Static characteristics of torque detection from carburized steel shafts

Static characteristics of a shaft torque sensor using low-profile pickup heads were studied for a carburized nickel chromium molybdenum steel shaft (SNCM420 in JIS). It was found that the hysteresis of the input-output relationship was generally small. The direction of traversal around the hysteresis loop was changed as the amplitude of the excitation current changed. It was shown that an optimum operating condition exists for the torque sensor in which hysteresis achieves a minimum value yet the sensitivity remains high. The optimum excitation current was 0.3 A at the excitation frequency 60 kHz, where the total power loss at the pickup heads was 0.37 W. Under this operating condition, the hysteresis was extremely small, and the linearity was better than 0.6%. Zero-level fluctuation and sensitivity fluctuation were ±3.2%/FS (FS: 400 Nm for 25 mmφ shaft) and ±1.4%, respectively