam towards the viewer, who perceives a larger lit area. Neon lamps could be coated with, or placed against a metallised reflective material 103B on one side to double the light from the other side.
220 2. Use of a spherical or parabolic reflector 103C (Fig 1C), like that in a small or pocket torch. The reflector is placed around the neon lamp which is in the focus position
usually occupied by the torch bulb so that the reflector efficiently catches most of the emitted light and reflects it (306) towards the viewer. This is more efficient than the lens.
3. For either of the above methods, the area around the viewing window should preferably be coloured in a contrasting colour (dark blue or black) so as to enhance visual contrast.
4. For any of the above methods, as well as for LED-based methods to be described later, image contrast may be improved by use, as a viewing window, of one or more of : circular polarisers, red filters (for red lamps), grey filters, or micro-louvered materials 103D in Fig 1C (the last being available from the 3M Corporation, St Paul, Minnesota, USA) all of which materials have been developed for use in maintaining visibility of self- luminous indicator devices when used under high ambient brightness conditions.
EXAMPLE 3 Light-emitting diodes (LEDs or solid-state lamps) are another visual display option. A very ordinary"high efficiency''red LED produces 4 to 7 mcd at 10 mA in a directed beam, and much brighter options (over 5000 mcd at 20 mA) are available. We noted that simply placing a high-brightness LED in series with the or each neon bulb did not provide useful output from the LED because the two types of device have contrary voltage/current require- ments. The neon lamp is rated at about 0.5 mA current, present only during a pulse of perhaps 1 mS per second, so limiting the solid-state lamp output to a small fraction of the possible amount.
One solution is to use a step-down transformer. Compact pulse transformers developed for the ignition of xenon flash tubes in cameras are widely available for about 1 US dollar, have an about 20: 1 turns ratio, and are used in step-up mode. One of these can be used in reverse (step-down) to better match the voltage/current demands of a LED with the current levels drawn by a neon-type tester and it does improve the LED current and hence brightness. A purpose-developed solution is to provide a pulse transformer having a higher ratio of turns than 1: 20, wound on a preferably saturable ferromagnetic (ferrite) core, with the primary current limited when under conditions of saturation by a series resistor. The saturable core has the effect of limiting the maximum current output from the transformer.
An inherent property of the core limits the amount of magnetic flux that can be supported.
Fig 4 shows some variants of a LED-based circuit employing a pulse transformer (primary 403, secondary 404, saturable ferrite core 402), preferably with a step-down turns ratio of from about 10: 1 to 40: 1 for increasing the quantity of current passed by the neon lamp (typically rated (when conducting) at 80 V, 0.5 mA) for supply from the secondary to the 255 LED (s) (typically about 1.5 to 3 V, 20 mA) so that LED brightness is increased. The usual LED forward current ratings of typically 20 mA are for steady currents; pulse currents can be 2-5 times higher depending on duration and the extent to which lifetime output degra- dation caused by use can be tolerated. A selected pulse transformer has a core that will become saturated at a certain ampere/turns number; for this circuit corresponding to a 260 selected output current limited to about 10 to 30-50 mA. (Capacitative coupling between windings, and air-inductive coupling causes the secondary current to continue to rise after saturation, though to a much lesser extent). Although the neon lamp 203 may be deleted, it is still desirable to retain the series resistor 205, and perhaps also the varistor 206 as further overload protection, such as to help protect the transformer from application of 265 excessive voltage and/or to prevent too much current flowing in the primary winding during saturation or in the event of an insulation breakdown inside the pulse transformer. If a saturable core is not feasible, secondary current through the LEDs can be limited by other well-known means such as zener diodes, series resistors or inductors.
A purpose-designed saturable pulse transformer may be adapted for direct connection to the 270 fence wire while providing reliable operation at that pulse level, thereby minimising the parts count. At least the series resistor is still considered desirable for reasons of safety. The transformer may be a three-terminal (autotransfbnner) device such as the type used in triggering xenon flashlamps for photography.
In Fig 4A, each of two LEDs 405 and 406, connected in reverse parallel configuration across 275 the pulse transformer output at A, B, acts as an indicator device and protects the other LED from inverse voltages. No rectifier is required. Both diodes should be mounted to be visible to a user because the original pulses are often substantially unidirectional. One or both LEDs will flash if sufficient pulse voltage is present; typically more than about 1.4-1. 8 volts for red-emitting diodes.
