Steam Sensor - Panasonic Microwave Ovens with Inverters Technical Manual

Steam Sensor

This sensor detects the presence of steam emitted by the food being heated and
then, based on how long it took to reach the steam stage, it gauges how much
longer it should cook, before shutting off.
The steam sensor works just like the effect called piezoelectricity. The
piezoelectricity effect generates electricity when mechanical shock is applied to
the general dielectrics material.
In the case of the steam sensor, this effect is called pyroelectricity, where
electricity is generated when heat shock (hot steam) is applied to the general
dielectrics material. See the figure below.
Steam
Sensor
When the food is heated by the microwave oven, the food temperature gradually
increases and steam is generated from the food. The steam sensor, which is
located near the cooling fan, detects the steam from the food.
The fan keeps one side of the sensor cool and the other side, which has the
element, receives and feels the hot steam from the oven cavity.
Principle of Steam Sensor
Dielectrics (Pyroelectricitic) Material
Figure 9
Steam Sensor Location
Figure 10
9