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Accelerometers: Removing All Guesswork From The Selection Process

Views: 280     Author: Kaylee     Publish Time: 2023-12-18      Origin: Site

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Accelerometers: Removing All Guesswork From The Selection Process

You are aware that you require an accelerometer, but how can you choose the best one for your purpose? If you're not familiar with the many kinds of accelerometers and how they affect your outcomes, you're not alone. The majority of engineers I speak with are shocked to hear how crucial accelerometer selection is; some were unaware that there were other kinds in the first place!

The three primary types of sensing technologies are piezoresistive, piezoelectric, and capacitive MEMS.But it's crucial to clarify exactly what you want to measure before you can even begin to think about which kind of accelerometer is ideal.

In order to help you choose the best accelerometer for your application, let's first go over the many measuring applications for accelerometers and then analyse the various types of accelerometers. To make this as brief and useful as possible, I'll provide a summary in the form of a table at the end of the post along with some useful links. I understand how frustrating it is to require all of this information yesterday and want to test by tomorrow, so let's get you back in the field doing what you love to do best—test!

Applications Of Accelerometer Measurements

As their name suggests, accelerometers monitor levels of acceleration, but they are also used in a variety of applications.I've categorised all the various applications into three primary categories for ease of reading:

1.Movement

"Slow" changes in location or velocity are what constitute motion.Waves, human motion, orientation tracking, and prolonged accelerations like rocket takeoffs are a few examples.

2.Motion

Oscillating motion about a point of equilibrium is called vibration.Electric motors, turbine or bearing monitoring, health monitoring, and resonance detection are a few examples.

3.Dismay

A abrupt change in acceleration that typically triggers a structure's resonance is referred to as shock.A few instances are shock absorber and dampener testing, automobile crash testing, and drop testing.

Piezoresistive, Piezoelectric, And Capacitive Mems Are The Three Types Of Accelerometers.

Pneumatic Acceleration Impact Testing Machine

It's crucial to identify DC and AC reaction before I go into the many types of accelerometers.

The ability to measure down to 0 hertz, which is necessary to determine the gravity vector and other prolonged accelerations, characterises a DC-response accelerometer.In shock applications, when you wish to integrate the acceleration data for velocity or displacement, it is also necessary.Without a DC response, accelerometers will have an intrinsic decay function that, especially over extended events, will cause a large amount of error during numerical integration.

Since an AC-response accelerometer is AC coupled, it is unable to detect continuous accelerations or static accelerations like gravity.Although there are high sensitivity accelerometers that can detect vibrations as low as 0.1 Hz, they are typically unable to detect sluggish vibrations (below a few hertz).Because of their large frequency response and strong signal-to-noise ratio, AC-response accelerometers are the recommended choice for any vibration testing.

If the terminology seems a little off (which is totally understandable!), For additional details on frequency response and other metrics used to measure an accelerometer's performance, see my blog post on accelerometer specs. With that out of the way, let's discuss the three primary kinds!

1.Mems Accelerometer Capacitive

Accelerometers can be made using a fabrication technique called Micro-Electro-Mechanical Systems (MEMS). Although piezoresistive accelerometers can also be made using this technology, capacitive accelerometers are usually what people mean when they talk about MEMS accelerometers.When a seismic mass is accelerated, capacitance variations in the mass cause capacitive MEMS accelerometers to function.

Accelerometers may now be produced at reduced costs and in smaller sizes thanks to MEMS fabrication technology.Because of this, they are now far more common in our daily lives (iPhones, Wii, etc.). Capacitive MEMS accelerometers are typically supplied as surface-mount devices (SMDs) that may be directly affixed to printed circuit boards (PCBs) due to their small size and inexpensive cost. A MEMS accelerometer is included in almost every mobile device, and accelerometers are also used in many other electronic devices for motion tracking and even disc drive safety (by sensing drops).

Because they are DC linked, capacitive MEMS accelerometers are ideal for monitoring low-frequency vibration, motion, and steady-state acceleration. However, their limitations include a narrow bandwidth, a poor signal to noise ratio, and the inability to measure acceleration levels lower than 200g. However, because they are inexpensive and simple to include into your electrical system, capacitive MEMS accelerometers have grown in popularity.

2.Accelerometer With Piezoresistivity

The other widely utilised sensor method for DC-response accelerometers is piezoresistive. As part of the accelerometer's seismic system, strain gauges experience resistance changes due to the action of a piezoresistive accelerometer. Because of their extremely broad bandwidth, piezoresistive accelerometers can be used to measure high frequency, short-duration shock events, such as those that occur during crash testing. In addition to providing protection for piezoresistive accelerometers, gas or fluid damping also increases the dynamic range by keeping the accelerometer from reaching its internal resonance frequency.

Because piezoresistive accelerometers have a zero hertz measurement range, they can also be utilised to precisely compute displacement or velocity data. Because of their often extremely poor sensitivity, piezoresistive accelerometers are not as helpful for precise vibration testing. Since piezoresistive accelerometers are also sensitive to temperature changes, a temperature adjustment is necessary, though many of them already have one built in. Because piezoresistive accelerometers are significantly more costly than capacitive MEMS accelerometers, they are typically not utilised for testing at lower frequencies and amplitudes. For impulse/impact measurements, where the frequency range and amplitude are usually high, piezoresistive accelerometers are by far the best type. Examples of these applications include testing weapons and automobile crashes.

3.Piezoelectric Accelerometer

Lead zirconate titanate (PZT) sensor components, which create a proportionate electric charge or output under acceleration, are commonly used in piezoelectric accelerometers. Because of their broad frequency response, high sensitivity, and simplicity of installation, piezoelectric accelerometers are the most popular type of accelerometer for use in test and measurement applications. They are also the preferred option for the majority of vibration measurements. Because of their enormous popularity, they come in a wide range of weights, sizes, forms, and sensitivity levels. Because of their extremely low noise levels, piezoelectric accelerometers must to be taken into account for all kinds of vibration and shock testing. Applications requiring velocity and displacement data due to their AC coupling are the only ones that are excluded. Along with not being able to detect vibrations lower than a few hertz, they are also unable to detect static accelerations. It's crucial to choose an accelerometer with a measurement range that is somewhat larger than the acceleration levels you anticipate because piezoelectric accelerometers need a charge amplifier, which can become saturated when the accelerometer experiences acceleration levels outside of its measurement range.

Hydraulic Acceleration Impact Testing Machine

In charge mode Due to its resilience to harsh environmental conditions, such as temperatures ranging from -200°C to +400°C, and the fact that some of them can even function in nuclear environments, piezoelectric accelerometers are sometimes regarded as the most durable sensor kind. A charge mode piezoelectric accelerometer has a high impedance, therefore noise immunity requires particular cabling. With these accelerometers, your system will usually be a little more complex and costly because you will also need a charge amplifier.

Mode of voltage The most often utilised kind of accelerometers nowadays are internal electronic piezoelectric (IEPE) devices. IEPE accelerometers are essentially piezoelectric charge mode accelerometers that have an integrated charge amplifier. IEPE accelerometers are therefore very simple to incorporate with your system and do not require any specific cabling. They will need a steady supply of DC power, but many modern data collecting systems come with one.Compared to charge mode accelerometers, the IEPE accelerometer's inherent microelectronic circuit restricts its capacity to withstand harsh conditions. The temperature range of IEPE accelerometers is typically at least -40° to +125°C, which is more than sufficient for the majority of applications.

In a different blog, we went into more detail about piezoelectric accelerometers, including their advantages and disadvantages as well as a general review of how they're made.

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