US 5339258

I'll search for this specific patent number and check for any litigation activity.

Summary of US Patent 5,339,258

Important note on the search request: I searched for litigation/docket activity on this patent. I found no CAFC 2026 docket (or any litigation) involving US 5,339,258. This is consistent with the patent's status — it lapsed in 2002 for nonpayment of maintenance fees, roughly 24 years before the requested 2026 review period, so a 2026 Federal Circuit appeal is essentially implausible. I cannot provide authoritative docket information that does not exist; if you have a specific case number, I can search that instead.

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Bibliographic data

A related family member is US 5,477,726 A (Stabinger; issued 1995-12-26), which is the most directly-related cited-by document.

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Abstract (verbatim)

A device for determining the density of liquids and gases uses an actuator to physically excite a sample of the material being tested. The oscillations induced by this excitation are detected by a sensor and amplified by an oscillation amplifier, and the amplified signal is used to drive the actuator in a closed-loop fashion. To compensate for errors in the density measurement process arising from non-ideal viscous effects of the sample, a phase change circuit or inverter may be shunted into the amplifier circuit to change the phase of the excitation signal. By observing the effects of the excitation phase change on the oscillation frequency of the sample, the sample's viscosity can be measured, and the system can compensate for its effects.

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Plain-language overview of the independent claim

The patent has 10 claims, of which only claim 1 is independent; claims 2–10 all depend directly or indirectly from it.

Claim 1 — An apparatus for measuring the density of a liquid or gas, comprising:

1. An oscillator containing the test sample (the sample-filled vibrating body, e.g., a vibrating tube whose resonant period shifts with sample density);
2. A sensor that detects the oscillator's oscillations and outputs a corresponding electrical signal;
3. An oscillation amplifier that amplifies the sensor signal;
4. An actuator that receives the amplified signal and drives the oscillator — i.e., a closed-loop (self-oscillating) feedback arrangement;
5. At least one phase-shifting circuit;
6. At least one change-over switch that selectively connects that phase-shifting circuit into the amplifier loop, so the excitation signal delivered to the oscillator is deliberately phase-shifted away from the oscillator's own motion;
7. Determining means responsive to the sensor signal that computes the sample density.

Core inventive concept: By switching between different excitation phase relationships and observing the resulting shift in resonance frequency, the instrument can measure the damping (viscosity) of the sample. Because viscous samples otherwise introduce a density-measurement error, extracting the damping constant lets the system correct that error — enabling accurate density readings for viscous liquids, not just the non-viscous liquids assumed by prior equations. The specification defines the damping constant via equation (3), b as a function of the two resonance frequencies f₁, f₂ and their associated phase differences φ₁, φ₂.

Dependent claims add: microprocessor control of the change-over switch(es) (claim 2), a density display (claims 3, 6), frequency measuring and memory circuits (claims 4, 5), two axially-spaced transducers for exciting zero-order and higher-order modes (claim 7), a microprocessor-controlled 180° switchable inverter (claim 8), and two specific inverter implementations — a parallel follower/inverter pair (claim 9) and a single inverting op-amp with a microprocessor-controlled ground switch (claim 10).

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Key prior art cited (for context)

AT 331,539 B (Kratky — the acknowledged starting point); AT 356,943 B (Kratky); US 4,524,610 A; US 4,606,498 A; US 4,926,682 A; US 4,838,084 A (Leopold); US 5,003,400 A; GB 2 236 591 A; WO 90/12306 A1; and the non-patent reference Langdon, R.M., "Vibratory Process Control Transducers," The Marconi Review, vol. XLIII (1980), No. 218, pp. 156–175.

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Uncertainty flags

• No litigation found. No CAFC, PTAB, or district court activity for this patent was located; the lapsed-2002 status makes 2026 appellate activity implausible.
• Assignee is "Individual." Google Patents lists no corporate assignee. If you need a definitive chain-of-title, that would require the USPTO Assignment database — I did not retrieve a recorded assignment document.
• Inventor name order. The patent front page and unifiedpatents list the inventors as Leopold, Stabinger, and Heimel in varying orders. Treat all three as the named inventive entity.
• Be aware there is an unrelated Japanese patent also numbered 5339258 (J-GLOBAL, a biotin-labeled luciferase method) — do not conflate it with US 5,339,258.

I'll search for litigation involving US patent 5339258 across patent litigation sources.

Let me search more targeted litigation sources for this specific patent.

Let me check a few authoritative litigation databases directly.

Litigation Search Results for US Patent 5,339,258

Bottom line: I found no evidence of any litigation involving US Patent 5,339,258. No district court case, ITC investigation, PTAB proceeding, or Federal Circuit appeal appears in the sources I searched. I cannot report a plaintiff, defendant, jurisdiction, case number, filing date, or outcome because no such case is on record in the material available to me.

What I searched and what I found

• Unified Patents litigation portal (portal.unifiedpatents.com): The patent's page (https://portal.unifiedpatents.com/patents/patent/US-5339258-A) reports the bibliographic data and abstract, but no litigation list and no assertion history. Its litigation/assertion fields are effectively empty.
• Google Patents (https://patents.google.com/patent/[US5339258](/patent/US5339258)/en): The "Cited By" table lists only later patents (e.g., US5477726A, US6311549B1, Anton Paar and Micro Motion documents) — these are citations, not litigation. There is no litigation section.
• General web search for "5339258," "5,339,258," and litigation/lawsuit/case terms returned only: (a) the patent's own pages; (b) a European search report citing the patent as prior art; (c) a scholarly paper citing it; and (d) unrelated results where the number coincidentally appeared (e.g., a CourtListener financial-disclosure record ID 5339258, and Argentine land-coordinate entries). None relate to this patent.

Caveats on completeness

• I could not run a live PACER docket query, a Westlaw/Lexis "KeyCite/LitAlert," or a CourtListener RECAP patent docket search, which are the definitive tools for this. My searches were web-index based.
• The absence of indexed results is strong but not absolute proof of an empty litigation history, particularly for older (1990s) cases that may not be digitized.

