Thimble type sensors

Standard Manufacturing Route for Thimble-Type Sensors 5.6.4.2.1 Shaping Thimble-Type Sensors... 

Sensor element temperature needs to rise to several hundreds degree centigrade in order to operate as oxygen sensor. Zirconia solid electrolyte is an insulator at normal room temperature and it cannot detect the gases. Therefore, gas detection is not possible until the necessary temperature of the sensor element is reached. Because the time of gas detection is short, a heater is embedded in the sensor element to achieve fast light off. The rod type heater is arranged inside of the side of the reference ambient air of the thimble type sensor element, and then the sensor element can be heated. Heating material is printed on the alumina sheet and is laminated. After that, it is wrapped upon the rod type ceramic and then sintered. Extension of the electrode is structured by terminal. 

Sensor elements in thimble-type 02 sensors represent about 75% of the oxygen sensor market today. These elements are mainly shaped by dry pressing and grinding of granulated Zr02. 

Fig. 17.15.5 shows comparative cross sections of a standard thimble sensor (LSH) and the first mass-produced planar type sensor (LSF). Fig. 17.15.6 explains the three-dimensional layer structure. The functional layers of the planar element are stacked in three sheets (Section 5.6.4.3, Fig. 5.6.8). 

Recently, faster activity is a requirement, beside the above mentioned thimble type oxygen sensor. The requirement is resolved due to the more compact sensor element and multilayered co-fired structure of the heater and the sensor element. By way of an example, the element portion of the thick film type oxygen sensor is described [5]. Zirconia powder for the partial stabilization is mixed with an organic binder and a solvent. A sheet is formed and electrode pattern is printed by Pt ink. For the heater, a pattern is printed by Pt ink and the... 

The thimble-shaped ceramic has a crimped talc ring at the edge of the metal shell, which is same as the thimble-type oxygen sensor element and it ensures the sealing for the outside of the thimble-shaped ceramic. 

Since the 1980s, oxygen sensors have also been designed in planar type. Although the planar structure requires lower size, lower power consumption for the heating elanent, and lower fabrication costs and enables better stability in the measurements, the physical principles governing the behavior of the sensors are essentially the same in both thimble and planar types (Tnller 2000 Park et al. 2009). Some planar sensors work with no air reference in one of their electrodes (Lopez-Gandara et al. 2009). 

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