280 In Fig 4B, one way to provide the secondary circuit with a raised voltage threshold is shown: by means of the series pair of back-to-back zener diodes 407,408 so that the LEDs will flash only if driven by an input pulse voltage sufficiently high to overcome the zener reverse breakdown voltage as well as the LED forward voltage. Zener diodes are but one example of a solid-state device with a controlled breakdown characteristic, as will be well 285 known to those versed in the art. A dual-level indicator could be made by using both Fig 4A and Fig 4B, in parallel, both connected at A, B, and with a current-limiting resistor 411 in series with the lower-voltage circuit. The zener diodes may be rated at reverse breakdown voltages between less than 4.7 to over 120 volts. Substitution of yellow, green, or blue LEDs
at 407,408 also provides an inherent higher voltage threshold since the forward voltage of a LED rises as the emitted wavelength shortens. In use, a circuit having green (or even blue) LEDs with zeners in a Fig 4b circuit, in parallel with a Fig 4A circuit using red LEDs would separately indicate a moderate fence pulse (red) and a strong pulse (green and red also).
Zener type properties allow deletion of the neon lamp 203, (as indicated by the dotted line 401A across the lamp) so that the pulse transformer primary is simply connected across a voltage divider comprised of resistors 205 and 206, (where 206 may comprise a varistor) or in series with one resistor. The transformer primary may be connected to a voltage divider comprised of capacitors rather than resistors, since the pulse-type voltage to be divided exhibits a high rate of change, although that is a more expensive option and the divider may be left fully charged which can cause a shock hazard.
Fig 4C shows one example pulse stretching circuit for use with a LED and the saturable pulse transformer of Fig 4. The pulse transformer output current is rectified within bridge rectifier 409 and charges a capacitor 410 which then discharges relatively slowly through a time-constant setting resistor 411 and LED 412, so that the perceived flash is brighter because it has a longer duration. Peaks of voltage and/or current are diverted into the capacitor rather than overloading the LED. (See also use of an inductor in Example 4) The reader will appreciate that for purposes of production either the circuit of Fig 2 or the circuit of Fig 4 with combinations of Figs 4A, 4B, and 4C may be selected from time to time according to component cost, component performance, and availability. All these circuits are energised by the pulse presently being measured rather than using a battery, and can be constructed upon versions of the printed circuit board 205.
EXAMPLE 4 Fig 5 shows a two-colour, LED-based, two-level self-powered display circuit with low parts count alongside a schematic test stick having at 101 an earthing tip ready to contact the ground 304. The tip is held by an insulating collar 105 onto the conductive shaft 102, to be supported by the user by means of the insulated handle 104 against a fence to be tested.
(The circuit is actually placed inside the stick, as shown in Fig 1; with pulse indicators 412, 502 replacing indicators 203,204). Part 205 is a current-limiting resistor of typically 100 K ohms, rated for 10 kV pulses, and connected at 201 to the conductive shaft of the stick. The exact resistance is a function of other parts values and in particular the transformer charac- teristics, and is selected so that the circuit can discriminate between substantially no pulse, a moderate pulse, and a strong pulse-terms which have to be defined in farmer's language.
206 is a voltage-dependent resistor or varistor (VDR), connected across a saturable-core 10 (402) step-down transformer primary 403. Both the VDR and the saturable core limit the secondary output and hence the peak current to be passed through the LEDs. Either limiter 325 might in practice be deleted, although having both present adds to reliability. The secondary winding 404 is the input to a bridge rectifier 409 (either a module or discrete diodes) rated for at least the VDR breakdown voltage, divided by the turns ratio of the transformer. The occasional pulse output from the rectifier charges a capacitor 410. If the capacitor voltage rises to above about 3 volts (for a GaInN blue chip), the LED 502 will emit light. If the 330 capacitor voltage rises only to between about 1.8 and about 3 volts, current will flow through the red LED 412 and through the inductor 501, which has both a current-limiting and a pulse-elongating function as the flux in the inductor builds up then decays. Inductor 501 should be about 100 microhenries (or more), carry up to 20-50 mA, and may have a series resistance of 5-10 ohms. Series resistors (503) are also shown for the LEDs by way of 335 further protection, but may be superfluous. With this circuit a red flash alone indicates a moderately strong pulse (for example, strong enough to give the farmer a shock), while a superimposed blue flash indicates a higher level, useful for checking how well the fence is performing. The relative brightness of the blue as compared to the red LED (which is limited in peak brightness by the onset of conduction through the blue LED) can be used 340 as a comparative indication of peak voltage because the human eye is suited to compare side-by-side brightnesses. As an alternative to a single blue LED, a green or red LED in series with a selected diode, diodes, or a zener diode will exhibit a similar threshold voltage.