Context that makes litigation unlikely

Several features of this patent, taken literally from the record, explain the absence of enforcement activity:

• Assignee is an individual. Both original and current assignee are listed as "Individual" (no corporate owner), with inventors Hans Stabinger, Hans Leopold, and Helmut Heimel. There is no operating company or NPE holding it.
• No patent family. The record shows "Family Members (0)" and "Family ID=25598327" with only the single US application.
• It was never maintained. Legal events show it lapsed for failure to pay maintenance fees, with the lapse effective 2002-08-16 (reminder mailed 2002-03-05; "PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES" 2002-09-18). Anticipated expiration is listed as 2012-05-01. Status: Expired – Fee Related.
• Key dates: priority 1990-11-22 (AT 237890A → AT395074B); US filing 1992-05-01 (App. No. 07/877,891); grant 1994-08-16.

One adjacent item worth flagging (not litigation)

The "Cited By" list shows US5477726A (priority 1990-11-22, granted 1995-12-26, inventor Stabinger) — a related US patent in the same technical family. This is a patent-family/citation relationship, not a lawsuit, and I did not search its litigation history separately.

If you need a definitive answer

To confirm the negative with legal certainty, I'd recommend running the specific patent number 5,339,258 through:

• PACER / CourtListener RECAP docket search (by patent number),
• Lexis LitAlert or Westlaw KeyCite patent-history reports, and
• the CAFC docket and ITC EDIS interfaces.

If you'd like, I can attempt narrower follow-up searches once tool access is restored, but based on everything retrievable now, there is no known litigation involving US 5,339,258.

Proceedings overview

Total AIA trial proceedings on file: 0. The USPTO Open Data Portal structured block returns no IPR, PGR, or CBM for US 5,339,258 — borne out by the patent's own bibliographic record, which shows no PTAB trial events in its legal-events history (the only post-grant-adjacent entries are fee-payment and lapse events) and no PTAB decisions in its "Cited By"/"Citations" tables. My independent web searches of PTAB petition filings (ptacts.uspto.gov), Google Patents' litigation/PTAB sections, and Federal Circuit / CourtListener-style sources surfaced no petition, institution decision, FWD, or appeal naming this patent. Bottom line for a defendant: there is nothing to work with and nothing to worry about — the patent lapsed in 2002-08 for non-payment of maintenance fees and cannot be asserted at all. The absence of PTAB activity here is not a "hardened patent" signal; it is a dead-patent signal.

No proceedings to rank

There are no {PROCEEDING_NUMBER} — {Petitioner} v. {Patent Owner} entries to report. I will not synthesize any. For completeness, here is why the empty set is the expected result rather than a search artifact:

• AIA trials did not exist during this patent's assertable life. Inter partes review, PGR, and CBM review became available for petitions filed on or after 2012-09-16. By then US 5,339,258 had already been expired for roughly a decade. The 1990-11-22 priority date and 1994-08-16 grant place it entirely in the pre-AIA, pre-PTAB era; the only post-grant vehicle that existed during its enforceability window was ex parte / inter partes reexamination (which is not an AIA trial and does not appear in the "PTAB proceedings on file" block).
• Legal status confirms non-enforceability. The record shows LAPS (lapse for failure to pay maintenance fees) on 2002-08-16, STCH on 2002-09-18 ("PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362"), and the final FP entry on 2002-10-15 with effective date 2002-08-16. Anticipated expiration is listed as 2012-05-01, but the patent did not survive to that date. Google Patents reports the status as "Expired - Fee Related."
• No parallel litigation footprint. Searches for district-court assertion of "5,339,258" returned nothing; the only third-party references to the number are the EPO search report for EP3015846A1 (Anton Paar), where US 5,339,258 appears as a cited prior-art document, and academic citations. The Unified Patents portal page at https://portal.unifiedpatents.com/patents/patent/US-5339258-A is a patent database entry, not a proceeding — its presence there does not indicate any Unified Patents challenge, and no Unified-filed petition exists. Do not let anyone tell you otherwise.

Strategic summary

Claim status: all 10 claims are UNTESTED and none are CANCELED or SUSTAINED. No tribunal has ever adjudicated the patentability of claims 1–10 in a post-grant forum. Claims 1–10 as issued stand unmodified in the printed patent, but that is an academic point because the patent lapsed. Original assignee is listed as "Individual" (inventors Hans Stabinger, Hans Leopold, and Helmut Heimel); no assignment to a corporate entity or NPE appears in the record, and no current owner is asserting it. For a defendant today, the operative fact is not claim scope — it is that the entire right to exclude ended on 2002-08-16.

Estoppel landscape: inapplicable. 35 U.S.C. § 315(e)(2) estoppel attaches only to a petitioner that obtained an institution decision. With zero petitions, zero institutions, and zero FWDs, there is no estoppel in any direction — no petitioner is barred from anything, and no patent owner has been spared anything. There is also no obvious defensive aggregator, litigation campaign, or repeat-petitioner pattern to trace. If you want prior art for the related family members still of interest (e.g., the 1995-12-26 Stabinger continuation US 5,477,726, which is itself long expired), US 5,339,258 is a § 102(b) printed publication as of 1994-08-16 and is already being used that way in EPO prosecution — see the search report for EP3015846A1, which cites "US 5 339 258 A (STABINGER HANS [AT] ET AL) 16. August 1994" for claims 2, 3, 7, 8 of that later Anton Paar case.

Pattern signals: none. The same petitioner has not filed anything, let alone multiple IPRs; the patent owner has never had a PTAB appeal to pursue; and no aggregator is in the chain. The family itself is the more interesting artifact — AT 395074 B (priority), US 5,339,258, US 5,477,726, and later Anton Paar filings — with the '258 functioning today purely as prior art against other people's density-meter applications.

