US 3753098

I'll search for authoritative information on US 3753098 and check for any litigation involving it.

Search results — litigation / docket check

I searched for patent number 3,753,098 and associated enforcement activity. Findings:

• No CAFC 2026 docket (or any court docket) naming US 3,753,098 was found. This is consistent with the patent's status: it is recorded as Expired – Lifetime, with anticipated expiration 1990‑08‑14 (17 years from grant, pre‑URAA term). A 2026 infringement docket on this patent would be highly unusual, and none surfaced.
• Caution — a related-looking case is a different patent. The well-known Rosemount, Inc. v. Beckman Instruments, Inc. appeal (Fed. Cir. 1984, 727 F.2d 1540; district court 569 F. Supp. 934) is frequently returned by searches that combine "Rosemount" and "Beckman." That case involved a Cardeiro pH-sensor patent referred to as the '525 patent, not 3,753,098. It is relevant here only because the two parties share this patent's chain of title (Beckman → Emerson → Beckman Industrial → Rosemount). I found no evidence that US 3,753,098 itself was ever asserted.
• Several searches returned unrelated hits (e.g., an "ARB" part number 3753098, a Belgian patent register "3753098" for a wireless-communication case). Per your instruction, I am not conflating those with the US patent number, and I flag them only to note they are false positives.

Uncertainty: I do not have authoritative confirmation from USPTO PatentCenter or a live CAFC docket search showing zero assignments/litigation beyond what Google Patents reports. The bibliographic and claim details below are grounded in the full patent text supplied and are reliable; the "no litigation" finding is a negative search result, not a positive confirmation of a complete docket history.

Summary of US 3,753,098

Note on inventor names: the patent front page is OCR‑garbled ("Maltesh K. sminiu," "John J. Hlnchey"); Google Patents lists them as "M Sambhu, J Hinchey." The full names above are the correct ones as best recoverable from the document.

Chain of title (recorded assignments):

• Original: Beckman Instruments, Inc. (1972 filing)
• 1984‑08‑13: assigned to Emerson Electric Co. (effective 1984‑03‑01), then to Beckman Industrial Corporation
• 1989‑08‑28: assigned to Rosemount Inc. (effective 1989‑05‑23)

Foreign family / also published as: DE 2322622 (A1/B2/C3), GB 1357874A, CA 975424A, JP S53‑35506Y2 (utility model JPS4935282U).

Prior art cited on the face: US 2,221,306 (Christie), US 3,173,969 (Kapff), US 3,376,501 (Peranio), US 3,548,304 (Lohnes).

Related copending application (cited in the spec): Serial No. 251,429, filed by Mahesh K. Sambhu — the companion measuring circuit/display meter for this cell. (A search hit for US 3,754,186 titled power-factor-measuring bridge circuitry matches the description of that copending application, but I cannot confirm the number from the provided text, so treat that association as tentative.)

Abstract (as issued)

A guarded test cell for power factor measurement of oil including a connector adapted to receive a triaxial extension cable. The cell includes a housing within which a tubular center electrode, tubular guard electrode and a tubular outer electrode are concentrically and removably mounted. The housing also includes a cover having a removable plug mounted in an opening formed therein in alignment with the axis of the hollow center electrode. A connector, adapted to receive the triaxial extension cable, is also mounted in the housing generally at right angles to the electrodes. The connector is provided with electrically isolated contacts which engage, respectively, the electrodes of the cell. The cell electrodes are adapted to be immersed in oil samples, such as samples of elevated temperature, and the plug in the cover can be removed to permit insertion of a thermometer into the oil within the hollow center electrode. The extension cable allows the cell to be energized from a remotely located measuring unit.

Plain-language overview of the independent claim

There is only one independent claim in this patent — claim 1. It is an apparatus claim to the test cell itself:

Claim 1 — the test cell (three functional blocks):

1. A housing made of a main body plus a removably secured cover, together defining a hollow central chamber, with at least two openings in the housing. In the described embodiment this is a molded insulating (plastic or Teflon) housing with a front plate opening (24) for the triaxial connector and a bottom plate opening (28) for the measuring unit, closed by an L‑shaped cover with a thermometer plug.

2. A measuring unit held in one of the openings, comprising three concentric tubular electrodes — a center electrode, a guard electrode, and an outer electrode — fastened together with insulating sleeves interspersed between them. In the embodiment: stainless-steel tubular center electrode, Teflon insulator, stainless-steel guard electrode, Teflon insulator, stainless-steel outer electrode, with the outer electrode carried in a stainless mounting block. The electrodes are the parts immersed in the oil sample; the guard electrode is the "guarding" element that isolates the measurement from stray fields.

3. A triaxial connector mounted in the other opening, with three electrically isolated contacts that respectively engage the three electrodes:

   • a center contact that conductively engages the center electrode,
   • a guard contact that engages a contact member secured to the guard electrode (the described "T‑connector" and guard contact),
   • an outer contact that engages a contact member connected to the outer electrode (the outer electrode's mounting block contacting the L‑shaped metal contact in the housing).

   The connector is configured to receive a triaxial extension cable, so the cell electrodes can be driven by a remote measuring bridge and read out on a remote meter. This remote-cable architecture is the core point of novelty over a self-contained cell.

Dependent claims (brief, for completeness):

• Claim 2: the cover has an opening aligned with the hollow center electrode and a removable plug in it — i.e., the thermometer access port for measuring elevated-temperature samples.
• Claim 3: the contacts and electrodes are made of stainless steel tubing and the insulators of Teflon (materials limitation on claim 1).
• Claim 4: the measuring unit is surrounded by a glass cup with openings in its sides (the sample-holding cup/outer container).

Practical gist: a concentric, guarded three-electrode oil test cell — the guarding and the triaxial (not merely coaxial) connection let the cell reject interference from nearby energized equipment and be operated remotely by a flexible cable, while a removable cover plug allows a thermometer to be inserted directly into the oil in the cell's hollow center electrode so hot oil samples from operating transformers can be tested.

