Published in June 2009 Australian Longwall Magazine
The trials tested data transfer between NLT’s Portable Wi-Fi Nodes and its voice over internet protocol (VOIP) phones.
The nodes have been developed in consultation with Queensland Mines Rescue as an extension of the company’s current Exia-approved Intrinsically Safe (IS) Wi-Fi Node.
The node is a wireless access point (WAP) using standard 802.11 protocols. It provides network access for Wi-Fi equipment such as two-way messaging through cap lamp and data capture. VOIP phones and personal digital assistants (PDA) will be used on the network when IS approved.
According to NLT Australia sales manager Chris Filmer the safety benefits of the portable node will become evident when used onsite by mines rescue personnel to establish communication in an emergency.
“Once a fresh air station is established, portable nodes will be placed out at specified intervals as the rescuers enter the hazardous zones. This will allow communication between rescuers back to the control point,” Filmer said.
The nodes can be used to re-establish a fibre network by bypassing damaged fibre cable between already installed hardwired nodes. The nodes can also be used in the everyday workings of a mine, supplementing current digital networks.
They will allow network coverage in development areas in the short term until hardwired nodes and antennae are installed.
The nodes will also allow coverage in areas of the mine where short-term projects, such as seal installations, are being carried out, increasing the safety of workers in the area and allowing them to communicate in real time.
An element of the trials at Newlands was to test the Wi-Fi communication with obstacles in the path of the communication. During the trial, two major obstructions were encountered – an area of discontinuity in the gradient of the roadway at about 12 cut through (about 500m from 6CT) and an Eimco was parked in the centre of the belt road at 8CT.
The access point (AP) to AP links were monitored using a laptop near the remote AP. “The laptop ran software which would try and push as much data through the link as possible, with the amount of real data passed through the link indicating the quality of the link,” Filmer said.
Data transfer node to node and node to VOIP phone in travel and belt roads was tested through steel machinery doors and seals, monitoring the megabits per second. Filmer said a consistent 1MB link was acceptable for VOIP communications, with anything lower deemed unacceptable.
“The Wi-Fi signal was capable of penetrating a steel vehicle door without a significant drop in performance, and will penetrate a double steel vehicle door, with a significant drop in performance but still establish communications.”
The tests showed acceptable signal strengths were achieved in node to node over 1300m, and node to VOIP phones up to 900m. Filmer said this was more than double the expected results.
“This reinforces the commitment by mines to install Intrinsically Safe-approved fibre networks underground will continue to have far-reaching benefits in safety and productivity,” he said.
He added that as technology progresses, more products will gain IS approvals, allowing services like cameras and live video streaming to use the fibre network. It will also allow data capture in real time from the longwall and development faces, permitting tracking of production and machinery optimisation from underground back to surface.
NLT said its next step would be to gain final IS approval. “As we are using the same internal electronics as its already approved big brother, this should be reasonably quick,” Filmer said.
“The nodes will be able to be utilised straight away in the mines with the NLT Digital System or other Wi-Fi applications needing a portable network.”
Filmer pointed out the product was a direct result of a requirement identified at an NLT focus group in 2007 and presented “another world first for NLT”
