Log mode is preferable for most STM samples, because the tip responds in a more symmetric manner (i.e., the same going up and coming down). Log mode tends to linearize the entire feedback loop since Z » ln(i). The asymmetric response of the Linear setting distorts data.
Optimizing Integral and Proportional Gains
The Integral Gain is usually the major contributor to the performance of the feedback loop due to its “long term” influence. For this reason, it is usually adjusted before Proportional Gain.
The integral term in the feedback calculation has the highest gain at low frequencies, and its effects diminish with increasing frequency.
A nominal Integral Gain value may be obtained by slowly increasing the value until the piezo begins to oscillate, then decreasing the value until oscillation ceases. Oscillation effects are best viewed in the Scope window and show up first in error signal (i.e deflection or amplitude).
The Proportional Gain parameter is typically set to 35 to 100% more than the Integral Gain value.