Miniaturised Inertial Sensors with Advanced Temperature Compensation

Inertial sensors play important roles in the majority of industrial machines and vehicles where they collect important data on the motion and position of machine components and their prevalence is expected to become even greater as IoT and 'Industry 4.0' become the norm. However, the principles behind these sensors have still not been perfected; no inertial sensor has been created that is not affected by changes in temperature. This means that temperature compensation is essential to ensure that the readings from the sensor are accurate.

LORD MicroStrain has developed a new range of inertial sensors that have advanced temperature compensation in a miniature OEM package - allowing the sensors to be used in almost any application. We spoke to Fritz Martin, Inertial Engineering Manager at LORD Microstrain, about the features of their new inertial sensors, and how he expects them to impact the industry.

What technology drives LORD Microstrain’s new range of CV5 inertial sensors?

At the component level, improvements in MEMs technology have led to the introduction of some low-cost accelerometers and gyros with much better performance than previous low-end and industrial-grade offerings.

In the CV5, we combine the best of these lower cost sensors with our fifth-generation fusion software running on a Cortex M7 processor. The M7 allows us to include auto-adaptive and auto-mag calibration features in a package and at a price that just wasn’t possible, even a year ago.

What applications are these sensors designed for?

Any application that requires a miniature, low cost, precision embedded OEM IMU/AHRS component. Because they are full 6DOF sensors, and because we offer a wide selection of acceleration and angular rate ranges, they can be used for any type of attitude or inertial sensing.

They have equal performance on all axis, like all of our inertial sensors, and thus have no restrictions on mounting orientation.

Inertial sensors are an essential component for attitude sensing in drones. Shutterstock | Newnow

What are the advantages of using miniaturized inertial sensors for OEMs? Does the small size impact the sensitivity of the sensor?

It is rare that we have a request for an inertial sensor where small size or light weight is not important. Low profile is also very important to many of our customers and often a reason why we are selected over a competitor.

It is a challenge to make a low-profile sensor without affecting precision and maintaining equal performance on all three axis, but because it is a priority, we have become expert at it, both in design and production.

Why is accurate temperature compensation important? How does the CV5 family’s temperature compensation compare to that of your competitors?

Producing a MEMs accelerometer or gyroscope that is not affected by temperature or vibration is kind of a holy grail for the industry. It hasn’t happened yet. That hasn’t prevented un-compensated sensors from being used in many applications with impressive performance in constant or narrow temperature ranges.

The problems occur when customers try to use these sensors in more traditional industrial and vehicle applications where high vibration, shock, and temperature extremes are encountered. The sensor performance quickly falls apart and they are forced to look for temperature compensated sensors.

They finally come to us when they realize that even among temperature compensated sensors, ours perform the best. Because we have been doing it so long and developed our own in-house proprietary calibration equipment, we have steadily improved our calibration to the point where the inertial performance specs are nearly invariant over temperature. And, we can do this in high-volume and at low cost.

What different models are available in the CV5 range?

Currently we offer a basic IMU (3DM-CV5-10), a VRU (3DM-CV5-15), and an AHRS (3DM-CV5-25). These use the same footprint as our original 3DM-GX3-25-OEM package. We will also offer a GNSS/INS version (3DM-CV5-45) in the near future.

What are the benefits of the auto-mag calibration that the CV5 range is equipped with?

The usefulness of a magnetometer for heading is not in how well it is calibrated at the factory, though that is important, it is how well it is calibrated once it is installed in a user’s system. Connecting to an external host running calibration software is very effective, but often awkward or even impossible to do, especially in an embedded application.

In fact, awkward is a mild description for some applications – I think “nightmare” is often used. I can guarantee you that for anyone that has embedded a magnetometer in an underwater vehicle, or drone, or fixed wing application, they are going to breathe a huge sigh of relief now that all they have to do is enable the auto-mag cal feature and forget about it.

The 3DM-CV5-25 from LORD Microstrain

How does the CV5 range’s auto-adaptive features work? In what situations is this technology at its most beneficial?

Auto-adaptive, simply stated, gives the sensor the ability to tell the difference between noise and reality when evaluating a reference measurement like gravity or magnetic heading.

This ability to differentiate means that the sensor is able to reject reference measurements corrupted by linear accelerations or temporary magnetic disturbances. The result is pitch, roll, and heading accuracies for our VRU and AHRS are almost as good as what are normally only expected from a full GNSS/INS.

What are the other key features of the CV5 inertial sensor range?

The mounting is carefully designed to decouple mechanical stresses from mounting surfaces. Those stresses can telegraph to the MEMs and cause a variety of bad behaviours. We also designed the package so that it can be mounted directly on a PC board, or it can be chassis mounted and connected to a PC board via ribbon cable.

We are committed to this footprint long-term so that customers can easily do drop-in replacement with newer models or move up and down the price performance curve as we introduce other “C” package variants in the future.

Where can our readers find out more about the CV5 range and LORD MicroStrain?

Please visit our website here for more information.

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About Fritz Martin

Fritz Martin is the Engineering Manager for Inertial Products at LORD Sensing Systems, MicroStrain. He has an M.S. in Scientific Instrumentation from U.C. Santa Barbara and a B.A. in Physics from Colby College. He has been working on inertial systems at LORD since 2004.