General Radio Co. v. ALLEN B. DU MONT LABORATORIES, 1214.

Citation38 F. Supp. 495
Decision Date11 April 1941
Docket NumberNo. 1214.,1214.
PartiesGENERAL RADIO CO. v. ALLEN B. DU MONT LABORATORIES, Inc.
CourtUnited States District Courts. 3th Circuit. United States District Court (Delaware)

R. Morton Adams and Baldwin Guild (of Pennie, Davis, Marvin & Edmonds), both of New York City, and E. Ennalls Berl (of Southerland, Berl, Potter & Leahy), of Wilmington, Del., for plaintiff.

Samuel E. Darby, Jr., and Floyd H. Crews (of Darby & Darby), both of New York City, and Herbert L. Cohen, of Wilmington, Del., for defendant.

NIELDS, District Judge.

This is a patent infringement suit. General Radio Company, a corporation of Massachusetts, charges Allen B. DuMont Laboratories, Inc., a corporation of Delaware, with infringement of Bedell Reissue Patent No. 20,945 covering a "Device for Indicating Oscillograph Curves as Stationary".

The original Bedell Patent No. 1,707,594 was granted April 2, 1929, and was purchased by plaintiff from Frederick Bedell, the patentee, May 29, 1934. The reissue was granted December 13, 1938, on application filed August 18, 1937. November 20, 1939, plaintiff, as assignee, disclaimed claims 1, 2, 3 and 5 of the reissue patent.

Allen B. DuMont, defendant's predecessor, was a licensee under the original Bedell patent. Thereafter plaintiff brought suit. Application for reissue was filed and was granted with 13 claims. After the grant of the reissue, defendant continued to manufacture and sell its apparatus and was notified of infringement. The pleadings were amended to allege infringement of the claims of the reissue patent. Legg patent No. 1,763,242 was pleaded in anticipation. In view thereof, plaintiff disclaimed claims 1, 2, 3 and 5 of the reissue.

An "oscillograph" is a device for picturing the characteristics of electric currents and voltages. Electrical engineers are interested in learning how quickly electric currents vary and how much. The usefulness of the current or voltage for the job at hand depends upon these characteristics. The engineer's task is to create devices to give to the current the desired characteristics. The oscillograph creates a graph which pictures the characteristics of the current.

At very frequent intervals the engineer is advised as to the magnitude or the strength of the current. The magnitude is recorded by dots corresponding to the magnitude of the electric quantity at each interval of time. Each dot is placed above a base line and the dots are connected by a line which will show the magnitude of electric current at any instant. The shape of this line or current will be smooth or irregular. Its shape is called the "wave form" of the electric quantity.

The curve in the oscillograph is made by a spot of light which is moved sideways equal distances with equal intervals of time and is moved vertically a distance proportional to the magnitude of the electric current at that instant. The spot of light as it sweeps across the face of the tube appears to be a line. This is due to the persistence of human vision and in the cathode ray oscillograph is due to the fact that the screen continues to glow after the spot moves on. If the spot traces the same path over and over the line appears brighter. If the variations occur again and again with regularity they are said to have a frequency. If the sweep circuit, which sweeps the spot of light sideways, sweeps it again and again, it has a particular frequency of repetition. If the frequency of the sweep circuit is made the same as the frequency of the periodic quantity under observation the spot will retrace the same path over and over again. The sweep circuit is then synchronized to the periodic electric quantity under observation. This has always been a necessity in oscillographs not merely to make the graph brighter but to make the image stand still. If the graph is formed in a new place each time it would appear to move or drift. Various ways have been devised for insuring this synchronism so that the image will stand still. Bedell's invention is concerned with insuring such synchronism in a cathode ray oscillograph using a gas-discharge tube oscillator.

A cathode ray oscillograph uses rays from a cathode to produce the spot of light. These rays are produced in a glass tube having various parts. The rays are composed of electrons. These electrons create a tiny spot of light when they impinge on the screen. They are very light in weight and can change direction of motion very quickly as they have practically no inertia. Also they are charged with a negative charge so that any other negative charge repells them and any positive charge attracts them. This control of motion is accomplished in the cathode ray tube by plates within the tube, one of which is made negative and the other positive, with the result that the electron rays in passing between the plates are deflected toward the positive plate. One pair of plates are called the horizontal deflecting plates; another pair are called the vertical deflecting plates.

