Manual of High Frequency Currents
Noble M. Eberhart, M.D., Ph.D., D.C.L., 1911
Types of Apparatus; DArsonval Type; Tesla Transformers; Impedance;
Direct DArsonval Currents; Auto-Conduction; Auto-Condensation; Resonator of Oudin;
Tuning Coils; Measuring the Current.
Types of Apparatus. There is no intention on the part of the
author to encumber this volume with lengthy descriptions of apparatus. For such
information, the reader is referred to the manufacturers of electrical outfits.
All high frequency instruments, however, are constructed
along two principal types -- that of DArsonval and that of Tesla -- and these should
be understood by the high frequency operator, since all machines represent one or the
other or a combination of these types.
In connection or combination with them, a third
instrument, the resonator of Oudin, is in such common use that it also calls for special
description. In speaking of high frequency currents, to be specific, we should
always state the form of current used, as DArsonval high frequency, or Tesla high
Fig. 11 and 12 - Portable Coils.
The DArsonval type of apparatus as it is manufactured
today consists of a combination of the DArsonval solenoid and an improved type of
the Oudin resonator. The Oudin current derived from this type of apparatus serves to
energize vacuum electrodes, the spray electrode, the so-called static spark
electrode, the portable ozone inhaler, and also is the current which is utilized for
obtaining the cold fulguration spark. The DArsonval solenoid in
this instance delivers a comparatively low potential and high milliamperage current.
The Tesla type of apparatus is designed along the same
general lines as is the DArsonval and has the same wide range of usefulness, but the
general characteristics of the current are different in that the Tesla type of apparatus
delivers a high potential, low milliamperage current.
If every physician employing high frequency apparatus
was aware of this difference it is the authors opinion that many cases of
misunderstanding and dissatisfaction would be cleared away.
In other words, the milliamperage reading of the meter is not
an indicator of the capacity or power of the apparatus. This means that 500
milliamperes of Tesla high frequency current is just as capable of producing deep
constitutional effects as 1,500 milliamperes on a DArsonval high frequency
The relative merit of the Tesla versus the
DArsonval apparatus more particularly as regards auto-condensation and
diathermy has been the subject of numerous discussions among electro-therapeutists.
The thickness of the di-electric (auto-condensation cushion) has also entered into this
discussion. It has been proved that either type is capable of producing results and
in consequence thereof the author does not feel capable of choosing himself as the sole
arbitrator in deciding which is better. He however, for the past three years has
been employing the Tesla type of apparatus in his individual practice and has been
deriving eminent satisfaction from its use. He employs a cushion of approximately
three inches in thickness this size being endorsed by the standardization committee
of the American Electro-Therapeutic Association.
As will be stated in Chapter VI, the author originated
the thin cushion as well as the portable thick pad, and the method of making these
different forms is given. He bows to the ruling of the committee referred to above
and now employs only the thicker cushion.
The DArsonval Current is one of high
frequency, not very high voltage, and high amperage.
It is administered as a bi-polar method, thereby producing
constitutional effects. DArsonval started with an induction coil attached to
the direct current. The terminals of the secondary coil were attached to the inner
layers of two Leyden jars, thereby charging one of them positively and the other
negatively. In the circuit between these two layers was placed an adjustable spark
gap. Between the outer layers of the jars was placed a solenoid or coil consisting
of fifteen to twenty turns of coarse copper wire. This combination of
condensers connecting on one side through a spark gap, and on the other through a coil of
wire, is an absolute necessity in order to obtain the DArsonval current,
and it therefore constitutes this type. See Fig. 13.
When the positive layer of the first receives a
sufficiently high charge, it jumps across the spark gap to neutralize the negative charge
in the second jar. Immediately the positive charge on the outer layer of the second
jar is released and passes through the coil of wire to neutralize the negative charge on
the outer layer of the first jar, and as it passes through this coil or solenoid, it
produces a high frequency current, keeping in mind the fact that the oscillation back and
forth through the condensers exists as described in Chapter II. The patient is
connected on that side of the condensers that discharges through the coil and is really on
a shunt or switch from that part of the circuit, and the reason the patient receives any
current at all, is because the solenoid possesses the property known as self-inductance,
which impedes the passage of the current, allowing part of it to go through the lesser
resistance in the patients circuit. The process of interfering with the
current as a result of the self-inductance is called impedance.
