Solartron 1260 - Effect of Sweep on Generator Loading

NEXT
...select
the
next
frequency units...
...i.e,
kHz...
...key in a
maximum
frequency
value of...
...900 (kHz)...
...and enter it.
"SWEEP LIMITS”
is displayed to
show
that
entry is
complete.
The
sweep is now set,
and a
series of
measurements can be
made.
7.1.1
Effect
of Sweep
on
Generator
Loading
Before
actually
commanding
a
sweep it is wise
to consider
how the
variation
in drive
frequency
will affect the
generator
loading.
In the
present example a
constant
drive
amplitude
of IV is used.
The
impedance
of
the
item
under
test
decreases
with
frequency,
therefore
we should
look at the
loading
at
900kHz. At
this
frequency the
reactance
of the
capacitor
(
=
1/coC)
~
17. IQ.
The
effect
of the lk
Q. parallel
resistance
is
negligible,
so
the
impedance
of the
item under
test
-
17. 7ft. The
current
drain on
the generator
output will
thus be
around
56.5mA,
which the
generator
can
supply
(max.
ac
current
output=
60mA).
To keep the
test
current
within
reasonable
bounds at
the higher
test
frequencies a
lower
drive
voltage
should be
selected:
two or more
consecutive
sweeps, each
covering
part of
the
test
band and
using
a
suitable
drive
voltage, can be set up
with
a
learnt
program (See
Chapter
11).
You can,
of course,
select
a
constant current
drive, by
entering
[current]
under the
GENERATOR
TYPE.
Then,
with the present
item under test,
you
should
consider
the
current at
the
low frequency
end of the
sweep: the
impedance
of the
item at
100Hz
approaches
lkfi,
therefore the highest test
current
which can
be obtained,
at
this frequency,
is
3mA. (The
maximum
drive voltage
is
3V.)
3.18
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