SRS Labs SR850 - Manual (Page 29)

2-17
SCANS and SWEEPS
This measurement is designed to use the internal oscillator to explore some of the basic lock-in functions.
You will need BNC cables.
Specifically, you will measure the response of the line notch filters by sweeping the internal reference frequen-
cy and measuring the sine output. Traces and strip chart displays will be used to record X, Y, R and
θ
as the
signal is swept through the input notch filters.
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. Press [INPUT/FILTERS]
Press the <Line Notches> softkey until Both fil-
ters are selected.
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.
Display the Input and Filters menu. This menu
allows the input configuration to be changed.
With the line notch filters engaged, signal inputs at
60 (50) Hz and 120 (100) Hz are removed. Note
that the line filter indicators at the top of the screen
are both on.
Scans and Sweeps