Eliminate Linearity Errors and Increase Repeatability With a Displacement Sensor Eliminate Linearity Errors and Increase Repeatability With a Displacement Sensor

Membrane potentiometers measure mechanical position by elastic deformation of their upper membrane. This position is used in the control loop of an electrical actuator’s motion. In outdoor applications, these membranes can suffer from a memory effect phenomenon when the sensor is in a frozen position caused by exposure to harsh weather conditions, like a mix of temperature and humidity for extended periods. Typically, such conditions affect the membrane and create a permanent deformation that causes future measurements to be inaccurate.

For our customer, this phenomenon was not only creating linearity errors, but it was also decreasing the repeatability of the actuator’s performance. Specifically, the customer was looking for a repeatability tolerance of ± 0. 2% across the life of the system, which was unachievable with a standard design.

Our ultraflat industrial potentiometer membrane (UIPMA) is an excellent solution for providing feedback on the position of an actuator — offering waterproof performance adapted to outdoor conditions — but it had to be improved in order to eradicate the memory effect on the upper membrane.

Based on the membrane technology — which includes a thin, waterproof design and an easy assembly method via an added adhesive layer — the design engineering team developed a design featuring new materials that remove susceptibility to humidity and temperature and improve endurance life and reliability.

This innovation and material selection was made in a relatively short time and was only possible by also developing an accelerated harsh environment life test system that specifically focused on temperature cycling and relative humidity exposition. It also included 3D behavior modeling with an emphasis on material parameters (dimensions and characteristics) and the functional distance of elastic membrane displacement to optimize deformation and ultimately reduce / eliminate the memory effect.

For optimized integration into the final design, the engineering development team also designed custom contacts that allow electrical interfaces to directly connect the sensor to the PCB. However, a number of other connection options would also be available if required.

With the customized UIPMA displacement sensor, the memory effect phenomenon was eliminated for our customer, and they reached the target repeatability of 0.2% for any environmental condition. This provided a reliable and accurate long term solution, which was previously not possible with this technology.