Development of a Torsional Ground Motion Pickup

This paper is mainly concerned with the cross-talk of a torsional vibration pickup, which was developed to measure the torsional ground motion with a minimum of cross-talk. The causes of the cross-talk considered in this paper are : (1) the static intrinsic errors of cross-spring pivot and (2) the unbalance of the mass element of seismic system. The cross-talk generation due to these causes is investigated in detail. Description of a balancing method utilising a rectilinear vibration table, which was devised to minimize the unbalance of the mass element under actual operating condition of the pickup, is included, together with the construction and performance characteristics of the pickup.