In the operation monitoring of industrial equipment, vibration analysis is an important means to evaluate the health status of machinery. As an instrument widely used in shaft equipment monitoring, the dual-channel vibration monitor CZJ-B3 has the core function of collecting vibration signals in real time through two independent channels and comparing and analyzing the data. However, in actual applications, if the difference in vibration amplitude between the two channels exceeds 15%, this phenomenon may be caused by sensor failure or real shaft imbalance. How to scientifically distinguish between the two is not only related to the safety of equipment operation, but also directly affects the formulation of maintenance strategies.

1. Potential causes of vibration amplitude differences

When the dual-channel vibration monitor CZJ-B3 detects that the difference in amplitude between the two channels exceeds 15%, it is first necessary to clarify the possible source of this phenomenon. From a technical point of view, the difference may be caused by the following two reasons:

Failure of the sensor or measurement system

The sensor is the core component of vibration signal acquisition, and its performance directly affects the measurement results. If the sensor itself has problems such as sensitivity deviation, poor contact of the signal line, electromagnetic interference or installation error, it may cause distortion of the two-channel data. For example, a short circuit or open circuit in the signal line will cause an abnormal signal in a certain channel, and improper grounding of the shielding layer may introduce external noise and interfere with the measurement accuracy. In addition, aging or damage of the sensor (such as moisture in the internal strain gauge, cold welding of the welding point, etc.) will also cause the output signal to be unstable, resulting in amplitude differences.

Real imbalance or looseness of shafting equipment

The vibration characteristics of shafting equipment are closely related to its mechanical state. If there are problems such as uneven mass distribution, bearing wear, coupling misalignment or loose foundation of the rotor, the vibration energy may be unevenly distributed in different axial or radial directions, which will be manifested as an amplitude difference between the two channels. For example, large shafting imbalance is usually manifested as a significant enhancement of the fundamental frequency (1X) vibration component, while structural looseness may show an abnormal increase in the 1X peak in a specific direction (such as the horizontal direction).

2. Typical characteristics and troubleshooting methods of sensor failure

On the premise of excluding real mechanical failures, the failure of the sensor or measurement system is often the direct cause of the amplitude difference. The following analyzes its typical characteristics and troubleshooting ideas from a technical perspective:

Intuitive manifestation of signal abnormality

Sensor failure is usually accompanied by obvious signal abnormality. For example, if the vibration value of a channel jumps frequently or has no output at all, it may be that the signal line is open or the sensor is damaged; if the fluctuation range of the values ​​of the two channels is very different, it may be related to electromagnetic interference or power supply stability. According to the instructions for use of the CZJ-B3 steam turbine vibration meter, when the display jumps, it is necessary to focus on checking whether the sensor plug wiring is reliable; if the display does not change, it is necessary to confirm whether the sensor is damaged or the signal line is short-circuited.

Electromagnetic interference and shielding issues

Electromagnetic interference is a common signal interference source in industrial environments. For example, inverters, motors or other high-frequency equipment may affect the output signal of the sensor through electromagnetic induction, causing amplitude fluctuations. In this regard, it is necessary to check whether the shielding layer of the sensor is intact, and ensure that one end of the shielding layer is floating and the other end is connected to the shielding end of the monitor CZJ-B3. In addition, if there is a strong interference source on site, consider replacing the double-layer shielded cable (coverage ≥85% copper mesh + aluminum foil) and adding a magnetic ring filter on the cable path to suppress high-frequency noise.

Sensor sensitivity and calibration error

The sensitivity setting of the sensor directly affects the measurement accuracy. If the sensitivity parameters of the two channels are not correctly matched, amplitude differences may occur. For example, the sensitivity range of the vibration meter CZJ-B3 is 20mv~99mv/mm/s. If the sensitivity setting of a channel is too low, the actual vibration value will be underestimated. In addition, long-term use of the sensor may cause sensitivity drift and requires regular calibration. According to the technical specifications, if the error is ≤±20%, it can be corrected by adjusting the calibration parameters; if the error is ≥±20%, the sensor sensitivity needs to be reset.

