US2223061A

US2223061A - Arrangement of noninductive terminals for variable condensers

Info

Publication number: US2223061A
Application number: US180854A
Authority: US
Inventors: Ducati Adriano Cavalieri
Original assignee: Individual
Current assignee: Individual
Priority date: 1936-12-19
Filing date: 1937-12-20
Publication date: 1940-11-26
Anticipated expiration: 1957-11-26

Description

Nov. 26, 1940. A. c. DUCATI 2,223,061

ARRANGEMENT OF NONINDI IGTIVE TERMINALS FOR VARIABLE CONDENSERS Filed Dec. 20, 1937 Qdriano Cawlieri Ducafz' ATTORNEYS Patented Nov. 26, 1940 UNITED STATES ARRANGEMENT OF NONINDUCTIVE TER- MINALS FOR VARIABLE CONDENSERS Adriano Cavalieri Ducati, Bologna, Italy Application December 20, 1937, Serial No. 180,854 In Italy December 19, 1936 2 Claims.

(Granted The present invention relates to precision electrostatic condensers and more particularly relates to a system of terminals for variable electrostatic condensers minimizing the inductance 75v or inductive reaction for the electrical connection to the condensers.

The greatest value of a precision variable condenser such as is employed in laboratories or in electrical measurements or comparisons is constancy of its capacity over a great range of applied frequency. The capacity of a precision variable condenser depends upon its inherent capacity which can be determined to a fraction of a micro-microfarad. However, the effective capacitance of the condenser depends also to some degree upon the frequency of the applied signal. The inherent inductance in the condensers of the prior art caused a variation in the effective condenser capacitance which changed with the frequency applied thereto, the higher the frequency range, the greater the variation in the effective capacitance of the condenser and therefore its determinable accuracy.

The inherent inductance of a. precision variable condenser is very important, particularly at the higher frequency such as in radio frequency or ultra-high frequency use, even though its value may be a one-hundredth or smaller part of a microhenry. I have found that the terminal con- 80 nections to the variable condenser produce the greater portion of the inductance of the condenser, and it is among the objects of my present invention to minimize the inductive reaction of the contacts to the variable condenser.

In accordance with my present invention, I contemplate arranging the terminal connections to the plates thereof in a manner to nullify or greatly minimize the inductance thereof as compared to the prior art condensers. In one form 40 of the invention, I provide the terminals to the stationary and rotary plates of the condenser concentrically arranged whereby any self-inductive reaction of any one terminal is cancelled or nullified by that of the other one. In a modi- 45. fication of my invention I provide two closely adjacent terminal posts adapted to greatly minimize the inductive reaction of the connection to the condenser plates. By thus minimizing the inductance of the variable condenser, the capa- 50 city thereof remains more constant over a much greater frequency range than the condensers of the prior art.

It is accordingly an object of my present invention to provide a novel system of terminal con- 55 tacts for a variable condenser.

It is another object of my present invention to provide a novel arrangement for connection to the stator and rotor plates of a precision electrostatic condenser.

It is still another object of my present invenunder the provisions of sec. 14, act of March 2, 1927; 357 0. G.

tion to materially minimize the inherent inductance of variable electrostatic condensers.

These and further objects of my present invention will become apparent in the following description taken in connection with the draw- 1 ing in which:

Figure 1 is an end view of a preferred construction of a variable condenser in accordance with my present invention with the turning knob omitted and represents the View taken along ll in Figure 2.. v

Figure 2 is a plan view of the condenser shown in Figure 1.

Figure 3 is a perspective view partly in section of a modified form of my present invention.

Figure 4 is a schematic view of still a further form of my invention.

Figure 5 is a diagrammatic illustration of the principle embodied in my invention.

' In Figure 1 I have illustrated a semi-circular type condenser construction comprising the fixed or stator portion and rotatable or rotatorportion II'. The stator portion I6 is affixed or mechanically secured to the terminal or contact rod I 2, together with the stud 13 as shown in Figures 1 and 2. The rotor section II is centrally secured to the rod I l together with the stud IS. A knob l8 may be affixed at the projecting end of the terminal post M as shown in Figure 2. The rods l2 and I4 may be of small diameter and of solid metallic conducting material such as aluminum, copper or the like, or may well be hollow or tubular in accordance with principles of design for minimizing condenser losses well known in the art.

In accordance with the principle of my present invention, the disposition of the rotor and stator plates l0 and II and the terminal posts [2 and M respectively are arranged whereby the terminals l2 and I4 may be as physically close together as possible, more so than any of the condensers of the prior art. As will be hereinafter pointed out, such close disposition of the terminal rods [2 and I4 parallelly arranged as seen in Figure 2 makes for a constancy of capacity for the unit with a minimum of inherent inductance.

