Archived posting to the Leica Users Group, 2000/12/15
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Martin Howard wrote: > > 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/ +--------------------------------------- I have never noticed any temporary blindness in any of my selenium meters, but CDS meters were very prone to the problem which we used to call memory. Exposure to a very bright light source would cause the meter to read high for a few moments. JOhn Shick