Lake Shore Model 218 Temperature Monitor User’s Manual
Sensor Considerations
2-5
2.3.4 Contact
Area
Thermal contact area greatly affects thermal conductivity because a larger area has more opportunity
to transfer heat. Even when the size of a sensor package is fixed, thermal contact area can be
improved with the use of a gasket material. A soft gasket material forms into the rough surface being
mated to increase the area of the two surfaces that is in contact. Good gasket materials are soft, thin
and have good thermal conductivity themselves. They must also withstand the environmental
extremes. Indium foil and cryogenic grease are examples.
2.3.5 Contact
Pressure
When sensors are permanently mounted, the solder or epoxy used to hold the sensor acts as both
gasket and adhesive. Permanent mounting is not a good solution for everyone because it limits
flexibility and can potentially damage sensors. Much care should be taken not to over heat or
mechanically stress sensor packages. Less permanent mountings require some pressure to hold the
sensor to its mounting surface. Pressure will greatly improve the action of gasket material to increase
thermal conductivity and reduce thermal gradients. A spring clamp is recommended so that different
rates of thermal expansion don’t increase or decrease pressure with temperature change.
C-218-2-2.bmp
Figure 2-2 Typical Sensor Installation in a Mechanical Refrigerator
