US 10557872

I'll run the requested searches, then summarize from the authoritative patent text provided.

Search results on the identifiers you asked for

No authoritative USPTO or CAFC records for 10557872 (or 10,557,872) were returned by the searches. The results were dominated by unrelated IP-office gazettes (INPI Argentina, IP Australia, CIPO, Belgian/French recueils) and unrelated litigation commentary; nothing matched this patent number, its title, or its assignee. Specifically:

• USPTO: no hit. I could not reach PatentCenter/Patent Full-Text directly through the search tool, so I cannot independently verify current fee/assignment status beyond the patent record itself.
• CAFC 2026 dockets: no hit. Nothing indicating any appeal, IPR appeal, or other Federal Circuit activity involving this patent. The only CAFC-related result was an academic article on the court's institutional design, unrelated to this patent.

Conclusion on litigation: Based on available evidence, I found no litigation or CAFC docket activity for US 10557872. State this as "not found," not as a verified negative — I do not have direct docket access here.

My summary below is therefore grounded in the authoritative full patent text you supplied, not in the search results.

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Bibliographic data (per the patent record)

Note on assignee naming: the record lists both "Testo SE and Co KGaA" (original) and "TESTO AG" (current, per the 2016 reassignment entry). I have not auto-corrected these; they are reproduced as listed.

Abstract (as printed)

"In a measuring arrangement (1) for contactless electric current measurement, it is provided to detect a common signal of a measuring coil arrangement (2) and a compensating coil arrangement (3) by a first detection device (4) and to detect a signal from at least one measuring coil (6, 7) of the measuring coil arrangement (2) separately therefrom by a second detection device (5, 23)."

Plain-language overview of the independent claims

The granted claim set has exactly two independent claims: claim 1 and claim 16. Claims 2–15 all depend from claim 1. There is no independent method claim in the displayed claim set, despite the title referencing a "method" — the method is described in the specification but, as shown here, is not separately claimed. (Flagging this as an observation on the claim set as presented.)

Independent claim 1 — compensated measurement plus a separately tapped measuring-coil signal

A contactless current-measurement device with:

1. A measuring coil arrangement containing a first measuring coil (6) and a second measuring coil (7).
2. A compensating coil arrangement where a first compensating coil (11) is connected to one end of the first measuring coil (6), and a second compensating coil (13) is connected to one end of the second measuring coil (7). A third compensating coil (12) is connected to the other end of the first measuring coil (6), and a fourth compensating coil (14) to the other end of the second measuring coil (7).
3. A first detection device (4) that reads the common (net, compensated) signal from the measuring coils and the compensating coils together.
4. A second detection device (5) that reads the first measuring coil's signal separately, i.e., without the compensating coils.
5. An electric conductor receptacle (8), with the two measuring coils sitting on opposite sides (35, 36) of it.

The core inventive hook: the same coil hardware yields two independent measurement variables — a compensated signal (good rejection of external/interference fields) and an uncompensated single-coil signal (useful for plausibility checking, activation, and high-current range switching).

Independent claim 16 — same front end, with a third detection device

Claim 16 repeats the claim-1 structure (two measuring coils on opposite sides of the receptacle, first/second compensating coils at one end of each measuring coil, first detection device for the common signal, second detection device for the first measuring coil alone) but omits the third and fourth compensating coils and instead adds:

• A third detection device (23) that separately detects the signal of the second measuring coil (7), in addition to the second detection device reading the first measuring coil (6).

Purpose: independently reading each measuring coil lets the device distinguish which side an external (non-clamped) conductor is on — the basis for the measuring-error and measuring-range-switching logic described in the spec.

Dependent claims worth noting

• Cl. 2: compensating coils aligned at 45°–135° (spec prefers 80°–100°, most preferably ~90°) to the measuring-coil axes.
• Cl. 3: first and second detection devices each have an amplification member (19, 20).
• Cl. 4: a digital signal processing device connected to each detection device (spec mentions FFT-based processing).
• Cl. 5 / Cl. 6: substantially identical cross-sections, winding densities and/or turns within each coil group.
• Cl. 7: measuring-coil turns exceed assigned compensating-coil turns (spec: measuring coil turns = sum of its compensating coils' turns).
• Cl. 8: measuring and compensating coils arranged in a common mesh (28) feeding the first detection device.
• Cl. 9: winding directions correspond.
• Cl. 10: air coils (coreless).
• Cl. 11–12: fork-shaped/rigid receptacle; mirror-symmetric layout; net magnetic flux sums to zero for a conductor outside the receptacle.
• Cl. 13: measuring error recognition device (31) — compares individual coil signal vs. common signal and issues an error notification when the common signal is less than the individual coil signal (indicates the conductor is outside the receptacle).
• Cl. 14: activation apparatus (32) — auto-wakes the measurement when a stored criterion (threshold, and individual signal not exceeding compensated signal) is met.
• Cl. 15: measuring range switching device (33) — switches from the compensated signal to the uncompensated measuring-coil signal above a threshold (small currents → compensated; large currents → uncompensated).

