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Accidental PLB activation

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Post  Col Douglas Sun Aug 06, 2017 8:15 am

Had an incident yesterday that is worth reporting.

We are detecting in the Pilbara area at the moment, and while out in a semi-remote area my PLB activated. This was unknown to me at the time because my PLB in kept in a case on my harness and the flashing strobe was not visible. The emergency services contacted my son who is second on the notification list, because they couldn’t contact my wife (first on the list). She is out here too.
Naturally the call frightened the hell out of my son, who asked the ES to delay the search until he could contact his mother (he knew that we were out here with another couple, and were all in constant radio contact, and I would only activate the PLB as the absolute last resort). They were not happy to wait but they gave him a few minutes and he managed to contact my wife (back at our camp) who was then able to radio me and I turned off the PLB.

The device is a KTI SA2G with GPS. KTI says that there have been other cases of PLBs being activated by metal detectors, but only if the device gets too close to the coil, especially underneath it. They say that the only way to prevent this is to wrap the device in some sort of ferrous foil. The issue apparently applies to all brands of PLBs.

After thinking about what may have caused the issue, I realised that when I’d finished detecting in one area, and prepared to move to another area I had inadvertently either not turned off the ZED (or accidentally switched it on again) when it put it in the back of the Landcruiser; then when throwing my harness on top of the machine the PLB must have been near the coil (possibly on top of it).

I’ve heard of GPSs being destroyed by getting too close to a coil, but was unaware of this potential problem with PLBs.

What did impress me about all this was how quickly the Emergency Sevices responded and how accurately they were able to pinpoint my position. My son and wife also commented on their calm and helpful professionalism when they were contacted.

Hope this is of interest.

Col

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Post  goldtalkleonora Sun Aug 06, 2017 8:57 am

Hi Col, that's a very interesting post. How could we confirm the detector setting off the PLB??...Minelab perhaps?? Just something i would like to follow up and get the word out to people.
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Post  Guest Sun Aug 06, 2017 9:19 am

Certainly handy to know. Will be sure to keep them seperate where needed.

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Post  Col Douglas Sun Aug 06, 2017 9:38 am

goldtalkleonora wrote:Hi Col, that's a very interesting post. How could we confirm the detector setting off the PLB??...Minelab perhaps?? Just something i would like to follow up and get the word out to people.

G'day Tony,

I'm almost certain the metal detector was the cause, because when I moved to the new site to detect, and I took the Zed out of the vehicle, it was turned on. At this stage of course I didn't know that the PLB had been activated but I just reprimanded myself for not turning off the machine.

When the PLB is activated there is a flashing strobe, but I have it stored in a little case so I couldn't see that. I have since wrapped it in aluminium foil. The KTI tech said this was not sufficient and that it need to be wrapped in a ferrous type foil. I still think the aluminium foil, although maybe not preventing it from activating, would (you would think) attenuate its transmission signal.

I think it has to be very close to the coil for an activation to occur. However the KTI tech seemed to be well aware of the problem, though no one seems to have mentioned it. Maybe one solution would be for KTI to line the little case that they provide with the device with an appropriate foil.

Col

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Post  Digginerup Sun Aug 06, 2017 10:17 am

Good post, any issue with accidental activation of PLB by metal detector operation is a subject that certainly requires investigation, other than the fact accidental activation's would be a waste of valuable resources and must be a real pain in the ass for emergency services what happens in terms of charges and costs in an accidental/false activation, please keep us posted if you can get any info from the PLB people or minelab.

Wayne. cheers
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Post  peterinaust Sun Aug 06, 2017 7:46 pm

Wow, thanks for posting. I keep my PLB at the back of my harness in the little pouch that comes with the harness, the battery carrier for the GPX I think.
I'll will be following this post if any more comes out. In the mean time will be extra care full. I would never have thought that this could happen!

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Post  Nightjar Mon Aug 07, 2017 3:03 am

Maybe this very important post should be pinned until such time as a positive solution is found to prevent this happening?
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Post  Col Douglas Tue Aug 08, 2017 6:51 pm

I have contacted KTi and have received a response.

This is what I asked:

Several days ago while prospecting with a metal detector in the Pilbara in the north of Western Australia my PLB (a KtiSA2G) activated without any input from me. Fortunately the Emergency Services was able to ascertain that the activation was accidental before launching a rescue operation.

I contacted KTi by phone after the event for advice on what I should do. The tech advised me that activation of a PLB with a metal detector is quite possible and that KTi in fact had done some tests using a metal detector confirming this and he further said that the only solution was to wrap the device in a ferrous type foil (aluminium foil is not sufficient).

I've posted the incident on several prospecting forums and it has generated quite a bit of interest.

For the purpose of accuracy could you give me the latest information that you have regarding the possible activation of a PLB by a metal detector. In particular:

1. How close can the PLB be to the metal detector coil (above and underneath) without the possibility of activation?

2. What is the best way of protecting the PLB?

3. Any other information that would be of interest to a metal detector operator when using a PLB.

I will post your responses so that prospectors carrying a PLB and using a metal detector are aware of the precautions that they have to take.

