  # Transformer Turns Ratio NomogramNovember 1965 Electronics World

 November 1965 Electronics World Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Electronics World, published May 1959 - December 1971. All copyrights hereby acknowledged.

Nomograms (aka nomographs) have always been a great method of providing a quick visual means of relating various quantities to each other. Careful adjustment of the numerical scales allows a straight line to be drawn between any two values to determine the value of the third (or more). An extreme example is the Link Coupling Nomogram which uses two straight line scales and a curve graph. As can be seen in this Transformer Turns Ratio Nomogram from a 1965 issue of Electronics World magazine, a square root function (TR=√Z1/Z2) can be easily accommodated with a straight line from the input impedance scale to the output impedance scale, and extending it to the third turns ratio (TR) scale. A similar nomogram can be constructed for turns ratio needed for specific input and output voltage, current, or power. A list of many other nomographs/nomograms is given at the bottom of the page.

Transformer Turns Ratio Nomogram

Warwick Electronic Inc., Pacific Mercury Div.

Simple method of determining the turns ratio for transformers employed for impedance matching.

This nomogram aids in the computation of the turns ratio for transformers used for impedance matching. The basic equation for the turns ratio is T.R. = √Z1/Z2, where Z1 is the primary impedance, Z2 is the secondary impedance, and T.R. is the turns ratio N1/N2.

The method of solution is illustrated in the example below.

Values other than those shown on the scales may be used by multiplying them by 10n where n may be positive or negative. If Z1 and Z2 are both multiplied by 10n, then T.R. remains unchanged. If only Z1 is multiplied by 10n, then T.R. is multiplied by 10n/2. If only Z2 is multiplied by 10n, then T.R. is multi-plied by 10-n/2. Using even values of n will simplify the con-version of scales.

Example: Find the turns ratio required for an audio output transformer to match a plate impedance of 500,000 ohms to a speaker whose impedance is 8 ohms.

Solution, Draw a straight line from 5000 on the Z1 scale to 8 on the Z2 scale. The line crosses the T.R. scale at 25. Since Z1 was multiplied by 100 then T.R. must be multiplied by 10. The turns ratio is therefore 250/1.

Posted December 22, 2022

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