Recommended next steps

• If you receive an assertion or demand letter citing US 5,339,258: treat it as a red flag about the sender. The patent expired on 2002-08-16 for failure to pay maintenance fees (37 C.F.R. § 1.362), confirmed at https://patents.google.com/patent/US5339258/en under Legal Events (LAPS 2002-08-16, FP 2002-10-15, "Expired - Fee Related"). An expired patent cannot be infringed going forward, and damages exposure after lapse is limited to pre-expiration past conduct — which, given lapse in 2002, is closed out by the 35 U.S.C. § 286 six-year damages bar. Verify the fee record directly at USPTO Patent Center (https://patentcenter.uspto.gov/, application 07/877,891) before responding.
• If the sender points to a different patent in the family, re-run this analysis on that number specifically. US 5,477,726 (granted 1995-12-26, same inventors, same priority chain) and the later Anton Paar patents (EP 3015846 A1, US 2016/0123861 A1, WO 2017/005243 A1) are separate rights with separate maintenance-fee and expiration histories. Nothing about the '258's status automatically transfers.
• There are no trial-stage milestones to track. No institution deadline, no oral hearing, no statutory 1-year FWD due date, and no Federal Circuit appeal docket exists because no proceeding was ever filed. I found no FWD to quote and no CAFC opinion to link.
• Plain statement required here: no PTAB activity exists on US 5,339,258. Nothing has been canceled, nothing has been sustained, and no claim has been tested. The consistent, independent signals — the ODP block, the legal-events history, the absence of any petition or decision in web-indexed PTAB materials, and the 2002-08-16 lapse — all point the same way.

Assignment / Ownership Reconstruction — US 5,339,258

Sourcing caveat (read first). I was unable to complete a direct live query of the USPTO Patent Assignment Center in this session (search-step budget exhausted before the assignment API/UI could be polled). The finding below therefore rests on (a) the Google Patents legal-events record, which is populated from the same USPTO assignment data and contains no assignment ("AS") events whatsoever for this patent, (b) the "Original/Current Assignee = Individual" fields in Google Patents and Unified Patents (which derive from the printed front page), and (c) the EPO/AT family records for the same invention. Verify directly at https://assignmentcenter.uspto.gov/ (search by patent number 5339258) and https://assignment.uspto.gov/patent/index.html. If a reel/frame exists that the aggregators missed, it will appear there.

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Inventors

Unusual patterns noted

• No employer-owned inventorship. All three were working in or with a private R&D lab (Stabinger's) and/or academia, not for a corporate assignee. This is a classic Austrian-inventor pattern where title stays with the inventors and the manufacturing/marketing partner takes an exclusive licence instead of an assignment. It is not a red flag — but it explains why no corporate assignee ever appears.
• Inventorship splits inside the same family. The sibling US patent US 5,477,726 (same 1990-11-22 priority, issued 1995-12-26) names Stabinger alone, while US 5,339,258 names all three. Ownership of this family was therefore fractionated across co-inventors from the start, which is a prerequisite for later "partial transfer" events (see EP 0 926 481 note below).
• No 12-month departure pattern derivable. Because there was no employer-assignee, the "inventors leave within 12 months → fire-sale" tell cannot arise here.
• The 1989 lab paper and the lab's own history page confirm the three men were still collaborating continuously from 1965 through at least the late 1990s — no abrupt inventive-entity break.

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Original assignee

There is no corporate original assignee. Google Patents, Unified Patents and EveryPatent all render the original and current assignee as "Individual." The US front page (PDF at patentimages) carries no (73) assignee field. Title therefore presumptively sat with the three named inventors as co-owners — the closest thing to an "operating" entity here is the exclusive licensee:

• Exclusive licensee: Anton Paar GmbH (Graz-Straßgang, Austria) — a mid-size, family/employee-foundation-owned analytical-instrument maker. Per Stabinger's own lab history, "Right from the beginning, Anton Paar GmbH in Graz-Straßgang has been the exclusive licensee for producing and marketing the density, sound, and viscosity meters developed by our company. This cooperation was terminated in 2014 but the exclusive licence is still in place until the end of January 2018." (http://www.lab-stabinger.at/en/)
• Product embodying the claims: Yes — Anton Paar's DMA-series oscillating U-tube density meters (the specification's own 1987–1991 DMA 48/DMA 38 generation) and later the Stabinger Viscometer SVM 3000 family. The specification's FIG. 1–3 viscosity-error discussion maps directly onto the DMA 48's "compensation of the viscosity-induced density error … by shifting the phase angle between the stimulation and the testing signal" (lab history page).
• Licensor status: Labor für Messtechnik Dr. Hans Stabinger remains an operating R&D firm in Graz; Dr. Stabinger and Dr. Heimel were still named as patentees on later family members (e.g. DE 10 2000 032 743 B4, granted 2013, assignees = Heimel, Leopold, Stabinger individually; EP 0 926 481, owners = Stabinger + Heimel). No bankruptcy, no dissolution.
• The US patent itself lapsed 2002-08-16 for non-payment of maintenance fees and expired in 2012 — the maintenance economics were apparently not justified because the commercial product (DMA/SVM) was protected and continuously refreshed by Anton Paar's own newer filings.

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Assignment timeline

No assignment (conveyance) records were found for US 5,339,258. The Google Patents legal-events table for this patent contains only statutory fee events and no assignment entries:

The 1997 "independent inventor" small-entity certification is affirmative evidence that as of 1997-12-02 the record owner was still an individual, not a corporation — no assignment to Anton Paar, to a holding company, or to any third party had been recorded by then, five years post-issuance.

Because there is no recorded conveyance, there is no correspondent of record, no reel/frame, no repeat-attorney signal, and no cascading-transfer chain to analyse for this patent. Per the stop rule for this section, the remaining analytics are supplied in abbreviated form for completeness.

Family note (not part of the US chain, do not conflate): the French national register for the sibling EP 0 926 481 records a "Transmission partielle de propriété" (partial transfer of ownership) on 2015-02-12, RNB No. 0204801 — i.e. co-owner interests in the European viscosity family did move in 2015. That is a different invention, different jurisdiction, and post-dates the 2012 expiry of the US patent; it does not evidence any US assignment.

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Timeline diagram

timeline
    title Ownership of US 5339258
    1990 : Priority filed in Austria
    1992 : US application filed by the inventors
    1994 : Patent issued to the three inventors
    1997 : Small entity claimed as independent inventor
         : No assignments of record
    2002 : Patent lapsed for unpaid fees

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NPE / troll-pattern signals

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Verdict

Insufficient data (no records, or only the original assignment).

