Stanford Research Systems SR844, User Manual

Page: 17 / 246

The Basic Lock-In 1-7
SR844 RF Lock-In Amplifier
8 Press
Freq
. Now the display shows the reference frequency, still
1.00 MHz .
9 Rotate the knob left to get to 999 kHz and
998 kHz .
The internal frequency may be adjusted with 3-digit
resolution.
Rotate the
knob
right to get to
1.01 MHz
and
1.02 MHz
.
The actual frequency is within 1 count in the 4th
digit of the displayed frequency. For example, when
set to 4.56 MHz, the actual frequency is within
0.001 MHz of 4.56 MHz.
10 Use the knob to adjust the frequency to
96 kHz
.
The X reading should vary less than 10%.
11 Press Sensitivity Down . The sensitivity changes to 300 mV (indicated below
the
Sensitivity Down
key). The
OVLD
indicators
in the CH1 and CH2 displays indicate that the
readings may be invalid due to an overload
condition. OVLD indicators in the Input, Time
Constant and Sensitivity areas are used to pinpoint
the source of the overload.
12 Press Shift then Sensitivity Up to perform
AutoSensitivity.
This adjusts the sensitivity so that the measured
magnitude, R, is a sizable percentage of full scale.
The instrument should end up on the 1 V scale and
the displays showing their previous values.
13 Disconnect the cable at the SIGNAL IN
connector. Watch the CH1 display bargraph drop down to zero.
The time constant is 100 ms, the bargraph falls
quickly but not instantaneously.
14 Reconnect the cable to SIGNAL IN. Watch the CH1 bargraph come back up.
15 Press
Time Constant Down
six times until
the time constant is 100
µ
s.
The Time Constant is adjusted using the left hand
pair of keys in the Time Constant area. The
indicated time constant should be
1 ,
x
100 ,
µµµµ
s . The
CH1 and CH2 values remain nearly unchanged but
may be noisy in the last digit.
16 Disconnect the cable at the SIGNAL IN
connector, then reconnect it. The bargraph falls and rises nearly instantaneously.
17 Press
Time Constant Up
until the time
constant is 3 s.
The indicated time constant should be
3
,
x1
,
s
. The
CH1 and CH2 displays remain nearly unchanged.
18 Disconnect the cable at the SIGNAL IN
connector. Wait until the CH1 reading drops
to zero. The bargraph falls slowly.