Abstract: A thin film magnetic data transducer which prevents capacitive coupling between the transducer and the disk of a disk drive system, has a magnetic circuit which is maintained at the same potential as the disk, usually ground potential. With the disk and the magnetic pole tips of the magnetic circuit at the same potential, capacitive charging and consequent current flow or arcing or discharge noise between the two are prevented. Noise from current due to the variable capacitive coupling of the coil to the disk during disk rotation is also eliminated. The thin film magnetic transducer is fabricated by depositing successive layers of an electrical insulating material, a magnetic material, insulating material, electrical conducting material for a planar coil, insulating material and magnetic material, in the order named on a substrate.

Abstract: A method and apparatus for operating a magnetic disk drive having a pole piece spaced apart from a magnetic disk surface by a predetermined distance to effectively form two plates of a parasitic capacitance capable of sustaining an undesirable electrical discharge capable of destroying data on the disk either by random discharge between the pole piece and magnetic disk or by discharge into imperfections on the disk. The invention comprises a circuit and method for applying a DC voltage to the pole piece and for simultaneously applying a DC voltage to the magnetic disk surface which is approximately equal to the DC voltage applied to the pole piece and thereby preventing the above parasitic capacitance between the pole piece and the magnetic disk surface from charging to a level sufficient to sustain any electrical discharge.

Abstract: Noise in the readback signal of a magnetic recording device resulting from spurious pulses in the readback signal produced by transitions of the magnetic remanent state of the yoke in the read/write transducer is eliminated by controlling the occurrence of the spurious pulses. Immediately following the completion of the write process, a decreasing amplitude alternating current is applied to the read/write coil of the transducer to drive the yoke remanent state to a stable or zero remanent state prior to the commencement of the read process.

Abstract: A digital phase lock loop utilizing a programmable delay line to phase shift the output of a crystal generated reference clock signal and lock it to digitized data transitions recorded on a suitable medium is provided. The output of the delay line is compared to the digitized data transitions in a phase detector to determine if the delay line output leads or lags the data transitions. The delay line is then reprogrammed to reduce the phase difference between the data transition and the delay output to a minimum value.

Abstract: An improved electrically-operated backup alarm for use on mobile construction and industrial machinery, including selectable lower and higher loudness levels, automatically adjustable loudness level with respect to varying ambient noise level in which the alarm is operating, high and low frequency compensation to substantially eliminate high and low frequency signal components of the sensed ambient noise, and compensation for responding to transient signal components of the sensed ambient noise.