There are no recorded post-issuance assignments for US 5,339,258 — the Google Patents legal-events table shows only fee events, and the USPTO's 1997-12-02 small-entity entry certifies the holder as an "INDIV INVENTOR," meaning the three inventors (Stabinger, Leopold, Heimel) still held title personally five years after the 1994-08-16 grant. The commercially relevant relationship was an exclusive licence to Anton Paar GmbH, an operating analytical-instrument manufacturer whose DMA density meters and Stabinger viscometers embody the claims — an operating-company licensing arrangement, not an NPE chain. Every troll-pattern signal is not present; the "insufficient data" label reflects the absence of any recorded conveyance to analyse, not any suspicion of concealment.

Verification link: https://assignmentcenter.uspto.gov/ (search patent number 5339258) — also https://assignment.uspto.gov/patent/index.html

I'll research the prior art references cited against US 5,339,258. Let me run targeted searches on the key references.

Found a key lead — let me dig into the Kratky foundational patents and the remaining cited references.

Prior-Art Analysis — US 5,339,258

1. Target patent confirmation

I searched for the exact number 5,339,258 (not 5,332,958, not 5,339,285, and not the unrelated Japanese J-GLOBAL "5339258" biotin-luciferase entry flagged in the earlier summary).

• US 5,339,258 A — "Apparatus for determining the density of liquids and gases from a period of an oscillator filled with a test sample"
• App. No. 07/877,891; filed 1992-05-01; priority 1990-11-22 (AT 237890 A → AT 395074 B); issued 1994-08-16; Expired – Fee Related (lapsed 2002-08-16).
• Source: https://patents.google.com/patent/US5339258/en (mirrors USPTO PatentCenter bibliographic data).

Note: the earlier-summary step reported no litigation for this patent, and my searches likewise surfaced no PTAB/CAFC activity. That is consistent with its lapsed status. I therefore did not find any AIA-style IPR record that re-litigated these references. The §102 analysis below is a technical/patentability assessment, not a docket-based one.

⚠️ One contradiction to flag: the earlier summary listed the "examiner" as Edward R. Cosimano. That name does not appear on the Google Patents record I retrieved, so treat the examiner field as unverified.

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2. The 19 cited references — organized by relevance

The examiner cited 19 references (patents + 2 copies of one NPL item). Below, each is given with its citation, priority/publication dates (as listed in the patent's citation table), a description, and the claim(s) it potentially anticipates under 35 U.S.C. § 102.

Group A — Kratky densitometer lineage (the closest art; includes the acknowledged starting point)

A1. AT 331,539 B — Kratky, Otto. "Device for measuring density." Priority 1972-10-25; published 1976-08-25.

• This is the reference the patent itself acknowledges as the starting point ("Such an apparatus was disclosed, for example, in Austrian Letters Patent 331,539"). Its disclosed excitation/detuning circuit = amplifier + limiter + temperature-dependent resistance bridge + summing amplifier + integrators for phase shifting.
• §102 candidate for claim 1 — strongest single candidate, but probably incomplete. It discloses the oscillator (a), sensor (b), oscillation amplifier (c), actuator (d), and even a phase-shifting element (e). What it does not show is a change-over switch (f) that selectively shunts that phase-shifting circuit into the loop to deliberately mis-phase the excitation and thereby measure viscosity. Its phase-shifting integrators serve temperature detuning, not viscosity correction. That difference is the heart of claim 1 → likely no anticipation of claim 1, but it is the reference that most nearly reads on it, and it is the natural §103 base.

A2. US 3,910,101 A — Kratky. "Devices for measuring density." Priority 1972-10-25; published 1975-10-07.

• Appears to be the US counterpart of the AT 331,539 family (same 1972-10-25 priority as AT 331,539 B and FR 2,208,525 A5). Discloses the closed-loop electromagnetically driven oscillator (pick-up coil → excitation amplifier → driver coil), amplitude-limiting diodes, and a frequency meter (Schmitt trigger + counter).
• §102: potentially anticipates the apparatus sub-combination of claim 1 (oscillator, sensor, amplifier, actuator, frequency-determining means); does not teach the switchable phase shifter or viscosity-correction concept.

A3. AT 356,943 B — Kratky. "Device for determining the density of liquids and gases." Priority 1978-10-30; published 1980-06-10.

• Later Kratky improvement (elastic-constant compensation by a tensioned cord). §102: relevant to the oscillator/detuning art, not to the claimed switched-phase-shift feature.

A4. FR 2,208,525 A5 — Kratky. Priority 1972-10-25; published 1974-06-21. French member of the same Kratky family; same §102 posture as A1/A2.

Related Kratky reference found in searching but NOT in the citation list — see §4 below (US 3,523,446), which is highly material.

Group B — Vibrating-tube / vibratory viscometer-densitometers

B1. US 4,524,610 A — Fitzgerald et al. (National Metal & Refining Co.). "In-line vibratory viscometer-densitometer." Priority 1983-09-02; published 1985-06-25.

• Straight elastic tube driven simultaneously in torsion and flexure; torsional amplitude held constant and power required to sustain it = viscosity-density product; flexural resonance frequency = density. Uses separate torsional and flexural driver/detector coils and a positive-feedback loop.
• §102: Highly relevant to claim 7 (multiple transducers exciting different modes) and to the general claim 1 architecture (drive/detector/sustaining-amplifier loop). Does not anticipate claim 1's phase-shifting + change-over-switch feature.

B2. US 4,606,498 A — Yissum Research Development Co. (Hebrew Univ. Jerusalem). "Densitometer." Priority 1984-04-10; published 1986-07-29. Vibratory densitometer; §102(a)/(b) printed-patent art but a different measurement principle (no switched phase shifter).

B3. GB 2,001,761 A — Straumann Inst. AG. "Device for measuring the density of a fluid." Priority 1977-07-27; published 1979-02-07. Vibrating-element fluid densitometer.

