Fluke 8506A Instruction Manual page 46

8
506
2-71.
The Thermal
True-RMS
Converter
uses three
front
panel function push buttons (V
AC
Hi
ACCUR,
V
AC NORMAL,
and
V
AC
ENH'D). The
high accuracy
mode
(V
AC
HI
ACCUR)
requires approximately
six
seconds
per reading, but the
resulting accuracies of
up
to
0.016%
rival
those of thermal
transfer
standards
(at a
fraction of the
time).
The
normal
mode
(V
AC-
NORMAL)
displays an
rms
value of the input (updated
every 0.5 second),
but,
with reduced accuracies
since
no
sensor
linearization
is
performed.
The
enhanced
mode(V
AC
ENH'D)
takes
one
initial
high accuracy
measurement.
This measurement
is
then used
to correct
subsequent measurements, which
are
made
at
normal
mode
speed
(0.5
second).
The enhanced mode
is
specified
as long as the following conditions are maintained: the
input cannot vary
more
than
±1%
from
that
used
for the
initial
high accuracy reading, the temperature cannot
vary
more
than ±1°C, and
the time lapse
cannot exceed
one
hour.
If
the input changes by
more
than
±1%
from
that
used
in the
initial
high accuracy reading,
another
high accuracy reading
is
taken
to automatically update
the correction
factor.
2"72„
Measurement
Parameters
2-73,
SAMPLING
2-74.
AC
Volts
Functions
2~75.
One
sample
is
taken
for
each
V
AC
reading.
Reading time
in
NORMAL
is
approximately
0.5
second.
HI
ACCUR
readings require
six
seconds.
ENH'D
requires
an
initial six
second high accuracy
reading, then
reverts to 0,5 .second normal
readings.
Any
of
these
reading times
may
be lengthened
slightly
when
mathematic
operations are
in effect.
The
SAMPLE
push
button
is
inoperative
when
the multimeter
is
set for
ac
volts
measurements
(pushing
SAMPLE
causes an Error
A).
A
new
high accuracy measurement
can
be
commanded
in
the
enhanced
mode (ENH'D)
by pushing
the
ENH'D
button
again. Similarly,
when
the
dc coupled
enhanced
mode
is
used,
a
new
high
accuracy
measurement
can
be
commanded
by simultaneously
pushing
the
ENH'D
and
V
DC
buttons.
NOTE
In
the
Enhanced
mode,
the
Thermal True
-
RMS
Converter
automatically takes a
new
reading
to establish
anew
correction factor
if
the range changes
(either
manual
or
autorange), the
filter
setting changes, or
the
difference
between
the reading
and
the present
correction factor
is
*=7%.
2-76.
DC
Volts, Resistance,
and
DC
Current
Functions
2-77.
The
multimeter averages
a selectable
number
of
samples
for
each
reading
(display
update)
in
V DC,
OHMS,
or
A
DC.
Noise
rejection
is
influenced by
the
number
ofsamples-per-readingand by
the
filter
selection.
Each
sample-per-reading
setting yields a specific
processing
time.
Additional processing time
is
necessary
when
mathematic
operations (such
as
OFFSET
or
SCALING)
are involved. Samples
taken
are
synchronous
to the line
frequency
for local (front panel) operation.
Synchronous
or
asynchronous
operation
may
be
specified
remotely.
2-78.
Sample
settings are specified as exponents
of two.
For example,
the
SAMPLE
push button can be used
individually
to
toggle between
settings 5 (2
exponent
5
=
32 samples-per-reading) and
7 (2
exponent
7
=
128
samples-per-reading). Further, any sample
setting
(exponent of
2)
from 0
t
hrough
17
may
be
made
using the
STORE
(numeric)
SAMPLE
sequence.
If
a
setting of 0
through
6
is
in effect
when
SAMPLE
is
toggled, the
multimeter
assumes
setting
7.
A
previous
setting of 7
through
17
is
changed
to setting 5
when
SAMPLE
is
toggled.
2-79.
The
SAMPLE
annunciator
is
controlled
by both
the
sample
setting
and
the
trigger.
At sample
settings
from
0 through
7,
SAMPLE
flashes
once
for
each
triggered
reading.
The
rapid reading
rate
at
0 or
l
setting yields an
apparent steady
indication.
At sample
settings 8
through
17,
the
flash rate
is
preset to that of
setting
7.
This
feature
insures a
reliable
reading-in-progress indication
at
these
slower reading
rates.
2-80.
TRIGGERING
2-81.
Each new measurement
is
initiated
with
a
trigger.
In
AUTO
triggering, the trigger
is
generated
internally at
the
end
of the required reading
time. Triggers
may
also
be
applied
locally
(from the
front panel) or remotely,
2-82.
Auto
trigger
commands
a continuously updated
reading.
The
frequency of
this
updating
is
influenced
by
the
number
of samples-per-reading
and by any
extra
processing time required by mathematic
operations.
The
SAMPLE
annunciator
flashes to indicate the triggering
of a
new
reading.
2-83. Local triggers can be manually
commanded
from
the front panel.
The
duration
of
each reading
is
determined
in the
same manner
as the auto
triggers
(samples, mathematics). Each
use of the
MANUAL/ EXTERNAL
push button
commands
an
immediate response
from
the multimeter; any
reading
already
in
progress
is
aborted and
a
new
reading begun.
During any manually
triggered reading,
use of
any
other
push
button
halts
the multimeter;
a
new
trigger must then
be entered. Conversely, between manually
triggered
readings, the
multimeter
is
inhibited;
no
display update or
SAMPLE
annunciation
is
evident.
During
this interval,
any measurement
parameter, mathematic
operation, or
special operation
may
be entered, but
is
not
initiated until
the next
manual
trigger
is
entered.
2-84. External
triggers are applied
through
the rear
panel
TRIGGER
jack.
A
local trigger manually
applied
from
the front pane! overrides a simultaneously applied
external
trigger.
2-24