Stanford Research Systems SR620, Руководство пользователя

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20 Configuration Menus
SR620 Universal Time Interval Counter
automeasure will automatically take a whole scan.
In the single scan mode automeasure will
automatically be disabled at the end of the single
scan. Pressing the "RESET " button will reset and
retake a single scan point and turning off
automeasure will pause the scan. A scan may be
reset by pressing the "CLR" button in the "graph"
section of the front panel. When delay scans are
enabled, the function of the EXT gate/arm input
changes dramatically, and so whenever the unit is
first turned on, scans will always be disabled.
The next line of the scan menu sets the number of
points in the scan. The maximum value is 250
points, corresponding to the horizontal resolution
of the scope display. Scans with fewer points will,
of course, be completed in less time. Each point in
the scan contains data from the number of points
specified in the SAMPLE SIZE.
Line 3 allows the dwell time (hoLd) to be set. The
dwell takes place at the end of every scan point to
allow time for the D/A values and the signal source
time to settle. The default dwell time is 10 ms.
Longer dwells may be set if required by the
system under test.
The dA Src line sets the source for the rear panel
D/A outputs (dA Src). The default setting for these
outputs is "chrt". The default function of the D/A
outputs is as analog outputs to strip chart (chrt)
recorders. D/A #1 outputs a voltage proportional
the the MEAN value of the current measurement,
and D/A #2 outputs a voltage proportional to the
JITTER. The scale factors for these outputs is the
same as those set for the scope displays. The
default function may be overridden by selecting
"dAc" instead of "chrt", allowing the D/A voltage to
be set and scanned.
The next menu allows the D/A voltages to be set.
The up/down keys may be used to adjust the
voltages from +-10 VDC in 5 mV steps. (If the
source has been set to "dAc" and not "chrt".) The
D/A will provide a voltage as set, and the set
voltage will be the starting point for each D/A scan.
The step size taken by each D/A may be
programmed in the next line of this menu. The
step size may be adjusted to any value from -10 to
+10 volts with 5 mV resolution. For D/A scans, this
is the last menu line which must be set. If the step
size is set for 0.0V the D/A outputs will always be
set to the programmed voltage. However, if the
step size is not zero the D/A voltages will only be
reset when the scan is reset and the actual output
voltage will be that corresponding to the current
scan point Vout = N*ste vstart. Line 7 is used to enable delay scans. The
SR620's scanning delay is a programmable delay
inserted between the EXT input and the sample
arming circuitry. These scans will, of course,
require an external trigger and the arming mode to
be set to EXT. This delay may be adjusted in step
sizes ranging from 1ms to 10ms with an initial
delay at the beginning of the scan of between 1
and 50000 step sizes. The delay will take one
step after each scan point (a maximum of 250
steps in a scan). For arming modes that require a
gate the delay will be followed by a gate of one
step size width (see ARMING section).
The delay enable may be set to "off", "hold", or
"scan". In the "off" position the delay is disabled
and the EXT input functions normally. In the
"hold" setting the delay is enabled but does not
step. This allows one to delay the EXT trigger by
a known amount. If one chooses "hold" and
selects "repeat" scan the SR620 will function
exactly as normal except for the delay between
EXT and arming. The "scan" setting will scan the
delay by one step size after each scan point.
NOTE: the arming mode must be set to EXT for
the delay scan to function, otherwise the delay
scan is ignored. If the delay scan is enabled the
EXT led will blink.
The gate width and delay step size is set in the
next line. Gate widths from 1 us to 10 ms may be
set in a 1,2,5 sequence.
The gate start position is set in the last line of the
scan menu. The start position may be set from 1
to 50,000 gate widths. The gate delay will be
increased by one gate width after each group of
measurements (per the SAMPLE SIZE).
EXAMPLE D/A SCAN
In this example, the frequency of a VCO will be
plotted as a function of applied voltage. The VCO
range is 1 to 6 VDC, and we want at least 200
points in the scan. The D/A #2 output will be used
to control the VCO.
First, set the SR620 to measure FREQuency of
the A input with a 0.01 s gate. Select a SAMPLE
SIZE of 1. Clear the DISPLAY REL and select
MEAN for the scope display. The rear panel output
for D/A #2 is connected to the VCO under test, an
the VCO output is connected to the A input.
In the CONFIG menu, SET lines 1 through 6 as
follows: