Gabriel Kiarie
July 27, 2023
Keywords: Time domain reflectometer, Protected Areas (PAs), Human Wildlife Conflicts (HWCs)
Data Collection at Ol Pejeta Conservancy for the Raspberry Pi TDR
Project
Electric fences are used to create Protected Areas (PAs) to help preserve
biodiversity, provide habitat to wildlife, and
reduce Human Wildlife Conflicts (HWCs). Electric fences are prone to faults that
affect their operation. The most common
causes of faults in electric fences include broken wires, overgrown vegetation
touching the fence, poor grounding, bad
connection, branches falling on the fence, and broken insulators. The faults need to
be detected and repaired for the
effective performance of the fences. The most common method of detecting faults in
an electric fence involves conducting
routine measurement of the fence voltage. If the voltage falls below a given value,
the fence is said to be faulty. To
locate the fault, an authorized person is required to walk along the fence measuring
the voltage of the fence. The
voltage drops continually up to the faulty point and then remains constant or drops
to zero past the fault. This method
of detecting and locating faults is inefficient, time-consuming, and laborious since
the fences are exceptionally long.
At the Centre for Data Science and Artificial Intelligence (DSAIL), we are
developing a Raspberry Pi based Time Domain
Reflectometer (TDR) to detect and locate faults in electric fences. The system works
using the principle of time domain
reflectometry. Read this blog to learn more about the TDR. The TDR has a time
domain reflectometry algorithm that
processes sampled signals to detect and locate faults in electric fences. The
algorithm was developed using data
collected from experiments conducted using two 15 m copper cables and the Raspberry
Pi TDR. Open circuit and short
circuit faults are common in electric fences. A short circuit fault occurs when a
live wire comes into contact with a
neutral wire. An open circuit fault in electric fences is caused by the breakage of
wires due to loose connections,
vandalism, or damage caused by animals. Breakage of electric fence wires will most
likely eventually result in a short
circuit fault. Open circuit and short circuit faults were simulated on one end of
the copper cables and a step signal
was applied to the other end. Signal samples were taken at the input using the TDR
and saved on the storage of the
Raspberry Pi.
Figure 1: The Raspberry Pi TDR.
Figure 2: Setup to simulate open circuit and short circuit faults using two 15 m
copper cables and the Raspberry Pi TDR.
The time domain reflectometry algorithm is based on change point detection using the
method of discrete gradient. The
performance of the time domain reflectometry algorithm was evaluated using electric
fences. A 108 m long section of the
electric fence at the Dedan Kimathi University of
Technology Wildlife Conservancy (DeKUTWC) and a 280 m long section of
an electric fence at Ol Pejeta Conservancy were
used. Two strands of the electric fence sections were used to simulate
open circuit and short circuit faults and data was collected from these experiments.
The time domain reflectometry
algorithm was able to detect and distinguish between the open circuit and short
circuit faults and predict the distance
to these faults within ±1.52m of the actual distance.
The Raspberry Pi TDR needed to be evaluated using a longer fence to ascertain its
applicability in monitoring long
fences. It is for this reason that we decided to visit Ol Pejeta Conservancy and
conduct experiments using a
longer
electric fence. Our goal was to simulate faults with a 1 km long fence and collect
data.
On 26th April 2023, we started the trip to Ol Pejeta Conservancy from
Dedan Kimathi University of Technology (DeKUT) at
around 8:30 am. The team comprised Mr
Mathenge
(a technologist at DeKUT), Dishan Otieno (an
undergraduate research
assistant at DSAIL), and I - Gabriel Kiarie, a
research intern at DSAIL. We arrived at Ol Pejeta at around 10:00 AM and
headed for the Conservation Tech Lab to meet Mr
Kennedy and brief him on our plans. We left the lab for the section of
the fence that we were to use for the data collection exercise. We were joined by a
ranger and a fence man on the way.
When we arrived at the fence, we began by inspecting it to assess its suitability
for use to conduct the experiments.
The fence was suitable and the fence man disconnected the energiser from it to allow
us to conduct the experiments. The
Raspberry Pi TDR was placed in an adapter box, connected to the top two strands of
the electric fence, and powered ON.
(a) |
(b) |
Figure 3: (a) Connecting the Raspberry Pi TDR to the electric fence; and (b) the
Raspberry Pi TDR connected to the
electric fence.
Open circuit and short circuit faults were simulated at intervals along the fence.
Open circuits were created by
disconnecting the junctions created at two of the fence’s segments. The end of the
fence’s wires was also treated as an
open circuit. Short circuits were created by connecting the two electric fence
strands using a conductor. The first
short circuit was created 12 m from the start of the fence. The other short circuits
were created at 30 m intervals from
the 12 m mark except the last one which was 10.7 m apart from the second last short
circuit. Figure 3 shows how a short
circuit was created.
3 open and 33 short circuit instances were created. For each instance, 20 files of
sampled signals were collected and
saved. Each file contains about 0.3 ms long sampled signal. In total, 720 files were
collected. The files will be
analysed and the results used to assess the performance of the Raspberry Pi TDR. The
section of the fence used was about
952 m long.
Figure 4: A conductor connected to two electric fence strands to create a short
circuit.
The data collection exercise was successful despite us racing against time and worrying about the impending rains. Being in nature, we also got to enjoy what it had to offer. I, in particular, was fascinated by the sight of a dung beetle rolling what seemed to be a perfectly moulded ball. For a moment I thought we do not give enough credit to the intelligence of some of the animals. We also got a chance to see an elephant from a very close distance.
(a) |
(b) |
Figure 5: (a) A dung beetle rolling a ball; and (b) a closeup snapshot of an elephant.