EXAMPLE 5 Fig 6 shows a bar-graph liquid-crystal display (LCD) circuit for indicating fence pulses. A 345 bar graph display conforms better to public expectations of a modern design of level detector (fence strength indicator) (though most bar-graph displays are based on battery- driven integrated circuits). Being a reflective type of display, a LCD is able to be viewed in bright light such as the noonday sun. The bridge rectifier 409 is the same as the bridge rectifier 409 in Fig 5. Fig 6 is an alternative circuit to be joined to the rectifier output of Fig 350 5. A common-anode three-bar liquid crystal display is shown at 600 with a connection to the anode at 601 and to one of the cathodes at 602. (Note that three bars; two active, are shown here by way of illustration only, less or more bars may be used in practice). The LCD 600 may be a purpose-made module, or parts of a standard seven-segment display may be connected in a meaningful pattern.
355 Each LCD cathode is connected to a NPN transistor collector (cf transistors 605,606 and 607, which may be replaced with FET devices or a transistor array, as is known in the art).
All transistors share a common base connection along a voltage divider across the bridge rectifier output, comprised of resistors 603 and 604. Each transistor has one (605 with 608), two (606 with 609) or three (607 with 610) zener diodes or other voltage dropping devices in the corresponding emitter leads. Surface-mount devices provide a compact circuit. This arrangement provides that each collector may or may not be grounded, depending on the pulse height applied to the common bases. If a collector becomes grounded by transistor conduction, the corresponding LCD cathode is at a different voltage than the anode and the panel briefly appears black (assuming standard LCD construction and chemistry); otherwise the cathode and anode voltages fluctuate together and the panel stays clear. Specific details of driving of the LCD module may alter from the circuit as shown, which is intended to illustrate the principles only. For example a 100K resistor might be required between each transistor collector and the positive bus. A capacitor in series with each cathode lead (602 for example) may provide AC conditions. This illustrative circuit does not provide proper AC drives and the LCD module may darken prematurely; on the other hand the total duty cycle of the test circuit is very low. For use of the farmer's test stick in dark conditions, a LED 502 in series with a protective resistor 503 is included within this circuit, to flash visibly when a pulse of electric fence power is detected. Most farmers check their cows at night if bloat or calving is likely, and bring them in for milking at or before dawn.
VARIATIONS The body of the stick may be constructed of materials other than stainless tube, such as plastics or wood with embedded conductive strips and the conductive material may be carbon-based or a conductive plastics material rather than metal.
A hook may be added near the base of the stick, so that the farmer can reach for collapsed wires.
The electric fence tester may be made with more elaborate display means than two lamps or other visual display units, so that the amplitude of the pulse can be judged more closely.
A piezo-electric sounder disk may be used to provide an audible correlate of each pulse.
A desiccant may be sealed into the interior of the stick, to maintain dry conditions within.
Other test devices such as soil thermometers may be added to the stick, although if these require active electronic devices driven by battery power, the intentions of the inventors are to avoid batteries if at all possible are breached.
INDUSTRIAL APPLICABILITY and ADVANTAGES The electric fence tester is easily constructed using (for example) stainless steel tubing for 390 durability and robustness, machined or moulded plastics bushes and handle, an internal wire to the earth contact at the end of the stick, and a small, simple, battery-less internal circuit board.
The tester is powered by the incoming electricity-no batteries are used-so reducing the risk of a"no pulse"negative result because the battery is flat.
395 The fence tester can be sealed tightly because no battery changing access is required.
The electric fence tester will facilitate the use of electric fences in the management of animals and the controlled feeding of pastures by making the process of fence maintenance and movement easier.
The invention provides a stick-like electric fence tester having a handy, multi-purpose 400 physical shape which raises the chance that a user will have the electric fence tester in his/her hand every time, day or night, that it is needed.
The components are cheap and assembly does not involve complex steps or alignment.
Finally, it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that 405 various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the following claims.