Shaft Displacement Measurement

Displacement Measurements on Main Shafts in Marine Industry

Main shafts are essential components of ship propulsion systems, as they transmit the power from the engine to the propeller. However, due to various factors such as ship construction accuracy, load distribution, bearing wear, and environmental conditions, the shafts may experience deviations from their design alignment. This can result in excessive vibration, stress, and fatigue, affecting the performance and safety of the ship.

To ensure optimal shaft alignment, it is necessary to measure the displacement values of the bearings that support the shafts. Displacement values are the vertical and horizontal positions of the bearings relative to the shaft reference line, which determine the shape and slope of the shaft line. By adjusting the displacement values, the load and stress on the bearings and the shafts can be balanced and minimized.

One of the most accurate and reliable methods for measuring and calculating the displacement values of the bearings is the eddy current method, which utilizes high-frequency magnetic fields. The eddy current method offers several advantages over other methods, such as:

High accuracy and resolution: The eddy current method can measure the displacement values with a precision of up to 0.001 mm1, which is much higher than other methods such as gap and sag, optical or laser sighting, jacking, or strain gauges.
Fast response time: The eddy current method can measure the displacement values in real time, without any delay or lag, which is crucial for dynamic alignment and vibration analysis1.

Non-contact measurement: The eddy current method does not require any physical contact between the sensor and the measurement target, which eliminates the risk of damage, wear, or friction1.
Immunity to environmental factors: The eddy current method is not affected by dust, oil, temperature, or humidity, which can interfere with other methods such as optical or laser sighting.

Position of vertical and horizontal displacement sensors

Position of vertical displacement sensors

Results of displacement measurements showing movements of shaft in mm– orbits charts

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