MEMS: Building a Smarter Sensor

Smart Solutions

MEMS: Building a Smarter Sensor

Sensors have been around in industrial environments for a long time as critical elements in process and environmental control. Often, smarter sensors have been built with specific applications and operating conditions in mind and they are relatively costly and time-consuming to manufacture.

by Frank Sauber

MEMS (micro-electronic- mechanical system) sensors were originally designed to replace or upgrade some of these industrial sensors with something smaller and more power-efficient. However, MEMS quickly took off in consumer applications such as gaming and smartphones thanks to their size, performance, and low power consumption; but they also took off because they can be manufactured in very high quantities. In the past decade, tens of billions of sensors have been shipped into high-volume consumer applications.

Now MEMS are coming back to industrial applications as one of the key enablers of smart industry trends like Industry 4.0 and IIoT. As industrial systems become more automated and autonomous, and with the proliferation of artificial intelligence and big data processing capabilities, the need is growing for various types of sensors that can provide critical data on processes, machine conditions, and safety; factories can use them to become safer and more collaborative for the people working in them. In industrial settings, accuracy is key. Whether temperature and pressure control in a manufacturing process, inclination measurement for equipment installation, or vibration measurement for condition monitoring, accuracy is indispensable. To build a great, accurate sensor that fits an application requires three key items:

  • First, the ability to measure a certain phenomenon – movement, vibration, sound, pressure, etc. Here the mechanical and electronic parts of the MEMS device are key, with a combination of a tiny moving mechanical part and an electronic part. The electronic part converts changes in the device characteristics due to the movement of the mechanical part into an electrical signal and then into digital information about the physical change being measured.
  • Next, the sensor needs to have all the right features to address the application in question – for example, the right size, the right power consumption, the right temperature range, and smart features that it needs to fulfill the application needs.
  • The final critical element is accuracy – a measure of how closely the output from a sensor matches the “true” or actual value of what is being measured. Accuracy in a sensor depends on its ability to deal with noise in the measurement environment, its stability over time and ambient temperature, and its tolerance, i.e. the limits of variation.
MEMS Smarter Sensor - Motors

Running hot and cold: Condition monitoring of motors through vibration testing requires a high degree of accuracy over time and in harsh environments.

While a sensor’s noise capability is a function of the sensor design (mechanical and electronic), the stability and tolerance are mainly functions of the testing and calibration processes, and the associated algorithms that are embedded in the sensor.

Highly accurate industrial sensors have been produced in relatively low quantities up to now due to the need for long test and calibration times for each sensor. This is where the consumer heritage of MEMS plays a significant role. High-volume consumer MEMS manufacturers like ST have a huge test and calibration capacity installed and therefore the ability to produce industrial sensors in large volumes (relative to the volumes of industrial sensors today) using the same test and calibration equipment used for consumer sensors. The tests are, of course, different from those for consumer sensors, using highly accurate stimuli, wider temperature ranges, a larger number of calibration points, multiple degrees of freedom testing, and high levels of parallelism in the testing processes.

Stability over time

In addition, since the functionality of the smarter sensors is often the same as those used for consumer applications, a small proportion of the consumer sensors can be sorted based on the best characteristics and then calibrated to meet the more demanding industrial requirements.

Take the example of condition monitoring of a motor through vibration measurement. This is an application that requires high accuracy in the measurement of the vibration and stability over time and temperature in a harsh factory environment.

The more accurate the measurement, the more insight can be gained into the evolution of the condition of the motor. This is an important enabler of predictive maintenance where data from a large number of motors is analyzed over time to produce insights into how and when a working motor should be maintained.

ST offers a range of compact, high-accuracy, high-stability, low-power industrial sensors such as accelerometers, gyroscopes, six-axis inertial measurement units (IMU) and magnetometer sensors. ST also offers a range of temperature and pressure sensors suitable for environmental monitoring. These sensors can be combined with micro controllers and connectivity to create smart solutions for industrial equipment monitoring throughout its life cycle – from transport and installation to long-term operational maintenance. During shipment, accelerometers can be used to monitor shock and vibration while temperature and pressure sensors monitor environmental conditions encountered during transport.

Smarter Sensor

Making double sure: An industrial sensor needs to meet stringent performance requirements including extended temperature range, sensing stability, and accuracy as well as ensure long-term availability, all of which require constant testing.

In the installation phase, a high-resolution, high-stability accelerometer can be used for inclination measurement and other accelerometers can be used for shock and vibration measurement. Environmental sensors also enable monitoring of conditions during installation. These measurements enable equipment manufacturers and end customers to be sure installed equipment hasn’t suffered deterioration before it is put into operation.

During equipment operation, accelerometers for monitoring inclination and shock as well as microphones and environmental sensors can be used to gather valuable information to enable condition monitoring and predictive maintenance. Smarter sensors have a great future ahead as one of the key enablers of smart industry trends and ST is working to make that a reality today.

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