2 – 10
Getting Started
of the TEC current limit value. Note that changing the TEC current
limit will return the tuning step size back to its default value of 10 %
of the limit.
Autotuning may also fail if the TEC polarity is incorrect. In this case,
the message
TE Cfg: Autotune
Check Polarity
is displayed. Correct the TEC polarity (see section 2.2.3.1 above) and
then repeat the autotune process.
2.2.5
TEC operation in CT mode
After entering the sensor configuration, TEC settings, and tuning
the control loop, the TEC controller is ready for operation. Turn the
TEC controller on by pressing the [TEC On
/
O
ff
] button. The
TEC
ON
indicator should illuminate. The temperature shown on the
large green display should settle to your setpoint (in this example,
25.005
◦
C). The overshoot is typically less than 60 mK in magnitude.
You can change the temperature setpoint by navigating to the [Set]
menu tree. Press [ ] repeatedly to reach the top item, “T:”. Turn the
wheel or directly type a new temperature, say 20.000
◦
C, and press
[Enter]. The TEC controller will adjust the output current and settle
the temperature to the new setting.
Temperature can also be adjusted in “live” tracking mode. Press
the [Live Entry] button to enter live tracking mode (the
Live
indica-
tor will illuminate). Turning the wheel now will cause “on-the-fly”
changes to the operating temperature. Pressing any button (includ-
ing the [Live Entry] button) will exit live mode.
Once the temperature has stabilized at the desired operating point,
many systems benefit from re-tuning. This is because of the in-
herent non-linearities in thermoelectric coolers, leading to a strong
temperature-dependence on the overall loop gain. If desired, repeat
the autotuning with the TEC on. The TEC controller will return to
the original setpoint after autotuning has completed. This re-tune
operation will often reduce the thermal drift significantly.
2.2.6
Thermal runaway
In general, it is possible to obtain outstanding temperature control
with a thermoelectric cooler. At the limits of a TEC’s cooling power,
however, the thermal e
ffi
ciency of the cooler diminishes. At some
point, a small increment in cooling current will actually lead to an
LDC500 Series Laser Diode Controllers