Influence of installation and protective measures

The installation position and method of the sensor are crucial to the measurement results. If the sensor is not installed strictly in accordance with the design requirements (such as not fixed vertically or horizontally to the measured point), signal acquisition deviation may occur. In addition, high temperature, steam scouring or mechanical vibration may accelerate sensor aging, and protective measures (such as adding a protective cover) need to be taken during installation. If the on-site environment is complex, it is recommended to refer to the installation specifications in the CZJ-B3 vibration monitor manual to ensure that the connection between the sensor and the device under test is stable and free of external interference.

3. Vibration characteristics and diagnostic methods of shaft imbalance

If the difference in amplitude between the two channels still exists after eliminating the sensor fault, it is necessary to further analyze whether it is a real imbalance problem of the shaft equipment. The vibration characteristics of shaft imbalance usually have the following regularity:

Key indicators of spectrum analysis

Through vibration spectrum analysis, the nature of the vibration source can be intuitively judged. For example, in the spectrum of large shaft imbalance, the fundamental frequency component usually dominates, and the amplitude increases with the increase of speed. In contrast, the spectrum of loose structure or loose bearing seat may contain 2X or 3X harmonic components. If the 1X component of both channels is significantly higher than other frequency components, it is more inclined to the conclusion of shaft imbalance.

Correlation between phase difference and vibration direction

Vibration phase difference is an important auxiliary means to judge the state of the shaft system. For example, loose bearing seat may cause the phase difference of the two channels to be close to 180°, while loose foundation may be manifested as random phase difference. If the phase difference of the two channels is stable and synchronized with the speed, it is necessary to focus on the tightness of the mechanical structure; if the phase difference changes irregularly, it may be related to sensor installation error or interference.

Correlation between operating status and load conditions

The vibration characteristics of shaft imbalance are often closely related to the operating status of the equipment. For example, a large imbalance problem may show a significant vibration increase when the equipment accelerates or decelerates, while structural looseness may be aggravated under specific load conditions. By comparing the vibration data under different working conditions, the root cause of the fault can be further verified.

To reduce the occurrence of sensor failures, it is recommended to regularly check the installation status, signal line connection and shielding effect of the sensor, and calibrate it according to the instructions of the CZJ-B3 vibration monitor. For shaft equipment, the rotor balance status, bearing wear degree and foundation stability should be regularly evaluated in combination with vibration monitoring data to eliminate potential risks in a timely manner.

When looking for high-quality, reliable rotational speed 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:
speed meter HZQW-03E
đầu dò nhiệt độ Wrnk2-131
Control SystemLVDT 2000TDGNK
Auxiliary switch for circuit breaker NQ22H123300
lvdt cost 2000TDGN
TEMP.DIGIT CONTROLLER DC2001-0-00A0-0000-89-0112-EN
pressure switch RCA218RZ097Z
Leak detection sensor for Leak detector EYK-JSK485
Vibration Sensor VRT-2T
AUTOMATIC VOLTAGE REGULATOR HWJT-09C
THERMOCOUPLE WRNK2
thermocouple type temperature sensor TC03A2-KY-2B/S5
Zero Speed Switch NJ10-30GM-N
Indicator Light AD16-22W/G23
Rotation Sensor speed SMCB-01
Turbine bolt electric heating rod ZJ-20-3
bolts heater 1.2311(4)-φ18X600
pressure transducer types PS531SPP10/BB32N3/S3M
Universal joint UK-108-M6-M6
Selenoid elevator Controller GL50E/86
Bimetal Thermometer WSS-561
Transmitter 2051TG4A2B21AS5B4E1M5Q4
Leak detector JSK-DG
magnetic blown auxiliary contact switch lxw22-11b-718-02
Vibration Sensor HS-2-1-2
Ethernet Switch MOXA
Pull cozd switch XY2CE2A250
thermal resistance WZPK2-231
INVERTER ACS550-01-031A-4