Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 270

November 8

The primary inductance values cited are from November 5th. The other values given in the table do not agree with those derived from the measurements of October 30th. Also, earlier data do not include values for half a turn of the regulating coil. It must therefore be concluded that the measurements from which the tabulated values were calculated are not described in the diary.

It seems that in measuring inductance from voltage, current, frequency and resistance Tesla had difficulty because of unreliability of the frequency determination. He therefore used the voltage ratio, when it is only necessary for the frequency to be constant. By this method he measured the inductance of the regulating coil plus connections, for various numbers of turns.

November 8

He attaches the table of calculated primary and regulating coil inductances plus that of the connections as a function of number of turns. The values for the primary are those of Nov. 5. Other values given in the table do not match those obtained on the basis of measurement data of Oct. 30. Also in previous data the values for the regulatory coil turns halves are not given.

From all this it follows that the measurement results from which the calculated values are obtained and which are shown in the attached table are not given in the notes.

It seems that Tesla was not satisfied with the inductance measurements on the basis of voltage, current, frequency and the resistance due to uncertainty of determining the frequency itself. That is why he applied the method of voltage ratio where it is only important that source frequency is not changed during the measurements.

By this method he performs the measurements in order to determine the regulating coil and the connection inductance for the various number of turns of the coil.

November 9

The measurements of mutual inductance in terms of the inductance of the primary when the secondary is open and short circuited are noteworthy. They were made at constant current and frequency, simplifying the calculation.

To reduce the oscillator frequency, in some cases Tesla used two special coils which he refers to only by wire gauge number. He compares the calculated and measured values for these coils. The values measured by the voltage ratio method are about 2% less than those found from voltage, current and frequency. The calculated values are lower than either. Correction of the measured values as described in the commentary to 26 October does not make much difference (about - 5%) because the D/l ratio is relatively small.

November 9

He performs the interesting measurements of the mutual inductance on the basis of the primary inductance when the secondary is open, and in short circuit. He measured inductances at constant current and frequency so the calculation procedure is simplified. The obtained mutual inductance he compared with the inductance determined previously by means of induced voltage under no load conditions. Tesla thinks that the difference originates from the influence of the secondary on the primary when the secondary is open. In some cases for the purpose of oscillator operating frequency reduction Tesla used two separate coils which he did not name but designated by numbers. He compared the calculated and measured values for these coils. The measured value on the basis of voltage the ratio method amounts to approximately 2% less than values measured on the basis of voltage, current and frequency. The calculated values are smaller in both cases. The correction of measured values according to comment of Oct. 26 is not large (approximately 5%) because the ratio D/1 is relatively small.