Physical Logic has introduced two new additions to its flagship range of MEMS accelerometers, based on its proven MAXL-CL-3030. The new products, the MAXL-CL-3050 and MAXL-CL-3070, provide extended sensing ranges of 50g and 70g respectively. Like their predecessor, the new products feature a low SWaP (size, weight and power) footprint and are ideal for tactical- and navigation-grade applications such as UAVs (unmanned aerial vehicles) and other robotic platforms.
Physical Logic’s MEMS accelerometers are closed-loop, providing superior scale factor linearity and stability as well as very low vibration rectification error (VRE) compared to open-loop configurations. Bias stability and temperature sensitivity are also enhanced, and Physical Logic’s most recent revision of the MAXL-CL-3030 provides a 1 year bias repeatability of less than 500 μg.
In designing the new sensors, Physical Logic’s engineers faced the challenge of meeting the demand for increased sensing ranges while minimising the penalty to other performance parameters. With open-loop MEMS accelerometers, the sensing range of the accelerometer is usually proportional to the spring constant. Since increasing the spring constant to achieve a higher sensing range also increases the bias charge sensitivity, this will automatically lead to a drop in performance for higher sensing ranges. For many applications this tradeoff is acceptable, however for navigation-grade accelerometers, high performance and high sensing range are both necessary.
In closed-loop operation, using capacitive sensing and feedback MEMS accelerometers, the tradeoff between performance and sensing range no longer applies, as the range is strongly determined by the feedback voltage. The MEMS design can thus be optimized for performance as well as sensing range. It is also necessary to consider the theoretical error budget for an accelerometer under closed-loop operation, and Physical Logic has developed a strong understanding of these issues and has developed and verified a theory for the closed-loop errors.
The first production units of the new sensors have undergone typical acceptance tests including temperature, vibration, and centrifuge measurements and analysis. These units have shown excellent scale factor linearity up to the high sensing ranges of 50 g and 70 g with a minimal penalty for the other performance parameters.
