A comparison of instrument response correction methods: Post-processing and real-time methods

Abstract

Industrial vibration monitoring often requires sensors with adjustable sensitivity and suitable frequency range. In practice, most industrial studies utilize either geophones (velocimeters) or accelerometers. In some cases, where low frequency content is of interest, larger sensor will be required. In difficult installation conditions, it can be advantageous to utilize smaller, higher frequency sensor elements (geophones or accelerometers) to simplify installation and maintenance. A frequency correction of sensors or the recorded waveforms will be needed to accommodate the frequency range of interest. Most accelerometers have relatively smaller sensitivity at low frequency which can affect the calculation of vibration velocity and displacement at low frequencies. Geophones are limited by their frequency response, which drops-off significantly their sensitivity below the resonant frequency of the sensor. Structural and ground vibrations that occur under the resonant frequency could be observed at test sites, but the recorded waveforms cannot be used directly for real-time assessment, and therefore it can be beneficial to artificially expand the frequency range below the sensor's frequency cutoff. Methods for such expansion, were developed and are well established in seismological studies and exploratory geophysics. Usually, these procedures are applied in data post-processing. These methods are not applicable when an operator requires real-time feedback of the measured vibrational amplitude, for example, monitoring of machinery foundations, where excitation control is necessary to avoid infrastructure damage.This paper presents an approach for instrument frequency extension in the necessary low-frequency range of common geophone elements in real-time applications and compares the results of the proposed technique in post-processing and in real time data collection systems.