Stanford Research Systems SR865A, Operation Manual

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2 Getting Started Chapter 1
SR865A DSP Lock-in Amplifier
SR865A Front Panel
The SR865A
’
s buttons and knobs are mainly used to configure the lock-in measurement,
while the touchscreen is mainly for data display. The touchscreen display is also used for
keypad entry.
Signal Path
The signal path settings configure input BNC’s, input gain, time constant and filters and
the sensitivity. Unlike previous generation lock-ins, the SR865A does not have a dynamic
reserve setting. The input range setting is simply the largest input signal before overload.
It is best to decrease the input range setting as much as possible without overload. This
increases the gain and utilizes more of the A/D converter’s range as indicated by the
signal strength LEDs.
The sensitivity determines the scale factor for the analog outputs (CH1 and CH2) as well
as the numeric readouts and bar graphs. The sensitivity does
not
affect the measurement
values, it simply determines how much signal corresponds to a full scale 10V output from
CH1 and CH2 outputs and a 100% bar graph. It also sets the scale for the 5 digit numeric
displays. The sensitivity should be viewed as an output function only.
Reference
The reference settings configure the lock-in reference frequency and source. In addition
to internal and external reference, the SR865A includes dual reference (detect at |f
int
−
f
ext
|) and chop (lock an SR540 chopper TO the SR865A f
int
) modes.
The SR865A can be synchronized to an external 10 MHz frequency reference (from
another SR865A or other source). This allows multiple SR865A
’s to run in phase sync
with each other in internal reference mode.