15
Theory of Operation
Temperature Controlled Autosampler Board (TCA)
Temperature Controlled Autosampler
Board (TCA)
The board controls all information and activities of all assemblies within the
ALS thermostat. The operator enters parameters, changes modes and
controls the module through the control module or Agilent ChemStation, that
is connected to the autosampler module. Autosampler and ALS thermostat
are connected via a control cable for signal exchange.
Step Down Switcher
The four Peltier assemblies (A to D) are driven by synchronous step down
switching regulators. Switcher 1 and 2 receive their power (+36V) from the
ALS thermostat internal power supply. Switcher 3 receives its power (+24V)
from the autosampler module via the interface cable. The maximum power
consumption for all Peltier assemblies is approximately 180 Watts in cooling
mode and 120 Watts in heating mode.
Regulators
The fans are equipped with hall sensors that allow to determination of the
actual speed of the fans. The speed of the four heat sink fans is variable and
will be set according to the actual temperature at the heat sink side of the
Peltier assemblies. The heat exchanger fan is always running at highest
speed. the speed will be reduced to a minimum when the sample tray is
removed from the autosampler.
Auto Range
When the ALS thermostat power cable is connected to the module the auto
range circuits checks the connected supply voltage. Default setting is a
connection to a 220-240V supply. If the non-regulated 36V is below a certain
limit the auto range circuit activates a switch on the primary board in the
power supply and switches to 100-120V operation.
Multiplexer
The ALS thermostat is equipped with four digital temperature sensors for
temperature control and diagnostics. Four are used to check the temperature
on both sides of the Peltier elements. The temperature sensor signals and the
signals from the hall sensors in the five fans are the input signals for the
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