Fig. 13 - Diagram of DArsonval Type.
The Tesla Transformer and Coil. Tesla started
with the alternating current, and by referring to our definition of high frequency
currents (Chapter I), it is seen that all that was required was the increasing of the
frequency to a point which we properly call high. To do this, he used as a primary ,
a coarse coil of wire consisting of a few turns only, while the secondary coil consisted
of an extraordinary number of turns of very fine wirethe result being that the
current induced therein was of very high tension and very high frequency. The Tesla
transformer or coil is especially adapted to the alternating current. It is employed
in all of the portable high frequency apparatus on the market. The Tesla primary
resembles the DArsonval current except the amperage is less. Fig 14 shows one
method of evolving the various currents.
Administration of the DArsonval Current.
There are three principal ways in which this current is applied to the body; first, the
direct bi-polar method, which has also been subdivided into two or three forms; second,
auto-conduction, and third, auto-condensation. In the first method, the patient is
directly connected to the terminals of the apparatus. Whether the patient holds the
two electrodes, or whether he is attached on one pole, while the other pole is connected
with an electrode in the hands of the operator, the method is still called direct
application. It should be borne in mind that the direct DArsonval current is
also known under several other terms, such as diathermy, electro-coagulation and
thermo-penetration. See Chapter XI. Referring back for a moment to the
component elements of the DArsonval apparatus. It is seen that solenoids and
condensers are fundamental parts. In the elementary DArsonval type we have one
set of condensers and one solenoid. It would appear, therefore, that the inventor
said to himself; If one solenoid gives a current of high frequency, let us add
another solenoid and see what that will do. Thus the second type,
auto-conduction, is constructed, and a large solenoid is connected in the shunt which
forms the patients circuit, and it is made so large that the patient may be placed
within this coil or cage when it is found that as the high frequency currents traverse the
coil, other high frequency currents are induced in the body of the patient. This is
Fig. 14 - Diagram of Tesla Type
Auto-condensation. Again reverting to our
elementary type instead of using the second solenoid, the next arrangement was the use of
an extra condenser, and the current passes from one terminal into one plate of the
condenser, while the other plate was formed by the body of the patient, hence the term
Oudins Resonator. Oudin discovered that
with a coil of wire properly tuned or adjusted to the coarse coil or solenoid of
DArsonval, the electrical currents of the latter produced currents of such strength
that they might be taken from the terminal of the larger solenoid and applied to the
body. They are of high frequency, high voltage and low amperage, resembling the
Tesla secondary. As ordinarily constructed, the DArsonval apparatus and the
resonator are combined in one instrument; the resonator proper consisting of a large coil
of fine wire placed above the coarse solenoid of the DArsonval machine. See
Tuning coils. The best results in resonance are
obtained when the coils are properly adjusted and attuned to one another. To
facilitate this, the wire that passes from one side of the solenoid is attached to a
sliding metal finger, which may be moved up or down on the solenoid, and thereby increase
or decrease the number of turns of wire employed. This permits proper adjustment of
the coils, at the same time it is found that the greater the number of turns included, the
sharper the resulting spark, and vice versa.
Fig. 15 - Diagram of Oudin Resonator.
Measuring High Frequency Currents. High
frequency currents cannot be measured with an ordinary meter. For DArsonval
currents the method customarily employed is the use of a hot wire meter. This is
really a thermostat instead of an electrical device. It is based upon the fact that
Fig. 16 - Hot Wire Meter.
Fig. 16a - Air Cooled and Air Cleaned Spark Gap.
of the high frequency current gives rise to heat and this heat causes
expansion in a platinum wire and thereby deflects the needle in proportion. Hot wire
meters are faulty, but give a relative idea of dosage when employed on the same apparatus.
One is shown in Fig. 16. Other methods of measuring these currents are by
Gaiffe and Meylons induction amperemeter, which measures the repulsive force
between the original current and the current which it induces in a coil attached to the
Fig. 17 - Large Combined Tesla, Oudin and DArsonval Type Coil.