ESI 250-DA - DC Capacitance Measurement Power and Supply Considerations

2.
4.
4.
2
THINGS
TO
WATCH OUT
FOR
(cont.
ii)
A
grounded
dc
generator
cannot
be
used because one
of
the detector terminals
is
grounded.
Leakage
capacitance
and
resistance
from the
dc
source
to
ground
will
be
across
bridge
arms
and
may
cause significant
errors.
Most
line
operated dc
power
supplies
have
high
leakage
capacitance
to
the ac
line
and
enough
dc
lecikage to
be
objectionable.
An
insulated isolated
battery
is
the
recommended
power
supply.
If
a
variable
supply
is
needed the circuit
'
shown
below
can be
used.
This
circuit
has
a maximum
output
of about one
watt
so
it
will
not
exceed
the
rating
of any
bridge element.
E
The
standard
capacitor
is subjected
to
the same dc voltage as
the \inknown
capacitor.
As a result
the maximum
allowable voltage must
be limited
to
the
standard
capacitor
rating of
500
volts.
(Him
250-DA
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