Re: [Rollei] OT Screws

[Jon Hart <jonhart51 >]

Richard,
     Thank you for an enlightening treatise.
D'Arsonval movements were once pretty common in all
types of meters, audio to automotive. I suppose they
are still used in analog meters, aren't they? I agree
the Westons are well-built if a bit perplexing without
the instructions. The easiest high-quality meter I
have used would have to be the Norwood Director Types
B and C. I have never taken them apart (and have no
intention of doing so),but I take it they are built
along the same lines as the Weston. My McKeown's is
rather vague regarding years of production for Weston
meters. Do you happen to know the era the IIs were
produced in? Also just how common were they (how many
people used them) in your opinion?

Jon
from unusually cold Deepinaharta, Georgia 

- --- Richard Knoppow <dickburk  > wrote:
>   The magnet is part of the meter. A meter is a
> small electric motor. The
> type in the Weston light meter is known as a
> D'Arsonval movement, one of
> the most sensitive and accurate types.   It has a
> coil of very fine wire
> through which the current from the Selenium cell
> flows. The current in the
> coil reacts with the magnet, rotating the coil
> around its pivot and moves
> the pointer which is attached to the coil.
>   The stronger the magnetic field, the more
> sensitive the meter.
>   The meters in Selenium cell light meters must be
> very sensitive if the
> meter is to be linear.
>   The magnets in these meters have a slightly
> eccentric pole pieces (the
> part near the coil) in order to shape the scale.
> 
>   Its very important in working on meter movements
> to avoid getting iron
> filings into them. You would be surprized how
> plentiful little chips of
> magnetic metal are. Its like getting dust on a
> negative. Once a bit of
> metal gets into the meter movement it may be
> painfully difficult  to get it
> out again.
>   Weston was mainly in the electric meter business
> and made very high
> quality ones.
> 
> ----
> Richard Knoppow
> Los Angeles,Ca.
> dickburk  
> 

__________________________________________________
Do You Yahoo!?
Talk to your friends online with Yahoo! Messenger.
http://im.yahoo.com

------------------------------