Capacitive and piezoelectric accelerometers for vibration analysis, motion studies, and structural health monitoring.
We are all familiar and have experience with acceleration. Acceleration is the rate of change of velocity over time. It’s when you speed up in your car, and it’s the rush back to the ground when you jump. Because acceleration is so integral to our daily lives, acquiring data about acceleration in a system can be extremely useful. The sensor used to do just that is an accelerometer. The general principles on which these sensors operate are change in capacitance and change in voltage, and their capabilities of measurement include both stationary accelerations, such as gravity when you’re standing still on Earth, as well as accelerations due to motion, such as speeding up your car. Essentially, accelerometers can either contain a network of capacitors within the sensor that change levels of capacitance as the accelerometer moves in different directions, or they can house a piezoelectric material that directly outputs voltage under changes in force. These differences in capacitance then produce a change in voltage (or change in voltage may be directly produced, in the case of the piezoelectric type), and through this data acceleration can be determined.7
Accelerometers can measure in up to three axes, and they utilize an analog input. A transistor can frequently be required in the circuitry for using an accelerometer in order to prevent system noise from affecting the sensor data. Additionally, accelerometers require calibration before use.
In terms of application, a study was published in 2008 that represented data acquired from US citizens by accelerometers. The premise of the study was to determine activity levels of Americans among each age group. The participants were asked to wear accelerometers on their person for the duration of a week. Based on the data acquired, researchers accomplished the first official assessment of American activity level. Accelerometers were crucial to the success of the study.1
7 Troiano, Richard P., et al. “Physical activity in the United States measured by accelerometer.” Medicine and science in sports and exercise 40.1 (2008): 181.
Recommended DAQ
Recommended DAQ: Nyquist 2 or Nyquist 3
Vibration analysis benefits from simultaneous sampling across X / Y / Z axes — NQ3 is built for this with its fully-differential simultaneous-sampling channels. NQ2 works for single-axis or non-time-correlated logging.
Code example
The DAQiFi Python SDK exposes a property-based API. Below is a minimal stream — discover the device, enable an analog-input channel, and print samples at 1 kS/s.
from daqifi import DAQiFiDevice
with DAQiFiDevice.discover_first() as dev:
dev.channels.ai0.enable()
for sample in dev.stream(rate_hz=1000):
print(sample)
For C#, Java, LabVIEW, or Node.js examples, see the open-source stack page or jump straight into the reference example app on GitHub.
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