B4. GB 2,187,286 A — Hatschek, Rudolf. "Fluid density measuring apparatus." Priority 1986-02-24; published 1987-09-03.

B5. GB 2,236,591 A — Marconi GEC Ltd. "Vibrating element apparatus for fluid density and/or viscosity determination." Priority 1989-10-05; published 1991-04-10. Same research line as the cited Langdon Marconi Review article (see NPL below). §102(a)-type art (published after the 1990-11-22 priority date; <1 yr before filing, so not §102(b)).

B6. WO 90/12306 A1 — Instrulab. "Vibrating densimeter sensor." Priority 1989-03-30; published 1990-10-18. Published ~1 month before the priority date → §102(a) art (and <1 yr before filing, so not §102(b)). Unlike the other Group-B items, its publication predates the critical date, so it must be taken seriously as anticipatory-type art for the generic densitometer elements.

Group C — Capacitive/transducer and other measurement principles

C1. US 4,926,682 A — Research Corp. of the Univ. of Hawaii. "Viscosity sensor." Priority 1988-06-03; published 1990-05-22. A flexible-membrane capacitive gas-viscosity sensor measuring membrane deflection rate / transient response — a fundamentally different (non-resonant-tube) viscosity principle. §102: §102(b) art, but it does not disclose the claim-1 combination (no oscillator-with-sample resonance loop, no change-over-switchable phase shifter).

C2. US 4,838,084 A — Leopold, Hans. "Density measuring instrument." Priority 1988-08-30; published 1989-06-13.

• Same inventor as the subject patent (Hans Leopold). Vibrating glass tube, electronic excitation system, period meter built around an Intel 80G31 microcomputer, Intel 8052/siemens SAB 80535 microcontrollers, and Peltier temperature control.
• §102: §102(b) art. Notably it discloses the microcomputer/period-meter "determining means" relied on in claims 2, 3, 5, 6 (microprocessor, display) and the frequency-measuring element of claim 4. It does not disclose the switchable phase shifter, so it cannot anticipate claim 1, 2, 5, or 8 as a whole.

C3. US 3,339,400 A — Automation Products (Banks). "Mass presence sensing apparatus." Priority 1963-08-12; published 1967-09-05. Vibrating U-tube driven at a fixed frequency (deliberately off-resonance); mass/density from amplitude change; includes an amplitude-limiting circuit between detector and vibrator. §102(b) art. Fails claim 1 (fixed-frequency drive; no phase-shifting circuit, no change-over switch).

C4. US 3,385,104 A — Automation Products. "Mass presence sensing apparatus." Priority 1963-08-12; published 1968-05-28. Companion to C3 (adds temperature-compensating spring bars). Same §102(b) posture; same failure to reach claim 1.

C5. DE 1,498,548 A1 — Automation Products. "Mass determination device." Priority 1963-08-12; published 1969-03-27. German counterpart of the C3/C4 family.

C6. EP 0,222,503 A1 — Schlumberger Electronics (UK) Ltd. "Transducers." Priority 1985-10-18; published 1987-05-20. Transducer art; §102(b) reference, not directed to the claimed switched-phase density correction.

Group D — US references qualifying as §102(e) art (filed before the 1990-11-22 priority date, published after)

D1. US 5,003,400 A — Lew, Hyok S. "Dual frequency density meter." Priority 1989-07-18; published 1991-04-09.

• Relevant: a densitometer that operates at two frequencies. Conceptually adjacent to the subject patent's use of two resonance frequencies (f₁, f₂) to derive damping. §102(e) art (US filing predates the priority date; publication is later).
• §102: candidate against the dual-measurement idea underlying claim 1, but its dual-frequency measurement is not obtained by a change-over-switchable phase shifter; no anticipation of claim 1.

D2. US 5,253,533 A — Krohne Messtechnik. "Mass flow meter." Priority 1990-07-28; published 1993-10-19. §102(e) art. Coriolis/mass-flow art; not directed to the claimed phase-switching density correction.

D3. US 5,237,853 A — AlliedSignal Inc. "Method and apparatus for measuring the density of a liquid." Priority 1990-10-15; published 1993-08-24. §102(e) art (US filing ~5 weeks before the priority date). Density measurement art; not directed to the claim-1 phase-switching feature.

Non-patent literature

NPL1. Langdon, R. M., "Vibratory Process Control Transducers," The Marconi Review, Vol. XLIII (1980), No. 218, Rugby, Great Britain, pp. 156–175. (Listed twice — "examiner" and "third-party" citations.)

• §102(b) printed publication (>1 yr before the priority date). Foundational review of vibratory (vibrating-element) process-control transducers, including density/viscosity. It supports the general architecture of claim 1 but does not disclose the specific change-over-switchable phase-shifting circuit recited in claim 1.

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3. Additional relevant references I found that are NOT in the citation list

These are material to claim 1 and worth knowing about, though the examiner did not cite them:

X1. US 3,523,446 A — Kratky (Kratky densitometer; issued ~1970). Found via search of the Kratky line. It expressly states:

"Each phase shift within the electrical system, however, alters the oscillating frequency as each deviation from the velocity which is proportional to the excitation would amount to a change of the mass of the oscillator."

This is, in essence, the physical principle the subject patent exploits (a phase shift in the excitation loop de-tunes the oscillation frequency), and it is framed as an error to be minimized ("this fact demands an extremely flat phase response"). So it is powerful §102/§103 art for the concept, but its teaching points away from deliberately switching in a phase shift — i.e., it argues against obviousness of claim 1's deliberate phase switching. ⚠️ I observed this in a patent PDF; I could not fully confirm its exact issue date/assignee within the search budget — treat the citation details as provisional.

X2. US 4,114,423 — "Device for measuring the density of liquid and gaseous substances and method for operating the device." Found via search. This reference discloses a phase shifter (element 60) that deliberately displaces the exciting force by ~45° relative to velocity to compensate the viscous force, with the density computed as D = k·((T₁/Tᵥ)² − 1). That is very close to the subject patent's core inventive concept (phase shift to correct for viscosity). ⚠️ It was not among the 19 cited references. If verified, it would be the single most on-point anticipatory/obviousness reference for claim 1 — I recommend confirming its date, assignee, and full text before relying on it. I could not complete that verification within the tool budget.

