Stanford Research Systems SR844, User Manual

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Overview 3-5
SR844 RF Lock-In Amplifier
Local Lockout
The front panel keys and the knob may be disabled by remote interface command (GPIB
or RS-232). Attempts to change the settings from the front panel will display the message
LOCL LOUT indicating that local control is locked out by the remote interface. Note that
the factory preset values leave the front panel keys enabled even during remote operation.
Local/Remote operation is discussed more fully later in this chapter (see the
Local
key),
and in Chapter 4, Interface Commands .
Front Panel Display Test
To test the front panel displays press
Local
and
Setup
together. Some of the front panel
LED’s will turn on. Note that the instrument is still operational; only the display is in test
mode. Press
+90
°
to increase the number of illuminated LED’s and
Phase
to decrease
the number. Use the knob to move the selected LED’s across the panel. Make sure that
every LED can be turned on. Pressing
Zero
shows a text message on the display. Press
any key other than Phase , +90
°
, or Zero to exit this test mode.
Display Off Operation
Enter the Display Test mode as explained above. Press Phase until no LED’s are lit. The
SR844 is still operating, output voltages are updated and the unit responds to interface
commands. To change a setting press any key other than
Phase , +90
°
or Zero ( Local or
AuxOut
are good choices) to exit the test mode, change the desired parameter, and then
re-enter Display Test mode.
Front Panel Connectors
There are five BNC connectors on the front panel.
SIGNAL
INPUT
The measurement range of the SR844 is up to 1 Vrms (+13 dBm), over
the frequency range 25 kHz to 200 MHz.
Do not exceed the
damage threshold of
±±±±
5V DC+AC.
CH1
OUTPUT The CH1 output provides a
±
10V analog output proportional to either
X or the CH1 displayed quantity.
CH2
OUTPUT The CH2 output provides a
±
10V analog output proportional to either
Y or the CH2 displayed quantity.
REFERENCE
INPUT The SR844 accepts sinusoidal and digital signals as external reference
inputs, including low-duty cycle pulse trains. The signal should be a
0 dBm sine wave or a 0.7 to 5 Vpp pulse. The reference input may be
terminated in either 50
Ω
or 10 k
Ω
, 40 pF.