Thanks for your anticipated response.

Col



This is the response from KTi:


Hello Col,

We have not conducted detailed research into this matter however we are happy to provide some assistance.

The safe distance from metal detector equipment will depend on the emitted field strength, pulse width and pulse rate. It appears that some modern metal detectors emit extremely strong magnetic fields and we understand that all three of the above factors are user-programmable in some devices.  Also the field directionality may vary significantly between devices as will stray radiation along wiring to other parts of the metal detector and battery.  Our very limited testing of one specific model did demonstrate that the field strength was considerably stronger 'beneath' the search coil than 'above' or to the sides. Field alignment is also a very significant factor and worst case must be considered for reasons of practicality.  We have no knowledge of the emission characteristics of specific devices and recommend you refer to data applicable to the equipment you use.  The one particular Codan unit we tested was capable of activating a PLB within 300mm beneath the search coil with factory default settings.

In terms of our general recommendation for this class of equipment: Considering a worst case scenario where pulses are repetitive and where pulse width / repetition rate fall in the region of 4.5 microseconds to 35 microseconds we recommend a maximum field of 50 microtesla.  Pulses outside this window are far less likely to be problematic however we recommend avoiding exposure to alternating fields exceeding 1 millitesla and static fields exceeding 10 millitesla. Whilst these figures tend toward conservative it should be noted that magnetic fields can easily be distorted and thus effectively magnified by the presence of other nearby metallic objects, including non-ferrous materials.

Enclosing a PLB within a magnetically shielded container should provide significant improvement however we have no numeric values to offer.

Regards,

Mark
.


Make of it what you wish, but in summary, there is no doubt that a metal detector can accidentally activate a PLB, and I can only suggest we should keep our PLB as far away from the coil as practicable.

Col

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Post  sandy2010 Wed Aug 09, 2017 1:08 pm

Interesting post.......
Surely it would be easy to install an audible alarm system similar to what we have on our mobile phones ????

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Post  GoldnQuartz Wed Sep 06, 2017 10:33 am

Very interesting for sure.

Placing the PLB in an iron cage with stop the electro-magnetic effects of the pulse induiction EM machines. This shielding is called a "Faraday Cage"

You should be able to fashion one easily by getting a thermo-insulation bag, the shiny foil-lined type for cold storage from supermarkets etc, and cutting and fashining something out of that but it will need to enclose the PLB completely.
Another alternative - also light weight, is to use some wire fly screen mesh, stainless steel, or whatver, you'll have to sew the panels together using a strand or two of the wire, and I would then line it so the device dsoesnt contact the sides, but you should be able to make it so you can still clip it on.

If that helps.

Cheers, GnQ

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Post  Guest Thu Sep 07, 2017 12:34 am

I have a KTI PLB for kayaking. What's reassuring is the fact that you received a detailed response from KTI rather than a generic "Every customer is important to us.........." palm off. An Australian company as well.

You'll probably want to take the PLB out of it's shielded case if you decide to use one before activating as the signal to the satellite may also be blocked.

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Post  adrian ss Wed Sep 13, 2017 9:54 pm

Hmmmm. I just read this topic.
I purchased a KTI SA2G-GPS a while ago, Has not arrived yet.
So did I choose incorrectly?
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Post  Guest Wed Sep 13, 2017 10:14 pm

adrian ss wrote:Hmmmm. I just read this topic.
I purchased a KTI SA2G-GPS a while ago, Has not arrived yet.
So did I choose incorrectly?

I looked at other units and decided the KTI was a good choice. Other brands may have the same sensitivity.

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Post  adrian ss Thu Sep 14, 2017 8:00 am

Just received word from AUPost that it will be delivered today.
This thread has been useful in that I now know to be wary of inadvertent activation due to EMI. scratch


PS:
Well there ya go; 5 mins after I posted,  AUpost delivered it to my door.

Hmmmmm ?
Somebody had  partially opened the box at one end without breaking the seal.

Double Hmmmmm :
The whistle is missing. Not a world ending disaster but annoying
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Post  bowerbird Fri Sep 15, 2017 5:39 pm

Hi Adrian ,did you get the lanyard with it ? the whistle is in the snap connector, very small , cheers BB

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Post  adrian ss Sat Sep 16, 2017 7:46 am

Well there ya go. Yep it is small allright.
Thanks BB
Accidental PLB activation Rscn2716
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Post  mintcar Wed Oct 04, 2017 6:30 pm

Hi all I have only just arrived at this post sorry for delay, I have had a Kti plb since May 2015 in June 2016 in back country the rescue chopper arrives I was using a 7000 the plb was in my backpack it had activated its self, I contacted kti and returned it to them in Aust and they contacted minelab to do some tests they returned it to me and said the kti should not do that again I am very careful not to have them close to each other hope this helps

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Post  gef50 Tue Mar 27, 2018 9:00 pm

I know for a fact that a HF transmitter 80 odd watts can kill a GPS unit ... did it to my mates ... accidental of course ..
in close proximity to the antenna
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