The Design and Implementation of Proportional Feedback Controller for the Distortion Improvement of Vibrator in Low Frequency Motion

Abstract

The Total Harmonic Distortion (T.H.D.) of acceleration involved in the vibrator power amplifier combination of the low-frequency primary vibration calibration system at CMS/ITRI is higher than 2% at frequencies below 2 Hz before control. This is outside the requirement of ISO 16063–11. A waveform comparison feedback control method to reduce the T.H.D. of the vibrator is proposed. This paper describes a method of distortion reduction on a low frequency vibration standard, where a laser interferometer is used, with feedback loop control software on the calibration scheme. The vibrator signal is measured by an accelerometer located on a moving platform that is driven by the vibrator, and compared with a pure sine signal to obtain an error signal. Through multiplication of the error signal by a factor k, it is combined with the original input signal of the vibrator to reduce the T.H.D. This paper shows the experimental results at 0.8 Hz and 1 Hz. The measured T.H.D. results are both below 2%. At the same time we also evaluate the typed A standard uncertainty for accelerometer voltage sensitivity. The standard uncertainty before and after improvement is 0.154% and 0.068%, respectively.