Advantages: Non-contact measurement can be achieved, the structure is simple, and it is not afraid of contamination by oil and other media. Eddy current sensors cannot measure large displacements, and a certain degree of linearity can only be guaranteed when the measurement range is small.
The eddy current sensor can statically and dynamically measure the distance between the measured metal conductor and the probe surface with non-contact, high linearity and high resolution. It is a non-contact linearized measurement tool. The eddy current sensor can accurately measure the static and dynamic relative displacement changes between the measured object (must be a metal conductor) and the probe end face.
In the state analysis, vibration research, and analysis measurement of high-speed rotating machinery and reciprocating machinery, the non-contact high-precision vibration and displacement signals can continuously and accurately collect various types of rotor vibration states. parameter. Such as the radial vibration, amplitude and axial position of the shaft. From the theoretical analysis of rotor dynamics and bearing science, the motion state of large-scale rotating machinery mainly depends on its core - the rotating shaft. The eddy current sensor can directly and non-contactly measure the status of the rotating shaft, such as unbalance and misalignment of the rotor. , early identification of mechanical problems such as bearing wear, shaft cracks and friction can provide critical information. Eddy current sensors are widely used in large-scale rotating machinery due to their long-term reliability, wide measurement range, high sensitivity, high resolution, fast response, strong anti-interference ability, unaffected by oil and other media, and simple structure. It is widely used in online monitoring and fault diagnosis.
Requirements for the object being measured
In order to prevent the magnetic field generated by the eddy current from affecting the normal output of the instrument, a certain range of non-conductive medium space must be left around the sensor head during installation. If more than two sensors are to be installed at a certain location at the same time, it is necessary to consider whether cross interference will occur. The specified distance must be maintained between the two probes. The surface area of ??the measured body should be more than 3 times the diameter of the probe. When the 3 times cannot be met, When the probe diameter is equal to the surface area of ??the measured body, the sensitivity can be reduced appropriately, but this is at the expense of sensitivity. Generally, when the diameter of the probe is equal to the surface area of ??the measured body, the sensitivity is reduced to 70, so when the sensitivity requirement is not high, the measurement surface area can be appropriately reduced.
Requirements for working temperature
Generally, the maximum temperature of imported eddy current sensors is not greater than 180°C, while domestic ones can only reach 120°C, and these data come from the manufacturer, including Very unreliable. According to various relevant data analysis, in fact, when the operating temperature exceeds 70°C, the sensitivity of the eddy current sensor will be significantly reduced, and may even cause damage to the sensor. In the nuclear power plant industry, turbine engine manufacturing, rocket Eddy current sensors that require high temperature resistance in fields such as launches, automobile engine inspections, and metallurgical steel furnaces must have high tolerance. It is reported that the eddy current sensor design engineers of the British Zhenshang Group have successfully developed such sensors that can withstand thousands of degrees Celsius. . The sensitivity of the eddy current sensor is affected by temperature. The eddy current sensor should be installed as far away from the steam seal as possible when measuring shaft vibration. Only special high temperature resistant sensors such as high and low temperature eddy current sensors can be installed near the steam seal.
Requirements for the probe bracket
The eddy current sensor is installed on the fixed bracket, so the quality of the bracket directly determines the measurement effect, which requires that the bracket should have sufficient stiffness to improve Natural frequency, to avoid or reduce the vibration of the measured body, the bracket is also stimulated to vibrate at the same time. Data show that the natural frequency of the bracket should be at least 10 times the mechanical rotation speed. The bracket should be parallel to the tangent direction of the measured surface. The sensor It is installed vertically on the bracket. Although the center line of the probe is deviated from the vertical direction by 15° and has no effect on the system characteristics, it is best to ensure that the sensor is perpendicular to the measured surface.
Requirements for initial gap
Various types of eddy current sensors only have good linearity in their readings under a certain gap voltage value, so when installing the sensor The appropriate initial gap must be adjusted, and characteristic tests will be conducted on each set of products to draw the corresponding characteristic curve. When using the sensor, engineering and technical personnel must carefully study the accompanying calibration certificate and carefully analyze the characteristic curve to determine Whether the sensor meets the gap to be measured. Generally, the larger the diameter of the sensor, the larger the measured gap will be.