ALTANA Temp-Gard Basic - Handbuch (Seite 30)

temp-gard basic Hardware
9
Barriers and Heat Sinks
Made from stainless steel the Thermal Barrier provides the thermal and mechanical
protection necessary for the data logger to travel through the hostile environment of an
industrial oven.
Ceramic insulation covered by a ceramic fiber cloth provides the primary thermal
protection. Heat sinks ( only in long-time barriers) provide additional, secondary protection
allowing the system to operate at high temperature for extended periods. The heat sinks
are filled with a non-toxic, non-flammable phase changing material. This material absorbs
the heat and maintains a temperature of approx. +50 °C until all the material has changed
from solid to liquid state.
Note: The ceramic insulation material will absorb moisture if stored in a damp
environment. Although this will not result in damage to the thermal barrier, its performance
will be degraded until the moisture is removed.
A steel pad on the barrier’s lid provides a convenient stage area for magnetically attached
probes.
Thermocouple Probes
Thermocouple probes utilize the Seebeck effect which, discovered in the 19
th
century,
results in a voltage proportional to temperature being produced at the junction of any two
dissimilar metals.
The actual voltage measured is proportional to the temperature difference between the
thermocouples “Hot” and “Cold” junctions, the “Hot” junction being the measurement
junction, and the “Cold” junction being the junction of thermocouple and measurement
instrumentation.
The practical implementation of thermocouples requires sophisticated electronics to
eliminate potential measurement errors. These potential errors include poor linearity over
the measurement range, and inaccuracy due to temperature variations at the Cold
reference junction.
To accommodate these the electronics in the measuring system must simulate a
temperature of zero degrees at this second junction, as well as compensating for any non
linearity over the range of the thermocouple operation.