Tape Flux Measurement Revisited
Analog magnetic recording standards specify the recorded signal magnitude in terms of short-circuit flux per unit track width, called fluxivity. Two flux measurement methods are standardized: a direct ac method using a high-efficiency head (AES7/ANSI S4.6) and a transfer-to-dc method using a fluxmeter (German standard DIN 45 520). A transfer-to-dc measurement made in the 1950s is used to calibrate the fluxivity of German calibration tapes. When these tapes are measured by the direct ac method, the fluxivity is 10% less than the stated value. Thus the 1950s German transfer-to-dc measurement was 10% more sensitive than the direct ac measurement. A new comparison of the two measurement methods shows that they actually have the same sensitivity; the experimental error of our measurements is about ±1%. Thus we conclude that the German measurement in the 1950s must have had a 10% error, and that the fluxivity on all of the calibration tapes based on the old German measurement is 10% less than the stated value'tapes identified as 320 nWb/m are actually 288 nWb/m.
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