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The Curve Buffer menu has six controls affecting the instrument's internal 100,000
point curve buffer, two status indicators and keys to access the Curve Trigger and
Curve Select sub-menu, and the Oscillator menu.
CURVE MODE
The curve buffer can be used in two different modes. In Standard mode selected
instrument outputs (chosen using the Curve Select Menu) are stored in the main
instrument memory, and the fastest time per point is 1 ms. In Fast mode, up to eight
instrument outputs are stored directly in the main FPGA memory, with the fastest
time per point being reduced to 1 µs. Fast mode is a new mode in the model 7270 but
in some ways can be considered as an extension to the Transient Recorder mode
found in earlier SIGNAL RECOVERY DSP lock-in amplifiers.
TIME PER POINT
This control defines the interval between each data point in the curve buffer. In Fast
mode the range is 1 µs to 1 s in 1 µs increments; in Standard mode it is 1 ms to
1000 s in 1 ms increments
CURVE LENGTH
This control defines the number of points to be stored in the internal curve buffer. If
the Curve Mode is set to Standard, 100,000 points are available, shared equally
between the curve types as defined by the Curve Select menu. Hence, for example, if
16 curve types are to be stored then the maximum curve length for each curve is
6250 points. Note that if the number of curves to be stored is increased beyond that
which may be stored at the current curve length, then the curve length is reduced
automatically.
If the Curve Mode is set to Fast, 100,000 points are available, with either five (for
single reference modes) or eight (for dual reference/harmonic modes) being stored.
CURVE START TRIGGER
This control sets the condition used to start acquisition into the curve buffer once this
has been armed, and has three settings, as follows:-
RISING EDGE EXTERNAL
Acquisition starts on receipt of the rising edge of TTL trigger signal at the
TRIG IN connector on the rear panel of the instrument.
FALLING EDGE EXTERNAL
Acquisition starts on receipt of a falling edge of TTL trigger signal at the
TRIG IN connector on the rear panel of the instrument.
INTERNAL
Acquisition starts directly when the Start Sweep key is pressed.
CURVE STOP TRIGGER
This control sets the condition used to stop acquisition into the curve buffer once it is
running, and has four settings, as follows:-
RISING EDGE EXTERNAL
Acquisition stops on receipt of the rising edge of TTL trigger signal at the
TRIG IN connector on the rear panel of the instrument.
FALLING EDGE EXTERNAL
Acquisition stops on receipt of a falling edge of TTL trigger signal at the
Chapter 5, FRONT PANEL OPERATION
5-41
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