Frederick R. Chamberlain

Low Concentration Media Tester

The system described measures the magnetic laydown density (Mr thickness product) of low concentraion magnetic media. The device functions well for media having an Mr thickness product as small as 0.1 milliemu/cm*. The system consists of a flux-guided paired magnetoresistive (FGPMR) head mounted in a card swipe reader, an amplifier channel, and a digital scope. It has been used to provide quick and simple quality control of the transparent magnetic layer coated on Advanced Photo System photographic film. The measurement is quick, easy and accurate.

Low concentration magnetic media tester

The system described measures the magnetic laydown density (M/sub r/ thickness product) of low concentration magnetic coatings, such as the coating on Advanced Photo System photographic film. The measurement is accurate for coatings having a magnetic coverage as small as 0.1 memu/cm/sup 2/. The system consists of a roller recorder, a flux guided paired magnetoresistive (FGPMR) head mounted in a card swipe reader, an amplifier channel, and a digital scope. Laydown density is measured by affixing a small coating sample to a plastic card, roller recording it to produce isolated transitions, and swiping it through the reader. The RMS signal output is linearly proportional to the laydown density.

Rotating magnet dispersion tester

The device described provides an in-line measurement of the concentration of magnetic particles dispersed in a flowing fluid. For a given magnetic material and particle size distribution, the output signal is linearly proportional to the particle concentration. It employs a rotating NdFeB cylindrical permanent magnet to generate a several hundred Oe, elliptically rotating, magnetic field. This field is applied to a matched pair of parallel coils: a measuring coil that contains the fluid line, and an empty bucking coil. The magnetic particles in the fluid rotate with the applied field, and the net signal from the two coils is proportional to the magnetic flux from the dispersed particles. The device has sufficient sensitivity to measure the very low concentration dispersions typical of those used for preparation of thin transparent coatings for magnetic recording on photographic film.