May 2017

Pressure sensors

Solution competence from die to system

The highest precision pressure measurement possible is a prerequisite for the automation of many industrial processes and is playing an increasingly important role in the introduction of Industry 4.0 concepts. At the same time, the demand for pressure sensors is continuously rising, especially in the automotive industry. As many as 20 pressure sensors are needed in the drive train alone – consisting of the combustion engine and exhaust system – to minimize fuel consumption and at the same time meet the ever more stringent emission requirements.

TDK is a competent supplier of pressure sensing solutions. From the development and production of miniaturized sensor dies (elements) to housed, application- and customer-specific pressure transmitters (systems), all TDK pressure sensor elements are based on the piezoresistive principle. This is characterized by high precision and exploits the physical effect by which pressure causes changes in the electrical resistance of a piezoresistive material (silicon) that are linear over a wide range.

For this purpose, the miniaturized sensor dies contain four integrated piezoresistors in a bending plate, which are connected as a Wheatstone bridge and deliver an analog output voltage that is directly proportional to the pressure. TDK is able to manufacture tiny elements that have an area of just 0.65 x 0.65 mm, or have extremely low profiles of just 0.24 mm.

 

The latest generation of EPCOS pressure sensor elements has dimensions of just 0.65 x 0.65 mm and is suitable for absolute pressure measurement from 0 to 10 bar.

In order to achieve the highest possible mechanical stability, the dies are mounted on glass substrate. Depending on the design, this means that absolute or differential pressures can be measured. Additional options for the design of the elements, such as the solderable metallization of the back side of the glass bodies for better bond to substrate or the passivation of the back side of the elements. Furthermore, as improved corrosion protection, the bonding pads can also be gold-plated.

Ideally suited to automotive applications

Based on the sensor elements (dies), pressure transmitters (systems) are manufactured that use an ASIC to perform the calibration and signal conditioning. In this way, the output voltages of 0.5 V to 4.5 V or output currents of 4 mA to 20 mA that are typical for industrial applications can be implemented. Likewise SENT (single edge nibble transmission) digital interfaces such as can also be integrated for automotive applications, as in the case of the TDK MiniCell® series of pressure transmitters. Especially for automotive applications, the pressure sensors have to be highly resistant to aggressive media such as exhaust gases or fuels. For this reason, the MiniCell series is designed with a stainless steel membrane that protects the electronics and sensitive sensor element. The pressure is transmitted by an oil filling between membrane and die. Thanks to their metallic encapsulation, these MiniCell transmitters also offer excellent shielding against EMI.

 

MiniCell® pressure transmitter for differential pressure measurement. This series is extremely robust and features high resistance to aggressive media.

TDK also manufactures application- and customer-specific sensor systems that feature specially designed plastic housings and terminal configurations for pressure and data lines, e.g. for monitoring diesel particulate filters. During operation, these filters become increasingly clogged with soot particles. The pressure sensor detects the resulting rise in exhaust gas pressure, and the regeneration of the filter is initiated. The particle filter is then burned clean by a brief increase in the temperature and the supply of oxygen. TDK also has also developed special fuel-resistant pressure sensors for the monitoring and control of the pressure in fuel tanks. They measure the pressure of fuel lines into order to achieve an optimal and energy-saving control of the fuel pumps.

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