Optical seismic detector

Claim 1

A servo accelerometer comprising: support member; a permanent magnet provided in fixed position on said support member; a coil positioned such as to be capable of producing a magnetic field which can magnetically interact with said permanent magnet; moveable supporting means including a vertical supporting rod and a horizontal supporting rod carried by said support member for supporting said coil moveably with respect to said permanent magnet; a light source provided in fixed position on said support member for emitting a light beam; light-receiving means provided in a fixed position on said support member for receiving said light beam from said light source, said light-receiving means being spaced apart from said light source; means coupled to said light-receiving means for producing a signal indicative of the position of impingement of said light beam on said light-receiving means; an optical system fixedly mounted on said movable supporting means intermediate said light source and said light-receiving means for magnifying the effect of lens displacement on said light-receiving means, said optical system comprising a quater pitch gradient index rod lens, said lens being affixed to said vertical supporting rod; and a servo amplifier for applying a driving current to said coil in response to said signal produced from said signal producing means.