Stanford Research Systems SR620, Руководство пользователя

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Configuration Menus 21
SR620 Universal Time Interval Counter
Scan Configuration Menu for D/A Scan
Example
Line Display Function
1
ScAn EnA rEPEAt Enable repeated D/A
scans
2 ScAn PtS 250 Take 250 point in each
scan
3 hoLd 0.01 S Minimum hold time
4
dA Src chrt dAc D/A #2 setup as D/A
5 dA ---.--- 1.000 D/A #2 starts at 1.0 VDC
6 StEP -.--- 0.020 250*.02V = 5V scan
Leave the CONFIG menu by pressing the
"RESET" key in the SAMPLE SIZE section. Then
press and hold the "START" key to turn on the
AUTO LED to initiate D/A scanning. After a few
seconds, press the "AUTO" key in the SCOPE
AND CHART section to scale the scope display.
Note : If the VCO stops running, then the SR620
will stop taking data, and everything stops. Clearly,
you should select a VCO voltage ramp so that the
oscillator never stops oscillating.
We chose D/A #2 to control the VCO so that D/A
#1 would still be available for its default function,
to output a voltage proportional to the mean value
(frequency). This will allow an XY chart recorder to
plot the linearity curve of the VCO, with the applied
voltage on the x-axis, and the measured frequency
on the y-axis. Of course, hardcopy of the scope
display ( which shows the linearity curve ) may be
printed or plotted.
EXAMPLE OF A TIME SCAN
In this example, the frequency of a VCO is
measured as a function of time after the control
voltage is stepped. The front panel 1 kHz "REF
OUT" serves as the EXT trigger and as a trigger to
the pulse generator that stepped the voltage to the
VCO. An internally generated 1 us gate will be
scanned in 1 us increments to record the
frequency of the VCO as a function of time on
successive triggers. Clearly, for this sampling
technique to work, the frequency of the VCO
needs to be reproducible from trigger to trigger.
The SR620 should be setup to measure the
frequency of the A input. It is important to select
an EXTernal gate in the GATE/ARM section. The
EXT LED will blink when the Delay Scan is
enabled in the CONFIG menu. Set the SAMPLE
SIZE to 10, and choose the MEAN for the scope
display. Select TTL for the REF OUT level, and
adjust the EXT trigger input threshold to 1 volt,
rising edge. Use autolevel for the A input.
The strip chart of the
mean for the D/A scan
is shown here. In this
case, the VCO
frequency decreases as
the control voltage
increases.
The cursor shows a
frequency of 1.9632
MHz at the 104th point
in the scan.