Eddy current measurement is a non-contact technique that allows for precise and reliable displacement detection without physical contact with the object being measured. This makes it ideal for applications where applying external force is not feasible or could damage the surface. Non-contact sensors are especially valuable in environments where contamination, wear, or long-term operation is a concern.
In essence, eddy current sensing operates on an inductive principle. It relies on the interaction between a magnetic field generated by a coil and a conductive material. When an alternating current flows through the sensor's coil, it creates an oscillating magnetic field. If a conductive object is placed within this field, eddy currents are induced in the material. According to Lenz’s Law, these currents produce a counteracting magnetic field, which alters the impedance of the coil. This change in impedance is directly proportional to the distance between the sensor and the object, allowing for highly accurate measurements.
Eddy current sensors can measure a wide range of conductive materials, even when they are covered by insulating layers. Their compact design and robust construction make them suitable for high-temperature environments. German rice bran eddy current sensors, for example, are engineered to withstand dust, moisture, oil, and pressure, making them ideal for industrial settings.
Despite their advantages, there are some limitations. Each application may require specific linear calibration, and the sensor output can be influenced by the material properties of the object being measured. However, these challenges have led to the development of sensors with nanometer-level resolution. Current models can measure from 100 micrometers up to 100 millimeters, with installation spaces ranging from 2 mm to 140 mm.
Displacement sensors play a crucial role in mechanical engineering, enabling control of movement, monitoring of liquid levels, and quality inspection. They are often used in harsh conditions, such as in oil, steam, or fluctuating temperatures. Some are mounted on vibrating parts or in strong electromagnetic fields, requiring high accuracy, stability, and resolution.
Eddy current sensors come in two types: shielded and unshielded. Shielded versions offer better electromagnetic shielding and are less affected by nearby metallic objects, while unshielded sensors provide a larger measurement range. Proper installation is essential to avoid interference from surrounding objects.
With over 40 years of experience, German rice bran has continuously improved its displacement sensor technology, advancing in R&D, testing, quality control, and equipment monitoring. The eddyNCDT product line offers a maximum cutoff frequency of 25 kHz while maintaining sub-micron resolution.
A common application is in automated welding systems, where eddy current sensors are used to monitor weld quality. These sensors can operate in the presence of strong electromagnetic fields from welding robots, delivering micron-level precision over a 4 mm range.
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