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From: moroney@jon.DEC (Mike Moroney)
Newsgroups: net.consumers
Subject: Ion Generators (CRT's actually)
Message-ID: <2366@decwrl.UUCP>
Date: Thu, 30-May-85 00:06:38 EDT
Article-I.D.: decwrl.2366
Posted: Thu May 30 00:06:38 1985
Date-Received: Fri, 31-May-85 04:46:46 EDT
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
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>Sun workstations (ANY CRT for that matter) *is* a negative ion generator.
>Therefore it is unlikely you need to protect it from other ion generators.
>When I touch with my finger the screen of my Sun 100U workstation, there
>is a crackle of discharge of static electricity between my finger and the
>screen.  The reason for this is that every CRT works on the principle of
>beaming electrons from the cathode at the back of the CRT to the phosphor
>inside the screen, which means that the negatively charged electrons tend
>to charge the screen negatively, hence the screen becomes a generator of
>negative ions unless it is thoroughly grounded.  Most CRT's have the
>cathode at a very high negative potential and the phosphor grounded to
>minimize this effect (as you wouldn't want to get a serious shock from the
>alternative arrangement of putting the cathode at ground potential and
>raising the screen to a large positive potential).  The higher performance

Not quite true.  Almost all CRT's have the cathode at about ground and a
very large positive charge on the anode, since the alternative requires some
tricky electronics.  You don't get a shock from touching your screen since
glass is a very good insulator.  I don't know myself whether the static charge
that accumulates on the screen is from the negative electrons hitting the
screen or stray positive charge from the anode, since glass isn't a perfect
insulator.

"There's a madness to my method."			Mike Moroney
						..decwrl!rhea!jon!moroney