If the vertical deflecting plates are appropriately connected to the periodic quantity which is to be studied, the spot of light produced on the screen of the tube will move farther and farther in a vertical direction. Thus there is a mechanism whereby the spot of light takes a vertical position on the screen corresponding at any instant to the magnitude of the periodic voltage under study.

In order to get a graph the spot must move sideways in proportion to time, while the spot is moving vertically in proportion to the varying magnitude of the voltage being studied. This sideways motion is accomplished by connecting to the horizontal plates a gas-discharge tube oscillator. This oscillator builds up a positive potential and then suddenly drops to low value and starts building up again. Being connected with the horizontal plates it gradually makes one of the horizontal plates more positive and the other more negative. Thus it gradually deflects the electron beam and in turn gradually sweeps the spot of light horizontally across the screen of the tube, then suddenly allows it to jump back to the starting point to begin sweeping to the right again. This whole circuit is usually referred to as the "sweep circuit".

The gas-discharge oscillator consists of a condenser, a resistance, a battery and a gas-discharge tube. The battery builds up a voltage across the condenser which acts as a reservoir. The resistance keeps it from building up too quickly. The actual speed with which it builds up can be regulated by making the resistance greater or less, also by making the voltage of the battery more or less. The gas-discharge tube remains inert while the voltage is building up. When the condenser has built up a voltage where the gas in the discharge tube begins to conduct current, the gas-discharge tube discharges and current goes through it in a rush from the condenser, thus discharging the condenser. This is accomplished suddenly and when it is accomplished the tube becomes inert again and the condenser begins to charge up again. Such charge is fed to it from the battery through the resistance. A gradual build up and discharge is repeated, and the voltage charge accompanying it is used to sweep the spot horizontally across the screen of the cathode ray tube. The frequency at which the gas-discharge tube oscillator oscillates can be controlled by adjusting the amount of resistance, or the battery voltage, or the size of the condenser.

With (1) a cathode ray tube, (2) a time-base oscillator connected to the horizontal plates, and (3) a means for connecting the voltage under observation to the vertical plates of the tube, we have a complete system for making a graph which will show the magnitude at any instant of the periodic voltage which is to be studied. If the graph is always to appear in one place the spot of light must traverse the same path as it moves across the face of the tube, and this means that the relationship between the frequency at which the spot is moved up and down and the frequency with which it is moved, again and again, across the screen, will have to remain exactly the same throughout the study of a particular periodic quantity. This means that the frequency of the gas-discharge oscillator must be synchronized with the frequency of the periodic quantity under study. Expressed differently, the frequency of the gas-discharge oscillator must be stabilized so that it can not vary from exact synchronism.

The adjustable controls in the gas-discharge oscillator may be readjusted if the frequency of the gas-discharge tube oscillator gets out of step with the periodic quantity under observation. Frequent manipulation of the controls is usually required to keep the graph stationary. The problem of locking the gas-discharge oscillator in step with the frequency of the periodic quantity under observation is the problem to which the Bedell invention is directed.

The cathode ray tube was used as an oscillograph as early as 1899. The periodic quantities then being studied were of low...

To continue reading

Request your trial
2 cases
  • General Radio Co. v. Allen B. Du Mont Laboratories, 7749.
    • United States
    • United States Courts of Appeals. United States Court of Appeals (3rd Circuit)
    • May 12, 1942
    ...in cathode-ray oscillographs. The invention and its place in the art are fully described in the opinion of the district court, 38 F.Supp. 495, and that detailed description need not be repeated here. It is sufficient to say that a cathoderay oscillograph is an instrument which is employed t......
  • THE JEMSON NO. 1, A. 15963
    • United States
    • United States District Courts. 2nd Circuit. United States District Court (Eastern District of New York)
    • April 17, 1941

VLEX uses login cookies to provide you with a better browsing experience. If you click on 'Accept' or continue browsing this site we consider that you accept our cookie policy. ACCEPT