[GreenKeys] Why Dual Coil Electromagnets?

[WA5CAB at cs.com]

There is another point which no one seems to have considered, the total 
magnetic circuit or the magnetic return path.

With a single magnet the magnetic circuit has no choice but to run through 
the armature hinge, which is  a high reluctance point.  Leakage flux in the 
region will cause stiction in the hinge bearings.  This is of little consequence 
in an ordinary relay but would act to decrease the range in a selector 
assembly.  With two magnets magnetically in series (never mind how they are connected 
electrically), the magnetic circuit can be mostly limited to the magnets, the 
selector armature and the bar or plate that the two magnets are mounted on.  
The remainder of the selector can be nonmagnetic if desired.

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
<wa5cab at cs.com> (Primary email)
<wa5cab at houston.rr.com> (Backup email)