Original poster: "Gary Peterson" <g.peterson@xxxxxxxxxxxx>I have placed a link to a short audio sample of a reciprocating mechanical oscillator in operation on the web at http://www.tfcbooks.com/mall/more/345ntem.htm . This particular machine was constructed by Walter Baumgartner and operated at the 1986 International Tesla Symposium during his presentation, "The Tesla Earthquake Oscillator." With the proper tools it should be possible for someone to estimate the device's isochronicity. Keep in mind that this is, at the very least, a third generation recording, two of which were on analog tape. Also the oscillator did not have thermal stabilization.
In regards to instrumentation, Tesla designed a stroboscopic device known as a tikker for the measurement of frequency and phase. The time reference was a mechanical clockwork with an escapement wheel. (Note that the RECIPROCATION ENGINE, Aug. 19, 1893, U.S. Patent No. 514,169, Feb. 6, 1894, is shown as an escapement-regulating mechanism.)
" . . an instrument was devised which is illustrated in Fig. 13 ab. It has proved itself to be so necessary and valuable an implement in experimental investigations that its description here may afford useful information. The cut is intended to show a substantial and carefully constructed clock mechanism with the usual escapement e, gearwheels ggg, and a 1-second pendulum P. A small shaft s, carrying a disk D of large diameter, was geared to the clockwork through a pinion p of a proper number of teeth, such as to give to the shaft a velocity best suitable for observations. . . . In order to reduce the weight of the [free-spinning] disk D as much as possible, a light frame, consisting of a circular rim with narrow spokes, was cut out of thin aluminum sheet, and black paper glued on the frame-all marks and divisions of the former being, of course, white. I found it convenient to draw concentric circles with a number of marks such that all vibrations within the range of the apparatus could be read off. In addition, a segmental piece of hard rubber N, supported on a bar T and properly marked, was used to read fractions or, respectively, take corrections for any irregularity in the rotation during a prolonged period of time. Near the disk was placed a vacuum tube or, in its place, an adjustable spark gap l, which was connected to the secondary of a small transformer, the primary of which was positively controlled by the mechanical or electromagnetic system the vibrations of which were to be determined. In preparing a spring of the desired period of vibration for one of the instruments described, for instance, the spring was provisorily mounted on the instrument and the latter put in operation. The disk, intermittently illuminated by the discharges of the secondary coil, was released from the pendulum and rotated until synchronism was attained, the revolutions being computed by observing the white mark m. The constants of the spring were then modified after a simple calculation from the first result, and in the second trial, as a rule, the vibration was so close as to enable the use of the escapement, the adjustment then being completed, generally by altering the weight of the hammer on the spring until the marks on the disk, by the nominal speed of rotation, appeared stationary in space.
"The apparatus described in Fig. 13 will be found very convenient and time saving in a great many lines of experimentation. By means of the same, it is practicable to rotate a body of considerable weight with uniform and adjustable velocity, and it lends itself to the operation of circuit controllers, curve tracers, and all kinds of such devices. It will be found most useful in tracing current or electromotiveforce curves and a variety of diagrams, and will afford material help in determining a number of physical quantities. But its most valuable use in the investigation of electrical vibrations is, perhaps, for the purpose of determining exactly the angular velocities of dynamos, particularly of alternators. Among the various quantities which, in alternate-current experimentation and practice, one has to determine very frequently, there are some, which even in a laboratory or shop in the midst of the disturbances of a city or factory can be ascertained with sufficient precision, while there are others which can be only approximated, particularly if, as is very often the case, practical methods of measure must be resorted to. So, for example, the close measurement of resistances offers no difficulty, nor does that of currents and electromotive forces, although the degree of exactitude is necessarily smaller; but in determining capacities, one is liable to make a considerable error, still a greater one in measuring inductances, and probably the greatest in estimating frequencies. In many places, such crude devices as speed counters or tachometers are still resorted to, and the experimenter is disappointed to realize that the accuracy of his long and painstaking tests is impaired because of his inability to determine exactly the frequency. To make matters worse, very often too, the latter is the largest and most important quantity. In view of these facts, a description of the method adopted by me for the determination of angular velocities may be of some value." [NIKOLA TESLA: LECTURE BEFORE THE NEW YORK ACADEMY OF SCIENCES, APRIL 6, 1897, Tesla Presents Series Part 2, Leland I. Anderson, Twenty First Century Books, 1994, pp. 61, 65-66; this instrument is also illustrated and briefly described in NT On AC, pp.158-159.]
Gary
Original poster: Ed Phillips <evp@xxxxxxxxxxx>I've read that before and found it most interesting. What a pity it is that we don't have all his lab records from that time to know exactly what he did, how he measured things, and what the results were! I suspect that to him ISOCHRONOUS meant to a part in a thousand at best, but plenty good enough for the purpose at hand. The note from the one remaining Alexanderson alternator at Grimeton, Sweden, appears to be stable (at least short term) to about 1 Hz out of 17.5 kHz but I haven't seen a description of the control mechanism for the prime mover.Ed