In the operation and maintenance of rotating machinery, early and accurate fault diagnosis is the key to ensure equipment safety and reduce maintenance costs. Vibration analysis, as an important means of condition monitoring, can effectively identify and judge the operating status and potential faults of equipment by collecting and analyzing mechanical vibration signals. ZHJ-2-01-02-10-01 vibration velocity sensor, as a commonly used vibration measurement element, is widely used in vibration monitoring of various types of rotating machinery. This article will explore how to use the vibration velocity value collected by the sensor, combined with the characteristics of the acceleration value, to make a preliminary judgment and identification of two common faults of mechanical looseness and misalignment.

I. Introduction to ZHJ-2 series vibration velocity sensor

The vibration detection sensor ZHJ-2-01-02-10-01 is a piezoelectric vibration velocity sensor. Its working principle is to use the piezoelectric effect of piezoelectric crystals to convert mechanical vibration into electrical signal output. This series of sensors usually have the characteristics of simple structure, high sensitivity, wide frequency response range, and strong anti-interference ability. It is suitable for measuring the vibration of the bearing seat, housing and other parts of rotating machinery. Although the main output is the vibration velocity signal, in practical applications, by combining with other types of sensors or through signal processing, other vibration parameters such as acceleration can be obtained or inferred, thus providing a basis for more comprehensive fault diagnosis.

Basic principles of vibration analysis

The vibration of a machine is a comprehensive reflection of various dynamic forces inside it. By analyzing the amplitude and frequency components of the vibration signal, the operating status and fault characteristics of the machine can be understood. In vibration analysis, velocity value and acceleration value are two important physical quantities, and they have different focuses when describing vibration characteristics.

Vibration velocity value: Vibration velocity is an important indicator to describe the severity of mechanical vibration, which is directly related to vibration energy. Higher vibration velocity usually means greater vibration energy, which may indicate more serious faults. In frequency domain analysis, the vibration velocity spectrum can clearly show the main vibration frequency and its amplitude, and is often used to judge low-frequency faults such as imbalance and misalignment.

Vibration acceleration value: Vibration acceleration is an indicator to describe the speed of mechanical vibration change, and is more sensitive to high-frequency vibration. Impact, friction of mechanical parts, and early failure of bearings often produce high-frequency vibrations, which are more obvious in the acceleration spectrum. Therefore, acceleration values ​​are often used for early diagnosis of bearing faults, gear meshing problems, mechanical looseness and other faults with rich high-frequency components.

II. Fault judgment based on comparison of velocity values ​​and acceleration values

In practical applications, although the ZHJ-2-01-02-10-01 vibration velocity sensor directly outputs a vibration velocity signal, by comparing the magnitude and frequency components of its velocity value, combined with the understanding of the mechanical structure and operating characteristics, it is possible to preliminarily infer whether there is a mechanical loose or misalignment fault. At the same time, if the system is equipped with an acceleration sensor or can obtain acceleration information through a data acquisition system, the comparative analysis will be more accurate and effective.

1. Judgment of mechanical loose faults:

Mechanical looseness usually refers to loose connections between mechanical parts, such as loose anchor bolts, loose fit between the outer ring of the bearing and the bearing seat, and loose pipe connections. These loosenesses will cause the overall stiffness of the mechanical structure to decrease, generate impact and friction during operation, and excite high-frequency vibrations.

Velocity value characteristics: In the early stage of mechanical loosening, the overall vibration velocity value may not increase significantly, especially in the low frequency band. However, as the degree of looseness increases, some low-frequency vibration may occur, usually the base frequency and its low-frequency components.

Acceleration value characteristics: Since looseness will cause impact and friction, the high-frequency components will increase significantly in the acceleration spectrum, and the total value of acceleration will also increase accordingly. This is one of the important characteristics for judging mechanical looseness. By comparing the velocity spectrum and the acceleration spectrum, if it is found that the acceleration has a significant increase in the high-frequency band, and the velocity value does not change significantly in the low-frequency band, it is very likely caused by mechanical looseness.

Frequency domain performance: Looseness usually produces rich harmonic components in the high-frequency area, and sometimes there will be a “modulation” phenomenon, that is, the high-frequency amplitude is modulated by the low-frequency signal.

