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SECTION
1
GENERAL INFORMATION
1.1
INTRODUCTION
1.1.1
The
Racal Instruments
Model 1994
timer/counter
is
a microprocessor-con-
trolled
instrument
offering high
accuracy measurements
with a
comprehensive
range
of
capabilities.
The
1994 can be provided with Option
41 Input C,
extending frequency
measurement
to
1.3
GHz.
8
M
y
1.2
MEASUREMENT
FUNCTIONS
1.2.1
Frequency
A
and
B
1.2. 1.1
Frequency
A
and
B
are used
to
measure
the
frequency
of the signal applied
to
Inputs
A
and
B,
respectively.
A
resolution
of
9 digits
is
available with a 1-second
gate
time.
1.2.2
Frequency
C
1.2.
2.1
Frequency
C
is
available as
Option
41.
A
resolution of
9 digits
is
available
_
with a 1-second gate
time.
1.2.3
Period
A
1.2. 3.1
Period
A
is
used
to
measure
the period of the
waveform
applied
to Input
A.
A
resolution of
9 digits
is
available with a
1-second gate time.
1.2.4
Time
Interval
1.
2.4.1
Time
Interval
provides
single-shot
measurements
of
the
time
interval
between:
1.
Separate
Mode:
An
event occurring
at Input
A
and a
later
event
at
Input
B
2.
Common
Mode:
Two
events occurring at Input
A
1.
2.4.2
The
arming
of the stop
trigger
circuit
can be delayed
to
prevent the
measurement
interval
being
stopped prematurely by
spurious pulses,
such as
those
caused
by contact bounce.
1.2.5
Total
A
by
B
1.2. 5.1
Total
A
by
B permits
events occurring
at Input
A
to
be
totalized.
The
counting
interval
can be controlled
by:
1.
Electrical start
and
stop
signals
applied
to
Input
B
(Total
A
by
B)
2.
Successive
operations
of
a
front
panel
key accumulating
counts
(Manual
Totalize)
1.2.
5. 2
Delayed arming
of
the stop
circuit to
prevent spurious
triggering
is
available
in
the Total
A
by B mode.
1-1
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