Vescent D2-105, Manual

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Last update: 2021/12/17 00:00 d2:laser_controller https://www.vescent.com/manuals/doku.php?id=d2:laser_controller
https://www.vescent.com/manuals/ Printed on 2021/12/18 07:41
Place Loop in proportional-only mode: Switch labeled “Proportional” is on, switch labeled “Diff 2.
On” is off.
Turn the gain all the way down (trimpot labeled “PROPGAIN” all the way CCW).
3.
Turn on temperature loop. 4.
Adjust set-point to approximately desired temperature. 5.
Turn up the gain. Keep increasing the gain until the temperature error (front panel BNC) just 6.
starts to oscillate or ring with very little damping. If oscillation too large, reduce gain. Measure
the period of oscillation.
Turn off the Laser Controller. Measure resistance between “GAIN” testpoint and “GND”
7.
testpoint. Turn down the “PROPGRAIN” until this resistance reads 1.7 times less than its original
value (i.e. from 500Ω to 295Ω).
Take the measured oscillation period in step 6 and divide by two. Set the Integrator time
8.
constant to this value. For instance, if you measured a period of oscillation of 14 seconds, turn
on the 4
th
(2.2s) and 5
th
(4.7s) switches in the integrator bank, to get a time constant of 6.9s.
Turn off the “proportional” switch. 9.
[Old models only] Turn the “DiffGain” trimpot all the way CW. (“DiffGain” not adjustable on 10.
newer models.)
Set the “Differential” switches to the same position as the “integral” one. This works out to
11.
setting a D time constant roughly equal to 1/8 of the period of oscillation. For the previous
example, set the 4
th
(0.47s) and 5
th
(1.0s) switches on to get a time constant of 1.5s.
Turn on the “Diff On” switch. 12.
Your thermal loop is now tuned. The “proportional” switch will remain in the off position for 13.
most plants. Power up the Laser Controller and wait for the temperature to stabilize. Change the
setpoint and observe the temperature error and verify that the oscillations are damped and the
temperature stabilizes. You may be able to get better performance by tweaking the poles and
gain.
NOTE: Depending on the thermal design, nested temperature loops can fight each other, causing
oscillations and instability. If you observe this, you will need to reduce the gain and/or increase the
time-constants on the slower stage.
Tuning Temperature Loop for Photodigm Mercury Lasers if you have an older D2-105
If you have a D2-105 with S/N 2674 or lower (PCBs with S/N 6986 and lower), then you may still be
able to tune the parameters of the loop to stably control the temperature of the TOSA by following the
protocol below:
If you are using the D2-105 laser controller to drive a Photodigm Mercury laser in a TOSA package,
the following may be helpful as a starting point for setting the thermal control loop parameters.
9)
Refer to figure 6 .
Set the Integral pole with S2 bank to:
Proportional = OFF
Time Constant = 0.47 seconds
Set the Differential pole with S3 bank to:
DIFF ON = ON
Time Constant = 0.1 seconds
Start with the PROPGAIN potentiometer all the way CCW and then slowly turn it CW until the
temperature stabilizes. BE VERY CAUTIOUS WITH THIS STEP! The TOSA TEC is very responsive
(capable of more than 50°C/s rate of change) and will take off quickly.