OPERATIONS
Operating the TE Controller from the Front Panel
26 LDC-3700 Series
CHAPTER 2
PARAMETER section of the front panel, the constant’s name will be displayed on the LASER
display, and the value will be displayed on the TEC display.
To adjust the value of C1, C2, or C3, press the (PARAMETER) SELECT button until it sequences to
CONST on the TEC side. The CONST indicator will be illuminated. The LASER display will read C1
and the value will be displayed on the TEC display. To change the value, press and hold in the SET
switch, and turn the ADJUST knob until the correct value is displayed. Release the SET switch to
store the new value. Pressing the SELECT push button will toggle through each constant (C1, C2,
and C3). When C3 is not used it should be set to zero.
The ILX Lightwave Application Note #18 contains information on sensor calibration constants for
AD590 and LM335 sensors. Since these devices are used over their linear range, the constants C1
and C2 are used in this case to determine a linear approximation of the temperature, rather than the
Steinhart−Hart non−linear approximation which applies for thermistors. The appropriate algorithms
are automatically implemented whenever the sensor type is selected via the rear panel SENSOR
SELECT switch.
Setting TE Control Loop Gain
For best temperature control loop performance, the control loop gain needs to be set. The GAIN
function sets the analog feedback gain which, in part, determines how fast the actual temperature
reaches and settles to the set−point temperature. If the gain is set too low (1 is lowest), the TE cooler
will take longer to reach the temperature set−point. If it is set too high (300 is highest), the actual
temperature may overshoot and may oscillate around the set temperature resulting in long
temperature settling times. The allowed GAIN values in the LDC−3700B’s Temperature Controller
are: 1, 3, 10, 30, 100 and 300. These values define the proportional loop gain of our hybrid PI
temperature control loop.
The gain setting depends on the type of TE module and thermal load that you are using, but we can
suggest guidelines for selecting the proper gain. Set the gain to 1 and increase it until the actual
temperature oscillates around the set temperature. Then reduce the gain to the next lower value.
To set the gain, press the (PARAMETER) SELECT switch until the GAIN indicator is lit. The TEC
display will show the value of the control loop GAIN. To change the GAIN, press and hold in the SET
switch, at the same time turn the ADJUST knob until the desired new value is on the TEC display,
INTERLOCK
OPEN CIRCUIT
CURRENT LIMIT
POW ER LI MIT
VOLTAGE LIMIT
OUTPUT SHORTED
LAS E
TE CURRENT LIMIT
T E M OD U LE OPEN
TEMP LIMIT
SENSOR OPEN
TEC
°
SAVE
CONST
GAIN
TEC
CAL PD
RECA LL
SET
SELECT
PARA M ETER
LASER
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