Generally it’s ok. Wifi handovers between APs are the main issue, our wifi clients have handover times of about 70 milliseconds or so normally which is fine with the engineering controls in place. A shift’s worth of operation usually involves a thousand or more handovers with no issues.
Our machines are run in exclusion zones, and every entrance to that area has a twin barrier setup that creates a “no man’s land” between machine and personnel. The width of that is dependent on the approach speed of the machine and the worst case scenario timeout of the safety system controlling that area. So if you stand on one side of the barrier and the machine comes at you full tilt and somehow loses wifi just as it hits its side of the barrier, it’s still guaranteed to stop before it hits you.
And yes, we rarely get interference, seeing as we usually operate several hundred metres underground. But you’d be surprised to see just how many wifi clients are floating around down there, most mining operations are heavily networked these days.
I was imagining one AP, not lots of APs as fixed infrastructure. Something about being underground and safety critical made me assume the place wouldn’t look like an office building.
70 millisecond handover is pretty good, I assume 802.11r? If you control the clients then all is good and fixable, but if they’re (thunderclap) external vendor controlled (lights flicker) I imagine some will keep trying to hang onto old out-of-range APs for too long.
The area we cover is usually up to a kilometre or two long.
We just use good old 802.11g. Our wifi clients are Moxa industrial units and I’ve found that they’re pretty consistently compatible with all sorts of AP hardware that sites use. Sites with Cisco hardware and controllers give us the most grief, Cisco loves Cisco and nobody else, of course.
As wifi is pretty much line of sight underground (it doesn’t penetrate rock), handovers usually mean there’s only one “best” new AP to choose from, the rest are down in the noise floor. There can be some interesting/annoying overlap on intersections. The machine travels past an intersection and is suddenly exposed to a strong AP just around the corner, so it hops to that… and that AP almost instantly disappears as the machine passes beyond the intersection and it gets blocked by the tunnel walls. That really gives the client a workout and is just usually the result of poor AP placement.
Mine sites are constantly adding and moving APs around, most places have a few hundred of them in their production areas. Line of sight range is about 50-100 metres for each AP, and tunnels are never straight for much more than that distance so there ends up being a lot of hardware. Panel antennas to extend range muck up the handovers as the sudden drop in the signal as you pass into the backlobe often doesn’t give the client enough time to scan the channels and find a new AP. 802.11r would help but we deal with a huge mishmash of AP hardware across sites so we stick with omni antennas to keep it as simple as possible haha
Mining might also be a better suit to the technology is general. No interference problems from neighbours :)
Do you get timeout/watchdogs trips all of the time or is it pretty reliable?
Generally it’s ok. Wifi handovers between APs are the main issue, our wifi clients have handover times of about 70 milliseconds or so normally which is fine with the engineering controls in place. A shift’s worth of operation usually involves a thousand or more handovers with no issues.
Our machines are run in exclusion zones, and every entrance to that area has a twin barrier setup that creates a “no man’s land” between machine and personnel. The width of that is dependent on the approach speed of the machine and the worst case scenario timeout of the safety system controlling that area. So if you stand on one side of the barrier and the machine comes at you full tilt and somehow loses wifi just as it hits its side of the barrier, it’s still guaranteed to stop before it hits you.
And yes, we rarely get interference, seeing as we usually operate several hundred metres underground. But you’d be surprised to see just how many wifi clients are floating around down there, most mining operations are heavily networked these days.
Wow, that’s really interesting, thankyou.
I was imagining one AP, not lots of APs as fixed infrastructure. Something about being underground and safety critical made me assume the place wouldn’t look like an office building.
70 millisecond handover is pretty good, I assume 802.11r? If you control the clients then all is good and fixable, but if they’re (thunderclap) external vendor controlled (lights flicker) I imagine some will keep trying to hang onto old out-of-range APs for too long.
The area we cover is usually up to a kilometre or two long.
We just use good old 802.11g. Our wifi clients are Moxa industrial units and I’ve found that they’re pretty consistently compatible with all sorts of AP hardware that sites use. Sites with Cisco hardware and controllers give us the most grief, Cisco loves Cisco and nobody else, of course.
As wifi is pretty much line of sight underground (it doesn’t penetrate rock), handovers usually mean there’s only one “best” new AP to choose from, the rest are down in the noise floor. There can be some interesting/annoying overlap on intersections. The machine travels past an intersection and is suddenly exposed to a strong AP just around the corner, so it hops to that… and that AP almost instantly disappears as the machine passes beyond the intersection and it gets blocked by the tunnel walls. That really gives the client a workout and is just usually the result of poor AP placement.
Mine sites are constantly adding and moving APs around, most places have a few hundred of them in their production areas. Line of sight range is about 50-100 metres for each AP, and tunnels are never straight for much more than that distance so there ends up being a lot of hardware. Panel antennas to extend range muck up the handovers as the sudden drop in the signal as you pass into the backlobe often doesn’t give the client enough time to scan the channels and find a new AP. 802.11r would help but we deal with a huge mishmash of AP hardware across sites so we stick with omni antennas to keep it as simple as possible haha