Nikola Tesla Books
Books written by or about Nikola Tesla
Following readings were taken today for the purpose of putting together a table of the inductances of the various turns of the regulating coil. The machine was specially run and all care was taken to get the readings as close as practicable. The method used in a previous case was again adopted which consisted in reading the e.m.f. across the two primary turns in series and simultaneously the e.m.f. across the two primary turns + connections + the turns in the regulating coil. The resistances as before stated being entirely negligible, the inductance in each case was given by the ratio of the e.m. forces and the known inductance of the two primary turns. By this method the error which might have been caused by a variation of Ï which could only be determined by taking the speed of the generator, the apparatus for the more exact determination of this quantity being unfortunately left in New York. The results are indicated in the following table:
| E.m.f. across two primary turns in series | E.m.f. across two primary turns + connections + turns of the regulating coil | Number of turns reg. coil | I | Ï | Increase of e.m.f. from step to step |
|---|---|---|---|---|---|
| 12.00 | 12.3 | 1/2 | 58.8 | 880 | |
| 12.00 | 12.45 | 2 1/2 | 58.8 | " | 0.15 |
| 12.00 | 12.70 | 4 1/2 | 58.8 | " | 0.25 |
| 12.00 | 13.05 | 6 1/2 | 58.8 | " | 0.35 |
| 12.00 | 13.40 | 8 1/2 | 58.8 | " | 0.35 |
| 12.00 | 13.80 | 10 1/2 | 58.8 | " | 0.40 |
| 12.00 | 14.20 | 12 1/2 | 58.8 | " | 0.40 |
| 12.00 | 14.60 | 14 1/2 | 58.8 | " | 0.40 |
| 12.00 | 15.00 | 16 1/2 | 58.8 | " | 0.40 |
| 12.00 | 15.40 | 18 1/2 | 58.8 | " | 0.40 |
| 12.00 | 15.80 | 20 1/2 | 58.8 | " | 0.40 |
| 12.00 | 16.20 | 22 1/2 | 58.8 | " | 0.40 |
| 12.00 | 16.40 | 23 1/2 | 58.8 | " | 0.20 |
This shows an increase per turn of about 0.20 V, except the few first turns.
Colorado Springs
Nov. 9, 1899
In some experiments it was necessary to use vibrations of lower frequencies and this made it necessary to insert additional inductances in the condenser discharge circuit. In such cases it was convenient to use the two primary turns only; in order to prevent a
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
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.
