Stanford Research Systems SR620, Руководство пользователя

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70 Calibration Procedure
SR620 Universal Time Interval Counter
Note : The AutoCal procedure automatically
adjusts bytes 0-3,40,45,50-180. That is, it
automatically adjusts the start and stop TACs, the
TAC linearity, the base time interval insertion
delay, the width of REF insertion delay correction,
and the freq/period insertion delay.
Calibration Procedure
Note : Allow 1/2 hour warmup before calibrating
the SR620.
Note : The factory value for a particular calbyte
may be recalled from ROM by displaying the
calbyte and pressing the "CLR REL" button. The
factory value for all of the calbytes may be recalled
by pressing the "CLR" button in the SCOPE and
CHART section.
Simple Calibration
It is rare that the SR620 will need a complete
recalibration. In virtually all cases this simple
calibration procedure will suffice.
Procedure:
1) Run
Autocal.
2) To calibrate the timebase, attach a precision
10MHz source to the A input. Measure its
frequency with a 1s gate. Adjust calbyte 4
until the display reads exactly 10.0MHz. The
allowable range of calbyte 4 is 0 to 4095 all
other numbers are set modulo 4096. If, with
the oven oscillator, the frequency cannot be
set with the calbyte remaining in range, set the
calbyte to midrange and adjust the coarse
adjustment screw on the oscillator until the
frequency is correct.
Note : Attach a x-y scope to the SR620 and look at
the histogram display. The mean value can be
read off of the histogram while the calbyte is
viewed and adjusted on the front panel.
Complete Calibration Procedure:
Note : All or any part of this procedure may be
done .
Necessary Equipment:
1) 100MHz or faster oscilloscope.
2) 10 - 20MHz pulse generator with 5ns or less
transition times such as Hewlett-Packard
HP8012.
3) Precision DC voltmeter such as Fluke 8840A.
4) 0 - 20 V stable dc power supply.
5) 10MHz frequency standard with better than 5
x 10-10 /day aging, such as a Cesium clock.
6) 180 degree rf power splitter with less than a
few hundred picoseconds phase shift between
the non-inverting and inverting outputs (such
as Mini-Circuits ZSCJ-2-1).
7) 2 equal ( less than ±1/2")length BNC cables.
8) BNC cable of known time delay. Can be
measured with SR620.
Trigger Input Calibration
Note : This description refers to channel A.
Channels B and EXT have the same procedure.
Wherever a particular value is noted the values for
B and EXT will be noted in parentheses (B,EXT).
Input Compensation
1) Connect the REF output to the A input with a
coax cable. Select TTL level for the REF OUT
level. Attach a compensated scope probe to
R413 (R443,R473)
2)
Adjust C402 (C422,C442) for best pulse
shape on the 10 us/div scope display.
Input Threshold Offset Calibration
1) With the input open, set the MODE to TIME
and the arming EXT. Turn off automeasure by
pressing the RESET key in the SAMPLE SIZE
section. Select TRIG for the DISPLAY and set
the TRIG threshold for 0 V.
2) Set the slope to + and calbyte 9 (10,8) to
2200.
3) Slowly reduce the value of calbyte 9 (10,8)
until the trigger light flashes. This is the
correct value.