Overview

Fence Hawk
Fence Hawk – click for larger picture.

The Fence Hawk™ is designed to work with ANY electric fence charger commercially available in the world.

We certify it for up to 25,000 volts, which is more than any charger on the market puts out, but we’ve tested it successfully at 40,000 volts.

It will also work on fences that are plugged directly into the power grid, up to 220 volts.

Other fence monitors measure the average voltage per second (hertz). A change in the hertz (cycles/second) will give a different voltage reading or output. This type of voltage measurement is extremely susceptible to false alarms and is only accurate for the hertz or cycle that the instrument is set to.

Lightning strikes on or near a fence or array monitored this way will often generate a false alarm.

Any alarm system that generates false alarms is worse than no alarm system at all.

Fence Hawk PCB – click for larger picture.

The Fence Hawk™ measures the absolute voltage on the fence. It doesn’t matter if it’s a 3,000 volt rabbit fence or a 15,000 volt rhino fence – the Fence Hawk works on all electrified fences.

Since the voltage pulse only lasts 50 to 100 microseconds (0.00005 to 0.00010 seconds), this is a good trick. But because we can do this, we know when the fence is being shorted, grounded or jumpered.

This also allows the Fence Hawk™ to give a separate warning for low voltage conditions, which are almost always caused by vegetation.

There are some other conditions that can cause low voltage, too, but the point is this: low voltage conditions should not generate a full-scale alert, which would be the equivalent of a false alarm.

The voltage drain from vegetation will still allow the fence to give a painful shock.

The goal here is to alert someone to clean the fence before the voltage drain makes the fence ineffective.

This method of monitoring also prevents false alarms from nearby lightning strikes. A Fence Hawk™ can take a half million volt lightning strike – directly on the fence – without damage, and without generating a false alarm. No other electric fence or high voltage array monitor can make this claim.

That’s why our warranty includes lightning damage, and does not require lightning protection on the fence or array.

Technical details below.

OPERATION

Input Power Requirements: 12 to 24 volts DC.

Power Usage: The input power usage is 0.3 watts. Current consumption is 0.025 amps at 12 volts.

High Voltage Input Pulse: Accepts up to 25,000 volt pulse. If lightning strikes the fence the Fence Hawk will survive over a half million volt pulse without damage.

Pulse Width Accepted: 50 microseconds to 10 milliseconds.

Pulse Period Accepted: 5 hertz to 0.5 hertz (from 5 pulses per second to 2 seconds between pulses).

Maintenance Output: Contact closure rated 0.5 amps @ 60 volts DC and 0.5 amps at 100 volts AC. This is sufficient for most piezo sounders. This maintenance output activates when the high voltage input pulse level drops below the “set-point level,” which is variable from 1.5 k-volt to 8 k-volts. This is sufficient for most fence and array applications.

Voltage Loss Output: Contact closure rated 0.5 amps @ 60 volts DC and 0.5 amps at 100 volts AC. This is sufficient for most alarm and/or communication circuits, but most sirens will require a power contact or relay. This output activates when high voltage input pulse drops below 0.2kv (200 volts).

Automatic Reset: All circuits will reset when the fence voltage returns to normal operating levels.

On some installations, a latching circuit or latching relay may be desired to hold the alarm “on” until manually reset. Please refer to the installation booklet for more details. The manual is at the bottom of this page.

INDICATOR LIGHTS (LEDs)

Fence Hawk Indicator Lights
Fence Hawk Indicator Lights – click for larger picture.

Green LED- Flashes for every high voltage pulse that is a higher voltage than the set-point or maintenance required voltage (normal operation).

Yellow/Amber LED – When solid on, indicates that the high voltage pulse is lower than the adjustable set point voltage, and your fence requires maintenance. The low voltage contacts will also close. Clearing the grass and weeds from the fence usually clears this indication (weed alert alarm).

Red LED – When solid on, indicates that the high voltage pulse has dropped below effective levels (200 volts) and immediate action should be taken to preserve the effectiveness of your perimeter fence (alert condition – alarm).

TERMINAL CONNECTIONS

Fence Hawk Connector View
Connector View – click for larger picture.

Terminals 1 & 2 are the “No Voltage” contacts and correspond to the REDindicator (Normally Open, Single Throw).

Terminals 3 & 4 are the “Low Voltage” contacts and correspond to the YELLOW indicator (Normally Open, Single Throw).

Terminals 5 & 6 are the power input and need to be connected to a power source of 12 to 24 volts DC. Any 12 volt DC power source with a minimum of 50 milliamp (0.050 amps) rating. Polarity protected. If unit is not working, check polarity at these terminals.

RETAIL PACKAGING

Fence Hawk Packaging
Fence Hawk Retail Packaging – click for larger picture.

The boxed unit measures 7 1/2 inches (190 mm) X 5 5/8 inches (145mm) X 2 7/16 inches (65 mm)

The boxes are printed to catch the eye and are readable in any stacking or shelving configuration.

An installation and operation booklet is included in each package.

A circuit layout is printed on the inside of the unit cover.

USAGE

This high voltage sensor – Fence Hawk™ RG-7781 – takes an electric fence charger pulse and analyzes it for peak voltage, pulse width and period.

The Fence Hawk™ can accurately measure voltage pulses from almost any fence charger or pulse source, including the spark plug voltage on a gasoline engine.

The design algorithm used in this device was determined for stability, longevity, and reliability under a wide set of usage parameters. (Patents pending.)

The green light will flash for every pulse that is higher than the maintenance voltage. The maintenance threshold voltage is set at 6 kv at the factory and is user-adjustable.

The “maintenance set-point voltage” is usually set about 1 kv to 2 kv less than the fence energizer output. Then creeping weed growth will be noticed before the fence voltage drops below an effective level.

This maintenance voltage is adjustable from 1.5 kv to 8 kv. If flora (grass, bushes, limbs and leaves) partially load or partially short out the high voltage and reduce the effective pulse voltage to below the adjustable maintenance level voltage set point, then the yellow LED will light and the maintenance contacts will close.

The maintenance function (Weed Alert™) has approximately a 100 second delay, to avoid false alarms.

If the grass or limb is blown off or removed and the charger pulse voltage is restored, then the maintenance alarm will reset itself and the maintenance contacts will open.

When the pulse voltage drops or becomes less than 200 volts, the “no voltage” contacts will close. There is a built-in delay of 6 seconds before the red LED will light and the alarm contact closes, to eliminate false alarms from spurious voltage spikes.

The algorithm used in this circuit also eliminates false alarms from reverse pulses that may occur from close proximity lightning strikes. If the voltage drop is intermittent the circuit will reset itself without generating an alarm. (For some security applications, a latching relay contact may be desired on some output relays.)

This device is designed for long life with ease and consistency of operation. All units have a one (1) year warranty – that includes lightning damage.

USER GUIDE

The Fence Hawk™ user manual in doc format (4 MB)
- http://perimetersecurityarray.com/images/fencehawkmanual.doc

The Fence Hawk™ user manual in pdf format (1 MB)
- http://perimetersecurityarray.com/images/fencehawkmanual.pdf

WARRANTY

Each unit is unconditionally guaranteed for a period of one year (12 months) from the date of retail sale. Sales slip shall accompany each returned unit. The warranty INCLUDES lightning damage. We reserve the right to either repair or replace the unit, at our discretion.

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