Newport 350B, User Manual, Page: 54 / 66

Maintenance and Service 53
Figure 16 TE Module Configuration
It is necessary to remove the heat from the hot side of the TE module. The amount of heat
to be dissipated is equal to the heat pumped from the cold side plus the input power to the
TE module. Although the amount of cooling is proportional to the current flowing
through the TE module, the power dissipated by Joule heating (input power heating) in
the TE module is proportional to the square of the current. Half of this heat must be
pumped from the cold side of the TE module. When exceeding a maximum current value
(I
max
), which is device dependent, the net cooling of the TE module decreases because
Joule heating is increasing at a greater rate than Peltier cooling. The manufacturer of the
TE module will state the maximum current for each TE module and this current value
should not be exceeded.
The LIMIT SET feature on the Model 350B Temperature Controller allows the user to
limit the maximum current flowing through the TE module.
7.4 Mounting Considerations
The physical arrangement of the TE module, thermistor, heatsink, and the device to be
cooled or heated are crucial to the operation of a Model 350B Temperature Controller.
This arrangement determines the thermal load and the rate of heat dissipation to which
the control circuitry must respond. To achieve optimum temperature control the thermal
path between the device to be cooled or heated and the face of the TE module must be as
short as possible and must have high thermal conductivity.
This arrangement also determines the delay that the control circuitry must respond to, and
affects the gain setting of the control loop. Another factor that must be taken into account
is the mass of the heat sink required to dissipate heat from the TE module. The better the
heat sink dissipates heat, thus reducing the thermal gradient across the TE module, the
more efficient the TE module is at removing heat from the device being cooled.
Figure 17 shows an arrangement that optimizes the cooling and temperature stability
achievable with the Model Temperature Controller.