X3. EP 0,487,499 A3 — Stabinger / Leopold / Heimel (priority AT 2378/90, 1990-11-22). This is the European counterpart of US 5,339,258 itself (same inventors, same priority, same abstract). It is a family member, not prior art, but it confirms the priority chain and the AT 395,074 B link noted earlier.

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4. Bottom line — most relevant prior art and §102 assessment

Most relevant prior art (ranked):

1. AT 331,539 B / US 3,910,101 A (Kratky) — the acknowledged starting point and the closest single reference. It discloses essentially every structural element of claim 1 except the change-over-switchable phase-shifting circuit used for viscosity correction.
2. US 3,523,446 (Kratky) and US 4,114,423 (uncited; see §3) — disclose the principle that an excitation phase shift alters the resonance frequency, and (in US 4,114,423) the use of a phase shifter to compensate viscosity. These are the most dangerous references if the claim-1 "change-over switch" limitation is construed broadly.
3. US 4,524,610 A (Fitzgerald) and US 5,003,400 A (Lew) — vibratory viscometer-densitometer and dual-frequency density meter; relevant to claims 1/7 architecture.
4. US 4,838,084 A (Leopold) — same inventor; discloses the microcomputer/period-meter "determining means" of claims 2–6.

§102 conclusion:

• No single cited reference appears to fully anticipate independent claim 1, because none of them discloses the combination of (i) a phase-shifting circuit and (ii) a change-over switch that selectively connects it into the oscillation amplifier to deliberately shift the excitation phase, together with the density-determining means. This is consistent with the fact that the case was allowed over these references.
• Claims 2–6 (microprocessor control, display, frequency-measuring/memory circuits) are each anticipated only in their sub-features by US 4,838,084 (microcomputer/period meter/display) — but not as complete claims, because the microprocessor is claimed as controlling the change-over switch, which is the novel element.
• Claim 7 (two axially-spaced transducers for zero/higher-order modes) is closely approached by US 4,524,610 (independent torsional/flexural drivers and detectors) and US 5,003,400 (dual frequency), but neither discloses the axially-spaced-transducer field-shaping feature as claimed.
• Claim 8 (microprocessor-controlled 180° inverter) and claims 9–10 (specific follower/inverter and single-op-amp inverter circuits) have no close anticipatory reference among the citations; the inverter circuits are conventional op-amp topologies, suggesting a §103 (design-choice) vulnerability rather than §102.

§102(e) caveat: US 5,003,400, US 5,253,533, and US 5,237,853 are US references with effective filing dates before the 1990-11-22 priority date but publication dates after; they qualify as prior art only under §102(e) (pre-AIA), and only as to subject matter actually disclosed.

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5. Uncertainty flags

• US 3,523,446 and US 4,114,423 (both flagged in §3) are the highest-value leads I surfaced but could not fully verify (dates, assignee, full text) within the search budget. Do not treat their bibliographic details as settled.
• Dates above are taken from the patent's own citation table / Google Patents listing; I did not independently re-verify each against the USPTO image files. Priority vs. filing vs. publication distinctions matter for §102(a)/(b)/(e), and a few (e.g., AT 331,539 B) merit a direct pull of the front page.
• US 3,910,101 A is presumed to be the US counterpart of the acknowledged AT 331,539 B based on a matching 1972-10-25 priority; I did not confirm the family link conclusively.
• No litigation or IPR record was found, so this is a paper patentability analysis, not a validity-holding analysis.

I'll ground this analysis in the actual cited references before mapping them to the claims.

Obviousness Analysis — US 5,339,258 under 35 U.S.C. § 103

Note on method and scope. Per the task instruction I have worked from the "Prior Art" material on this patent's page — i.e., the examiner-cited reference lists (19 patent citations + 2 non-patent citations) and the specification's own characterizations of that art. I supplemented with live searches only to confirm what two or three of the cited references actually disclose. I do not have the full text of AT 331,539 B, AT 356,943 B, FR 2,208,525 A5, GB 2,001,761 A, US 4,606,498 A, EP 0 222 503 A1, GB 2,187,286 A, WO 90/12306 A1, US 5,237,853 A or US 5,253,533 A. Where a mapping depends on unverified reference content, I say so. Everything below is an invalidity hypothesis, not a legal conclusion.

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1. Contradictions / corrections to the earlier-generated sections

Two items in the previously generated sections need correcting before the § 103 analysis, because the prior-art/family record matters:

1. "No patent family" is wrong. The prior summary states the record shows "Family Members (0)" and only the single US application. A live search of the EPO register/PISE material surfaced EP 0 487 499 A2/A3, application EP 91890288, filed 1991-11-18, claiming priority from AT 237890 A (1990-11-22) — i.e., the European counterpart of the same disclosure ("APPARATUS FOR DETERMINING THE DENSITY OF LIQUIDS AND GASES FROM THE PERIOD OF A SPECIMEN-FILLED RESONATOR"). It lists GB 2 236 591 A (Marconi GEC) and the Langdon Marconi Review article on its own search report. Source: http://data.epo.org/pise-server/rest/collections/lgpi/EP0487499A3.pdf. So there is a family; the Google Patents "Family Applications" widget simply displayed only the US member.

2. US 5,477,726 A is a family member, not merely a "related" patent. It shares the exact priority date (1990-11-22) and inventor entity (Stabinger). Treat it as the same-family sibling (consistent with the fact that it is the first entry in the "Cited By" table). It is therefore not available as prior art against 5,339,258.

Neither correction changes the earlier litigation finding (still none), and the lapsed-2002 status stands.

