Ultrasonic transducers, eddy-current sensors, and LVDTs for motion tracking, NDT, and vibration sensing.
Measurement of position and displacement has widespread impact upon many different applications. Some applications include backup cameras in cars, vibration sensing of rotating systems, and part identification and design confirmation, among many others.
Two common sensors for measuring change in position are the ultrasonic transducer and the eddy current sensor. Both are robust, capable sensors that thrive in extreme environments involving widespread temperature ranges, high pressure, as well as dirty operating conditions. However, they operate and receive information about displacement in two different ways. The ultrasonic transducer detects the waves produced by the very particles that make up materials when they are exposed to electricity. The transducer acts as both the creator of the electrical signal pulses as well as the receiver of the resulting ultrasonic waves from the material. As proximity to an object changes, so do the waves created by the particulate vibrations. Therefore, based on the changes in the response of the material, the data acquired by the transducer can be used to determine the distance the sensor is from an object.
The second common sensor used in determining displacement is the Eddy current sensor. This device uses magnetic field produced by electromagnetic induction to collect data. In the sensor, as alternating current is initiated, which in turn produces an alternating magnetic field. As the sensor approaches a conductor, the induced magnetic field in the sensor a second induced field, this time in the material itself. Therefore, the sensor then uses the interactions of the two magnetic fields to produce a voltage proportional to the distance between the sensor and the conductor.
Another relevant application of these sensors is Non Destructive Testing and Evaluation of parts. In an experiment conducted in 2006, both Eddy current sensors as well as ultrasonic transducers were used to examine metallic plates for inherent flaws. Through detections in minute height differences on the surfaces of the plates (due to tiny cracks, imperfections, porosities, etc), flaws in the parts were easily discovered and characterized before the plates were put into any kind of applied structure. Through the use of these two sensors, a classification system was developed to help guide the evaluation of parts before implementation.5
Depending on the sensor, either an analog or digital interface can be used to acquire data. Additionally, sensors suitable for use with the Nyquist will generally use a 5 V power. Though the sensors are incredibly good at their jobs, they do require calibration before use.
5 Buonsanti, Michele, et al. “Ultrasonic pulse-echoes and eddy current testing for detection, recognition and characterisation of flaws detected in metallic plates.” Proceedings of the 9th European Conference on Non-Destructive Testing. 2006.
Recommended DAQ
Recommended DAQ: Nyquist 2 or Nyquist 3
Position sensors range from 0–5 V analog encoders (NQ1/NQ2) to bipolar differential signals on LVDTs and eddy-current probes (NQ3). Pick by sensor type.
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.
← Back to Data Acquisition Wiki · Browse DAQiFi DAQ devices → · Open-source stack →