Re: RFID tags in Arctic conditions?

> Passive sensors would be a stretch here, I don't think it'll work in this case. IIUC the distance can be tens of meters and the devices may have a thick layer of snow over them.

OK have a look again at that page

http://www3.sympatico.ca/colin.kydd.campbell/

Down around "question 40" they mention one of the benefits as being up to 20m range. Now, I've never designed an RFID system ("aha!" says the reader, and stops reading) but I suspect the range will depend more on the ariel design than anything else. I had a long chat once with one of the guys at http://www.telegesis.com/ who impressed me because where other blokes who'd try to sell me RFID and PICs with built in RF circuits were basically trying to sell a predesigned system, which they didn't really understand, he BEGAN talking at a level above me and I had to ask him several times to explain some concept which was, to him, basic. However I could tell he was not bullshitting. Telegesis offer a variety of radio comms solutions and one thing I learnt was to tailor the frequency to the situation (f'rex we wanted underground comms, turns out this IS possible, but not with the out-of-the-box solutions offered by microcontroller manufacturers etc). He was quite scathing about supermarket RFID tags, pointing out they've chosen a poor frequency - blocked by water, which most of their produce contains - and most people just use rectangular ariels, which are very directional, simply because they're well known; if you understand rectangular ariels' characteristics you can shoplift in relative safety by sneaking produce out of shops in certain orientations...

Anyhow, though I have no connection with Telegesis, I would suggest that if your budget can stretch to it, you discuss frequency choice and ariel design with them - or someone else who really understands the fundamentals of RFID and radio propagation, rather than just a reseller of an extant system.

Many Lithium batteries are spec'd down to -20C but will work further down. It is important to have an indepth conversation with an engineer from a company such as Duracell.

I have heard that sea emergency buoys used to use Li thionyl chloride, but not any longer, because it was found that after a few years of storage their peak current was much, much lower than in the lab tests when they were designed, so the flashing lights didn't flash, etc. THAT is the kind of nasty feature which will bite a project for extreme conditions like this.
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Nemo
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