SRS Labs SR850 - Manual (Page 25)

2-13
OUTPUTS, OFFSETS and EXPANDS
This measurement is designed to use the internal oscillator to explore some of the basic lock-in outputs. You
will need BNC cables and a digital voltmeter (DVM).
Specifically, you will measure the amplitude of the Sine Out and provide analog outputs proportional to the
measurement. The effect of offsets and expands on the displayed values and the analog outputs will be
explored.
1. Disconnect all cables from the lock-in. Turn
the power on while holding down the [
←
]
(backspace) key. Wait until the power-on tests
are completed.
2. Connect the Sine Out on the front panel to the
A input using a BNC cable.
3. Connect the CH1 output on the front panel to
the DVM. Set the DVM to read DC Volts.
When the power is turned on with the backspace
key depressed, the lock-in returns to its default
settings. See the Default Settings list in the Menu
section for a complete listing of the settings.
The display is the "normal" lock-in display. The
lock-in setup is displayed across the top of the
screen. The sensitivity, reserve, time constant,
prefilters and input configuration are all easily visi-
ble. Watch how these indicators change as you
change parameters. The upper numeric readout
and bar graph shows the value of X (Rcos
θ
) and
the lower graph shows the the value of Y (Rsin
θ
).
The input impedance of the lock-in is 10 M
Ω
. The
Sine Out has an output impedance of 50
Ω
. Since
the Sine Output amplitude is specified into a high
impedance load, the output impedance does not
affect the amplitude.
The lock-in defaults to the internal oscillator refer-
ence set at 1.000 kHz. The reference mode (Intrnl)
and frequency are displayed at the bottom of the
screen. In this mode, the lock-in generates a syn-
chronous sine output at the internal reference
frequency.
The sine amplitude is 1.000 Vrms and the
sensitivity is 1 V(rms). Since the phase shift of the
sine output is very close to zero, the upper display
(X) should read close to 1.000 V and the lower dis-
play (Y) should read close to 0.000 V.
The CH1 output defaults to X. The output voltage
is simply (X/Sensitivity - Offset)xExpandx10V. In
this case, X = 1.000 V, the sensitivity = 1 V, the
offset is zero percent and the expand is 1. The
output should thus be 10 V or 100% of full scale.
Outputs, Offsets and Expands