Uncertainties / caveats

• No litigation or CAFC 2026 docket tie to 3,753,098 could be located; the closest match is the 1984 Rosemount v. Beckman case on a different patent. I cannot rule out unindexed or non‑US proceedings.
• The figures/text are OCR-imperfect (e.g., duplicated or garbled figure descriptions; "FIG. 4" is the only figure caption preserved). My description of structural details relies on the numbered parts as recited in the body, which are internally consistent.
• I could not independently verify the copending application Serial No. 251,429's granted patent number from the supplied text; the US 3,754,186 hit is a plausible but unconfirmed match.

I'll search for litigation involving US patent 3753098 across patent litigation databases.

Initial searches returned unrelated documents (different patents with similar numbers). Let me target patent litigation databases directly.

Let me try a few more targeted litigation-specific searches to be thorough.

Litigation Search Results for US Patent 3,753,098

No litigation is known or discoverable involving US Patent 3,753,098.

What I searched and what I found

I searched patent-litigation-oriented sources (Unified Patents litigation portal, CourtListener/RECAP, and general web searches pairing the exact number "3753098" with terms like infringement, lawsuit, plaintiff, defendant, district court, and complaint).

Every hit was a false positive from a different identifier, which I am expressly not reporting as litigation for this patent, per your instruction not to return similar numbers:

• EP 3753098 B1 — "Power converter with wide DC voltage range" (a 2019-era European patent; unrelated to the US patent at issue).
• Belgian publication no. 3753098 — "communications sans fil" (unrelated).
• "WL 3753098" — a Westlaw citation in Chu v. Chinese-American Planning Council (S.D.N.Y.), i.e., a case-number fragment, not the patent.
• Crafeo/Cimline "‘375 patent" and U.S. Patent 4,244,479-type "‘375" references — a different patent (the "’375 patent" in that line of cases is not US 3,753,098).
• Various court opinions mentioning 35 U.S.C. § 1498 — matched only on the statutory string, not the patent number.

None of these involve US 3,753,098.

Why the absence of litigation is consistent with the record

This conclusion is corroborated by the patent's own prosecution/status record (Google Patents, fetched 2026-09-30):

Because the patent expired around August 1990, and because the record shows only prosecution-era and post-issue assignments (not enforcement activity), there is no basis for a live or recent infringement suit. The "Family" section lists only the single US application (US00251381A) and its foreign counterparts (CA975424A, GB1357874A, DE2322622C3, JPS5335506Y2) — again, publication data, not litigation data.

Caveats / limitations (stated explicitly, per your rules)

• I could not run a direct, definitive query against the Unified Patents litigation caselist or PACER docket for this exact patent because my search steps were exhausted before I could pull those specific databases at the case level.
• A patent this old (expired 1990) would, in the normal course, fall outside the window of modern electronic litigation records that tools like Docket Navigator, Unified Patents, RPX, or PACER comprehensively cover. Pre-1990s patent enforcement suits are often not digitized, so I cannot state with absolute certainty that no suit was ever filed — only that no litigation involving this patent is discoverable in the sources I was able to consult, and that the patent's expiration and prosecution history give no indication of enforcement.
• If a definitive negative is required for a legal opinion or clearance analysis, it should be confirmed with a paid database search (Docket Navigator, LexMachina) covering 1973–1990 federal filings and any Court of Federal Claims § 1498 actions, since the assignees (Beckman/Emerson/Rosemount) sold oil-testing instrumentation that could theoretically have been involved in a government-contractor procurement dispute.

Bottom line: Based on available information, there is no known litigation involving US Patent 3,753,098. If you need a certifiable "no suits ever filed" determination, a manual PACER/LexMachina archival pull for the 1973–1990 period is recommended, as such records are not fully web-searchable.

Proceedings overview

Zero AIA trial proceedings are on file for US 3753098. The USPTO Open Data Portal (the canonical structured source in this prompt) returns no IPR, PGR, or CBM for this patent; targeted web searches of PTAB-related sources also surfaced nothing, and no Federal Circuit appeal of any PTAB decision on this patent exists. The breakdown is therefore 0 active / 0 claims invalidated / 0 claims sustained / 0 settled / 0 institution denied.

Bottom line for a defendant: this is not a "hardened by IPR" patent — it is a patent that has been dead for over three decades. US 3753098 issued 1973-08-14 on a 1972-05-08 filing, and its pre-URAA term was 17 years from grant, so Google Patents records an anticipated expiration of 1990-08-14 (and it is flagged "Expired - Lifetime"). AIA trials did not exist until 2012-09-16, i.e., 22 years after the patent lapsed. Any demand letter citing US 3753098 today has no infringement theory behind it at all — there is nothing left to invalidate, and no need to file anything at the PTAB.

Proceedings on file

None. There is no proceeding number to report, and I will not manufacture one. For completeness against the checklist you asked me to fill:

• Type: N/A — no IPR, PGR, or CBM was ever instituted or even requested on this patent per the ODP structured data.
• Filed: N/A
• Status: N/A (the "Expired – Lifetime" legal status in the patent record is the patent's own term status, not a trial status).
• Judge panel: N/A — no PTAB panel has ever touched this patent.
• Petition grounds: N/A — no petitioner, no § 102/§ 103/§ 112 ground, no art.
• Institution decision / FWD / settlement / appeal: N/A on all four. There is no FWD to link to and no CAFC docket number to cite.
• Defensive value of the absence: An asserted patent that is actually being enforced attracts IPRs almost by reflex. A 1973 patent that expired in 1990 and drew zero PTAB petitions is not a "litigation-tested survivor"; it is simply outside the universe of enforceable patents.

One note on search hygiene: queries for the bare number "3753098" return false positives — an unrelated European publication (BE/EP record "3753098 — COMMUNICATIONS SANS FIL") and an aftermarket Ford Bronco part number. None of that is US 3753098.

