PROBLEMS CONCERNING MOUNTING OF PICKUPS FOR VIBRATION LEVEL METER

Abstract

A vibration level meter with weighting network corresponding to human vibra- tion sensation has recently been planned by the Acoustic Society of Japan to assess vibration pollution. However, weight, size and position of a sensing element of a vibration pickup of the vibration level meter have not been standardized. To determine optimum values for them, the contact resonance was examined on combinations of eleven mounting materials and seven vibration pickups on a vibration table of electro- dynamic type in vertical and horizontal directions.
It was found that the vibration pickup which had weight of 300 g was desirable for vertical and horizontal vibrations under almost all mounting conditions except in the case of some special materials. The contact resonance frequency between the pickup and the mounting material was able to be elevated to a considerably high frequency for vertical vibration, but for horizontal vibration it was lowered until near half the value in vertical vibration. Therefore, vibration occurring in human environment is desirable to be measured by a VL range of the vibration level meter, in which the weighting circuit of the amplifier has the same frequency characteristics as those of human vibration sensation below 90 Hz and above it the cut-off frequency nature is -18 dB/oct. Vibration pickup of the vibration level meter was able to be calibrated without bolting on the vibration table below 90 dB (0 dB=10-3 cm/sec2).