8125-A70-C01-D02-E10 front probe

8300-A11-B90，8200-A80-D01，8200-A40-D02

8125-A70-C01-D02-E10 preamplifier eddy current displacement probe

8111-03-A30-C01-D01-E10 eddy current probe

The sensor can measure the relative position between the measured object (which must be a metal conductor) and the probe end face. Eddy current has good long-term reliability, high sensitivity, strong resistance, non-contact measurement, fast response speed, and is not affected by media such as oil and water. It is often used for long-term real-time monitoring of parameters such as shaft displacement, shaft vibration, and shaft speed of large rotating machinery. It can analyze the working condition and fault causes of the equipment, effectively protect the equipment, and carry out predictive maintenance. From the theoretical analysis of rotor dynamics and bearing science, the operating state of large rotating machinery mainly depends on its shaft, and eddy current displacement sensors can directly measure the state of the shaft, with reliable and trustworthy measurement results. In the past, acceleration sensors or velocity sensors were used for measuring mechanical vibrations. By measuring the vibration of the casing, the shaft vibration was indirectly measured, and the reliability of the measurement results was not high.

When selecting a probe, it is recommended to choose a probe with a standard linear range greater than 20% of the measured object's movement range;

If the area of the measured surface cannot meet the size requirements of the specimen, a small probe with an extended linear range can be selected;

If the probe cable is not protected by a pipeline, it is recommended to choose an armored probe to prevent the cable from being easily damaged;

If there are no special installation restrictions, standard installation types of probes are usually selected;

The non threaded probe is designed for easy installation: when using screw hole installation, a suitable length of non threaded probe can reduce the length that needs to be screwed into the screw hole;

The length of the probe housing depends on the distance between the installation position and the measured surface. If there is no special need, it is recommended to choose a length of 40 or 50mm;

When installing with screw holes, the probe cable should be selected as 0.5m or 1.0m long to avoid breaking the cable when rotating the probe, and an extension cable should also be selected;

▲ Install probes inside the machine, ensuring that the total length of the probes allows the cable joints to be located outside the machine to prevent internal oil contamination of the joints;

8125-A70-C01-D02-E10 front probe

The working mechanism of the sensor system is the eddy current effect. When the power supply of the sensor system is turned on, a high-frequency current signal will be generated in the preamplifier, which is sent to the head of the probe through a cable and generates an alternating magnetic field H1 around the head. If no metal conductor material approaches within the range of the magnetic field H1, all the energy emitted into this range will be released; On the contrary, if a metal conductor material approaches the probe head, the alternating magnetic field H1 will generate an eddy current field on the surface of the conductor, which will also generate an alternating magnetic field H2 in the opposite direction to H1. Due to the reaction of H2, the amplitude and phase of the high-frequency current in the probe head coil will be changed, that is, the effective impedance of the coil will be changed. This change is related to both eddy current effects and magnetostriction effects, which are related to parameters such as the conductivity, permeability, geometric shape, coil geometry parameters, excitation current frequency, and distance from the coil to the metal conductor of the metal conductor. Assuming that the metal conductor is homogeneous and its performance is linear and isotropic, the physical properties of the coil metal conductor system can usually be described by parameters such as the magnetic permeability μ, electrical conductivity σ, size factor r of the metal conductor, distance δ between the coil and the metal conductor, coil excitation current intensity I, and frequency ω. Therefore, the impedance of the coil can be represented by the function Z=F (μ, σ, r, I, ω). If we control μ, σ, r, δ, I, and ω to be constant, then impedance Z becomes a single valued function of distance δ. According to Maxwell's formula, this function can be obtained as a nonlinear function with an S-shaped curve, which can be approximated as a linear function within a certain range. In practical applications, the coil is usually sealed in the probe, and the change in coil impedance is converted into voltage or current output through the processing of electronic circuits encapsulated in the preamplifier. This electronic circuit does not directly measure the impedance of the coil, but uses parallel resonance method, as shown in Figure 1-3. In the preamplifier, a fixed capacitor CCC C01 21 2C is connected in parallel with the probe coil Lx and the transistor T to form an oscillator. The oscillation amplitude Ux of the oscillator is proportional to the coil impedance, so the oscillation amplitude Ux of the oscillator will change with the distance δ between the probe and the measured object. After detection, filtering, amplification, and nonlinear correction, Ux outputs a voltage Uo. The relationship curve between Uo and δ is shown in Figure 1-4. It can be seen that the curve is in an "S" shape, that is, it is linear at the midpoint δ 0 in the linear region (corresponding to the output voltage U0), and its slope (i.e. sensitivity) is relatively large. At both ends of the linear region, the slope (sensitivity) gradually decreases, and the linearity deteriorates. (δ 1, U1) - Linear starting point, (δ 2, U2) - Linear ending point.