Strategic summary

Claim status — all claims expired, none canceled, none sustained. US 3753098 has 4 claims (claim 1 is the only independent claim; claims 2–4 depend from it and add, respectively, the cover opening with removable plug, stainless-steel/Teflon materials, and the glass cup with side openings). Because no IPR ever ran, there is no claim-level "canceled vs. sustained" ledger to draw from a Final Written Decision — but the practical answer is the same for every claim: 1, 2, 3 and 4 all lapsed with the patent term ending 1990-08-14, and the last recorded assignment chain (Beckman Instruments → Emerson Electric 1984-08-13 → Beckman Industrial 1984-08-13 → Rosemount Inc. 1989-08-28) stopped moving a year before expiry. There is no reexamination certificate on the record either. A defendant therefore faces no live claims at all, let alone frozen-but-surviving ones.

Estoppel landscape — § 315(e)(2) is inapplicable and irrelevant. Estoppel is a disability the PTAB imposes on a petitioner; with no petition and no institution, no one is estopped. Conversely, there is no ground a defendant needs to preserve: 35 U.S.C. §§ 271 and 284 reach only infringement occurring while the patent was in force, and § 286's six-year damages lookback cannot revive a term that closed in 1990. If you wanted a belt-and-suspenders validity challenge for some reason, IPR of an expired patent is technically permitted, but it would be a pointless expense — and any prior art from the 1938–1970 references already cited on the face of the patent (Christie US 2,221,306; Kapff US 3,173,969; Peranio US 3,376,501; Lohnes US 3,548,304) needs no PTAB clearing.

Pattern signals — none, and that is the point. No repeat petitioner, no serial IPR filings, no Patent Owner appeals, no defensive aggregator (Unified Patents or similar) in the chain. Patents that get asserted in the modern era attract exactly this kind of activity; US 3753098 has attracted none because it cannot be asserted. The later family/publication data (DE 2322622, GB 1357874, CA 975424, JP utility model) is 1970s foreign filing housekeeping, not litigation signaling. Citations by this patent family are limited to unrelated later art (e.g., Siemens DE 3205020, Agar Corp GB 2179454, and the Emerson terminal-assembly connector patents) and carry no estoppel or defensive weight against this patent.

Recommended next steps

• If you are a defendant and someone is asserting US 3753098 against you: do not file an IPR, and do not budget for one. The correct move is a short letter (and, if a case is filed, a Rule 12(b)(6) motion) pointing out that the patent expired on 1990-08-14 — 17 years after its 1973-08-14 grant under pre-URAA law, as reflected in the "Anticipated expiration" entry in the patent record — so there can be no infringement under § 271 and no recoverable damages under § 284/§ 286. Cite the patent record itself (https://patents.google.com/patent/US3753098/en) for the filing/grant/expiration dates and the "Expired – Lifetime" status, and the full text of the claims for the fact that only claims 1–4 ever existed.
• Treat the assertion itself as a red flag. A demand letter citing a 1973 patent that lapsed in 1990 is a strong indicator of a baseless or fraudulent assertion, and may warrant state-law/UDAP or fee-shifting analysis rather than a validity defense.
• If you are evaluating the art for other purposes (e.g., as § 102 prior art against a modern patent, or for freedom-to-operate history on oil power-factor test cells): the substantive content is still usable as a printed publication. Cite the 1973 specification, not the claims — the disclosure of the concentric center/guard/outer electrode stack, Teflon insulator sleeves, glass sample cup with side openings, and the triaxial connector with a spring clip engaging the hollow center electrode is the part with technical value.
• Active-proceeding milestones: not applicable — there are no proceedings, so there is no institution deadline, no oral hearing date, and no statutory one-year FWD clock running against anyone.
• Verification note: the absence of PTAB activity is drawn from the structured ODP block in this prompt, corroborated by negative web results. Because ODP ingest can lag, a fresh PTAB E2E / PatentCenter check immediately before filing is a reasonable final confirmation — but given a 1990 expiration, I would be very surprised if anything appears.

I'll verify the assignment records through the USPTO Assignment Center and cross-reference public sources before building the chain.

Assignment Record Analysis — US 3,753,098

Source note / limitation up front: The reel/frame numbers below are drawn from the Google Patents "Legal Events" reproduction of the USPTO assignment index (fetched 2026-09-30), not from a direct live query of Assignment Center. I was unable to pull the correspondent-of-record fields or the underlying cover-sheet images in this session. Treat the reel/frame + party + date data as reliable (it is internally consistent across Google Patents' "reassignment," "Legal Events," and "Patent Citations" modules) and treat any correspondent statement as unverified. Verify at https://assignmentcenter.uspto.gov/ (or https://assignment.uspto.gov/patent/index.html) before relying on it.

Inventors

• The front page lists both men under the assignee Beckman Instruments, Inc., Fullerton, CA, and the patent names a copending application by the same inventor (Serial No. 251,429, filed by Mahesh K. Sambhu — the companion power-factor bridge/display circuit). Both are consistent with the inventors being Beckman employees at the time of filing; the patent text itself does not state employment, so "employer = Beckman" is inferred from the assignment record, not stated.
• Unusual-pattern check: I found no evidence of inventors departing the original assignee within 12 months of filing, and no evidence of an inventor-originated follow-on portfolio. Not determinable from the available record — employment/tenure data for 1972–73 Beckman personnel is not in the assignment file. There is nothing here resembling the "all inventors exit, then fire-sale" precursor pattern.
• Naming caution: the OCR front page garbles the names ("Maltesh K. sminiu," "John J. Hlnchey"). This does not affect the assignment chain; assignments are recorded against the patent/application number, not the inventor name.

Original assignee

Beckman Instruments, Inc. (Fullerton, California) — named on the issued patent.

• Primary line of business: analytical and scientific instrumentation (the "Beckman" brand), including the oil/coolant test instrumentation to which this cell belongs. This was an operating company, not a holding vehicle.
• Product embodying the claims: The patent itself is directed to a physical test cell (claim 1 apparatus: concentric center/guard/outer electrodes + triaxial connector), and the spec situates it in a portable, cable-connected oil power-factor measurement instrument. That is a product-shaped disclosure, and the copending Sambhu application (measuring bridge + display meter) confirms a complete instrument was contemplated. I could not positively identify the commercial catalog model number in this session, so treat "shipped a product" as highly likely but unconfirmed by a specific model reference.
• Current status: Beckman Instruments no longer exists as an independent entity. It merged into SmithKline Beckman in 1982, and the industrial-instrumentation business relevant here was acquired by Emerson Electric Co. (see timeline). The remaining life-sciences business passed through subsequent transactions (Beckman Coulter today). So: acquired / dissolved as a separate entity, not a bankruptcy.

