[Gb-ccb] Caltech Backend Telecon Monday 07 July 4pm EDT

[John Ford]

Richard Lacasse writes:
 > All,
 > 
 > Martin Shepherd wrote:
 > 
 > > 
 > >>Seems quite attractive for noise abatement on the
 > >>digital signals.  If I recall the earlier meeting, we decided that the
 > >>optos were an unnecessary feature.  Maybe we should do it, since it is
 > >>pretty cheap and a definite win.
 > > 
 > > 
 > > That would be fine with me. However, assuming that by opto-isolation,
 > > we are talking about optic fibres, rather than opto-isolator chips and
 > > wires, the feasibility of this would presumably hinge on the
 > > availability of fibre-connectors with a metal screen going right up to
 > > the borders of the fibre. I'll see what I can find.
 > > 
 > 
 > All I had in mind were wires and opto-isolator chips.  A differential driver 
 > would drive a shielded twisted pair and at the far end there would be a 
 > termination network and opto-isolator chip.  No current has to flow through the 
 > grounds or power supplies of the end with the opto-isolator chip, so shield 
 > currents are minimal.

This is also what I had in mind.  

The optical fiber approach would also work, but would probably cost
more.  Maybe not too bad if we used the plastic AMP fiber system.  The
waveguide beyond cutoff ports in the RFI boxes are the way to go in
that case for shielding the penetrations.

I don't think we can isolate the 2 chassis, so it's probably not worth
the extra cost and trouble to use optical fiber for digital control
signals, rather opto-isolators are probably the way to go.

John