MEMS Accelerometers: Open Loop and Closed Loop Sensors for Inertial Sensing and Navigation

Open Loop Accelerometer for Long-Range Air-to-Ground Strike Weapon

Feature Article by Physical Logic
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Physical Logic presents its MAXL-OL-2040 tailor-made Open Loop MEMS accelerometer, that is designed to replace expensive quartz pendulum accelerometers in INS used for Long-Range Air-to-Ground strike weapons. 

According to the company, the high-performance Open Loop solution is affordable and enables customers to win tenders for these important defense applications. 


Physical Logic is developing and manufacturing Open-Loop and Closed-Loop MEMS accelerometers for tactical and inertial navigation applications. They are based on an in-plane mechanical design and a fully differential capacitive sensing architecture.

Physical Logic’s technical team offers its customers the design of a customized accelerometer interface PCB for all products. Our customers provide the mechanical and electrical interface, and we tailor design an electronic PCB.

In this way we work together with our customers to design and implement impactful solutions. For example, a tailor-made PCB is often applied to Closed Loop accelerometers; however, we received a customer request for a solution supporting development of a non-expensive INS, but with performance similar to more expensive tactical grade modules for a long-range air-to-ground strike weapon application.

One solution was to use Physical Logic’s Closed Loop MEMS accelerometer which easily met all performance parameters, including the required Scale Factor Linearity; however, the Open Loop MEMS accelerometer was a better fit towards the challenge of a smaller and even less expensive sensor. Analysis of the performance of the Open Loop accelerometer showed that it required an improvement in the Scale Factor Linearity over the full sensing range. We were able to close this gap by adding a feature of Scale Factor calibration over the full sensing range.

Standard IMU/INS scale factor calibration is performed by measuring Earth Gravity (from 1g to -1g). A full acceleration sensing range calibration requires testing in a very accurate test centrifuge, a procedure which requires a longer and more expensive calibration by the IMU manufacturer.

Therefore, a custom PCB was designed containing an Eprom component to enable saving of compensation parameters to allow compensation over the entire sensing range of the accelerometer. All manufacture and testing are provided by Physical Logic.

Physical Logic environmental test line includes temperature ovens, a vibration table, and a state-of-the-art precise test centrifuge for up to 200g acceleration, made by Acutronics.

The plots below show Scale Factor errors over the full sensing range before compensation (blue line) and after compensation (red line).

Scale Factor errors 1

Scale Factor errors 2

With compensation, the maximum error over the full sensing range is below 500 ppm, meeting the customer’s requirements.

Our Open Loop accelerometer series of accelerometers MAXL-OL-2000 was designed to fill the gap between traditional MEMS accelerometers and quartz pendulum mechanical accelerometers. The improvement of Scale Factor linearity for the customer proved we succeeded in this company mission. We also offer a 70g Open Loop accelerometer which allows Physical Logic’s accelerometers to be implemented in an even wider range of defense applications.

Our Closed Loop accelerometers series MAXL-CL-3000 with typical Scale Factor Linearity value below 100ppm, can meet even more precise long-range applications and meet C-SWaP requirements.

To learn more, contact Physical Logic Ltd.: Visit Website Send Message View Supplier Profile
Posted by Caroline Rees Caroline co-founded Unmanned Systems Technology and has been at the forefront of the business ever since. With a Masters Degree in marketing Caroline has her finger on the pulse of all things unmanned and is committed to showcasing the very latest in unmanned technical innovation. Connect & Contact