2-5
Ultra Trace Oxygen Analyzer Operational Theory 2
Teledyne Analytical Instruments
temperature minimizes the cell offset (typically less than 75 PPB). A second
benefit of the TEC system is that by regulating the cell temperature the
analyzer becomes tolerant of thermal transients.
The TEC module is a solid-state semiconductor heat – pump. Passing
DC current through the TEC module produces heat flow though the device.
One side of the device will become hot and the other side will become cold.
The TEC module is attached to a heat-sink which is cooled by a fan. This is
required to maintain the hot side at an acceptable temperature. The hot side
temperature limits the overall performance of the TEC module. The fan
draws air into the bottom of the analyzer, this air is forced over the heat sink
and exits through the left side of the analyzer. The power for the TEC device
is supplied by a Pulse Width Modulated (PWM) proportional switching
temperature controller. The temperature controller PCB supplies a 12 volt
pulse whose duty cycle is proportional to the cooling required. The tempera-
ture controller PCB uses a thermistor to monitor the temperature of the of cell
block. Power for the fan, and the temperature controller PCB is supplied by
a separate 12VDC power supply.
Figure 2-3. Characteristic Input/Output Curve for a Micro-Fuel Cell