The harm of lateral force on the core of the travel displacement sensor TD-1-100mm

In the turbine control system, the hydraulic motor stroke displacement sensor (such as the TD-1 series) undertakes the core task of converting mechanical displacement into electrical signals. Its working principle is based on the differential transformer (LVDT) technology, and the displacement is accurately measured through the linear motion of the iron core in the coil. However, as a key component of the sensor, if the iron core is subjected to lateral force during operation, it may cause measurement errors, equipment damage and even system failure. The root cause of this phenomenon lies in the contradiction between the structural characteristics of the sensor and the physical laws, and a systematic analysis is required from the perspectives of design principles, mechanical influences and protective measures.

I. Mechanical characteristics and functional positioning of the iron core

The iron core of the TD-1-100mm displacement sensor is designed as a non-contact motion structure, and its movement in the spiral coil must strictly follow a linear trajectory. The movement direction of the iron core directly determines the difference in the induced voltage in the secondary coil, which in turn reflects the displacement. If the core is subjected to lateral force, its motion trajectory will deviate from the axis, leading to the following problems:

• Magnetic circuit distortion: The offset of the core will change the magnetic coupling relationship between the coil and the core, destroy the original impedance balance, and invalidate the linear relationship between the output voltage and the displacement. For example, in the stroke monitoring of the steam turbine oil motor, a slight deflection of the core may cause nonlinear fluctuations in the sensor output signal, causing the control system to misjudge the valve opening.

• Mechanical stress concentration: The lateral force on the core may cause local deformation or jamming, especially in a high-vibration environment. This stress concentration will accelerate the mechanical wear between the core and the coil and shorten the life of the sensor.

• Signal interference enhancement: The offset of the core may introduce additional electromagnetic noise. For example, when the core vibrates due to lateral force, its relative motion with the coil will generate high-frequency harmonic signals, which will interfere with the extraction of the main signal and reduce the measurement accuracy.

II. Sources of lateral force and hazardous scenarios

In actual applications, the lateral force on the core of the LVDT position sensor TD-1-100mm may be caused by a variety of factors:

• Installation error: If the sensor is not strictly aligned with the axis of motion of the oil motor piston during installation, the push-pull action of the piston may transmit the lateral force to the core. For example, in a steam turbine high-pressure oil motor, the assembly gap between the piston and the sensor bracket is too large, which may cause uneven force on the core during movement.

• External vibration: When the steam turbine is running, the vibration of the equipment foundation or pipeline system may be transmitted to the sensor through the mounting bracket. Under conditions with high dynamic frequencies, these vibrations may cause resonance of the core and aggravate lateral displacement.

• Mechanical shock: During the rapid start-stop or emergency shutdown of the oil motor, the inertial force of the piston may exert an instantaneous lateral impact on the core through the connector. For example, when the turbine protection system is triggered, the impact force of the valve closing may cause the core to deviate from the axis, resulting in a sudden change in the sensor output.

• Environmental interference: When a strong magnetic field or a metal foreign body approaches the sensor, it may exert lateral force on the core through magnetic induction or physical collision. For example, in situations where the installation space is limited, a metal bracket that is not properly isolated may rub against the core and interfere with its normal movement.

III. Protective measures and design optimization

To avoid the harm caused by the lateral force on the core, comprehensive measures should be taken from the installation process and operation and maintenance of the LVDT displacement sensor TD-1-100mm:

1. Installation process specifications

Errors during the installation process are one of the main causes of lateral force on the core, and the following standards must be strictly followed:

• Axis alignment detection: Use a dial indicator or laser rangefinder to measure the parallelism of the sensor axis and the axis of motion of the oil motor piston to ensure that the deviation is less than 0.05mm/m. For example, when overhauling a steam turbine, precise alignment is achieved by adjusting the tightness of the bracket bolts.

• Improvement of fixing method: Avoid using a fixing method with excessive rigidity, and give priority to flexible clamps or floating mounting structures. For example, an elastic clamp is used to fix the sensor, allowing it to be fine-tuned within the range of ±2mm to adapt to the thermal expansion effect of the piston.

• Environmental isolation measures: A shielding cover is set around the sensor to prevent the intrusion of metal dust or foreign objects. For example, a dust cover with IP67 protection level is installed on the sensor housing near the oil motor to reduce external interference.

2. Operation and maintenance strategy

During long-term operation, the LVDT stroke sensor may gradually lose its ability to resist lateral forces due to mechanical fatigue or environmental changes. The following means are required to ensure reliability:

• Regular calibration and diagnosis: Use a high-precision calibration device to detect the linearity of the sensor output signal. If the nonlinear error is found to exceed 0.1%, it is necessary to disassemble and check the core status. For example, during the turbine overhaul cycle, a full stroke scan test is performed every six months.

• Vibration monitoring and early warning: Arrange vibration sensors in the sensor installation area to monitor the vibration frequency and amplitude of the mounting bracket in real time. For example, set the vibration threshold through the DCS system, and trigger an alarm when the amplitude exceeds 0.5mm, prompting the operation and maintenance personnel to check the installation status.

• Emergency treatment plan: Design redundant measurement circuits or backup sensors for sudden lateral impacts. For example, connect two TD-1 sensors in parallel on key oil motors, and automatically switch the main channel through software algorithms to avoid single failures leading to measurement failures.

The lateral force problem of the iron core of the turbine oil motor stroke displacement sensor TD-1-100mm is essentially a contradiction between mechanical accuracy and environmental complexity. By optimizing the structural design, standardizing the installation process and improving the maintenance strategy, the impact of lateral force can be minimized to ensure the long-term stable operation of the sensor.

When looking for high-quality, reliable LVDT 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

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