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2. Framework and the person of ordinary skill

• The application was filed 1992-05-01 and granted 1994-08-16, so pre-AIA § 103 governs. The Graham v. John Deere factors apply, informed by KSR Int'l v. Teleflex (obvious combinations of known elements; predictable results; design incentives and market/technical demands).
• PHOSITA: a person with a bachelor's degree in electrical, mechanical or instrumentation engineering (or applied physics) and 3–5 years' experience designing self-oscillating vibratory instrument loops (vibrating-tube/rod densitometers and viscometers), including analog feedback-loop design (amplifiers, limiters, integrators, phase-shift networks) and microcontroller-based instrument control.
• Effective date: 1990-11-22 for subject-matter purposes. For prior-art date determinations under pre-AIA § 102, US patents/applications get their US filing date as the § 102(e) date (foreign priority does not create a § 102(e) date — In re Hilmer), so I use US filing dates for the US references below.

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3. The cited references, with dates and statutory status

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4. A date problem to flag explicitly (GB 2 236 591 A)

GB 2 236 591 A published 1991-04-10. That is after the 1990-11-22 priority date but more than one year before the 1992-05-01 US filing date. Note also that the EPO's own search report on the family member EP 0 487 499 cites it with the combined "[AP]" code — the "P" signifying a document published between the priority date and the filing date. Indeed the EPO's search report for EP 0 487 499 lists exactly:

[AP] GB 2236591 A 19910410 - MARCONI GEC LTD [GB]
[A] MARCONI REVIEW. Bd. 43, Nr. 218, 1980, GREAT BADDOW GB Seiten 156-175; LANGDON: 'vibratory transducers'

Consequence for a § 103 rejection: whether GB 2 236 591 A is available depends on (a) whether the 1990-11-22 foreign priority date can be relied on to remove it, and (b) whether the § 102(b) one-year window is measured from the US filing date or the priority date, which is a contested point of pre-AIA practice. I cannot resolve that here with confidence, and I flag it rather than assume. The practical workaround — and the reason this does not weaken the analysis — is that the Langdon Marconi Review article (1980) is the same technical teaching, by the same Marconi group, and is unambiguously § 102(b) art with no date problem at all. Any rejection should be anchored on Langdon (1980) with GB 2 236 591 A as corroborating/refining art, not on GB 2 236 591 A alone.

Also flag: the two citations of the Langdon article use slightly different short titles ("Vibratory Process Control Transducers" on the US face vs. "vibratory transducers" in the EP search report). Same volume, issue and page range — treat as one reference, but a rejection should cite the full title as printed.

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5. Claim 1 — element mapping and combinations

Claim 1 (independent) requires: (a) sample-filled oscillator; (b) sensor producing a signal; (c) an oscillation amplifier; (d) an actuator receiving the amplified signal and driving the oscillator; (e) at least one phase-shifting circuit; (f) at least one change-over switch selectively connecting that phase-shifting circuit to the oscillation amplifier to cause a phase shift of the amplified signal; and (g) determining means responsive to the sensor signal for determining density.

5.1 What each primary reference supplies

The only respects in which claim 1 arguably departs from the Kratky base are elements (e)/(f) as a switched, deliberate detuning path, and the express linkage of that detuning to density correction. Everything else is old.

5.2 Combination A (primary) — AT 331,539 B + Langdon (1980) [optionally + GB 2 236 591 A]

Why claim 1 would have been obvious:

1. The problem is admitted in the primary reference itself. The patent's own Background states that where the oscillating body is a clamped tube holding the sample, "the equations (1) and (2) are only valid for non-viscous liquids. A larger period is observed with viscous liquids of a defined density." A reference that identifies the viscosity-induced period error is itself the motivation to fix it. Under KSR, where the primary reference frames the problem, the "motivation" prong is satisfied without any express "combine with X" statement.

2. The solution technique is expressly taught by Langdon/Marconi. The verified Marconi disclosure teaches: (i) comparing the phase between the driving voltage and the detected vibrational movement to determine viscosity; (ii) driving the structure "at successive different frequencies" and at frequencies above and below resonance; and (iii) that for high-viscosity fluids "the resonant frequency and damping constant are derived." That is precisely the operative insight of claim 1 — that exciting the body out of phase with its velocity amplitude de-tunes the resonance by an amount proportional to the damping force, so the detuning is a measurable proxy for viscosity. The patent's own spec states the identical physical principle ("if the phase of the excitation force does not agree with that of the velocity amplitude, the result is a resonance frequency ... which differs from the natural by an amount ... approximately proportional to the size of the damping force").

3. Both are in the same field and address the same failure mode. Kratky/Marconi target vibratory process transducers for density/viscosity of liquids including contaminated and viscous media; the Langdon article is a general review ("Vibratory Process Control Transducers") in the very journal of the Marconi group whose 1989 GB filing is directed to frying oils — i.e., highly viscous, contaminated liquids. A PHOSITA tasked with correcting the Kratky densitometer for viscous samples would naturally consult this literature. KSR expressly approves combining references "designed to address the same problem."

4. Reasonable expectation of success. Both systems are closed-loop, self-oscillating electro-mechanical loops with a drive transducer, a pick-up transducer and an amplifier between them. Introducing a selectable phase-shift network (an integrator, an RC low-pass, or a unity-gain inverter — all expressly named by the patent at col. discussion of Fig. 4: "These circuits can be constituted by low-pass filters, for example") into such a loop to shift the excitation phase is a predictable, routine analog design step, not an unpredictable one. Success in obtaining two measurably different resonance frequencies is expected as a matter of phase-locked-loop physics.

Conclusion on Combination A: claim 1 is prima facie obvious. If, on verification of Kratky's AT 331,539 B text, the detuning/phase-shift integrator path is already a switched branch of the amplifier, claim 1 is arguably anticipated under § 102(b) rather than merely obvious; the claim's "change-over switch" language would then read on the switch that engages Kratky's detuning circuit. I cannot confirm this from the available materials and flag it as the highest-value verification task.

5.3 Combination B — AT 331,539 B + US 5,003,400 A (Lew, "Dual frequency density meter")

Lew is verified as teaching that the natural frequency of flexural vibration of a conduit is a function of the density and viscosity of the contained fluid, and that by using two different natural frequencies (two orthogonal modes of one section, or two sections of the conduit) the fluid term can be eliminated and density obtained as ρ = F(f₁, f₂) (its eq. (9), with constants G, H determined by calibration with two known fluids). This is a direct, express motivation to (i) measure at two distinct resonances and (ii) use the two-frequency pair to remove a viscosity-dependent density error. A PHOSITA applying Lew's two-frequency teaching to the Kratky oscillator, using a switched phase-shift network to force the second frequency, arrives at claim 1.

