Stanford Research Systems SR620, Руководство пользователя

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Front Panel Operation 9
SR620 Universal Time Interval Counter
SETTING THE INPUTS
SETTING TRIGGER LEVELS
The trigger levels are set by rotating the trigger
level adjust knobs. These knobs may have a full
scale range of ±5.00V, ±2.50V, or ±1.25V. The
full scale range is set in the CONFIGURATION
menu (see that section of the manual for details).
In all cases the trigger level resolution is 10mV
and the actual level may be displayed on the front
panel. The trigger inputs have about 40mV of
hysteresis and the trigger levels are corrected for
this hysteresis so that the inputs will trigger at the
selected voltage independent of the selected
trigger slope.
The LED's above the trigger knobs will flash when
the input comparator triggers. The A and B inputs
may also be set to autolevel by rotating the knobs
completely counter-clockwise. The "AUTO" LED
under the knob will come on and the trigger
threshold will automatically be set to the midpoint
of the signal. Autolevel will work for a signal faster
than about 10Hz and a duty cycle greater than
about 0.0001%. The autolevel circuit will not
change the trigger level until the input stops
triggering for more than 1/2 second. Then it will
try to reset the trigger level to a new value. The
red LEDs behind the words "START" and "STOP"
will flash each time the autolevel circuit tries to
adjust the trigger threshold.
NOTE : in width and rise/fall time modes, which
use only one input, the A trigger knob sets the
start trigger voltage and the B trigger knob sets the
stop trigger voltage.
SETTING TRIGGER SLOPES
The A and B inputs can be set to trigger on either
a rising or falling edge by pressing the "SLOPE"
buttons. The EXT input can be set to rising edge
or falling edge by pressing the "LOGIC" button. If
the EXT input is being used to supply a gate pulse
the SR620 will use the time above threshold as
the gate if POSitive logic is selected and the time
below threshold as the gate if NEGative logic is
selected.
INPUT TERMINATION
The EXT, A, and B input may all be terminated in
either 1MOhm or 50 Ohms by pressing the
"INPUT" or "TERM" buttons. If the inputs are
terminated in 50 ohms and the input signal
exceeds ±6V peak the 50 Ohm terminator will
automatically be removed to prevent damage to
the terminator. When this overload condition
occurs the 50 ohm LED will flash.
UHF PRESCALERS
In frequency and period modes the input signal
may be fed to the SR620's UHF prescalers to
measure signals between 40MHz and 1.3GHz. To
engage the prescalers press the "INPUT" button
for the desired channel repeatedly until the UHF
LED comes on. The sensitivity of the prescalers
may be adjusted by adjusting the channel A and B
trigger knobs. Setting the knobs for 0V or to
autolevel will set the sensitivity to maximum.
Setting the knobs to 5V will reduce the sensitivity