Vescent Photonics
D2 Series Product Manual
1.5.2. User Control of the Poles and Gain
If you remove the right side panel on the Laser Controller, for each stage of temperature control, you will
see the panel shown in Figure 1. The set of click switches labeled “Integral” control the PI (ω
1
) pole.
Clicking the first switch, labeled “proportional,” into the on position removes the integral gain. If the
“proportional” switch is in the off position, then the sum of the times for all switches in the on position
gives the RC time-constant for the PI pole. For example, if the 2
nd
(0.47s) switch and the 4
th
(2.2s) switch
are in the on position (and the rest off), then the time constant is 2.7s and ω
1
=
1
/
2.7s
= 0.37 Hz.
Similarly, the switches labeled “Differential” control the D (ω
1
) pole. If the first switch, labeled “Diff On”
is in the off position, then there is no differential pole. If the “Diff On” switch is on, then the D pole has
an RC time-constant given by the sum of the times of all the switches in the on position, same as with the
Integral bank of switches.
The “PROPGAIN” trimpot tunes the overall gain of the system and is adjustable by a factor of 200.
Additionally, the TSET1 trimpot is used to adjust the set-point temperature for stage 1 (stage 2 is
controlled on the front panel).
The “STBY / SERVO” switch can disable temperature controller for either stage by placing the switch
into STBY (standby) mode. In this mode, a red light will be shown on the front-panel to show that the
stage has been disabled.
1.5.3. Tuning the Thermal Loop
Although there are numerous methods for tuning the loop parameters, these instructions will use the
Ziegler-Nichols tuning method.
For nested stages (one stage is inside a housing whose temperature is controller by another stage), we
recommend tuning the outside stage first with the inside stage turned off. Then tune the inside stage while
the outside stage is turned on. For the stage directly controlling the laser temperature, we recommend
16
Figure 1: Side Panel Adjustments for Temperature Control.
