Stanford Research Systems SR620, Руководство пользователя

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58 Troubleshooting Tips
SR620 Universal Time Interval Counter
Error Indicators
STOP LED No Stop within 20 s of Start
(this may not be an error, the
LED is just a warning to
indicate that the time interval
is large).Blink indicates B
input autolevel attempt.
START LED No Start within 20 s of Stop
(+-TIME, this may not be an
error, the LED is just a
warning to indicate that the
time interval is large).Blink
indicates A input autolevel
attempt.
CLOCK
LED Unit warming up or Ext
timebase error. See "cAL"
CONFIG menu for timebase
selection.
WRONG VALUE
Verify the setting of the instrument by reading
each front panel LED. Is the REL set? Are a very
large number of samples specified? Is the AUTO
LED in the SAMPLE SIZE section turned "ON"?
Are the inputs terminated correctly? Have the
slope, threshold, and input coupling been set
correctly? Are there multiple edges on your input
due to cable reflections?
To gain confidence that the instrument is working
correctly, try measuring the WIDTH, FREQ, and
PERIOD of the REF. ( Refer to the Quick-Start
instructions for step-by-step details.) To verify that
the input section is working, use the 1 kHz REF
OUT (set to TTL level) to supply a signal to the A
or B input and measure WIDTH, tr/tf, FREQuency,
and PERiod. Measure the length of a cable in the
+TIME MODE by connecting it between the REF
OUT and the B input. ( Select REF as the START
SOURCE, select positive slope for START and
STOP, and set B's threshold pot for AUTOLEVEL.)
EXCESSIVE JITTER
The most common causes of excess jitter are (1)
incorrect trigger thresholds, (2) noise or amplitude
fluctuations on the input signals, (3) insufficient or
excessive amplitude on the inputs, slow input
signal slew rates, (5) improper slope selection
(check the MEAN value to be certain that you are
measuring the correct time interval), (6) improperly
terminated inputs.
SCOPE DISPLAY PROBLEMS
Scope display problems are usually due to the set-
up of the X-Y scope. Make certain that the scope
is in the XY mode, with 1V/div, terminated into 1M
Ohm. (The XY mode is sometimes difficult to
setup: some scopes have multiple controls which
must be in the correct position to operate in the XY
mode. Please refer to your scope's operation
manual.) A jumping or distorted display will result if
the scope is ac coupled. If the scope has cursor
read-outs, turn these read-outs "off" to avoid a
blinking display. A poorly compensated scope
input will cause minor distortion of the display.
PRINTER and PLOTTER PROBLEMS
The printer must be connected to the PRINTER
PORT on the back panel. Plotters may be
connected to either the RS-232 or the GPIB port.
You must set parameters in the OUTput menu in
the CONFIG section to specify whether you are
using the printer or a plotter. If you specify a
plotter, you need to specify the Plot Port as GPIB
or RS-232. If you specify GPIB for the Plot Port,
then you need to set the plotter's GPIB address. If
RS-232 is specified, the BAUD rate is fixed at
9600. ( For more details, see the section on
CONFIG.)
GPIB INTERFACE PROBLEMS
For proper operation the GPIB address of SR620
must be set to match that expected by the
controlling computer. The default GPIB address is
16, and so it is a good idea to use this address
when writing programs for the SR620. Any
address from 0 to 30 may be set in the CONFIG
menu. To check the GPIB address, press the
"SEL" key in the CONFIG section to select the
"ctrl" menu. Then press the "SET" key twice to
view the GPIB address. The up/down keys in the
SCOPE AND CHART section may be used to set
the GPIB address.
The SR620 will ignore its front panel key pad
when Remote Enable (REN) has been asserted by
the GPIB. This "REMOTE" state is indicated by the
REM LED in the STATUS section. To return to
LOCAL operation (ie. to enable the front panel)
press the "SEL" key in the CONFIG section.
Controlling programs may inhibit the ability to
return to LOCAL operation by asserting the Local-
Lockout state (LLO).
A linefeed character is sent with and End or
Identify (EOI) to terminate strings from the SR620.