 |
|
LockGuard Example Script:
The LockGuard is an advanced probe crash prevention routine running as a background process on the DSP
processor. As a software solution, it has the advantage over hardware implementations by responding in real time to operational parameters. Moreover, user scripting can
fine-tune the LockGuard’s behavior to suit a variety of special requirements. For example, its high-level
functionality becomes necessary in very sensitive AFM experiments. Or, to exemplify its software-side
effectiveness, the LockGuard can reduce the detuning of the PLL in the event of a PLL unlock, effectively
withdrawing the probe from the sample.
In the example script on the right, the LockGuard monitors both phase and excitation amplitude. When either of these exceeds a specified margin, the probe is
|
|
| retracted. The script is written in two parts: The top file creates the front-end interface dialog box in Tcl, and the bottom directs the controller function in the PLLPro’s own scripting language. The dialog box is shown as produced. |
| |
|
• |
Constant Signal (CS) in Lock-In Mode:
High-Q cantilevers are sensitive to transients when
they are moved in the z direction. Any ringing can be
substantially reduced by a control loop that maintains a
certain detected amplitude, much like in Self-Oscillation
CS or PLL CS Modes. |
|
• |
Plot any of these signals:
ADC 1 signal (from 8 inputs)
ADC 2 signal (from 7 inputs)
Self-Oscillation phase shift
Self-Osicillation loop gain
PLL Mode phase shift
Excitation amplitude
Phase shift
∆f |
While sweeping:
Frequency detuning
Excitation amplitude (in CE)
Detected amplitude (in CS)
Self-Oscillation phase shift
Self-Oscillation loop gain
PLL Mode phase shift |
|
• |
Use one of the DACs to generate a reference signal for
an interferometer:
When detecting AC signals many interferometers need
to feed back the DC offset of the interferometer signal
into a reference (fiber) piezo channel. Sometimes an I or
a PI controller needs to be implemented. This can be
done with a script on the PLLPro controller.
|
|
• |
Change the Q of the cantilever:
Using the analog phase shifter in the self-oscillating
path, you can effectively sum signals back into the drive
signal to dampen or enhance the effective Q-factor of
the cantilever. With this you can scan with a varying
cantilever Q or quickly dampen the probe oscillation
after a quick pullback. |
|
|
