Magnetoresistive transducers for the measurement of magnetic tape speed

A method of employing space-periodic magnetoresistive transducers for the direct measurement of the speed of magnetic recording tape is described. The method is, in principle, similar to that devised for measuring strip speed in steel mills, using an inductive transducer. The wavelength-selective transducer is connected in a feedback configuration to an inductive write head placed upstream of the transducer, and the system records an ideally constant-wavelength pattern on the tape, so that the frequency of the transducer output is a direct measure of the tape speed. A digital variable delay line is used to compensate for slight variations in the recorded wavelength caused by variable phase delays encountered in the feedback loop. The error in the speed measurement is less than 0.1%. Three different experimental transducers are investigated, each of which is less than 2 mm long and utilises trackwidths of 100 ¿¿m or less.