Assignment timeline

Recall that the USPTO Assignment Search database indexes recorded documents only back to August 1980 (per USPTO's own documentation). The 1972 inventor→Beckman assignment is therefore almost certainly not in the online searchable set — its absence is a database-coverage artifact, not a gap in the chain.

Three post-issuance recordings are indexed:

1. 1984-03-01 (executed) / recorded 1984-08-13 — Reel 004319 / Frame 0695

   • Conveyance: Assignment (of assignors' interest)
   • Assignor: Beckman Instruments, Inc.
   • Assignee: Emerson Electric Co. (a Missouri corporation)
   • Correspondent: not retrieved — unverified. (The patent's prosecuting attorney of record was James M. Thomson; that is prosecution counsel, not the assignment correspondent, and should not be conflated.)
   • Context: Acquisition — Emerson buys the Beckman industrial-instrumentation business.

2. 1984-04-25 (executed) / recorded 1984-08-13 — Reel 004328 / Frame 0659

   • Conveyance: Assignment
   • Assignor: Emerson Electric Co. (a Missouri corporation)
   • Assignee: Beckman Industrial Corporation (a Delaware corporation)
   • Correspondent: not retrieved — unverified. Same recording date as entry 1, consistent with a single batch filing by one corporate-law department.
   • Context: Internal reorganization — Emerson immediately drops the acquired assets into its "Beckman Industrial" subsidiary. (Executed ~7 weeks after the parent acquisition.)

3. 1989-05-23 (executed) / recorded 1989-08-28 — Reel 005243 / Frame 0057

   • Conveyance: Assignment
   • Assignor: Beckman Industrial Corporation
   • Assignee: Rosemount Inc. (Minnesota)
   • Correspondent: not retrieved — unverified.
   • Context: Internal reorganization inside Emerson — Beckman Industrial folded into Rosemount Inc., an Emerson subsidiary since 1976. This is a corporate-family consolidation, not a sale to a third party.

No "Change of Name," "Security Agreement," "Merger," "License," or "Release" conveyance appears in the indexed record for this patent; all three are plain assignments. No assignment to any non-Emerson-affiliated entity appears.

Correspondent-repeat flag: I could not obtain the correspondent fields, so I cannot confirm or refute a repeat correspondent across the chain. What is visible is the inverse tell: all three recordings move the patent within a single corporate family (Beckman → Emerson → Beckman Industrial → Rosemount), on ordinary corporate-effective dates, which is the signature of law-department housekeeping rather than an NPE recording campaign. If you need the correspondent-angle cleared, pull the three cover sheets at Reels 004319/0695, 004328/0659, and 005243/0057.

Timeline diagram

timeline
    title Ownership of US 3753098
    1972 : Filed by Beckman Instruments
         : Inventors assign to Beckman
    1973 : Patent issued
    1984 : Emerson Electric acquires Beckman unit
         : Transferred to Beckman Industrial Corp
    1989 : Assigned to Rosemount Inc
    1990 : Patent reaches anticipated expiration

NPE / troll-pattern signals

1. Shell-entity transfer — Not present. Every assignee is an operating industrial conglomerate or its named operating subsidiary (Emerson Electric, Beckman Industrial Corp., Rosemount Inc.). No "IP / Holdings / Licensing / Ventures" suffix appears, and none of the three reel/frame entries (004319/0695, 004328/0659, 005243/0057) names an address-agnostic single-purpose LLC.
2. Known asserter in the chain — Not present. None of Beckman Instruments, Emerson Electric, Beckman Industrial, or Rosemount matches any entity on the public NPE lists (Acacia, Marathon, IV, IPNav, Wi-LAN, Conversant/Mosaid, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, etc.). Rosemount/Emerson is a large operating manufacturer, not a monetization vehicle.
3. Repeat correspondent across the chain — Unclear / unverified. Correspondent fields were not retrievable this session, so this signal cannot be scored either way. Note the structural counter-indication: all recordings are within one corporate family, which is inconsistent with the "rotating lawyers over rotating shells" pattern.
4. Cascading transfers — Weak at most / not an NPE cascade. Two assignments were executed within ~8 weeks in 1984 (effective 1984-03-01 and 1984-04-25; both recorded 1984-08-13, Reels 004319/0695 and 004328/0659). But both are same-family (Emerson → its own new subsidiary), with a common recording date — the opposite of a chained-LLC cascade with shared principals. Not present as an NPE indicator.
5. Pre-litigation transfer — Not present. No infringement suit naming this patent is discoverable (consistent with the prior litigation section), so no assignment is "arranged to enable assertion."
6. Bankruptcy fire-sale — Not present. No Chapter 7/11 conveyancing appears; the 1984 and 1989 transfers are acquisitions/reorganizations, not distressed sales. Beckman's corporate events were mergers/divestitures, not a bankruptcy estate.
7. Privateering — Not present. The 1989 transfer keeps the patent inside Emerson (Rosemount), a competitor-adjacent operating company; there is no evidence the patent was handed to an outside NPE to assert against others.
8. Defensive aggregator (anti-NPE) — Not present. The chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN. It terminates at an operating company.

Verdict

Defensive / non-asserting — with an explicit caveat that the chain terminates at an operating corporate family (Emerson / Rosemount), not at a classic defensive aggregator. None of the five verdict labels maps cleanly; this is the nearest non-NPE fit.

Justification: The entire recorded chain — Beckman Instruments → Emerson Electric (Reel 004319/0695, executed 1984-03-01) → Beckman Industrial Corp. (Reel 004328/0659, executed 1984-04-25) → Rosemount Inc. (Reel 005243/0057, executed 1989-05-23) — consists exclusively of assignments among operating companies and their own operating subsidiaries. There is no shell-entity transfer, no known asserter, no pre-litigation transfer, and no assertion activity; the patent reached anticipated expiration around 1990-08-14 while still inside the Emerson family, where it has been functionally neutralized. Because the correspondent-of-record fields could not be retrieved, signal #3 (repeat correspondent) remains unclear and should be cleared against the three cover sheets before any formal opinion.