In order to provide for a 180 rotation for the rotor I l in the preferred physical arrangement as described and without mechanically interfering with the terminal post l2 of the stator 10, the cut-away section H5 in the rotor plate ll obviates the mechanical interference between the rotor plates II and the post [2 as will now be evident. I further provide a cut-away'portion I! in the stator plate, to permit closer positioning between the posts l2 and I4 and avoid the necessary projecting portion of the stud l5 and post H as will also now be evident. Accordingly, it is to be understood that the design of the condenser plates Ill and H with the provided cutaway sections IE and II are for permitting as physically close positioning of the terminal posts l2 and I4 as practicable and furthermore permit a full 180 rotation of the rotor section ll of the condenser. It is to be further understood that the illustrations I have made are with a single plate rotor and single plate stator for simplicity of illustration and that a plurality of such plates may be used with the modifications I have described as will beevidentto those skilled in :the art; Terminal leads I9 are connected to the extremity of the parallel terminal rods l2 and 54. The non-inductive arrangement of the flexible leads |9 may be arranged in any manner known in the art, the present invention being particularly concerned with the minimizing of inductive reaction of the electrical condensers per se.

A modified form in applying my invention to variable condenser construction is illustrated in Figure 3 wherein a fixed or stator plate section 20 is arranged opposite the rotor plate 2| adapted to be rotated by the central connection rod 24 to which it is secured, A knob 28 is preferably aflixed to a projection of the central rod 24 as shown in the figure. The knob 28 is naturally of insulation material to permit handling by the operator.

The stator 20 is secured to a metallic tube 22 which is concentric about and co-extensive with the central rotor connection rod 24. It is to be understood that the tube 22 preferably completely surrounds the rod 24 and is broken away in the illustration. Insulation bushings 25 electrically separate and maintain the

connection posts

22 and 24 in proper mechanical and electrical relation. The wire-leads 29 connect to the

terminal rods

22 and 24 as shown to connect the condenser to the necessary electrical circuits.

to prevent mechanical interference between the v ure is included to illustrate this principle.

rotor 3| and the terminal rod 33 of the stator plate 30. The terminal rod 34 of the rotor plate 3| is adapted to be secured to a knob or other element for rotation. It is to be understood that the mechanical disposition of the

terminal rods

33 and 34 are similar to the hereinabove described arrangement in connection with Figures 1 and 2 of rods l2 and M to cause minimum inductive action by the terminal rods.

The principle of minimizing the inherent inductance vof the terminal connections for the variable condensers of my present invention is predicated upon the phenomena of minimizing inductance by arranging two conductors in parallel and in close juxtaposition and in causing similar currents to fiow therein in opposite directions. The schematic diagram forming Fig- The two conductors 40 and 4| are arranged in parallel. These conductors may be the opposite plates of a condenser or may well represent the parallel terminal rods I2 and I4 of Figure 2; or 22 and 24 of Figure 3. The horizontal arrows represent the direction of the current i flowing therein. The current i in the conductors 40 and 4| are necessarily of substantially equal value due to the series relation. The transverse arrows between theplates Mland 4| represent; the capacitive relation or reaction C between these plates or conductors which, being a geometric entity is substantially constant .for wide frequency ranges. V

I have placed corresponding arrows upon the Figures 2 and 3 to represent the direction of flow of the currents in the parallel terminal contacts and condenser plates to indicate how the principle of minimizing the inductive reaction of them is effected by my invention.

It is to be understood that the terminal rods of the condensers are arranged to be placed as close together as possible to minimize as much as possible the inductive reaction thereof as will now be understood by those skilled in the art. The cut-away portions illustrated in some of the modifications permit close positioning of the terminal rods. In the modification of Figure 3, the concentric relation of the terminal rods affords the theoretical minimum of inductance therefor. My invention is applicable for all types of variable condensers irrespective of their shape or. use and is designed to minimize the inherent inductance therein to provide. a substantially constant effective capacitance of the condenser over wide frequency ranges and particularly for high radio frequency precision measurements.

Having described particular embodiments of my invention, modifications which fall within the broader spirit and scope of my invention may be evident to those skilled in the art and accordingly, I do not intend to be limited except as set forth in the following claims.

I claim:

1. A high frequency precision variable condenser comprising a stator section of substantially semi-circular shape, a rotor section of substantially semi-circular shape, a terminal rod secured solely to one region of said rotor adapted to rotate saidrotor, a second terminal rod secured solely toone region of said stator, said rods being parallel and arranged mechanically close for minimizing the inductive reaction thereof, said rotor section having a cut-away portion to permit the close positioning of said rods and full effective one-hundred and eighty degree rotation of said rotor, whereby the fiow of high frequency current in the condenser through said rods, rotor and stator substantially cancel inductive reaction therein to provide a stable efiective capacitance for the condenser when operated at high frequencies.

2. A high frequency precision variable condenser comprising a stator section of substantially semi-circular shape, a rotor section of substantially semi-circular shape, a terminal rod secured solely to one region of said rotor adapted to rotate said rotor, a second terminal rod secured solely to one region of said statonsaid rods being parallel and arranged mechanically close ,for minimizing the inductive reaction thereof, said rotor section having a cut-away portion to permit the close positioning of said rods and full effective one-hundred and eighty degree rotation or said rotor, said stator having a cut-away portion opposite the position of said rotor, and said second rod being asymmetrically placed on the stator, whereby the flow of high frequency current in the condenser through said rods, rotor and stator substantially cancel inductive reaction therein to provide a stable effective capacitance for'the condenser when operated at high frequencies.

ADRIANO' CAVALIERI DUCATI.