Federal Circuit IP

Grace Instrument Indus., LLC v. Chandler Instruments Co., LLC (Fed. Cir. 2023)

By Tucker Mottl Published March 3, 2023

Grace Instrument Indus., LLC v. Chandler Instruments Co., LLC, 57 F.4th 1001 (Fed. Cir. 2023) (Chen, Cunningham, Stark; appeal from S.D. Tex. Case No. 4:20-cv-01749 (Hanen, J.))

Issue – Indefiniteness

Patent at issue:  U.S. Patent No. 7,412,877 (“the ’877 patent”)

Independent claims 1 and 4 of the ’877 patent concern:

A pressurized device comprising:


(b) an enlarged chamber with reduced openings positioned between the at least one top section and the at least one bottom section for communicating pressure with said top section and said lower section within said pressure vessel,

Viscometer comprising:


(e) an enlarged chamber with reduced openings positioned between the at least one top section and the at least one bottom section for communicating pressure located above said bob,

Important Points from the Specification:

The only mention of an enlarged chamber in the ’877 patent’s specification is: “By providing an enlarged chamber such as chamber 45 or chamber 49, and reduced openings for said enlarged chamber such as gap 25 and gap 27.”

The ’877 patent addresses the problem of “provid[ing] a high pressure viscometer wherein viscosity [of sample fluid] is determined under conditions closely simulating down-hole conditions [(g., 40,000 psi and 600º F) … and] that eliminates measurement errors due to seal frictions.”

The ’877 patent discusses prior art with a seal between sample fluid and pressurization fluid or with a slurry cup but notes that the seal induces friction and the slurry cup may permit mixing, either of which may induce measurement error.

The ’877 patent provides that the objective of the invention is to prevent mixing between pressurization fluid and sample fluid.


Relying on extrinsic evidence (e.g., dictionary definition of “enlarged”), the Southern District of Texas found the term “enlarged chamber” indefinite because “enlarged is a term of degree that necessarily calls for some comparison against some baseline.” (internal quotation marks omitted). The district court rejected arguments that “enlarged chamber” could be defined by its purpose.


Phillips standard requires consideration of intrinsic evidence—(1) claim language, (2) in view of the specification (which is the “single best guide to the meaning of a disputed term”), (3) considering prosecution history—before then considering extrinsic dictionary definitions that do not contradict intrinsic evidence.

Phillips further includes discussion of inherently defining claim terms, including that:

a “claim term may be clearly redefined without an explicit statement of redefinition,” and

“even when guidance is not provided in explicit definitional format, the specification may define claim terms by implication such that the meaning may be found in or ascertained by a reading of the patent documents”

Nautilus standard a “patent is invalid for indefiniteness if its claims, read in light of the specification delineating the patent, and the prosecution history, fail to inform, with reasonable certainty, those skilled in the art about the scope of the invention.”

Factors Considered

  • Problem to be Solved: The ’877 patent’s specification explains that one of the drawbacks of most liquid pressurized viscometers is the mixing between tested sample and pressurization fluid, which leads to inaccurate test results.
  • Prior art solution: The ’877 patent’s specification explains prior art viscometers attempted to remedy this inaccuracy by using a seal between the pressurization fluid and sample fluid, but that a seal may induce friction error causing inaccurate measurement.
  • Invention: The ’877 patent explains that the current invention solves this problem through use of an enlarged chamber such as chambers 45 and 49 (’877 patent at 11:28-32) and that “chamber 45 and chamber 49 are large enough so that at maximum rated pressure, chamber 49 is still at least half filled with sample fluid. This ensures the accuracy of the measurement because measurement zone below anti mixer bottom fin 82 is always totally filled with sample fluid.” (’877 at 6:2-6).
  • Inherent Definition: “Enlarged chamber” is large enough to prevent the pressurization fluid from mixing with the sample fluid.
  • Confirmed by prosecution history: Office action response distinguishing U.S. Patent No. 4,633,708 because the invention has “an enlarged chamber with reduced openings for communicating pressure, [such that] pressurization oil will not contaminate [the] test sample.”
  • The intrinsic record provides sufficient definition of enlarged chamber as “large enough to prevent, during elevated pressurization, commingling of sample and pressurization fluids in the lower measurement zone.”
  • District court erred in reliance on extrinsic evidence to find term indefinite.

Result – Indefiniteness finding vacated; remanded.