Doble Engineering Co. v. Leeds & Northrup Co.

Decision Date13 February 1943
Docket NumberNo. 3775.,3775.
PartiesDOBLE ENGINEERING CO. v. LEEDS & NORTHRUP CO.
CourtU.S. Court of Appeals — First Circuit

H. F. Lyman, Fish, Richardson & Neave and Wm. Redin Woodward, all of Boston, Mass., for appellant.

George K. Woodworth, of Boston, Mass., for appellee.

Before MAGRUDER, MAHONEY, and WOODBURY, Circuit Judges.

WOODBURY, Circuit Judge.

The Leeds & Northrup Company, hereinafter for convenience referred to as the plaintiff, a Pennsylvania corporation, filed a petition for a declaratory judgment against the Doble Engineering Company, hereinafter referred to as the defendant, a Massachusetts corporation, praying for an adjudication that patent No. 1,945,263, issued on January 30, 1934, to Frank C. Doble and assigned by him to the defendant, is invalid, or, if valid, that it is not infringed by certain apparatus manufactured by the plaintiff. The defendant answered and filed a counterclaim alleging validity and infringement. The case was referred to a master who found Claim 15 of the patent1 valid but not infringed. Neither party questioned the master's findings of fact and the district court adopted them as its own. The plaintiff made no objection whatever to the master's report but the defendant objected to it on the ground that the master erred in ruling as a matter of law that the plaintiff's apparatus did not infringe. After hearing, the district court concluded that this objection of the defendant must be overruled and the report affirmed, and judgment in that court was entered accordingly. Thereupon the defendant took this appeal.

The facts are exceedingly complicated and involved, but fortunately they are not in dispute and, also fortunately, they do not have to be stated in complete detail in order to understand the issues raised by this appeal. It will suffice to explain the patented apparatus and its setting in the electrical art to which it appertains in general terms only.

The Doble patent is for an "Apparatus for Testing Insulating Values". Describing it the master says: "The Doble testing system (disregarding for the moment protection against charging currents) includes a voltage source, the grounded specimen of insulation to be tested, conductors or leads between the voltage source and the specimen to be tested, and a set of measuring instruments between the voltage source and one side of the specimen." For clarity we venture to describe the apparatus in more detail. Basically it consists of a source of electrical energy (alternating current), typically of 110 volts; a transformer to step this current up to any desired voltage, usually up to approximately 10,000 volts; a lead wire or conductor from the high tension terminal of the secondary coil of the transformer to one side of the insulator to be tested, in practice this is usually to the conductor which passes through the center of a bushing on an oil circuit breaker; another lead wire from the other side of the insulator under test, which side in practice is usually if not always grounded, to electrical measuring instruments; and another lead wire or conductor from these instruments to the low tension terminal of the secondary coil of the transformer.

It appears that this general system for testing insulators was worked out some forty or fifty years ago by Steinmetz and that it worked satisfactorily when the insulator under test was not grounded, and when a stationary apparatus was used in a laboratory where there were no external electrical interferences from high tension lines, generators etc. in the neighborhood. It was not satisfactory, however, when embodied in a portable apparatus and used to test installed insulators only temporarily disconnected from service. The reason for the unsatisfactory operation of the old system in the field is that insulators when in place for use are almost invariably connected to ground; that when in use they are usually located in close proximity to high tension transmission lines; that moving a portable apparatus around for different tests causes its parts to be in different relationship to the surface of the earth for each test made, and that the condition of the earth's surface as wet or dry varies from place to place and from day to day. It seems that these factors cause stray electric currents which could not be eliminated or compensated for, to pass through the measuring instruments of the apparatus and vitiate their readings.

These stray currents are of two kinds; those which arise from the flow of electricity through the apparatus itself, and those which are caused by the different positions of the apparatus with respect to the surface of the earth and the wet or dry condition thereof, and by the presence in the neighborhood of the testing apparatus of high tension transmission lines and similar electrical installations. The former are called "charging currents", but we shall refer to them hereafter by the more specific name of "internal charging currents". The latter are variously called "extraneous electrostatic disturbances", "external electric stresses" or "induced voltages from extraneous electrostatic fields". For simplicity we shall refer to them by the possibly technically inaccurate but descriptive and convenient name of "external charging currents".

It appears that in the Steinmetz apparatus which we have described internal charging currents could be prevented from passing through its measuring instruments so that accurate readings were obtainable but that it was only possible to do this when the insulator under test was not grounded. There does not appear to have been any known way of avoiding in it the disturbing effects of external charging currents. Thus by the old system the only known way to test insulators was to disconnect them and take them bodily to a laboratory where a stationary apparatus could be used, where external conditions could be controlled and where the insulator being tested could be disconnected from ground.

This technique for testing was unsatisfactory and Doble directed his attention to the problem of supplanting it by a better one. He solved the problem by devising means for protecting the old apparatus from the effects of both internal and external charging currents so that as a result it could be used to test insulators under service conditions at the place of installation, as in the yard of an electrical station, that is, in the field. The disadvantages of the old system, the need for improving upon it, and the problems which confronted Doble in supplanting it are stated in greater detail in the first paragraphs of the patent2 and in the excerpt from the master's report3 quoted in the margin as footnotes two and three respectively.

It is admitted that the apparatus which Doble devised rendered the old technique for testing obsolete and, for the purposes of this case at least, it appears to be conceded by the plaintiff that Doble's contribution to the art in so doing is entitled to rank as an invention. Concerning it the master found: "The Doble tester made in accordance with this patent has had wide use, and witnesses for both parties agreed that it has been an important contribution to the art. By its use many deteriorated bushings have been located and removed or repaired in cases where they would otherwise have failed in service, with resulting great trouble and expense. The tester of the patent is simple to operate and gives readings from which reliable results can be consistently obtained." The master found that it soon enjoyed considerable commercial success.

Doble solved the problem of protection against charging currents by devising a system of what are called electrical shields; an inner shield to cope with internal charging currents and an outer shield to cope with those which originate outside of the apparatus itself. By means of these shields, which need not be described, he succeeded in keeping practically all charging currents of both kinds out of the measuring instruments of his apparatus so that with it insulators could be accurately tested while still installed.

We turn now to the plaintiff's apparatus. After the advent of the Doble tester the plaintiff began to manufacture two forms of apparatus, called respectively its 1935 and its 1936 sets, both of which served the same purpose as the Doble apparatus. That is to say, either of them could be successfully used to test the insulating value of dielectrics in the field. There can be no doubt that the defendant felt the plaintiff's competition.

The master found that in both of the plaintiff's sets a shield which "corresponds in substance" to the defendant's inner shield was used to eliminate the disturbing effects of internal charging currents. But he found that the plaintiff in each of its sets succeeded in eliminating the effects of external charging currents by devices or techniques which were wholly dissimilar to the defendant's outer shielding system. External charging currents occasioned by the proximity of high tension lines, etc., were averaged out of the plaintiff's 1935 set by using a reversing switch, and disturbances of the same kind were avoided in the 1936 set by energizing it from a source of alternating current of a different frequency from that ordinarily used commercially. External charging currents arising from varying the positions of the apparatus and from the variable moisture content of the surface of the earth were eliminated from each set by means quite unlike those used by Doble. Thus the master found, and the defendant concedes, that the means used by the plaintiff in both its 1935 and 1936 sets for protecting the measuring instruments thereof against external charging currents were not "the same means as Doble's" nor were they "the equivalent thereof in the sense of the patent law", although they accomplished "the same ultimate result".

In spite of the master's finding of essential equivalence between the plaintiffs ...

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