Verify: https://assignmentcenter.uspto.gov/ (patent number 3753098) and https://assignment.uspto.gov/patent/index.html.

I'll verify the patent against the USPTO and gather details on each cited prior-art reference.

Let me verify the Christie reference US 2,221,306 specifically and confirm the USPTO record.

Prior-Art Analysis — US 3,753,098

0. USPTO record check (confirming, not repeating, the prior sections)

My web searches for the number 3753098 did not surface a raw USPTO PatentCenter page, but they are consistent with the record already established from the authoritative full text: US 3,753,098 A, application US 251,381, filed 1972‑05‑08, granted 1973‑08‑14, assignee Beckman Instruments, Inc., inventors Sambhu & Hinchey. Per the strict rule, I treat all identifiers literally and did not fold in the lookalikes my searches returned (e.g., EP 3753098 B1 "Power converter with wide DC voltage range," a Belgian register entry 3753098, and unrelated triaxial-cell technical literature). Those are different identifiers and are excluded.

Because the patent's front page (supplied in the full text) expressly lists the references cited by the examiner under "[56] References Cited", that list is the anchor for this analysis. It contains exactly four U.S. references.

1. The four cited references (as listed on the face of US 3,753,098)

Full-citation details and the § 102 analysis follow for each.

Reference A — US 2,221,306 (Christie)

Full citation: Soren L. Christie, Conductivity indicating system and method, U.S. Patent 2,221,306; filed March 2, 1938; issued November 12, 1940.

Brief description (with a limitation on my sourcing): US 2,221,306 is a Christie conductivity patent in the same family as the Christie documents I could retrieve full text for — US 2,221,307 (Christie, "…electrode structures for continuously testing the conductivity of a flowing fluid") and US 2,258,045 (Christie, "Electrode structure for conductivity testing," a division of the March 2, 1938 application, Serial No. 193,484). Those related Christie cells disclose a two-electrode conductivity cell with concentric/coaxial geometry: an inner cylindrical electrode (e.g., electrode 6) inside an outer sleeve electrode (e.g., electrode 7), separated by insulating nipples/sheaths with the fluid under test flowing through the intervening annular current path, wired to a conductivity-measuring instrument. I was not able to pull the body text of ’306 itself, so its precise disclosure is characterized here by inference from its sibling Christie patents — flagged as an uncertainty, not a verified quotation.

• Related Christie full texts reviewed: https://patentimages.storage.googleapis.com/74/8a/08/dcaecfee0a2d7c/US2221307.pdf and https://patentimages.storage.googleapis.com/a1/98/f8/4f25604fbb995b/US2258045.pdf

Potential § 102 anticipation:

• Claim 1 — No. Christie ’306 shows, at most, a two-electrode concentric cell with interspersed insulation and a fluid annulus. Claim 1 requires three concentric tubular electrodes — center, guard, and outer — plus a triaxial connector with three electrically isolated contacts. Christie discloses neither the intermediate guard electrode nor any triaxial connector. It cannot anticipate claim 1.
• Claims 2, 3, 4 — No. The removable thermometer-plug cover (2), the stainless-steel/Teflon limitation (3), and the glass sample cup with side openings (4) all depend from claim 1's three-electrode-plus-triaxial combination and find no counterpart in Christie.

Actual relevance: Christie is the closest § 103 art for the concentric tubular electrode with interspersed insulating sleeves sub‑combination of claim 1 — i.e., the examiner cited it to show that coaxial, sleeve‑insulated conductivity electrodes for fluids were known. It is background, not anticipatory.

Reference B — US 3,173,969 (Kapff)

Full citation: Frederick Sixt Kapff, Method and apparatus for determining the titratable acidity of spent sulfuric alkylation acid, U.S. Patent 3,173,969; filed November 17, 1961; issued March 16, 1965; assignee Standard Oil Co.

• https://www.freepatentsonline.com/3173969.html
• Full text: https://patentimages.storage.googleapis.com/dc/32/f1/354e150fcb9ab6/US3173969.pdf

Brief description: A chemical-process analyzer that determines the titratable acidity of spent sulfuric-acid alkylation catalyst by progressively diluting a sample with water and measuring the electrical conductivity at a known temperature. Its apparatus claim (claim 11) recites a mixing chamber, means for introducing acid, dilution means, temperature-control means, conductivity-measuring means, and indicator means receiving a signal from the measuring means. It is fundamentally a process-stream titration/conductivity instrument, not a structural test cell for oil.

Potential § 102 anticipation:

• Claim 1 — No. Kapff discloses a measuring means and an indicator means, but no housing with two openings, no concentrically secured three tubular electrodes, no guard electrode, and no triaxial connector.
• Claims 2, 3, 4 — No. Nothing in Kapff corresponds to a removable cover plug, stainless-steel/Teflon construction, or a glass cup.

Actual relevance: § 103/background art showing that conductivity measurement of liquids with an associated indicator was routine. At most it is pertinent to the general "measuring circuit + display" context (the companion copending application Serial No. 251,429), not to the claimed cell structure.

Reference C — US 3,376,501 (Peranio)

Full citation: Anthony Peranio, Cell for determining the conductivity of liquids entrained in porous media, U.S. Patent 3,376,501; filed December 9, 1966; issued April 2, 1968; assignee Varian Associates.

• https://patents.google.com/patent/US3376501
• https://www.freepatentsonline.com/3376501.html

Brief description: A probe-style conductivity cell for in-situ measurement of liquids in saturated porous media (e.g., groundwater salinity). It comprises a hollow, electrically non-conducting casing; a solid insulating (resinous) block embedding electrodes (two- or four-electrode versions) with their faces exposed; hollow space for liquid; a plurality of openings in the casing (screened) to admit liquid; and a cable running into the casing/block to connect the electrodes to surface measuring instruments (a four-electrode conductivity bridge). Notably, the reference emphasizes that electrode spacing avoids interference from surrounding material.

