Stanford Research Systems SR844 User Manual page 17

Press Freq.
8
9 Rotate the knob left to get to 999 kHz and
998 kHz.
Rotate the knob right to get to 1.01 MHz and
1.02 MHz.
Use the knob to adjust the frequency to
10
96 kHz.
11 Press Sensitivity Down.
Press Shift then Sensitivity Up to perform
12
AutoSensitivity.
13 Disconnect the cable at the SIGNAL IN
connector.
14 Reconnect the cable to SIGNAL IN.
Press Time Constant Down six times until
15
the time constant is 100
16 Disconnect the cable at the SIGNAL IN
connector, then reconnect it.
17 Press Time Constant Up until the time
constant is 3 s.
18 Disconnect the cable at the SIGNAL IN
connector. Wait until the CH1 reading drops
to zero.
µ
s.
The Basic Lock-In
Now the display shows the reference frequency, still
1.00 MHz.
The internal frequency may be adjusted with 3-digit
resolution.
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.
The X reading should vary less than 10%.
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.
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.
Watch the CH1 display bargraph drop down to zero.
The time constant is 100 ms, the bargraph falls
quickly but not instantaneously.
Watch the CH1 bargraph come back up.
The Time Constant is adjusted using the left hand
pair of keys in the Time Constant area. The
indicated time constant should be 1,
CH1 and CH2 values remain nearly unchanged but
may be noisy in the last digit.
The bargraph falls and rises nearly instantaneously.
The indicated time constant should be 3, x1,s. The
CH1 and CH2 displays remain nearly unchanged.
The bargraph falls slowly.
SR844 RF Lock-In Amplifier
1-7
µ µ µ µ
100, s . The
x