Section
111 Model 34SSA
frequency,
and use of the
Auto-Cal and High
Resolu-
tion
modes.
When
the
Sample Rate buttons
are pressed,
the
display rate of the
reading are
changed. By depress-
ing the
Decrease 2 button on the
front panel, the
display rate can be
decreased.
Each time this button is
pressed, the
display rate is
divided
by
two. The rate may
be
divided
a
maximum of six times for
a display rate
of
1/64
of
the maximum
rate. The 3455A
can be reset to
the maximum
rate by depressing
the maximum button,
after
the
display rate has
been decreased.
Table 3-1 gives
the maximum number
of readings the
instrument can
display on the front
panel, in local
operation.
Table 3-1. Maximum
Front
Panel
Reading Rates.
Func
Function
High
Resolution
Auto
Calibration
Maximum Sample Rate
Maximum Sample
Rate
DC
Volts
ON ON
3
readings/sec
(60 Kzl
2.5 readings/sec
(SO Hz)
OFF ON 5 readings/sec
(60
Hzl
3.5
readings/sac
150 Hz)
ON
OFF 6 readings/sec
160 Hz)
5
readings/sec
ISO
Hz)
OFF OFF 24 readings/sec
(60 Hz)
22 readings/aec
(50
Hz)
Ohms
ON ON
2
readir>gs/sec
160 Hz)
1.8 reading/sec
(50 Hzl
OFF ON 45 readings/sec
(60 Hz)
4 readings/sec
150
Hzl
ON OFF
3
readings/sec
(60 Hz)
2.5 readings/sec
ISO Hzl
OFF
OFF 12 readings/sec
(60
Hz)
1 1 readings/sec
150 Hz)
AC Volts Not
Applicable
ON 1.3 readings/sec
(60 Hz)
1.1 readings/sec (50 Hz)
Not
Applicable
OFF 1.3 readings/sec (60
Hz)
1.1 readirtgs/sec (50 Hz)
Fast
AC Volts
Not
Applicable
ON 4.5 readings/sec
160 Hzl
3.5 readings/sec
ISO
Hz)
Not
Applicable
OFF
13
readings/sec
(60
Hz)
12 readings/sec
(50 Hz)
|
3 3B.
Auto Range.
3-39.
The
AUTO RANGE feature of the 3455A can be
used
to
automatically uprange and
downrange
the in-
strument to the
optimum range. This action takes place
when an input measurement is taken. Upranging is dene
when
the reading is ISO^e of full
scale and downranging
at 14^0 of full scale. The Auto Range operation can be
observed by applying 1
.4 volts
to the input of the
34SSA. The range selected by the
instrument is the
I
V
range.
When
the input
voltage exceeds 1.5 volts, the
345SA upranges to the 10 V range.
When
the input
voltage
is decreased
below 1.4 volts, the 1 V range is
again
selected. The
uprange
points, the
downrange
points, and the accuracy of the instrument should be
kept in mind
when
making a
measurement. Time-
varient inputs may cause the 345SA to constantly
uprange and
downrange.
If this happens, manually set
the instrument to the
higher range.
3-40.
Measurement
time
may also change, when the in-
strument is
in
the Auto Range mode. If the instrument is
not on the optimum range, a reading is taken and the
34S5A
will
either
uprange
or
downrange. Another
reading is then taken and if the optimum range has been
found the reading
will
be displayed. If not, the instru-
ment
continues
to
uprange
or
downrange. A reading
is
taken on
all intermediate non-optimum ranges until the
correct range is found. The measurement time on each
range
should
be
added
to the total
measurement time.
3-41.
GUARDING.
3-42.
Common-Modi Voltagoo.
3-43.
Common-mode voltages
are
those which
are
generated between the power line ground point of the
source and the LO input and power line ground point
of
the 3455A. Currents caused
by
common-mode voltage
can be included in the measurement circuit, causing
measurement errors.
3-44.
Guard CennKtion.
3-45.
Figure
3-3
illustrates three methods of connecting
the 34SSA Guard terminal
to
reduce
errors
caused
by
common-mode voltages,
in
example
A,
Guard
is at
nearly the same potential as the LO measurement ter-
minal so that currents caused
by common-mode
voltage
flows
through Guard and not the measurement
circuit,
in example B, the 345SA guard
switch
is closed connec-
ting guard to the LO input terminal. This allows
common-mode current to
flow
through lead
resistance
Rb
causing some measurement error. This connection
may be used if common-mode voltages are not expected
to be a problem. Example C is similar to A with the ex-
ception that connecting guard in this manner allows any
common-mode
current
generated between
the source
low and
powerline
ground to flow in the measurement
circuit.
NOTE
The from
panel
guard pushbutton applies
only
for
front
panel inputs. Be sure to
wire
rear panel
guard connections yourself,
if-
using the
rear panel input
terminals.
3-46.
Guirding
Information.
3-47.
More detailed
information on
purpose and
methods of guarding may
be found in -hp-
Application
Note
No. 123,
“Floating Measurements
and
Guarding”. This
application note is
available through
your
nearest -hp- ^les and
Service Office.
3-6
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