[Test-Equipment] Re: H-P 400 series, addendum

[Fred Olsen]

> Gary Chatters wrote:
> The input connector to the E/EL is a BNC, so apparantly can only
> measure ground referenced signals.  The F/FL/GL have binding posts,
> so appear to be able to measure floating or differential signals.
> I haven't found anything in the specifications that I have about
> this difference.

Gary, under the heading of "no good deed goes unpunished" I'll have to
admit that I just don't remember.  ;<)
All of the tube versions have a ground-referenced input and a grounded
case, so if one needs to measure an elevated signal it's necessary to
'float the boat' with a ground buster.  CAREFULLY!

I no longer have the references here, but a quick check of the skiz, an
internal inspection, and/or a check of any manual reference to something
like "maximum input voltage above ground" or "may be floated up to ..."
rating should provide the answer.
That said, I THINK that they were all grounded input but I'm not
certain.  I don't recall a ground symbol at the 400F's 'low' input, so
perhaps it was circuit rather than earth ground.  The E/F/G(L) can also
operate from external +/- DC supplies, so ground isolation could also be
achieved with battery power or from ungrounded DC power supplies.  The
latter would require caution to not exceed the elevation rating of the
supplies.

Anyone else elaborate please?

Fred