Archived posting to the Leica Users Group, 2000/12/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
weber_leou@itri.org.tw jotted down the following:
> Why the CdS meter cell need power?
I believe that all CdS meters need batteries: the CdS cell regulates a
circuit by varying resistance as light falls upon it. A battery is needed
to drive the circuit and provide the voltage/current to vary, which then
drives the read-out.
Selenium meters generate voltage/current in response to infalling light and
do not require batteries, but function poorly in low light and -- if I
recall correctly -- are prone to "temporary blindness" by exposure to strong
light sources, causing them to give incorrect readings to weaker light until
they've "recovered" for a little while.
More info at:
http://www.picture.com/infocus/articleSelect.asp?MODE=GETSELECTED&ID=26
M.
- --
Martin Howard |
Visiting Scholar, CSEL, OSU | What boots up must come down.
email: howard.390@osu.edu |
www: http://mvhoward.i.am/ +---------------------------------------