1.9
Reference oscillator output
1 – 9
8. Press [Shape] to select
Square
. Verify the waveform changes to
a square wave with
±
10 V (20 V peak to peak).
9. Turn the
REFERENCE knob counterclockwise, to reduce the
amplitude to 1.00 V on the REFERENCE display. Press [Shape]
to return to
Sine
output.
10. Enable the DC bias by pressing [On
/
O
ff
] in the DC Bias block.
Press [Modify] in DC Bias, and then adjust the Bias setting
by turning
REFERENCE counterclockwise, to near
−
2.000 V.
Verify the waveform on the scope is now shifted to an average
of
−
2 V.
11. Press the DC Bias [On
/
O
ff
] to turn o
ff
the bias, and verify the
waveform returns to zero-centered. Press DC Bias [On
/
O
ff
]
again to re-enable the
−
2 V DC Bias.
12. Press the [Ampl] button to select Amplitude again, and then
turn
REFERENCE counterclockwise until you reach the limit.
Turn the knob slow counterclockwise to reach 10.0 mV. Notice
that the SR124 will not allow the Amplitude to decrease below
10.0 mV with the DC Bias enabled and set to
−
2 V.
13. Press DC Bias [On
/
O
ff
] to disable the Bias. With the REFER-
ENCE focus still on Amplitude, turn
REFERENCE counter-
clockwise to 9.99 mV. Notice the sound of the relay click.
14. Now press DC Bias [On
/
O
ff
] to attempt to re-enable the Bias.
The SR124 should beep, and the
AMPL
annunciator will flash,
indicating the present value of Amplitude is incompatable with
(too small for) the requested (
−
2 V) DC Bias.
15. Press DC Bias [Modify]. The old value (
−
2 V) should be dis-
played, but the SR124 beeps in warning that this value is
presently unaccessable. Turn the
REFERENCE knob in ei-
ther direction; the displayed BIAS value will jump to
−
100 mV.
This is the limiting value for DC Bias when the amplitude is be-
tween 0.1 mV and 9.99 mV. Full details of the interdependence
of DC bias and Amplitude can be found in section 3.4.
SR124
Analog Lock-In Amplifier
