The Logarithmic mode subtracts the log of the Input Signal from the log of the Setpoint to generate the
error signal.
err = log((InputSignal - 0.001) / (Setpoint - 0.001)) / log(1000)
• Divide: This mode helps to compensate the effects of increased loop gain due to increases in the
Setpoint that occurs with the Linear mode. The Proportional Gain is set to zero by default. Typical
starting values for the Integral Gain range from 10 to 100 m/s. The physical unit for the Proportional
Gain is OutputUnit. The physical unit for the Integral Gain is OutputUnits / s.
The Divide mode subtracts the Input Signal from the Setpoint, then divides by the Setpoint to generate
the error signal.
err = 1 - (InputSignal / Setpoint)
G.3. STM Mode
This setting can be found on the Z PI Controller's properties panel in Hardware Space. It is typically
hidden on the Dashboard. Its purpose is to control when the Bias polarity and Setpoint polarity are
linked. This is useful for STM measurements because inverting the Bias Polarity would cause the tip to
crash unless the Signal Polarity is also inverted.
Note
When STM Bias Mode is enabled and linear feedback is selected, the error signal for a
negative Setpoint will be
err = Setpoint - InputSignal.
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