Eddy current speed displacement sensors are widely used in the speed and shaft displacement monitoring of rotating machinery due to their non-contact measurement, fast response speed, and high reliability. The eddy current sensor probe model 8300-A25-B90 is one of the common models. However, in actual industrial environments, the surface condition of the measured shaft is often difficult to maintain ideal, such as scratches or coating peeling due to long-term operation. These surface defects will significantly affect the measurement accuracy of the eddy current sensor, and thus affect the equipment status assessment and protection strategy based on speed and displacement information. This article will deeply explore the possible interference of scratches and coating peeling on the measured shaft surface on the 8300-A25-B90 eddy current sensor, and analyze the corresponding compensation methods.

I. Working principle of eddy current sensor

The eddy current sensor 8300-A25-B90 works based on the principle of electromagnetic induction. The probe is equipped with a high-frequency oscillation circuit to generate an alternating magnetic field in the coil. When the probe is close to the surface of the conductive object to be measured (usually metal), the alternating magnetic field will induce eddy currents on the surface of the object to be measured. The size and distribution of the eddy currents are affected by the conductivity and magnetic permeability of the material of the object to be measured and the distance between the probe and the object to be measured. In turn, the magnetic field generated by the eddy current on the surface of the object to be measured will react to the probe coil and change the equivalent impedance of the coil. The sensor 8300-A25-B90 measures the change in this impedance and converts it into a voltage or current signal output, thereby reflecting the distance between the probe and the object to be measured or the change in the surface state of the object. In the application of speed measurement, protrusions (such as keyways or gears) are usually set on the measured shaft. The sensor generates a pulse signal by detecting the distance change caused by these protrusions, and then calculates the speed.

Interference of shaft surface defects on speed measurement

When there are defects such as scratches or coating peeling on the measured shaft surface, the measurement process of the eddy current sensor 8300-A25-B90 will be disturbed by the following:

Influence of scratches:

Distance change: Scratches on the shaft surface will cause slight changes in the local distance between the 8300-A25-B90 sensor and the shaft surface. Although the scratch depth is usually small, these small distance changes may cause fluctuations in the output signal in high-precision speed measurement, especially when detecting small protrusions on the shaft surface, which may cause distortion of the pulse signal.

Material discontinuity: There may be micro cracks or stress concentrations in the material at the scratch. These discontinuities will affect the distribution and intensity of local eddy currents, resulting in nonlinear changes in the sensor output signal.

Influence of coating peeling:

Material property changes: The coating on the shaft surface is usually to improve wear resistance, corrosion resistance, etc. If the conductivity and magnetic permeability of the coating material are different from those of the base material, the integrity of the coating is critical to the induction and distribution of eddy currents. The peeling of the coating will cause the sensor to sense the characteristics of different materials in different areas, resulting in abnormal output signals.

Signal amplitude and phase shift: The barrier effect of the peeling coating area on eddy current is different from that of the intact coating area, which will cause the amplitude change and phase shift of the sensor output signal. In speed measurement, this may cause the amplitude of the pulse signal to be unstable, affecting the subsequent signal processing and speed calculation.

Frequency response change: Different materials respond differently to electromagnetic fields of different frequencies. The peeling of the coating may cause the frequency response of the output signal of the sensor to change when detecting bumps at different speeds, introducing measurement errors.

II. Compensation method

In order to reduce or eliminate the influence of shaft surface scratches and coating peeling on the measurement accuracy of the eddy current speed displacement sensor, the following compensation methods can be adopted:

Signal processing algorithm:

Filtering and denoising: Digital filtering algorithms such as median filtering and Kalman filtering are used to smooth the sensor output signal, filter out local noise and fluctuations caused by surface defects, and extract effective speed pulse signals.

Adaptive threshold: In speed calculation, the adaptive threshold method is used to detect the peak value of the speed pulse. This method can dynamically adjust the threshold according to the local characteristics of the signal to reduce misjudgment caused by signal amplitude fluctuations.

Signal correction: If the distribution of surface defects is relatively fixed, the error model can be established by pre-calibration methods, and corresponding corrections can be made in signal processing.

Hardware improvement:

Multi-probe layout: Multiple eddy current probes 8300-A25-B90 are used to measure at different positions in the axial or circumferential direction. By averaging or weighting the signals of multiple probes, the impact of local surface defects can be reduced and the overall robustness of the measurement can be improved.

