Test Environment for an Elastic Mechanism—Related to a Kirchhoff Plate—for Usage as Pressure Sensor

Control of pressure is a decisive factor in many technical applications as pump control, injection moulding, press control, and many more. Issues as high plant safety and high process reliability require suitable methods of monitoring and control of pressure. The large range of applications with specific technical framework conditions result in many different solutions for specific tasks. Pressure switches come to action when control of minimum required pressure or maximum pressure are desired. Combination of both leads to complete control of pressure which is an important influencing factor in plastics processing. Giving the example of injection moulding importance of the control of pressure is obvious. To guarantee proper injection scales especially in toolmouldings with high complexity it can be necessary to use several pressure sensors simultaneously. Having found the final geometry of the injection system and having determined the locations where the pressure is of high interest, proven and tested pressure sensors are the best choice. Finding those locations can be elaborate and means extensive effort while testing. Common state-of-the-art pressure sensors most often transform mechanical deformation into electrical signals and these in turn are converted into the value of pressure. Separate pressure chambers might be necessary, often the pressure range is limited, and usage of electrical components lead to constraints concerning temperature range. Using a flexible element and determining the pressure by its deformation eliminates thermal insulation and electromagnetic shielding. Keeping such a flexible element as simple as possible can result in a thin plate with a ram on its outer side to measure its deflection. To convert deflection into pressure it is necessary to know the stiffness of the flexible element. Regarding the flexible element as Kirchhoff plate with a constant bending stiffness implies linear dependency between working pressure and resulting deflection theoretically. This interrelationship is aimed for because it simplifies conversion significantly. To proof this dependency practically a test rig was constructed. As substitution of the pressure a variable but defined load can be applied. Furthermore the test rig can be heated and can be used as test bench for durability analysis. Measurements with different plates show the expected linear dependency within the measurement range which means constant stiffness.