Microtron® or piezoresistive?

Selecting the most appropriate accelerometer to measure vibration or shock phenomena can sometimes be quite confusing. The first point on the decision tree is usually do you need a device to measure steady state / DC response or are you investigating a more dynamic event? In applications that are measuring steady state or low frequency phenomena the next decision point is usually "What sensor type would be most appropriate and combines the highest output with the best shock immunity?" The answer to that question is the subject of this Measurement Endeavors - Quick Tip.

For steady state applications there are two primary technologies offered by the industry, variable capacitance (VC) and piezoresistive (PR).

Endevco's VC product offering known as Microtron® devices are designed with integrated electronics and temperature compensation that condition and optimize the sensors' output to look similar to a standard PR device. Microtron devices have a high-level output and provide gas-damping, extreme shock protection up to 20,000g without damage and can work with a less-than-stable power supply. This relaxed power requirement permits measuring accelerations in a mobile environment, where your power might be 12VDC, 8V or 18V. Although Microtron® devices can be more expensive than PR devices; they can have lower total-cost-of-use due to these less stringent power supply requirements, and a reduction or even elimination of additional amplification.

Microtron® devices are very well suited for measuring very low g level - down to 2 g full scale, especially if they also include high g events such as projectile launches, flight testing or inclination testing. These devices are perfect for providing high quality data while surviving high-speed transient events.

Alternatively, PR devices generally have a higher usable frequency than Microtron® devices. PR accelerometers are also capable of accurately handling much higher g levels (as high as 200,000 g linear response). These devices are passive, temperature compensated resistive devices which generally have low output, so they need to be amplified, both to provide gain and to buffer their output. They also require an accurate, stable, and quiet power supply for reliable operation. Since they have no integrated circuits, they are less complex and physically smaller. It is easy (though modern amplifiers almost completely negate the need) to implement a Shunt Calibration system. Additionally, PR devices are often less expensive than Microtron® accelerometers.

For applications that require measurement or survival in high g environments, involve very high frequency data collection- up to 200 KHz and require that smallest package available PR devices are probably the most suitable type of device.

The bottom line here is, as in most applications, your requirements will dictate which technology and associated electronics you need. Low g measurement with high g survivability suits Microtron®. High g measurement, small package size and high frequency requirements are better suited for PR devices.

Hoping all your Measurement Endeavors are successful! - Endevco Application Support team - Celebrating 60 years of trusted measurements.


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