The principle and use of vibrometer
For high-speed turbines and centrifugal compressor units that are automatically started and stopped, abnormal vibrations will promote fatigue of mechanical materials, lowering of strength, premature damage of parts or friction of moving parts and static parts, and deteriorating the operating conditions of the unit. In addition to the use of probes for eddy current axial displacement meters, vibrometer sensors can also be installed on the unit.
The types of vibrometers are mechanical, electric and electronic. Among them, the non-contact eddy current vibrometer has been widely used. Its principle, structure and eddy current axial displacement meter is basically the same, the difference is that the probe is located close to the location of the bearing, and in the vibration measurement requirements of the shaft diameter and the journal concentricity within 0.013mmn, The end face of the probe is perpendicular to the axis, that is, the vibration of the rotor is measured by measuring the vibration value of the bearing body.
There are many reasons for the vibration, such as the unbalance of the rotor itself, the interference of the centering and the vibration of the driver. The influence of complex factors such as the disturbance of the gas resonance in the piping system. The full amplitude measured by the vibrometer is a comprehensive vibration value. If the cause and effect of the vibration fault are specifically analyzed, a frequency conversion filter spectrometer or vibration spectrum can be added to the original receiving and indicating instrument. Analyze the device to measure and record the vibration at different frequencies.
During the operation of the piston compressor and centrifuge, abnormal vibration may occur due to various reasons. When the amplitude exceeds the allowable limit value, the corresponding abnormal vibration protection device is set to issue an alarm or stop automatically.
The following briefly describes the use of vibrometers in equipment testing:
In recent years, many companies use pulsed vibrometers, oil analyzers, and multi-channel chronographs to monitor equipment status. Due to the lack of standardized management and technical guidance, after the instrument is delivered to the workshop, it is difficult to carry out this task because of different technical levels, unstable performance of the instrument itself, and inconvenient operations. However, after a period of exploration, many companies implemented equipment inspections, introduced many advanced instruments, applied vibration detectors to equipment status testing, played an important role in equipment maintenance, and promoted equipment management to a new level. .
The correct measurement method and determination basis are very important:
1ã€Measurement point selection: using the vibrometer, test the bearing and axial end point of the main equipment, and equipped with on-site inspection record table, each measurement point must correspond to each other.
2. Measurement period: After the equipment is just overhauled or near to overhaul, it needs to be measured once in two weeks; once in normal operation, it is measured once a month; in case of significant changes in the measured value and the previous measured value, the test density should be increased to Prevent accidents and cause downtime.
Normally, when the equipment is in normal operation, the detection speed value is in the range of 4.5 to 11.2 mm/s (over 75 kW units) for monitoring purposes. If over 7.1 mm/s, it is necessary to consider arranging major repairs. In addition to considering the motor capacity of the equipment, the determination of this value must also consider the aspects of strong work continuity, high safety and reliability.
After the application of the vibrometer in management, the following inspirations are obtained:
1. The use of a vibrometer to check the state of the equipment, although it cannot be used as the only basis for determining the equipment overhaul period, is really necessary as a reference condition. Because of the low speed of pumps, fans and other equipment, the damage caused by vibration is not unique. For example, there are no problems with the vibrometer, but the impeller is seriously corroded and an overhaul is required. Therefore, the determination of equipment overhaul cycle should be comprehensively considered from the aspects of vibration meter test results, equipment operation time, and the efficiency of the total station.
2. The application of vibrometer test is also very necessary as a means of acceptance after equipment overhaul. It should be pointed out that since the equipment is of different ages, the inspection value of its acceptance shall not be stipulated in a unified way. The inspection value of the accepted pump group before overhaul shall be used as the basis, and the inspection value after acceptance of repaired values ​​shall not be measured. Uniform regulations should be based on the inspection value of the pump group before acceptance, and the revised value should be lower than the pre-repair value. In addition, the application of vibrometer can also find the installation of the pump group (including poor alignment, loose anchor bolts long-term operation), as well as the pump cavitation phenomenon.
In short, the vibrometer is used in conjunction with other detection instruments to facilitate the analysis of the operational status of the equipment. Such as vibrometer and oil analyzer, motor fault detector, alignment instrument and other instruments used together, can more accurately determine the operation of the equipment.
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