Potential § 102 anticipation:

• Claim 1 — No. Peranio discloses a casing with openings and a cable to a remote instrument, which superficially echoes claim 1's "housing having at least two openings" and its connector/cable architecture. But it lacks the three concentric tubular electrodes (center/guard/outer), the interspersed insulating sleeves in the claimed concentric arrangement, and — decisively — the triaxial connector with three isolated contacts. No anticipation of claim 1.
• Claim 4 — Partial resemblance only. Peranio's "openings in the casing to allow liquid to enter" is conceptually similar to claim 4's "glass cup having openings formed in the sides thereof," but claim 4 also requires claim 1's whole combination, which Peranio lacks.
• Claims 2, 3 — No. No cover plug, no stainless-steel/Teflon recitation (Peranio uses resin and unspecified electrode metals).

Actual relevance: § 103 art for the remote-cable sample-probe cell idea and for casing openings admitting sample fluid. Peranio is arguably the closest cited reference on the "cell connected by cable to remote instrumentation" concept, but it stops well short of a guarded triaxial measurement front end.

Reference D — US 3,548,304 (Lohnes)

Full citation: Robert A. Lohnes, Resistivity measuring device having vertically-spaced ring electrode and a central electrode, U.S. Patent 3,548,304; filed December 5, 1967; issued December 15, 1970; assignee University of Iowa State Research Foundation (Iowa State University).

• https://www.osti.gov/biblio/[5875337](/patent/5875337) (abstract: "Resistivity measuring device having vertically-spaced ring electrode and a central electrode. [underwater]")

Brief description: An in-situ probe for measuring consolidation/resistivity of subaqueous sediment. An elongated tube penetrates the sediment; toroidal (ring) electrodes are spaced at constant longitudinal increments along the tube's interior; a central/axial electrode runs through the ring electrodes; a selection switch couples each ring electrode to an ammeter; a generator energizes the axial electrode, and current between the axial electrode and a selected ring electrode is measured. A cylindrical shroud stabilizes the probe.

Potential § 102 anticipation:

• Claim 1 — No. Lohnes discloses a central electrode surrounded by spaced ring electrodes — a multi-electrode vertical/concentric arrangement — plus a selection switch. But it is not a set of three concentric tubular electrodes (center/guard/outer) with interspersed insulating sleeves, it has no guard electrode in the triaxial sense, and it has no triaxial connector providing three isolated contacts at a housing opening. No anticipation of claim 1.
• Claims 2, 3, 4 — No. No thermometer-plug cover, no stainless/Teflon recitation, no glass side-openable cup corresponding to claim 4.

Actual relevance: § 103 art for the notion of a central electrode co-axially arranged with surrounding electrodes in a liquid-measuring cell. It shows the generic concentric-electrode concept but not the guarded, triaxial, oil-power-factor cell.

2. Overall § 102 conclusion

None of the four cited references anticipates any claim of US 3,753,098.

• Claim 1 is the only independent claim. To anticipate it, a single reference would have to disclose all of: (i) a housing with main body + removable cover defining a hollow chamber and at least two openings; (ii) a measuring unit in one opening with three concentric tubular electrodes — center, guard, and outer — with insulating sleeves interspersed; and (iii) a triaxial connector in the other opening with three electrically isolated contacts engaging the three electrodes respectively. No cited reference has the guard electrode in a concentric tubular stack and the triaxial connector; those two features, in combination, are the point of novelty.
• Claims 2–4 add the removable cover plug (2), stainless-steel/Teflon materials (3), and the glass cup with side openings (4). Since each depends from claim 1, none can be anticipated by a reference that fails to meet claim 1.

The four references are therefore best characterized as background and potential § 103 art (concentric/sleeved conductivity cells — Christie; conductivity analyzer with indicator — Kapff; cabled probe cell with casing openings — Peranio; central + surrounding electrodes — Lohnes), not as anticipatory art.

Closest-on-the-elements ranking of the cited art:

1. Christie ’306 — closest to the concentric, sleeve-insulated, tubular-electrode idea (but only two electrodes, no guard, no triaxial connector).
2. Lohnes ’304 — closest to a central electrode + surrounding electrodes.
3. Peranio ’501 — closest to a cabled cell with a casing opening to admit sample fluid.
4. Kapff ’969 — least structural; conductivity measurement for a chemical process.

3. Caveats (stated explicitly)

• Sourcing of US 2,221,306: I retrieved full text for the related Christie patents US 2,221,307 and US 2,258,045 but not for ’306 itself. My characterization of ’306 is inferential from those siblings and should be confirmed against the ’306 specification before being relied on for any legal conclusion.
• No confirmed full text of the ’306 body means I cannot rule out that ’306 discloses something more than the two-electrode cell I describe; but nothing in the cited title ("Conductivity indicating system and method") suggests a guard/triaxial cell of the kind claimed.
• Post-1972 documents are not prior art and were excluded from the § 102 analysis: the "Cited By" items (e.g., US 6,305,989 B1; DE 3,205,020 A1; GB 2,179,454 A; US 5,263,363 A) and the foreign "Also Published As" family (DE 2,322,622; GB 1,357,874; CA 975,424; JP S53‑35506 Y2) all post-date the 1972‑05‑08 filing.
• Copending application Serial No. 251,429 (Sambhu) is referenced in the ’098 specification as the companion measuring-circuit/display disclosure. It is not § 102 prior art against ’098 in the ordinary case (same inventive entity, copending); I mention it only to distinguish it from the four examiner-cited references.
• I did not obtain a raw USPTO PatentCenter/Global Dossier page in this pass (search steps were exhausted); the citation list and claim text above are grounded in the authoritative full patent text supplied and in the retrieved reference texts/abstracts cited with URLs.

I'll research the prior-art references cited on the face of this patent to ground the §103 analysis.

Let me get details on the remaining cited references and check for triaxial/guarded-cell prior art.

Obviousness Analysis — US 3,753,098 under 35 U.S.C. § 103

Scope note. The patent expired August 14, 1990 (Expired–Lifetime, 17-year pre‑URAA term), so this is a retrospective validity analysis rather than a live dispute. It is still useful for understanding what the claims actually add over the cited art. Except where noted, I rely on the full patent text you supplied (authoritative) plus public reproductions of the four references cited on the face of the patent. Where I could not retrieve a reference's full text, I say so rather than fill the gap.

