Frequency Response Measurement Using Curve Storage And Frequency Sweep - IBM 7220 Instruction Manual

NC
LEN 20000
TADC 6
As soon as a trigger occurs, the acquisition starts. Once it completes the acquired
data may be transferred to the computer using:-
DC. 5
The input routine of the program must be prepared to read and store 20,000
responses to this command.
6.5.06 Frequency Response Measurement using Curve
Storage and Frequency Sweep
In this example, a more sophisticated version of that given in section 6.5.03, the
internal oscillator frequency sweep generator is used in conjunction with curve
storage, allowing the acquisition of a frequency response without the need for the
computer to perform the frequency setting function for each point.
As before, the lock-in amplifier's internal oscillator output signal is fed via the filter
stage under test to the signal input. The oscillator frequency is stepped between a
lower and an upper frequency and the signal magnitude and phase are recorded.
The required sequence of commands is therefore as follows:-
IE 0
VMODE 1
FET 1
AUTOMATIC 1
FLOAT 1
LF 0
OA. 1.0
OF. 100.0
SEN 27
TC 8
AQN
The next group of commands set up the frequency sweep:
FSTART. 100.0
FSTOP. 1000.0
FSTEP. 10 1
SRATE. 0.1
There will therefore be 100 steps (100 Hz to 1000 Hz inclusive in 10 Hz steps). Now
we need to specify the curve storage:
Chapter 6, COMPUTER OPERATION
Clear and reset curve buffer
500 ms recording time at 40 kHz = 20,000 points
Set ADC1 sampling to burst mode, fixed rate (≈ 40 kHz),
external trigger, and arm trigger
Transfers ADC1 values in floating point mode
Set reference mode to internal
Single-ended voltage input mode
10 MΩ input impedance using FET stage
AC Gain control automatic
Float input connector shell using 1 kΩ to ground
Turn off line frequency rejection filter
Set oscillator amplitude to 1.0 V rms
Set initial oscillator frequency to 100 Hz so that AQN
runs correctly
Set sensitivity to 1 V full-scale
Set time constant to 10 ms
Auto-Phase
Set initial oscillator frequency to 100 Hz
Set final oscillator frequency to 1000 Hz
Step size = 10 Hz, linear law
100 ms per step
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