What Are The Error Sources Of A Dynamic Torque Sensor?
Errors in dynamic torque sensors can be broadly categorized into two types: sensor body errors and engineering application errors. In practical applications, these errors are often caused by the superposition of multiple factors. Any oversight in the design or usage can lead to measurement deviations of one percent or even greater.
Sensor Body Related Errors:
Nonlinear Errors and Hysteresis: Ideally, the output should have a strictly linear relationship with the torque. In reality, there will be a certain deviation from the curve, resulting in nonlinear errors. Incomplete overlap of the output during loading and unloading will produce hysteresis errors. These two factors are typically determined by the elastomer design, strain gauge bonding process, and material properties.
Sensitivity Drift and Zero-Point Drift: Temperature changes, long-term loading, and material creep can cause the sensitivity and zero point to drift slowly over time and with temperature, resulting in zero-point errors and proportional coefficient errors. These are very typical problems in long-term dynamic testing.
Installation and Mechanical Structure Errors:
Alignment Errors and Additional Bending Moments/Axial Forces: If the sensor is not aligned with the shafts on either side, or if there is eccentricity or tilt, additional bending moments and radial forces will be introduced during rotation, directly contaminating the torque signal. In experiments, even an installation misalignment as small as 0.5° can introduce errors of several percent.
Insufficient Stiffness and Resonance: Insufficient stiffness of the supporting structure and improper selection of couplings can lower the system's natural frequency, causing resonance at specific speeds and resulting in periodic fluctuations in the output, manifested as a sudden increase in error at a certain speed point.
Dynamic Operating Conditions and Signal Chain Errors
Insufficient Bandwidth and Dynamic Response: Rapid changes in dynamic torque, coupled with insufficient bandwidth or large phase delays in the sensor and downstream amplifier/acquisition system, can lead to amplitude attenuation and waveform distortion, equivalent to underestimating or lagging the measured value. This is particularly evident in motor start-stop and impact load testing.
Signal Transmission and Contact Issues: In rotating operating conditions, slip rings or wireless methods are commonly used to transmit signals. Changes in slip ring contact resistance, wear, and the distributed parameters and impedance mismatch of long cables can all cause signal attenuation, noise, and waveform distortion, thereby increasing measurement errors.
Environmental and Electromagnetic Interference Errors
Temperature, Humidity, and Thermal Gradients: Changes in ambient temperature affect the characteristics of strain gauges and compensation circuits, and also alter mechanical fit clearances and torque transmission efficiency. High humidity or condensation environments accelerate the degradation of adhesive layers and insulation materials, significantly increasing zero-point instability. Electromagnetic interference and noise coupling: Electromagnetic noise generated by frequency converters, high-power motors, switching power supplies, etc., can couple into the measurement link through power lines, signal lines, and even spatial radiation, causing output jitter or drift, especially noticeable in dynamic low-torque measurements.
Calibration and operating condition errors: Mismatched calibration methods and conditions: Directly using static calibration results for high-speed rotational dynamic testing ignores speed-related effects, potentially resulting in statically acceptable results but deviations approaching 2% at several thousand rpm. Simultaneously, the uncertainty of the calibration device itself can also become a source of systematic error.
Overload, fatigue, and aging: Frequent use near or exceeding the measurement range, impact torque, and prolonged full-scale loading can cause performance degradation of the elastomer and strain gauge, manifesting as decreased sensitivity and increased zero-point drift. Even if they can still function in the short term, they will introduce significant systematic deviations.