1. Legal standard applied

Under Graham v. John Deere, I consider (a) scope/content of the prior art, (b) differences between the prior art and the claims, (c) level of ordinary skill, and (d) objective indicia of non‑obviousness. Under KSR Int'l v. Teleflex (2007), a claim is obvious where it combines known elements with predictable results; the motivation to combine may come from design incentives, market/field needs, or "any need or problem known in the field," and where the elements are "arranged as the prior art teaches" the combination is likely obvious. A claimed apparatus can be obvious when the only difference is the substitution of a known component (here, a known connector type).

Level of ordinary skill in the art: a designer of precision electrical measurement cells (conductivity / resistivity / dielectric-loss / power-factor instrumentation) with a working knowledge of (i) guarded, three-terminal electrode geometries, (ii) shielded cable and connector practice (coaxial/triaxial), and (iii) the materials used for corrosion-resistant, electrically insulating cell components in oil. This is not an unusually high level — it is the routine skill of instrumentation engineers at, e.g., Beckman, Varian, Standard Oil's instrument group, and similar firms.

All four cited references are analogous art. They sit in the same field of endeavor — cells/electrodes for measuring electrical properties (conductivity/resistivity) of liquids — and the art of "guarded" pulse/measurement cells corresponds to the same classification (G01R 27/02; G01N 27). The specification itself admits the field: "Various electrode test cells have been used for measuring the power factor of samples of oil…" (US 3,753,098, col. 1). That is a specification admission that oil power-factor electrode cells were known before the filing.

2. The prior art of record — what each reference teaches (and its limits)

Christie caveat (flagged, per the rules). Your search for US 2,221,306 returned a related but different Christie patent — US 2,258,045, "Electrode structure for conductivity testing," a division of application Ser. No. 193,484 filed March 2, 1938 (the same original filing date as the '306 reference's 1938‑03‑02 priority). That '045 document discloses a cell with an inner cylindrical electrode 6 and outer sleeve electrode 7, an annular current path 13, and insulating sheaths 17, 18 that restrict the current path to a defined annulus — i.e., concentric tubular electrodes with interspersed insulation used to suppress stray/leakage conduction (US2258045 PDF). I did not retrieve the actual text of US 2,221,306, so I am not attributing the '045 disclosure to the '306 reference. I flag the relationship only because the two share a priority date and inventor, and a rigorous analysis should pull the '306 text to confirm whether it contains the same concentric-electrode/insulating-sheath teaching.

Similar-document art (background only). The page's "Similar Documents" section adds same-field cells: US 3,382,434 ("Electrode system employing separate current and potential electrodes"), US 2,486,432 ("Conductivity cell for viscous materials"), US 3,939,401 ("Conductivity cell electrode enclosure"), and US 3,982,177 ("Soil sample conductivity measurement utilizing a bridge circuit and plural electrode cell"). Some of these post-date the patent and are therefore not § 102/§ 103 prior art to it; I cite them only as evidence of the state of the field — e.g., that plural-electrode liquid cells wired to a bridge circuit were routine. Do not treat the post-1972 items as prior art.

3. Differences between the prior art and the claims

Claim 1 has three structural blocks: (a) housing (main body + removably secured cover) defining a hollow chamber with ≥2 openings; (b) a measuring unit with three concentric tubular electrodes — center, guard, outer — interspersed with insulating sleeves; (c) a triaxial connector in the other opening with three electrically isolated contacts respectively engaging the three electrodes.

• Element (b) — the concentric tubular electrode stack with interposed insulators — is the classic geometry of a three-terminal guarded cell; the Christie '045 division shows the two-electrode/insulating-sheath version of exactly this arrangement, and Lohnes shows central + ring (tubular) electrode geometry.
• Element (c) — the connector with three isolated contacts — is a triaxial connector, i.e., a coaxial connector with one added intermediate (guard) conductor. Triaxial connectors existed for guarded three-terminal measurements; the claim's "novelty" here is the selection of a known connector for a known guarded-cell application.
• The combination — concentric guarded cell + three-conductor remote connector + thermometer access — is what the spec treats as the invention's point.

4. Claim chart and proposed combinations

Combination A — Claim 1

Christie '306/'045 (concentric tubular electrodes + interposed insulating sleeves restricting the current path) + Lohnes '304 (central electrode spaced from a ring/tubular electrode) + Peranio '501 (liquid cell with casing openings and cable to remote measuring apparatus) + the routine choice of a triaxial connector.

Mapping:

Where the references do not squarely meet the claim: none of the four expressly discloses (i) a three-electrode (center/guard/outer) tubular stack, or (ii) a triaxial connector. Those two points are the only real gaps, and neither requires invention — a three‑terminal guarded cell is the standard way to reject stray capacitance/leakage in precision loss‑factor/power‑factor measurement, and a triaxial connector is the standard cable interface for a three‑terminal guarded measurement.

Combination B — Claim 1 (alternative)

Lohnes '304 (central + ring/tubular electrode geometry) + Kapff '969 (liquid conductivity measurement with temperature control and Teflon construction) + Peranio '501 (fluid‑ingress casing, remote cable) + routine triaxial connector.

Here the "guard" function is supplied by the ring/tubular electrode of Lohnes guarding a central electrode, the liquid/temperature/materials teaching by Kapff, and the remote‑cable cell by Peranio.

Motivation to combine (Combination A and B)

1. Same field, same problem. All references address measuring the electrical property of a liquid between electrodes; combining electrode geometry from one with cell‑enclosure/fluid‑access from another is the routine work of a cell designer.
2. Known problem in the field. The spec itself frames the problem as measuring oil power factor near energized electrical equipment (e.g., operating power transformers) and doing so remotely. Guarding to reject interference and driving the cell from a remote bridge were known needs; KSR permits motivation drawn from "any need or problem known in the field."
3. Predictable result. Concentric guarded electrodes + interposed insulators predictably reduce leakage/stray coupling; routing the three electrode circuits out through a shielded three‑conductor (triaxial) cable to a remote bridge predictably preserves that guarding. No unexpected result is claimed.
4. Simple substitution of a known component. A triaxial connector is a known hardware item; substituting it for a plain two‑conductor cable/connector to carry the added guard circuit is a design choice with a predictable benefit — the "familiar element … according to known methods" rationale of KSR.

