General Functions - THORLABS ITC8 Series Operation Manual

6 Features
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1.2.3 General functions

The combined modules ITC8xxx are bipolar current sources for laser diodes
combined with a thermoelectric controller. The different module types operate the
same way, they only differ in maximum current, resolution and accuracy.
(Refer to chapter 1.3, "Technical data" starting on page 7)
The combined modules ITC8xxx contain a transimpedance amplifier input for the
monitor diode (input impedance 0 Ω). Both polarities of the monitor diode are
allowed. The monitor diode may be operated either photovoltaic (without bias
voltage) or photoconductive, i.e. with bias voltage.
All modules are equipped with an input for either IC temperature sensors of the
AD590/592 , LM335 series or thermistors, PT modules have only an input for
thermistors and PT100 elements..
All necessary value settings are done by keypad and rotational encoder or via remote
control by a computer. Only the laser diode current limit (hardware limit) has to be set
manually as "absolute limit".
In an automated test set-up for different laser diodes no manual settings are
required.
With the modules ITC8xxx, the laser diode current in constant current mode, the
monitor diode current in constant power mode, and temperature or thermistor
resistance are set with a resolution of 16 bit.
The limit values for the laser diode current (software limit), the monitor diode current
(limiting the optical output power) and the limit value for the TEC current (software
limit) are set with a resolution of 12 bit. The monitor diode current, the actual
temperature and actual resistance are read back with 16 bit, the laser diode current,
laser diode voltage, the limit for the laser diode current (hardware limit), the TEC
current and TEC voltage with 15 bit plus sign.
The P-, I- and D-share of the analog control loop are set via three independent 12 bit
D/A converters.
The built-in mains filter in the mainframe and the careful shielding of the transformer,
the micro processor and the module itself provide an excellent suppression of noise,
ripple and other interferences.
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