2. Judgment of misalignment fault:

Misalignment means that the axes of the rotating machinery are not on the same center line, including coupling misalignment and bearing misalignment. Misalignment will cause periodic alternating stress and produce vibration related to the speed.

Speed ​​value characteristics: Misalignment usually produces higher vibration speed values ​​at the base frequency (1 times the speed) and its multiples (especially 2 times the speed). As the degree of misalignment increases, the amplitude of the frequency component will also increase accordingly.

Acceleration value characteristics: Compared with mechanical looseness, the high-frequency vibration caused by misalignment is not obvious, so the total value of acceleration and the amplitude of the high-frequency component may not increase significantly. However, when the misalignment is more serious, due to the additional alternating loads on components such as bearings, a certain degree of high-frequency vibration may also occur, causing changes in the acceleration value.

Frequency domain performance: Misalignment mainly shows a higher amplitude in the low frequency band (1 times, 2 times, and sometimes 3 times the speed). Coupling misalignment may also be accompanied by a significant increase in axial vibration.

III. Practical application and analysis steps

In practical applications, when using the ZHJ-2-01-02-10-01 vibration velocity sensor for fault judgment, the following steps and methods can be combined:

Data acquisition: Use the vibration sensor ZHJ-2-01-02-10-01 to collect vibration velocity signals at key parts of the machine (such as bearing seats, housings, etc.). Signal processing: Perform spectrum analysis on the collected time domain signal to obtain the vibration velocity spectrum.

Benchmark value comparison: Compare the current vibration velocity value and spectrum with the normal operating benchmark value of the equipment to observe whether there are abnormal frequency components and amplitude changes.

Acceleration information reference: If conditions permit, combine the data collected by the acceleration sensor or the acceleration information obtained by the data acquisition system to compare the amplitude changes of the velocity value and the acceleration value in different frequency bands.

Fault mode identification: If the velocity value increases significantly in the low frequency band (especially 1 times and 2 times the speed), and the acceleration value does not change significantly in the high frequency band, it tends to be judged as a misalignment fault. If the acceleration value increases significantly in the high frequency band, and the velocity value does not change significantly or increases slightly in the low frequency band, it tends to be judged as a mechanical loose fault.

It should be noted that actual faults are often the result of the coupling of multiple factors and require comprehensive analysis. Based on the preliminary judgment results, combined with the structural characteristics, operation history and on-site inspection of the equipment, the type and degree of the fault are finally determined.

When looking for high-quality, reliable vibration 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:
Differential Pressure Sensor Switch BH-072036-072
Steam turbine bolt electric heater ZJ-22-7(R)
High-temperature cable HSDS-30/L
SPEED MONITOR XJZC-03A/Q
Water flow monitor LJZ-2
rtd pt100 cable WZPM2-08-75-M18-8
Water level camera probe P-WS01
Oil pressure sensor 32302001001 0.08-0.01Mpa
TRANSFORMER;CONTROL SG-100VA
Remote Bimetal Thermometer WSSY-411
PRESSURE SENSOR R412010767
Relay REL 52005 (P3U30-5AAA1BBAA)
linear sensors TDZ-1E-32
mag pickup speed sensor CS-1-D-080-10-01
LVDT Position sensor 3000TDZ-A
magnetic pickup speed sensor G-100-02-01
Analog Output Module XGF-DV4A
Excitation Regulator Power Supply Module 4NIC-FD360
Bleed Valve Limit Switch 328A7435P1
THEMOCOUPLE WRN2-12
Flame lens objective front end YF-A18
Vibration Gauge 330105-02-12-10-02-00
Pressure Switch GIVS0-11
Position Sensor SP2841 100 002 001
red light XB2-EV444
MODULE VIBRATION MONITOR JM-B-6Z/311
DIGITAL PRESSURE GAUGE 300PSI XP2I
high temp thermocouple wire type k WRN2-630
Pressure sensor BD-sensor 26 600G
Indication AD16-22B/R34/AC/DC400V
LVDT transmitter LTM-6A-I
TRAFO MANAGEMENT RELAY WDZ-5242A-521133-D240482
Universal joint SQ8L-TJ
Sensor speed CS-1 G-065-05-1
linear throttle position sensor DET150A