EBV Special I Industrial Sensors
Automotive know-how for industrial sensors
Klaus Schlund, the Director of EBVchips, explains to CIE how working with Sensata Technologies EBV Elektronik was able to develop TITAN, a powerful new range of industrial sensors
T
ake a pressure sensor, manufactured in its millions each year for automotive applications, and then add a special 4/20mA interface for industrial applications and you have a new pressure sensor that despite its high quality and technical specifications remains cost effective. That is what EBV Elektronik’s did when it came to defining and developing its latest product - Titan - within EBVchips. Its decision came in response to industrial customers wanting a more cost efficient device that didn’t compromise on quality or precision.
EBV selected the Dutch/American company Sensata Technologies to partner it in developing and working on the Titan project. Sensata produces 75 million pressure sensors, based on a capacitive ceramic technology, each year mainly for the automotive industry. Although these sensors fulfil the stringent automotive quality criteria required they all have a ratiometric 0/5V output. However, a 4/20mA output is the industrial market‘s usual standard and the sensors, without the current interface, were only suitable for very dedicated industrial applications.
Ceramic as a base Sensata manufactures its pressure sensors using ceramic technology. In the automotive industry sensors have been used in a host of different applications,
14 February 2012
the first and adopted most widely was the pressure sensors used in the air conditioning’s compressor loop. However, enhanced versions of this ceramic-based pressure sensor are now also present in automatic gear boxes, fuel applications for low pressure systems (diesel) and in the measuring of oil pressure. As a result the prices for those sensor types have been falling dramatically, and that is due in no small part to the mass production required to meet the demands of the automotive industry and their growing adoption in the consumer space. At the same time there are no significant quality problems with these sensors because the automotive suppliers have already assured a very high base quality in terms of manufacturing.
The basic element in these sensors comprises of a ceramic substrate with a thickness of around 3mm and a thin, flexible ceramic membrane of about 0.6 to 1.2mm. The ceramic membrane is attached to the ceramic substrate using a glass bonding process. Regarding their assembly sensors with different pressure ranges distinguish themselves only through membranes with different thicknesses as well as the electronic calibration. On both ceramic parts there is a thin gold layer that is connected to the electronics via contact leads. Both gold layers form a capacitor with it’s capacity changing as a function of the pressure put
Components in Electronics
onto the membrane. The capacitor’s capacity is in the 15pF range. Using a proprietary charging/decharging process Sensata was able to evaluate the change of capacity relative to a reference capacitor in order to generate an output voltage between 0 and 5V. This process has proven itself in many generations with Sensata systematically improving the electronics and the calibration and the temperature stability while leaving the basic process untouched.
Each single sensor is calibrated at room temperature. As part of the production process these sensors are validated at 23°C and 135°C. Also in the upper and lower pressure range a calibration is conducted. All these measures are purely analogue without using digital electronics. In manufacturing as well as in the field this process has proven to be extremely stable. Within a core range the sensor elements show rather linear characteristics, it’s only at the lower and upper end of the scale that there are larger non-linearities.
Titan provides 4/20mA output Sensors for industrial applications need a 4/20mA output, so the Titan pressure sensor, with an industrial output interface, were developed as a response. EBV with Sensata defined a backend electronic circuit for converting the 0/5V signal
into a 4/20mA output current. EBV was responsible for the definition of the industrial interface and by using Sensata‘s pressure technology, originally developed for automotive applications, was able to develop a sensor suitable for its industrial customers. The sensors can be used in process automation systems and other applications.
The complete 4/20mA sensor solution, that is the Titan product range, is being marketed by EBV as part of it’s EBVchips activities. EBV deliberately did not look to limit the term ‘EBVchips’ to only silicon, in fact it includes hybrids, modules or encoder or in this case industrial sensors in a screw mounting housing.
Many options Currently those EBVchips pressure sensors are available in brass versions for the three pressure ranges 0 – 10bar, 0 – 20bar and 0 – 35bar. Also available are variants in stainless steel for the 0 – 45bar range. If required and the appropriate volume is needed EBV Elektronik and Sensata are able to produce other variants equipped with different connectors, different mechanical connection or packaging. At present the pressure sensors are classified according IP65, IP67 and IP6K9 (all with cable).
Because the sensor is powered via the signal line, Titan sensors only use two connection lines according to SAE
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