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1.3. 2.1
The
manually
set trigger level
is
entered
into
an
internal store.
1.3.
2. 2
The
auto-trigger
level
is
derived by measuring
the positive
and negative
peaks
of the input
signal.
If
the
peak-to-peak
value
exceeds
5.1V, or
if
either
peak
is
outside the
range
+5.
IV, the
X10
attenuator
is
automatically switched-in.
The
trigger
level
is
then
set
to
the
mean
of the
measured
value.
1.3.
2.
2.1
When
operating
in
auto-trigger
with the
X10
attenuator
in-circuit,
the
attenuator
will
be switched-out
if
the
peak-to-peak
value
is
less
than 4.6V
and both peak
values are within the
range
±4.6V.
1.3.
2. 2. 2
The
trigger levels
in
use are available at
pins
mounted on
the rear
panel.
The
voltage
range
is
±5.1
V
regardless of
whether
the
attenuator
is
switched-in
or out.
1.3.3
Input
C
has
a
nominal
input
impedance
of
50
ft
and
is
AC-coupled.
Protection against excessive
signal levels
is
provided by a
5V rms
fuse
in
the input
BNC
connector.
1.4
LOW-PASS
FILTER
1.4.1
An
internal
low-pass
filter
can be
introduced
to
reduce the bandwidth
of
Input
A
to
50
kHz
(nominal).
1.5
MATH
COMPUTATION
1.5.1
When
the
Math
function
is
active, the displayed value
is
(Measurement
Result-X)
Y/Z
where
X,
Y,
and
Z
are values entered
into
stores within
the instrument by
the
user.
X
is
set to
0,
Y
and
Z
to
1
when
the instrument
is
powered-on.
By an
appropriate choice of values
for
X, Y,
and
Z, offset,
normalized,
and
scaled
displays
can
be achieved.
1.6
SPECIAL FUNCTIONS
1.6.1
The
1994
provides
a
set
of
Special
Functions,
permitting
extended
measurements and
capabilities
beyond
those provided
by
the front-panel
keyboard. See
Subsection
3.4.10 for
details.
1.7
ERROR
INDICATION
1.7.1
Certain
errors
in
counter operation
will
result
in
the display
of
error codes.
See Subsection
3.4.11
for details.
1.8
EXTERNAL ARMING
1.8.1
External
arming
of the start
and
stop trigger
circuits for
the
measurement
interval
can
be
carried
out by
means
of
signals
applied
to
a
rear-mounted
BNC
connector.
Any
combination
of
internal
and
external
arming
can be selected by
use of
the appropriate special function.
1.9
DISPLAY
FORMAT
1.9.1
The
display uses
an engineering format, with
a
9-digit
mantissa and
1-digit
exponent.
Overflow
of the
most
significant
digits
can be
used
to
increase the display
resolution.
1-3
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