Appendix B: Auto-Tune Method; Figure B.1 - Tuning Process - Newport LDC-3706 Series User Manual

Appendix B:
Auto-Tune Method
The LDC-3706 Laser Controller currently uses a single auto-tune method. The auto-tune
algorithm will calculate a thermal system's appropriate PID coefficients through a mathematical
PID analysis process. The figure and text below describe the tuning process.
Figure B.1 – Tuning Process
The auto-tune procedure requires a temperature or resistance setpoint, a maximum TEC current,
and a minimum TEC current value to be entered in order to begin. The setpoint is set using the front
panel adjust section to set the TEC setpoint to the desired value. The maximum and minimum TEC
current are set by setting the I+ and I- values through the limits submenu of the TEC parameter
menu. In the example shown, a temperature setpoint above ambient is entered, and maximum and
minimum TEC current values are set to +2.0 and -2.0 Amps, respectively. When auto-tune is started
by the user, the instrument will set the current to the minimum TEC current level, which causes the
maximum possible rate of heating. When the instrument detects that the temperature has reached
the temperature setpoint value (Point 1 on graph), the PID calculation procedure begins.
During auto-tune, anytime the actual temperature exceeds the setpoint temperature, the current is
set to the maximum TEC current value, which causes the maximum possible rate of cooling. This is
seen on the graph at point 1 and point 2. When the temperature exceeds the setpoint temperature at
point 1, the current immediately switches to the maximum value, as seen at point 2. Eventually, the
December 2019 111 LDC-3706 Series Laser Controller