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Pressure Sensor in Printed Circuit Board Technology
Keywords: Pressure sensor, Printed circuit board technology, long-terme performance
The aim of the described development was the substitution of the pressure sensors formerly produced by Sauter AG with the new cost-efficient PCB pressure sensors. The production of capacitive pressure sensors requires a diaphragm with a defined distance to plates. In the former technology an elastomer diaphragm, pole plates, two metal springs and further parts in an injection-moulded case are used. The aim of the development is the reduction of effort and costs for the sensor and the electronics belonging to it. The basic structure of the developed pressure sensors consists of a membrane in a cavity inside of a printed circuit board stack. The copper of the board forms the electrodes. The diaphragm consists of an elastomer coated flat spring. The electronics for measuring the distance between the membrane and the electrodes using the change of the value of the capacitance and the analogue-digital conversion is placed directly on the surface of the PCB stack. No cables are necessary. The basic parameters of the sensor are: pressure ranges 0…150 Pa 0…300 Pa high sensitivity low Offset-Drift high long-time stability Size of the sensor: 33 * 38 *7.5 mm Size of the membrane: 28 mm Distance between membrane and electrodes: 0.4 mm Square root function Permissible positive pressure ±10 kPa Perm. operating pressure pstat ±3 kPa Perm. ambient temperature–0...60 °C reduced accuracy–20...80 °C Long-term performance and temperature influences were the most critical points of the development process. The success of the development shows that it is possible to overcome long-term problems in high precision mechanical systems made in PCB technology with suitable materials. The high effort to find out the suitable materials shows the very long way between the principle function of a device in a new technology and the production. The costs are reduced by a factor of 3. New versions are under development.
Martin Hämmerle,
Sauter AG
Basle, CH-4016 ,
Switzerland


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