Optimize probe design: For specific application scenarios and possible surface defect types, optimize the structure and size of the probe to reduce its sensitivity to local surface defects. For example, increasing the sensing area of ​​the probe can average local non-uniformity.

Temperature compensation: Temperature changes on the shaft surface may also affect the output of the eddy current sensor 8300-A25-B90. The use of temperature compensation technology can reduce the measurement error caused by temperature changes and improve the measurement accuracy in complex environments.

Regular maintenance and calibration:

Regular inspection: Regularly check the surface condition of the measured shaft, promptly detect and deal with defects such as scratches and coating peeling, and reduce interference from the source.

Regular calibration: Regularly calibrate the eddy current sensor 8300-A25-B90 to ensure its measurement accuracy under actual working conditions. During the calibration process, the actual shaft surface condition should be simulated as much as possible to improve the effectiveness of the calibration.

Choose the appropriate sensor model and installation location:

Choose a low-frequency response sensor: For speed measurement, it may be more appropriate to choose a low-frequency response eddy current sensor 8300-A25-B90 that is insensitive to high-frequency local defects.

Avoid damaged areas: When installing the sensor, try to choose relatively intact areas on the shaft surface and avoid known scratches or coating peeling areas.

Software compensation:

Material property calibration: If the conductivity and magnetic permeability of the coating material and the base material are significantly different, a corresponding material property correction model can be established in the software to adaptively adjust the measurement parameters according to the changes in the sensor signal.

Multi-sensor fusion: Combine other types of speed sensors (such as photoelectric sensors, Hall sensors, etc.) for data fusion, take advantage of the advantages of different sensors, and improve the reliability and anti-interference ability of the entire speed measurement system.

By combining signal processing algorithms, hardware improvements, regular maintenance and calibration, selecting appropriate sensor models and installation locations, and software compensation, the measurement errors caused by surface defects can be significantly reduced, the application value of eddy current sensors in complex industrial environments can be improved, and reliable data support can be provided for the stable operation and fault warning of equipment.

When looking for high-quality, reliable eddy current sensors, YOYIK is undoubtedly a choice worth considering. The company specializes in providing a variety of power equipment including steam turbine accessories, and has won wide acclaim for its high-quality products and services. For more information or inquiries, please contact the customer service below:
E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229
Yoyik offers various types of spare parts for steam turbines, generators, boilers in power plants:
SET TAKE UP ADJUSTER ASSEMBLY GT2150007
Stainless ammonia manometer YA-100-BF
THERMOCOUPLE WRN2-336
HP Actuator LVDT Position Sensor HTD-250-6
Transformer Coil Temperature Device BWR-04J(TH)
Sensor VIbrasi Turbine and generator DWQZ
magnetic pickup DF6101-005-065-01-09-00-00
linear transducers ZDET-100B
Bolt electric heating rod ZJ-20-T7
odul Control Valve MST-3Z-J-D-EN
GAUGE VACUM BELOWS 45-1188-SS-04B-20IW
FLOW SWITCH ZNJC09010101
hydraulic cylinder with linear transducer 0508.902T0201.AW021
Thermocouple WZPK2-233
Armor Sensor EZ1081-04-00-010 & EZ1901-040
pressure indicator switch BPSN4KB25XFSP19
probe 2401B-0.01
Signal modules – analog 6ES7232-4HD32-0XB0
BEARING TEMP SENSOR WZPK2-248
GAUGE LEVEL MAGNETIC UHZ-51/1-Z/A-S27*3-III-10-800-735-D
Hydrogen Leakage Probe LH-1500C
Displacement transmitter 4000TDZ-A
VELOCITY SEISMOPROBE 9200-01-20-10-00
protect unit 7SJ6241-5EB90-3FE0
Speed Sensor D 110 05 01
HP DIFFERENTIAL EXPANSION PR6423/010-010
Speed sensor A5S0DS0M1415B50-5M
ALARM SIRINE-WARN ING HORN TGSG-06C
Sensor Proximity Turbine PR6426/010-010
Sealing subssembly for double color gauge 0019 BMA.T.BBK.G
vibration measurement units JM-B-35
Two positionfour-way solenoid valve YDK24DHS
Level Transmitter 5301HA2H1N3AM00145BANA M1
Thyristor T589N18TOF
Bo mạch đấu nối in/out van ME8.530.024