Stanford Research Systems SR620, Руководство пользователя

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Sample Arming 11
SR620 Universal Time Interval Counter
SAMPLE ARMING
The SR620 Time Interval counter has a wide
variety of arming modes that allow the user great
flexibility in controlling the desired measurement.
The various measurement modes and their
respective arming modes are discussed in detail
below.
NOTE : references to delayed or scanning gates
are discussed at the end of this section
TIME MODE
In this mode, the unit measures the time interval
between a Start and a Stop pulse. The time
interval is a positive number if the Start occurs
before the Stop and negative if the Stop occurs
before the Start. The SOURCE LED's indicate the
source of the START pulse.
Source LED
Start Source Stop Source
A A B
B B A
REF REF B
(The knobs which are directly above each input
set the voltage threshold for that input when in the
TIME mode.)
Usually, A will be selected as the Start source and
the time interval from A to B will be measured. The
internal 1kHz REF output may be selected in
cases where the front panel REF out will be used
to trigger an event, and the "event" will provide a
Stop pulse to the B input. A simple example of this
would be the measurement of cable lengths. The
length of a cable may be measured by selecting
REF as the Start source, and connecting the cable
between the REF output and the B input.
When REF is used as the Start source, the rising
edge of REF is used when a positive slope is
selected for the A input, and the falling edge is
used when a negative slope is set. In this case,
the threshold knob above the A input has no effect
on operation.
TIME INTERVAL ARMING
There are several arming modes for Time interval
measurements. The arming mode controls when
the instrument will be ready to take a sample. Start
and Stop pulses are ignored when the instrument
is not armed. The ARM LED will turn on when the
unit is armed. The SR620 remains busy for about
800us after receiving a Start/Stop pair and may
not be rearmed during this time.
+TIME MEASUREMENTS (-1ns to 1000s)
In
+TIME arming the Start input is armed as soon
as the instrument is ready and Stop is armed
when a Start is received. In this mode only a
positive or zero time interval may be measured.
In
+TIME EXTERNAL mode the Start input is
enabled by the GATE and Stop is armed by Start.
A delay from an EXT input may be set or scanned
in the CONFIG menu, otherwise the EXT input will
be the trigger.
Time Arming Mode Function
+TIME Start
arms automatically, Stop is armed by Start
+TIME EXTERNAL Start is armed by EXT input, Stop armed by Start
+TIME EXTERNAL STOP HOLDOFF Start is armed by leading edge of EXT input and the Stop is
armed by the trailing edge.
±TIME
Starts and Stops are armed by Start/Stop pair
±TIME COMPLEMENT Starts and Stops are armed by Stop/Start pair
±TIME EXTERNAL Starts and Stops are armed by EXT input