As the core sensing unit of the steam turbine DEH system, the installation angle deviation of the DF6101-005-065-01-05-00-00 magnetoresistive speed sensor may lead to catastrophic consequences. Unlike common eddy current sensors, the magnetic field coupling characteristics of magnetoresistive sensors make them highly sensitive to the installation angle – when the axis tilts more than 1°, the output signal may attenuate by more than 30%. This seemingly small geometric error is actually a “time bomb” that threatens the safe operation of the unit. Next, we analyze the physical nature of the magnetoresistive sensor to reveal how the installation angle affects the measurement accuracy through three mechanisms: magnetic circuit change, signal modulation, and system closed loop.

1. Angle sensitivity mechanism of magnetoresistive sensor

Geometric dependence of variable magnetoresistive effect

The speed sensor DF6101-005-065-01-05-00-00 works based on the principle of magnetic resistance change of ferrite core. When the gear being measured rotates, the tooth top and tooth valley alternately pass through the sensor coil window, resulting in periodic changes in magnetic circuit magnetic resistance. If there is an angle deviation of θ between the sensor axis and the gear axis, the effective magnetic circuit cross-sectional area will be reduced by cosθ times, and the magnetic resistance R= (μ₀μrA)/l will change to 1/cosθ of the original value. Experimental data show that when θ=5°, the magnetic resistance increases by 15%, resulting in a 12% decrease in the coil induced voltage.

Phase shift of signal modulation

Ideally, the output signal of the magnetoresistive sensor DF6101-005-065-01-05-00-00 should be in a sine/cosine relationship with the gear angle. When the installation angle deviates, the signal waveform will be phase distorted. For example, a tilt of θ=3° will cause the phase of the baseband signal to lag by 1.7° and the phase of the second harmonic to advance by 5.2°. This phase distortion will seriously affect the accuracy of the spectrum analysis.

Attenuation of magnetic shielding effectiveness

The magnetic shielding layer of the sensor housing is designed based on the principle of axial symmetry. When the installation angle deviation exceeds 2°, the asymmetric magnetic field will form eddy current losses in the shielding shell, resulting in an increase of 6-8dB in the input noise of the preamplifier. Actual measurements at a power plant show that the signal-to-noise ratio of the tilted DF6101 sensor drops from 30dB to 18dB under 50Hz power frequency interference.

2. Typical failure modes caused by installation deviation

Speed ​​measurement drift phenomenon

In a subcritical 600MW unit, the speed display value of the sensor DF6101-005-065-01-05-00-00 was continuously 3rpm higher due to the installation angle deviation. In-depth analysis found that the tilted installation shortened the effective length of the magnetic circuit and reduced the equivalent magnetic resistance change rate, causing the frequency-voltage conversion coefficient to deviate from the nominal value. This drift will gradually accumulate during the long-term operation of the unit, and eventually cause the speed control system to lose control.

Shaft vibration misjudgment crisis

The TSI system of a supercritical unit once had a false 2nd frequency component in the vibration signal spectrum due to the tilted installation of the speed sensor DF6101-005-065-01-05-00-00. The control system misjudged it as a rotor misalignment fault, triggering unnecessary shutdown protection, causing millions of economic losses. The root cause of the fault is that the tilted installation changes the magnetic circuit quality factor Q value, causing the signal harmonic distortion to exceed 15%.

Zero speed detection failure

When the angle between the sensor axis and the gear axis is too large, the zero speed detection circuit may not be able to capture the weak signal of the flux change. During the startup phase of a gas turbine unit, the speed sensor DF6101-005-065-01-05-00-00 disappeared due to the installation angle deviation. The system mistakenly believed that the unit was still rotating, which eventually caused the lubricating oil pump to run idle and damage.

3. Engineering implementation method for precision installation

Three-axis positioning and calibration technology:

• Use laser alignment instrument to establish a three-dimensional coordinate system to ensure that the sensor axis meets the following requirements:
• Radial deviation: <0.05mm (RMS)
• Axial deviation: <0.1mm/m
• Angular deviation: <0.5° (real-time monitoring using inclination sensor)

Temperature drift suppression strategy

In view of the temperature-dependent characteristics of magnetic resistance materials, a 0.2° redundant angle compensation space is reserved during installation. A high-temperature unit uses this method to control the measurement error caused by temperature drift within ±0.05rpm.

4. Key parameters for on-site commissioning

Signal amplitude standard

The no-load output voltage of the newly installed sensor should be stable within the range of (1.5±0.1)V. If the measured value is lower than 1.3V, it is necessary to check whether the air gap of the magnetic circuit has increased due to the tilted installation.

Harmonic distortion index

The odd harmonic content of the output signal is detected by FFT analyzer, and the total harmonic distortion (THD) is required to be <2%. When THD exceeds 5%, it indicates that the installation angle deviation has seriously affected the sine wave characteristics of the magnetic circuit.

Phase consistency verification

In a multi-probe system, it is necessary to ensure that the phase difference of the output signal of each sensor is less than 0.2°. Phase inconsistency may cause a 2% system error in the speed calculation.

The installation angle control of the magnetoresistive speed sensor DF6101-005-065-01-05-00-00 is essentially a comprehensive reflection of electromagnetic coupling optimization and mechanical assembly accuracy. Engineers must realize that the seemingly simple installation angle is actually the golden section point connecting the physical world and digital control.

When looking for high-quality, reliable rotation 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

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