Equivalent Drag Cup Resistance

A method is given for calculating the equivalent resistance of a drag cup which can be used in many varied applications. An equivalent circuit of series and parallel resistances is utilized, coupled with a derivation of a maximum power equation to produce a practical method for obtaining the equivalent resistance of a drag cup. A sample calculation is given which is tailored for slide rule use. Actual test data on a-c tachometers have shown good correlation with calculated results.