From: John Woodgate
Subject: Re: Se Photocell "exhausted"?
Date: Mon, 23 Dec 2002 20:14:37 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 23 Dec 2002 21:17:51 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that J. Hill
wrote (in <3E0745C9.firstname.lastname@example.org>) about 'Se Photocell
"exhausted"?', on Mon, 23 Dec 2002:
>I have an old Weston lightmeter. It uses a Selenium (Se) photocell, and
>it does not need a battery. The meter isn't working, and in a
>photography forum someone said that the Selenium cell becomes "exhausted."
>I find this explanation unlikely because my understanding of the way
>photocells work tells me that the photoelectric effect is a property of
>the element Selenium. If the selenium is exhausted, where did the
>photoelectric effect go to? Has the Selenium transmuted into another
No, it oxidizes in air and maybe also picks up sulfur from sulfur
dioxide. And about 1 part per octillion* of mercury vapour will kill it
in short order.
The selenium-iron diode is more than a bit of a peculiarity, because
selenium is a group six element and has no business behaving like a
group 4 element, which all the legitimate semiconductors either are, or
pretend to be if they are compounds.
>Most importantly, if the Selenium really is "exhausted," is there a way
>to "revitalize" it? A dunking in Geritol, perhaps? :)
No, there's no way, AFAIK, of fixing it.
* slight exaggeration - only about six orders of magnitude.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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