Electric Techniques
Rev. C Dimension 3100 Manual 16-353
16.5 Troubleshooting
The Surface Potential feedback loop can be unstable. This instability may
cause the Potential signal to oscillate or remain at either +10 V or -10 V. Below
are suggestions for verifying that the feedback loop is working properly with
no oscillation.
1. Go into Scope Mode and look at the Potential signal. If oscillation
noise is evident in the signal, reduce the FM gains. If oscillations
persist even at very low FM gains, increase the Lift scan height or
reduce the Drive amplitude until oscillation stops.
2. If the tip crashes into the surface, the Lock-in signal unstabilizes
and causes the feedback loop to malfunction. To prevent this
problem, increase the Lift height and reduce the Drive amplitude.
Once oscillation stops, you may increase the FM gains for
improved performance.
3. In Scope Mode, if the Potential signal is perfectly flat and shows no
noise even with a small Z-range, the feedback loop is probably
stuck at ±10 V. Verify this by changing the value of Real-time
planefit to None in the Channel 2 panel and increasing the Data
scale to the maximum value (20V). If the scope trace is at one of
the limits the potential signal is railed. Common reasons for this
include:
• Inappropriate Drive phase: For an MESP cantilever
verify that the Interleave Drive phase is set to –90 degrees.
For Versions 4.23 and lower, set the Feedback Control
Drive phase to –90 degrees.
• Incorrectly set toggle switches on the Extender Module:
Verify toggle switches are set to Surface Potential and
GND/Surface Potential.
• Incorrect electrical connection: Verify that the sample is
connected properly to ground or a power supply. Verify that
the jumpers in the base of the MultiMode are set properly
for your configuration.
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