Tektronix DC 501 Instruction Manual page 6

operating lnstructions~DC S01
readirtg
will
be
displayed.
To
change the display time,
which
is
continuously
variable
from about
0.1
second
to
10
seconds,
or
to
hold
a
display indefinitely, turn the
DISPLAY TIME
control.
Totalizing (Counting
Number
of Events).
The
DC
501
will display the
accumulated
number
of
pulses applied to
the External
or
Internal input
circuit
up
to
9,999,999
pulses.
Input
signal rate
should
not exceed 100
MHz.
Before applying the
signal,
set
the
MEASUREMENT
INTERVAL
switch
to
MANUAL.
Apply
the signal
and
push
the
START
button.
The
GATE
indicator will
light
and
the progressing count
will
be
displayed.
Adjust
the
ATTEN
and
TRIGGER LEVEL
controls
as rtecessary to
obtain
a
steady count.
To
stop the counting,
release
the
START
button.
The
GATE
light will
go
out and
the
displayed
count
will
be
held.
The
displayed count
will
continue by
pressing the
START
button
again.
The
counter can be
reset
to zero
at
any time
by
pushtng the
RESET
button.
Signal
Connection
Coaxial cables and probes
offer
very convenient means
of connecting the
signals to the front-panel
INPUT
BNC
connector.
These
devices are shielded to prevent pid(up of
electrostatic interference.
A
10X
attenuation
probe not
only reduces the
size
of the input
signal,
but
is
also
presents
a high
input impedance to allow the
circuit under
test
to
perform
very
close to
normal
operating conditions.
Input
and output
data access to the
DC
501
is
made
via
the plug
in
connector contacts
at
the rear of the
main
circuit
board.
Fig.
1-1
identifies the contacts
and
their
associated Input/output assignments.
An
optional multi-pin
connector,
to
which
these
data can be hard-wired
to
provide external
access,
is
available to
install
on
the rear
panel of the power module.
Input Attenuation
and
Trigger Level
Adjustment
Signals to
be counted may
have a
wide
variety of
shapes
and amplitudes,
many
of which
are unsuitable
to
drive the
counting
circuits.
Because
of
this,
the signal
is
first
passed
through an
attenuator, then
applied to a signal-shaping
circuit
which
converts
it
to rectangular pulses of uniform
amplitude. This
circuit
includes a reference
level adjustable
between
-*-
and
-
2
volts to
which
the incomirtg
signal
is
compared,
allowing the
300
millivolt sensitivity
window
of
the signal-shaping
circuit
to be
adjusted to
a convenient
amplitude on
the
incoming waveform
(see Fig. 1-2).
Obtaining
a steady, reliable reading
is
dependent
upon
the
proper
selection of input attenuation
arKl
proper
adjust-
ment
of the
TRIGGER LEVEL
control.
Generally, the
best
point
on
a
waveform
for triggering
the
counter
is
where the slope
is
steep
and
therefore usually
free 0 * no'se
0"
?
sme-w?'-?
sigr»?'.
o'-
exemple,
the
steepest slope
occurs
at
the
zero-crossirtg point.
Noise
pulses or other
signal
components
of sufficient
amplitude
to
produce unwanted
trigger
pulses
will
cause an
erratic or
incorrect
count.
Fig.
1-2
shows
the
TRIGGER LEVEL
control adjusted to avoid
error. In
critical
measurement
applications, monitor
the
incoming
signal
with
a test
oscilloscope.
Measurement
Interval
and
Display
Time
Controls
The
MEASUREMENT
INTERVAL
switch
selects
the
time
interval (also called gate time)
during
which
the
DC
501
counts.
The
internal
time-base
circuit
derives gate
times
from
an
accurate
1-MHz
reference signal to
make
frequency measurements. These
gate times
are
0.01
s,
0.1
s,
1
s,
or 10$.
The measurement
interval selected
determines
the
measurement
range
and
resolution. Also, the displayed
decimal
point
is
positioned correctly
and
the correct
measurement
units
(MHz
or
kHz)
are indicated for the
corresponding switch
position.
Contact
Atsignmanl
28B
Sacond dacima) point (D2I output.
Z7A
27B
MHz
light
output.
26A
Ratat input/output.
2SA TS^
(Tima Slot Ztrol output.
25B
External lean clock
input.
24B
Intamal
Kan
clock
(2
kHz)
output.
23B Overflow
output.
228
MSD
(moat significant
digit)
20B
ft
20A
4
BCD
output,
serial
by
digit.
218 2
19A
1
198 Data good
output.
17A
Signal
input ground.
16A
Signal input.
Fig. t
1.
Input'Output ssignmcntsor
piug-in
conn«clO>
contacts.
1-2
S'