From the operating principle to the advantages and limitations: Learn everything you need to know about capacitive ceramic sensors in this tech article.  

The heart of a pressure transmitter has always been the sensor. That is why the right technology for the application is of paramount importance when dealing with: gases, liquids, abrasive and corrosive media. An incorrect sensor choice can be costly, requiring more frequent calibrations or the replacement of the instrument. There are different pressure measuring technologies on the market: Mono and poly crystalline silicon sensors; thin film strain gauge on stainless steel sensors; ceramic thick film DMS sensors and capacitive ceramic sensors. All technologies have strengths and weaknesses, but none of them can serve all applications. 

Capacitive Ceramic Pressure Sensors - operating principle  

The capacitive ceramic sensor works, as its name implies, like a capacitor: The capacitor takes the form of a plate capacitor consisting of two cylindrical ceramic parts - ceramic membrane (anode) and a ceramic substrate (cathode).  

The material of the electrodes is tantalum, applied with the help of thin film technology. The membrane and substrate are connected to each other in a mechanically tight and hermetically sealed assembly with a metal soldering ring.  

When pressure is exerted on the membrane, the distance between both electrodes is decreased, resulting in additional electrons crossing which causes an increase in capacity. This linear signal is converted to an analog signal by the application-specific integrated circuit (ASIC) mounted on the back of the sensor.  

Capacitive Ceramic Pressure Sensors - advantages 

Capacitive ceramic sensors are made for the most extreme environments with aggressive media and overload potential. Manufactured of highly pure ceramics (99.9% Al2O3) it has proven itself to be highly resistant against the most varied process media and is chemically neutral. In addition, 99.9% Al2O3 complies with the requirements of FDA Class VI for the food and pharmaceutical industry.  

Thanks to the measuring cell construction, the overload resistance is a great advantage of this technology. Due to this property and the possibility of being supported by the substrate, the capacitive ceramic sensor may be overloaded up to 40 times its nominal pressure depending on the measuring range. 

The ceramic capacitive measuring principle uses a dry measuring cell without any oil filling for pressure transmission and the cell construction makes the sensor vacuum resistant. Based on the sensor compensation, the sensors feature excellent long-term stability as well as a behavior almost free of any hysteresis. Signal processing enables the realization of measuring ranges customized for the respective application.  

Capacitive Ceramic Pressure Sensors - limitations   

Although there are many upsides to using capacitive ceramic sensors, like all measuring technology there are also downsides.   

The measuring range is limited on the high end to 100 bar. A ceramic sensor cannot be welded directly to the process connection, as with a piezoresistive sensor. Thus, in mounting a ceramic sensor to the process connection, an O-ring must be used. This can require additional knowledge from the end user and can increase the complexity. And finally, because the focus of the ceramic sensor is the process automation market, they can often cost more than a silicone-based sensor.  

Conclusion  

Quality capacitive ceramic pressure sensors minimize downtime, decrease drift and calibration costs, increase quality, and enhance process yields. Ceramic pressure sensors provide machine builders with robust and reliable pressure measurement for higher safety and efficiency in OEM applications. Work-in-process failures are minimized by capacitive ceramic technology, leading to cost optimization.  

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