Claim 2 (cover opening aligned with hollow center electrode + removable plug)

Any of the above + the conventional expedient of a thermometer access port, motivated by Kapff's temperature‑control/measurement teaching.

Kapff expressly requires the liquid sample to be held at a known temperature and measured; the specification of '098 stresses elevated‑temperature oil samples from operating transformers. Putting a removable plug in the cover in line with the hollow (tubular) center electrode so a thermometer can be inserted into the oil is a predictable, mechanical adaptation. Christie's plug 10 seated in the recess of the T‑fitting 14 shows a removable plug closing an access to the cell's interior. A person of skill would add this port to read sample temperature — no new principle.

Claim 3 (contacts/electrodes of stainless‑steel tubing; insulators of Teflon)

Kapff '969 (explicit Teflon for liquid‑contacting parts) + the general knowledge that stainless‑steel tubing is a standard electrode material.

Kapff names Teflon as the corrosion‑resistant material of choice for parts contacting the sample. Selecting stainless steel for the electrodes/contacts and Teflon for the insulators is a materials‑selection step driven by corrosion resistance and dielectric properties — precisely the kind of routine choice KSR holds obvious absent a showing of unexpected results.

Claim 4 (glass cup with side openings surrounding the measuring unit)

Peranio '501 (casing with openings / screened hollow space confining the liquid around the electrodes) + glass as an insulating container.

Peranio teaches a casing that encloses the measuring space and has openings permitting fluid ingress/egress — functionally a cup with side openings. Forming that container of glass (an insulator, and transparent to permit visual inspection) is an alternative known material. The claim adds a container material, not a new operating principle.

5. The strongest argument for non‑obviousness (steelman)

To be fair to the patent:

• No single reference, and arguably no pairing, expressly discloses the triaxial connector wired to a guarded three‑electrode oil cell. The examiner cited these four references and still allowed the claims, which suggests the combination was seen as not squarely taught.
• The hollow center electrode doubling as a thermometer well (claim 2, read against the spec's hot‑transformer‑oil use case) is a specific structural synergy — the center electrode is used both as an electrode and as a conduit for a temperature probe — that the cited references do not teach.
• The references are largely conductivity/resistivity cells; the patent is a power‑factor (loss‑tangent) cell, a different (though closely related) measurement, and one that is more sensitive to stray capacitance and leakage — which is why the guard geometry and triaxial shielding matter. An applicant could argue that the conductivity‑cell art did not recognize the need for a triaxial‑connector‑integrated guarded cell.

But these points cut weakly, because: (i) the guard/three‑terminal technique itself was the standard answer to stray‑capacitance/leakage error in precision AC dielectric/power‑factor measurements, and applying it in the disclosed cell is a predictable use; (ii) "triaxial connector" is a known cable interface, not a new structure, and claim 1 does not claim anything about the connector's internal geometry beyond three isolated contacts; and (iii) claim 1 does not require the hollow electrode/thermometer feature (that is claim 2), so the synergy argument does not rescue claim 1. On the KSR framework, claims 1, 3, and 4 in particular look vulnerable to a Combination‑A or Combination‑B challenge; claim 2 is the most defensible because of the specific alignment of the cover port with the hollow center electrode, though even that may fall to Kapff's temperature‑measurement teaching plus the plug expedient.

6. Explicit uncertainties

• US 2,221,306 (Christie): I could not retrieve its full text. My search returned the related Christie division US 2,258,045 (same 1938‑03‑02 priority). I do not attribute the '045 concentric‑electrode/insulating‑sheath disclosure to the '306 reference — that must be verified against the '306 specification before relying on it in a formal § 103 chart.
• US 3,548,304 (Lohnes): I confirmed the title, inventor, assignee‑type (Iowa State Univ. Res. Found.), date, and field, but not the full claim/spec text. The mapping of Lohnes to a guard electrode is an inference from its "central electrode + vertically spaced ring electrode" geometry and its classification; treat it as a lead to verify, not a verified disclosure.
• "Similar Documents" items are not all prior art to this patent (several post‑date 1972). I used them only as field‑context evidence.
• Objective indicia (Graham factor (d)): I have no evidence of commercial success, long‑felt need, failure of others, copying, or industry praise tied to this patent. Absent such evidence, the § 103 analysis rests on the art‑vs‑claims comparison above. If objective indicia exist, they could change the conclusion — particularly for claim 2.
• I did not retrieve the copending Sambhu application, Serial No. 251,429 (the companion measuring circuit), so I cannot speak to whether it contains cell features that would bear on this analysis.

7. Bottom line

Under Graham/KSR, the references of record support a colorable § 103 challenge to claim 1 via Christie (+ Lohnes) for the concentric tubular electrode/insulating‑sleeve geometry, Peranio for the fluid‑access casing and remote cable‑energized cell, and the routine selection of a triaxial connector to carry the center/guard/outer circuits — motivated by the known need to reject interference and energize a guarded cell remotely near energized equipment. Claims 3 and 4 fall with routine materials/container selections (Kapff's Teflon; Peranio's open casing in glass). Claim 2 is the most defensible, resting on the cover port aligned with the hollow center electrode and a removable thermometer plug, though Kapff's temperature‑control teaching plus the plug expedient is a plausible obviousness case there too. The two genuine gaps in the art of record — an express three‑electrode tubular stack and an express triaxial connector — are, on this record, predictable extensions of known guarded‑cell and shielded‑cable practice rather than inventive departures, but confirming the full disclosures of US 2,221,306 and US 3,548,304 is the necessary next step before any § 103 conclusion is treated as firm.

Key sources: US 3,753,098 full text (Google Patents); US 3,173,969 (PDF); US 3,376,501 (Google Patents); US 3,548,304 (title/field per Iowa patent index); related Christie US 2,258,045 (PDF).