Practical design of the preamplifier: The structure of the preamplifier makes the high-frequency socket concave, making it less likely to damage the high-frequency socket. Three terminal wiring terminals are embedded and fixed, directly connected to the internal circuit to ensure reliable connection. Fault tolerance of preamplifier: Any wiring error at the power supply end, common end (signal ground), and output end will not damage the preamplifier. Power polarity error protection and output short circuit protection are provided. The preamplifier is an electronic circuit board, and except for a few calibration components, all other components are sealed with epoxy resin adhesive to improve the preamplifier's anti vibration and moisture-proof performance. After the preamplifier is calibrated at the factory, each calibration component is also sealed with silicone. After the user calibrates it themselves, this should also be done

The irregular surface processing condition of the tested object can cause additional errors in the actual measurement values, especially for vibration measurement. This additional error signal is difficult to separate from the actual vibration signal in electrical terms. Therefore, the tested surface should be smooth and free of defects such as scratches, holes, protrusions, grooves, etc. (except for protrusions or grooves specially designed for keyshifters and speed measurements). Usually, for vibration measurement, the surface roughness Ra of the measured surface is required to be between 0.4 μ m and 0.8 μ m (recommended value by API670 standard), and it is generally necessary to perform diffraction or polishing on the measured surface; For displacement measurement, due to the filtering or averaging effect of the indicator instrument, it can be slightly relaxed (generally the surface roughness Ra does not exceed 0.8 μ m to 1.6 μ m).

The characteristics of the sensor are related to the conductivity and magnetic permeability of the measured object. When the measured object is a magnetic material (such as ordinary steel, structural steel, etc.), due to the simultaneous existence of magnetic and eddy current effects, and the magnetic effect is opposite to the eddy current effect, some of the eddy current effects need to be offset, resulting in low sensitivity of the sensor induction; When the measured object is a non-magnetic or weakly magnetic material (such as copper, aluminum, alloy steel, etc.), due to the weak magnetic effect, the eddy current effect is relatively strong, so the sensing sensitivity of the sensor is high. Figure 1-9 shows the output characteristic curves of the same sensor when measuring several typical materials. The sensitivity corresponding to each curve in the figure is: copper: 14.9 V/mm, aluminum: 14.0 V/mm, stainless steel (1Cr18Ni9Ti): 10.4V/mm, 45 # steel: 8.2 V/mm, 40CrMo steel: 8.0 V/mm (factory calibration material). Unless otherwise specified at the time of ordering, the sensor system is usually calibrated with 40CrMo material specimens before leaving the factory. Only the tested material of the same series can produce characteristic equations similar to those of 40CrMo; When the material of the tested object differs significantly from the composition of 40CrMo, it is necessary to recalibrate according to the steps described in Chapter 3, otherwise it may cause significant measurement errors. Because the shafts of most steam turbines, blowers, and other equipment are made of 40CrMo material or similar materials, the sensor system is factory calibrated with 40CrMo material, which can be suitable for most measurement objects. Phase detector measurement is achieved by setting a groove or convex key on the measured axis, called a phase detector mark. When this groove or convex key is turned to the installation position of the probe, it is equivalent to a sudden change in the distance between the probe and the measured surface. The sensor will generate a pulse signal, and every time the shaft rotates, a pulse signal will be generated, indicating the position of the shaft in each rotation cycle. At the same time, by counting the pulses, the rotational speed of the shaft can be measured; By comparing the pulse with the vibration signal of the shaft, the phase angle of the vibration can be determined, which is used for dynamic balance analysis of the shaft and fault analysis and diagnosis of equipment. The groove or convex key should be large enough to generate a pulse peak to peak value of not less than 5V (API670 standard requires not less than 7V). Generally, if a φ 8 probe is used, the width of this groove or convex key should be greater than 7.6mm, the depth or height should be greater than 1.5mm (recommended to use 2.5mm or more), and the length should be greater than 10mm. The groove or convex key should be parallel to the axis centerline, and its length should be as long as possible to prevent the probe from facing the groove or convex key when the axis moves axially. In order to avoid excessive changes in the gap between the probe and the measured surface due to axial displacement, the phase detector probe should be installed radially on the axis rather than axially. The key phase detector probe should be installed on the driving part of the unit as much as possible, so that even if the driving part of the unit is disconnected from the load, the sensor will still have a key signal output. When the unit has different speeds, multiple sets of phase detectors are usually required to monitor it, so as to provide effective phase detection signals for various parts of the unit. The phase identification mark can be a groove or a convex key, as shown in Figure 2-5. The API670 standard requires the use of a groove type. When the mark is a groove, the installation probe should adjust the initial installation gap towards the complete part of the shaft, rather than towards the groove. When the mark is a convex key, the probe must adjust the initial installation gap towards the top surface of the convex, and cannot adjust towards other complete surfaces of the shaft. Otherwise, when the shaft rotates, it may cause collision between the convex key and the probe, cutting off the probe. In order to facilitate the quick determination of the position of the phase detector signal, the installation position of the phase detector probe should be marked on the machine housing, and the angle position of the phase detector mark should be marked on the exposed part of the shaft.