Engineer not sitting on the fence with his invention

2015-08-13 17:52
Draadsitter (Picture: Ernst Pretorius)

Draadsitter (Picture: Ernst Pretorius)

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Johannesburg – A few years ago engineer Ernst Pretorius woke up at 02:00 with an idea.

Horrific images of his friend's dairy cows with their tendons hacked and meat cut out of them while they were still alive, inspired him to invent a special device, the draadsitter (fence sitter).

Thieves had been targeting his friend's cows for meat, he said. 

The draadsitter is a box, about the size of a man's hand, attached to fence posts between 100m and 200m apart. It has sensors to detect movement and tampering. 

Pretorius was recently awarded his first contract to install it locally, on a 30km stretch of fencing at the world's biggest rhino farm. If it works there, the owner wants to install it at several other farms.

"It’s such a simple principle. It’s just amazing nobody thought of it in the past," Pretorius said.

He has had it patented in 58 countries and demonstrated it at a Zambian copper mine and the Kruger National Park. People in countries, including Ireland and Australia, have shown interest, he said.

'Miracles still happen'

"I funded it out of my savings and retirement money and that was running out. The day I got the deposit from the rhino farm was the last day I had to pay the deposit for the patents, so miracles still happen in this day and age," he laughed.

The plan is to start supplying it to the public early next year.

Pretorius believes it has uses globally, given the need to secure borders and protect wildlife.

The units attached to the fence posts cost R6 600 each. The base unit, which sounds the alarm and indicates where along the fence tampering has taken place, costs about R10 000.

This meant that securing a 10km stretch of fence, with each unit 200m apart, cost about R340 000. Each unit was powered by two AA batteries, which last up to three years.

Pretorius plans to combine the unit with a drone, to be hidden near the fence. As soon as someone tries to scale the fence, the drone automatically takes off and sends images back to a control room.

Another feature he hoped to introduce was incorporating an algorithm which would allow the unit to determine whether someone was climbing up the fence, down the fence, cutting it or bumping against it, purely by the sound detected.

The system was cheaper and more effective than electric fences and optic fibre systems; had a tamper alarm; could detect fires and had an alarm for when the batteries were running low, he said.

Read more on:    johannesburg  |  technology

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