Chapter 6, COMPUTER OPERATION
6-37
TC 11 Set time constant to 50 ms
AQN Auto-Phase
The frequency sweep would be performed and the outputs recorded by sending the
following commands from a FOR...NEXT program loop:
OF. XX Set oscillator frequency to new value XX hertz
Software delay of 200 ms (4 × 50 ms) allowing output to
stabilize
MAG. Read Magnitude in volts
PHA. Read Phase in degrees
FRQ. Read reference frequency in hertz. This would be same as
the oscillator frequency since the unit is operating in
the internal reference mode.
until the stop frequency is reached.
6.5.04 X and Y Output Curve Storage Measurement
In this example, the lock-in amplifier is measuring a current input signal applied to
the B input connector and the measured X channel output and Y channel output are
recorded for 10 seconds at a 100 Hz sampling rate. The acquired curves as read back
to the computer are required in floating point mode.
The sequence of commands is therefore as follows:
IE 2 Set reference mode to external front panel input
IMODE 1 Normal current 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
SEN 18 Set sensitivity to 1 nA full-scale
TC 11 Set time constant to 50 ms
AQN Auto-Phase
Now the curve storage needs to be set up:
NC Clear and reset curve buffer
CBD 19 Stores X channel output, Y channel output and sensitivity
(i.e. bits 0, 1 and 4)
LEN 1000 Number of points = 100 Hz × 10 seconds
STR 10000 Store a point every 10 ms (10,000 µs)
The data is acquired by issuing:
TD Acquires data
As the acquisition is running, the M command reports the status of the curve
acquisition. Once this indicates the acquisition is complete (i.e. parameter 1 = 0,
parameter 2 = 1), the acquired data may be transferred to the computer using:
DC. 0 Transfers X channel output values in floating point mode.
DC. 1 Transfers Y channel output values in floating point mode.
The input routine of the program must be prepared to read and store 1000 responses
to each of these commands.
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