Chapter 6, COMPUTER OPERATION
6-37
X[.] X1[.]
X2[.]
XOF[n
1
[n
2
]] XOF1[n
1
[n
2
]]
XOF2[n
1
[n
2
]]
XY[.] XY1[.]
XY2[.]
Y[.] Y1[.]
Y2[.]
YOF[n
1
[n
2
]] YOF1[n
1
[n
2
]]
YOF2[n
1
[n
2
]]
AQN AQN1
AQN2
AS AS1
AS2
AXO AXO1
AXO2
6.5 Programming Examples
6.5.01 Introduction
This section gives some examples of the commands that need to be sent to the lock-
in amplifier for typical experimental situations.
6.5.02 Basic Signal Recovery
In a typical simple experiment, the computer is used to set the instrument controls
and then to record the chosen outputs, perhaps as a function of time. At sampling
rates of up to a few points per second, there is no need to use the internal curve
buffer. The commands to achieve this would therefore be similar to the following
sequence:
IE 2 Set reference to external front panel input
VMODE 1 Single-ended voltage input mode
AUTOMATIC 1 AC Gain control automatic
FLOAT 1 Float input connector shell using 1 k to ground
LF 0 0 Turn off line frequency rejection filter
ASM Auto-Measure (assumes reference frequency > 1 Hz)
TC 13 Set time constant to 200 ms, since previous ASM changed it
Then the outputs could be read as follows:
X. Reads X channel output in volts
Y. Reads Y channel output in volts
MAG. Reads Magnitude in volts
PHA. Reads Phase in degrees
FRQ. Reads reference frequency in hertz
The controlling program would send a new output command each time a new reading
were required. Note that when using an output filter slope of 12 dB/octave a good
"rule of thumb" is to wait for a period of four time-constants after the input signal
has changed before recording a new value. Hence in a scanning type experiment, the
program should issue the commands to whatever equipment causes the input signal
to the lock-in amplifier to change, wait for four time-constants, and then record the
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