Hardware Space Components
position, but the Upper Bound will still allow the tip to retract under normal feedback loop control. In most
cases this control will be hidden on the dashboard. It is typically only set during an experimental
Procedure.
The Feedback Loop is a Proportional-Integral (PI) controller that allows independent settings of the
Proportional and Integral feedback parameters. Two different sets of controls are provided for this
purpose. One set of controls are labeled Gain (3) and Integral Cut Off Frequency (4) and the other are
labeled Proportional Gain (5) and Integral Gain (6). Although one set can be mathematically calculated
from the other set, they are both appropriate for different situations. The Proportional Gain and Integral
Gain are the correct set to use for the Z feedback control. The Gain and Integral Cut Off Frequency
are used in the Amplitude and Phase controls in the PLL circuit.
Important
The Proportional Gain and Integral Gain are the correct set to use for the Z feedback
control.
Tip
The Gain and Integral Cut Off Frequency should be hidden on the Dashboard to avoid
confusion.
The Feedback Loop parameters carry the standard SI units. The units of the Proportional Gain are
Output Units/Input Units. In the case of STM, this would be Meters/Amp (or nm/nA). The units of the
Integral Gain are Output Units/Input Units/second. Again in the case of STM, this would be Meters/Amp-
Seconds (or nm/nA-S).
The Limit Mode (7) dropdown box should be left in the Absolute Mode position.
The Tip Control (8) dropdown box enables and disables the feedback loop, as well as allowing the Z
position to be set to the center of its dynamic range or to the fully retracted position. The four choices in
the dropdown box are:
• Freeze: This setting disables the feedback loop and maintains the present position of the probe until
the Tip Control is changed. The Freeze settings works by moving the Upper Bound and Lower
Bound to the current position of the feedback loop. The feedback loop remains active, but its range of
motion has been reduced to zero. Pressing Unlimit will move the Upper Bound and Lower Bound to
their maximum positions to allow the feedback the full range of motion. The Bounds can also be set to
less than their full range of motion, or only one Bound can be moved if required by the user defined
procedure.
• Retract: This setting sets the output of the feedback position to its fully retracted position.
• Center: This setting sets the output of the feedback position to the center of it range of motion.
• Unlimit: This is the “Un-Freeze” setting of the feedback loop. The Unlimit works by setting the Upper
Bound to the maximum retracted range of the feedback loop and the Lower Bound to the minimum
extended range of the feedback loop. This provided the feedback loop with its full range of motion.
The Feedback (9) dropdown box provides three types of feedback algorithms for controlling the output of
the feedback loop. In each case the Input signal is compared to the Feedback Set Point and the resulting
error signal is output to the PI section of the feedback loop. The PI settings of the feedback loop will be
very different for the three different types of feedback control, so this setting should not be changed while
the probe is close to the surface. The three Feedback types are:
• Linear: The Linear setting subtracts the Input signal from the Set Point to generate the error signal.
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