Inclination sensors

Sensors formobile applicationsPressure sensorsSystem descriptionPressure sensorsThe ifm pressure sensors have been developed for monitoring the systempressure in hydraulic and pneumatic applications. Mobile applications cannotbe imagined without pressure sensors either. ifm offers a series of differenttypes for the different applications. All units have one thing in common:They have a one-piece housing and need no moving parts such as pistons orsprings. The result: The sensors are robust against mechanical influence andwork completely without wear and tear or fatigue.The sensor has a ceramic measuring cell. The advantage of this material: It isresistant to corrosion and absolutely long-term stable. In the long run thisguarantees a continuous accuracy of the measured values. ifm sensors arealso resistant to dynamic pressure peaks and have a high overload resistance.Theyare resistant to pressure peaks which typically occur on fastclosing valves. In view of the resistance to impact and vibration the electronicsensor components are mounted on a flexible film instead of on a rigidprinted circuit board.Operating principleThe most important element of the sensor is the ceramic pressure measuringcell made of aluminium oxide (Al 2 0 3 ). It has a disk made of aluminium oxidewith a layer of gold resinate (thick layer paste) at the inside. This gold layerforms a measuring electrode and a reference electrode on the aluminiumoxide disk. The counterpart is a second disk of aluminium oxide to whichanother gold layer is applied. This layer forms a second measuring electrode.Aluminium oxide is used in view of its excellent chemical resistance to highstrain and its high resistance to pressure peaks. The two disks are connectedby means of a glass frit with the electrode layers being opposite each other.The distance is approximately 10 μm. After assembly the structure of theceramic cell is similar to a plate capacitor. The capacitance is invertly proportionalto the distance between the electrodes. If this distance changes by asmall value I because the pressure applied to the cell rises, the capacitance ischanged by C.C+C= 1/I+IThis shows that the ratio between pressure changes and capacitance (C) islinear if the pressure is proportional to the distance (I). The distance betweenthe electrodes is determined with a constant loading process. The capacitoris loaded by a current source over a certain period of time. The current differenceat the beginning and at the end of the loading process is a measure ofthe deflection of the diaphragm. To compensate for interference and toimprove the ratio signal / interference, the signal difference is determined onthe basis of the measuring and reference electrodes. This signal is then processedby a microprocessor.pressuremeasuring cellelectrodesceramicsPressure sensorson a valve unit.diaphragmThe ceramicmeasuring cell:In case ofoverload thediaphragm issupported bythe base. Thisprovides securityin case ofextreme strain.Visit our website: www.ifm.com106