As the core supporting component of large rotating machinery such as steam turbines, water turbines, and compressors, the operating status of sliding bearings directly determines the safety and stability of the equipment. The oil film between the bearing and the journal is the key to ensuring the smooth operation of the bearing. The rationality of the oil film clearance directly affects the lubrication effect, friction loss, and equipment life. Once the oil film clearance is abnormal, it is easy to cause major faults such as bearing wear, burning, and even equipment shutdown. The traditional oil film gap monitoring method has drawbacks such as response lag, strong interference, and inability to monitor in real time. However, eddy current sensors, with their advantages of non-contact measurement, high precision, and strong anti-interference ability, have become the core technology solution for online monitoring of bearing oil film gaps, providing reliable support for the operation and maintenance of rotating machinery.
The eddy current sensor is based on the eddy current effect in electromagnetic induction to measure the oil film gap. Its core consists of a probe, an extension cable, and a preamplifier. The working principle is simple and reliable. The preamplifier generates a high-frequency alternating current of 100kHz-2MHz, which is transmitted to the probe coil through an extension cable, creating an alternating magnetic field around the coil; When the probe approaches the shaft neck (metal conductor), an alternating magnetic field will induce a closed eddy current on the surface of the shaft neck. The reverse magnetic field generated by this eddy current will weaken the original magnetic field of the probe coil, causing a change in coil impedance; The impedance change is linearly related to the distance between the probe and the shaft neck (i.e. oil film gap). The preamplifier converts the impedance change into a 4-20mA current signal or a 0-5V voltage signal, which is transmitted to the data acquisition system and finally converted into the actual value of the oil film gap, achieving real-time monitoring of the gap.
Compared with traditional monitoring methods, eddy current sensors have significant advantages in monitoring the oil film clearance of bearing shells, perfectly adapting to the complex operating environment of sliding bearings. Firstly, it has non-contact measurement characteristics. The probe does not directly contact the shaft neck, which neither wears down the measured component nor interferes with the oil film state, and can work stably for a long time; Secondly, the measurement accuracy is high, with a resolution of up to 0.1 μ m and a linear error of less than 0.3%. It can accurately capture micrometer level changes in oil film clearance, meeting the high-precision requirements of oil film monitoring; Thirdly, it has strong anti-interference ability and is not affected by factors such as oil pollution, dust, electromagnetic interference, etc. The probe adopts an IP67 protection level sealing design, which can adapt to the harsh environment of high temperature and oil pollution inside the bearing box. The working temperature range covers -55 ℃ to 150 ℃; Fourthly, it has a fast response speed and a frequency response range of 0-10kHz, which can capture the dynamic fluctuations of the oil film gap in real time and avoid fault omission caused by lag.
In practical applications, the scientific installation layout of eddy current sensors is the key to ensuring monitoring effectiveness. Usually, probes are installed in the horizontal, left, right, vertical, and vertical directions of the bearing seat to achieve full coverage of the oil film gap. The probe axis needs to be perpendicular to the journal surface, with an initial gap of 2-5mm reserved during installation, matched with a sensor measuring range of 0-10mm. By combining multiple probes for monitoring, horizontal rotor movement and vertical journal displacement can be captured simultaneously. Not only can the absolute value of oil film clearance be monitored in real time, but also hidden dangers such as rotor eccentricity and local wear of bearing shells can be determined by the difference in displacement in each direction. For example, in a 300MW steam turbine high-pressure cylinder bearing of a certain thermal power plant, it was detected through eddy current sensors that the oil film clearance in the vertical downward direction increased from 0.2mm to 0.8mm. A warning was issued 2 hours in advance, and the operation and maintenance team promptly replaced the worn bearing, avoiding major faults caused by journal collision.
With the advancement of industrial intelligence, the application of eddy current sensors in oil film gap monitoring is upgrading towards intelligence and networking. The new sensor integrates a temperature compensation module that can automatically correct the impact of environmental temperature on measurement accuracy, maintaining stable accuracy over a wide temperature range; At the same time, it supports edge computing and industrial Ethernet access, which can transmit monitoring data to the equipment health management platform in real time, realize visual display of oil film gap data, trend analysis and fault warning, and promote the transformation of equipment operation and maintenance from "fault repair" to "predictive maintenance". Data shows that using eddy current sensors for online monitoring of oil film gaps can reduce over 30% of unexpected downtime, lower maintenance costs by over 25%, and significantly improve equipment operational reliability.
In summary, eddy current sensors, with their core advantages of non-contact, high precision, anti-interference, and fast response, effectively solve the technical problem of online monitoring of oil film clearance in sliding bearing bushings, and provide key data support for the safe and stable operation of large rotating machinery. In the context of the transformation of industrial production towards intelligence and efficiency, optimizing the installation layout and calibration process of eddy current sensors, promoting their deep integration with intelligent operation and maintenance platforms, will further play their core role in oil film gap monitoring, help enterprises reduce operation and maintenance costs, improve equipment life, and achieve safe and efficient operation of rotating machinery.