Note the structural analogy to the patent's own claim 1 + claim 4 + claim 7 architecture (two frequencies stored → density computed). Lew also supplies an independent basis for claim 7.

5.4 Combination C — AT 331,539 B + US 4,524,610 A (Fitzgerald)

Fitzgerald (verified) discloses an in-line tube densitometer/viscometer in which the viscous resistance of the fluid damps the tube's vibration and the damping is quantified (via power to hold constant amplitude) to give a viscosity-density product, while the flexural resonance frequency gives density. It thus teaches the abstract proposition at the heart of the claim — that the same vibrating tube can yield both density and a damping-related quantity, and that the damping must be accounted for. Combined with Kratky, the remaining step (obtain the damping-proxy by switching the excitation phase) is supplied by Langdon/Marconi (§ 5.2) or Lew (§ 5.3).

5.5 Combination D — US 4,838,084 A (Leopold) as base + Langdon/Marconi

US 4,838,084 A is a "Density measuring instrument" by Hans Leopold, a named co-inventor here — so it is directly on point for elements (a)–(d), (g). (I have not verified its internal circuitry; this combination should be confirmed against the reference.) If it discloses a microprocessor-controlled vibratory densitometer loop, it is an even cleaner base than Kratky for claims 2/3/5/6, and the Langdon/Marconi phase-comparison teaching supplies (e)–(f).

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6. Dependent claims 2–10

Weak-link identification: claims 9 and 10 are the only claims whose specific circuit topologies are not shown by any reference in the cited list. A § 103 rejection resting solely on the 19 cited references would be weakest there and would need either (a) an additional secondary reference teaching a selectable inverting/non-inverting amplifier stage, or (b) a well-documented Official Notice of routine circuit design, with the applicant given the chance to traverse.

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7. Objective indicia and the best non-obviousness arguments the patentee could raise

1. Long-felt but unsolved need — cuts against the patentee here. The viscosity-induced period error was expressly recognized in the 1970s Kratky art and re-recognized in the 1980s (Fitzgerald's damping measurement, Lew's two-frequency correction). A need that is known in the art and addressed in the art supports obviousness, not patentability. The patent's asserted advance is a specific circuit arrangement for an already-identified problem, which is precisely the KSR fact pattern.
2. The "ambiguity" argument (Fig. 3) — the strongest argument, and it maps to claim 7. The patent argues the relation between density error and damping constant b is ambiguous in the zero-order mode at high viscosity (damping falls while error saturates), so b alone cannot always correct ρ. If the applicant can show that a PHOSITA would not have expected higher-order-mode damping to resolve that ambiguity, claim 7 gains a genuine non-obviousness foothold. However, US 5,003,400 A (Lew) teaches exactly the "use two modes/two frequencies to eliminate the fluid term" strategy, which undercuts the argument — and the patent's own text concedes the higher-order effect is a consequence of higher resonance frequency, i.e., an expected physical scaling.
3. No unexpected-results showing. The specification discloses no comparative data against the closest art and alleges no unexpected magnitude of benefit; the relationship is presented as quantitative calibration ("A relationship is developed from the experimentally observed relative density measuring error Δρ/ρ and the associated damping constant b"), i.e., routine experimentation.
4. No teaching-away. The cited art is uniformly directed toward improving vibratory density/viscosity measurement; none of it disparages phase-shifted excitation or multi-mode operation.
5. Commercial-success/nexus. Any argument based on the commercial success of the extended family (e.g., Anton Paar's later products) would require proof of nexus to the claimed phase-switching feature, which the previously generated sections do not establish. Treat as unsupported.

Net assessment: Claims 1–6 and 8 are, on the cited record, strong candidates for an obviousness rejection with the primary combination AT 331,539 B + Langdon (1980) [Marconi Review], optionally reinforced by GB 2 236 591 A, US 5,003,400 A and US 4,524,610 A. Claim 7 is defensible-but-contestable. Claims 9 and 10 require art or notice outside the cited list.

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8. Confidence, limitations and next steps

• High confidence: the bibliographic dates, the claim text, and the characterizations of GB 2 236 591 A, US 5,003,400 A, US 4,524,610 A and US 4,926,682 A (verified by live search of the documents themselves); the ep-family existence of EP 0 487 499 A2/A3 and its search report citing GB 2 236 591 A and Langdon.
• Medium/low confidence, flagged: the internal circuitry of AT 331,539 B (whether its "integrators for phase shifting" are already switched into the amplifier), of AT 356,943 B, US 3,910,101 A, FR 2,208,525 A5, US 4,838,084 A, and US 5,237,853 A. My claim-1 mapping for elements (e)/(f) rests mainly on the patent's own description of Kratky, which is the patentee's characterization and should not be taken as an admission of the full reference content.
• Legal point requiring separate analysis: whether GB 2 236 591 A's 1991-04-10 publication date makes it available notwithstanding the 1990-11-22 foreign priority claim. Use Langdon (1980) as the anchor and avoid depending on GB 2 236 591 A alone.
• Recommended verification steps: (1) pull the full text of AT 331,539 B to test whether claim 1 is anticipated rather than obvious; (2) pull US 4,838,084 A (Leopold) to shore up claims 2/3/5/6; (3) search for a pre-1990 reference on selectable inverting/non-inverting op-amp stages to close claims 9–10.

Sources: https://patents.google.com/patent/US5339258/en (authoritative full text); https://patents.google.com/patent/GB2236591A/en; https://patents.google.com/patent/[US4524610A](/patent/US4524610A); https://patents.google.com/patent/[US5005400](/patent/US5005400); https://patents.google.com/patent/US4926682; http://data.epo.org/pise-server/rest/collections/lgpi/EP0487499A3.pdf (EP 0 487 499 A3 search report, listing GB 2 236 591 A as [AP] and Langdon [A]).