Stanford Research Systems SR620, Руководство пользователя

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Sample Arming 13
SR620 Universal Time Interval Counter
Time interval samples may also be armed by
pressing the MAN key when in the EXT arming
mode.
WIDTH
Pulse widths may be measured in the WIDTH
mode. The pulse source may be either the A input,
the B input, or the internal 1 kHz REF source.
The Start threshold and slope are set by the
controls just above the A input. The Stop threshold
and slope are set by the controls just above the B
input. If the Start slope is positive, the Stop slope
will be negative, and the time from a rising edge to
a falling edge will be measured. These controls
are not used when measuring the width of the
internal 1 KHz REF.
As pulse widths are always positive times, only the
+TIME arming modes are available. The three
arming modes for WIDTH measurements are
shown here. The trigger source may be either the
EXT input or the EXT triggered internally
delayed/scanned gate.
RISE and FALL TIMES
The transition time for an input may be measured
in this mode. Either the A or B input may be
selected as the source to be measured. The
selected source is used as the input to both
comparators. The threshold knob above the A
input is used to specify the Start voltage threshold,
and the knob above the B input is used to specify
the Stop voltage threshold. The rise time of the
input is reported if positive slope is selected, and
the fall time is reported if negative slope is
selected. Either slope key changes both
comparators' slope LED's.
For example, to measure the 20-80% rise time of
a one volt input, the A threshold would be set to
0.20 VDC, the B threshold would be set to 0.80
VDC, and the slope would be set to positive to
measure the rising edge. The 80-20% transition
time of the falling edge could be measured by
setting the slope to negative and adjusting the
trigger thresholds. Reported times are not
corrected for the finite bandwidth of the input of
the instrument. The inputs have a bandwidth of
about 300 MHz, and so the 10-90% transition time
of an infinitely fast input would be reported as 1.2
ns. When measuring 10-90% transition times, the
actual transition time may be found by:
T actual = sqrt (T measured2 - 1.2 ns2 )
As transition times are always positive numbers,
only +TIME and +TIME_EXT arming modes are
allowed.