Specific inconsistencies in the text as presented (not corrected)

Per your instruction to interpret identifiers literally, I flag rather than fix these:

1. Claim 1, fourth compensating coil: reads "connected to an other end of the second measuring coil (7) from the second compensating coil (12)" — but the second compensating coil was defined immediately above as (13). The numeral (12) appears mismatched (and in the spec, 12 is a compensating coil assigned to the first measuring coil 6).
2. Claim 4 recites a "digital signal processing device (19, 20)," but numerals 19 and 20 are the amplification members in the spec; the digital signal processing devices are 21 and 22.

Uncertainty statement

• I have high confidence in the bibliographic data, abstract, and claim analysis above, since these come from the authoritative full patent text you provided.
• I have low confidence / no evidence regarding any USPTO post-grant proceedings (IPR/PGR/reissue), current maintenance-fee status after the 4th-year fee paid 2023-07-25, or any CAFC activity. The searches returned nothing relevant, so treat "no litigation found" as an absence of evidence rather than a verified clean docket.

I'll search for litigation involving US patent 10557872.

Let me try additional searches on litigation databases.

Let me run more targeted searches specific to this patent number.

Litigation Search: US Patent No. 10,557,872

Result: No litigation found

Based on my searches of litigation-covering sources (Unified Patents litigation resources, Justia federal docket records, CourtListener, Dockets.Justia, and general case-reporting databases), I found no litigation involving US Patent No. 10,557,872 ("Measuring arrangement and method for contactless electric current measurement," assigned to Testo SE & Co. KGaA / TESTO AG).

No district court complaints, CAFC appeals, PTAB proceedings (IPR/PGR), or ITC actions asserting or challenging this specific patent appear in the results.

Important caveat — do not misattribute a similar case

My search surfaced a case involving the same patent owner (Testo SE & Co. KGaA and Testo, Inc.) as a defendant:

• Parker-Hannifin Corp. and Parker Intangibles, LLC v. Testo, Inc. and Testo SE & Co. KGaA
• Court: U.S. District Court for the Eastern District of Pennsylvania
• Case No.: 2:22-cv-00135 (Judge Schiller)
• Filed: January 12, 2022
• Status: Ongoing as of the April 24, 2023 opinion (motion to dismiss counterclaims granted in part/denied in part)

This case does NOT involve US 10,557,872. The patents asserted there were US 10,281,183 ("Hose Free Sensor System for Refrigeration Unit") and US 10,739,051 ("Hose Free System for Refrigeration Unit") — unrelated refrigeration/HVAC sensor patents. I am flagging it only to prevent it from being incorrectly listed as litigation over the '872 patent. Per the instruction not to return results for similar numbers, I am excluding it from the litigation list, and provide it here solely as a warning against conflation.

Bottom line

• Known litigation involving US 10,557,872: none identified.
• The patent appears in the record as active (adjustment/expiration listed as 2036-10-16), but there is no evidence of assertion in court or before an agency.

Confidence and limitations

I must be explicit about the limits of this answer: my searches were restricted to publicly indexed web sources and general docket aggregators. Patent litigation can be missed if a case is very recent, sealed, filed under a different patent-number formatting, or not indexed. I could not complete additional verification searches (e.g., a direct Lex Machina/Docket Navigator query or a full PACER/Unified Patents case-list pull for the specific number), so this should be treated as "no litigation found in searched sources" rather than a categorical negative. If you need a definitive litigation clearance, I recommend a paid docket search (Docket Navigator, Lex Machina) on the exact number 10,557,872, and a check of the '872 patent's family members (EP 3 112 883, CN 106645864, DE 10 2015 008 516) in their respective jurisdictions, where parallel assertion activity would be more likely.

I'll verify the structured data and search for any PTAB activity, Federal Circuit appeals, or related proceedings involving this patent.

No PTAB hits. Let me run a few more targeted checks to be sure I'm not missing a recently-filed or differently-indexed proceeding.

PTAB / AIA Trial Analysis — US Patent No. 10,557,872

Patent: Measuring arrangement and method for contactless electric current measurement
Patent Owner: Testo SE & Co. KGaA (assignment to TESTO AG recorded 2016-08-09)
Filing date: 2016-06-29 · Granted: 2020-02-11 · Adjusted expiration: 2036-10-16
Independent claims: 1 and 16 (16 claims total)

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Proceedings overview

Total AIA trial proceedings on this patent: 0. The USPTO Open Data Portal (ODP) structured proceeding list returns no IPR, PGR, or CBM for US 10,557,872 — therefore the breakdown is active: 0 · claims invalidated: 0 · claims sustained: 0 · settled: 0 · institution denied: 0.

The bottom line for a defendant is the inverse of the "hardened patent" scenario: there is no PTAB record at all. No claim of this patent has been tested in an AIA trial, no claim has been canceled, and no Federal Circuit mandate addresses its validity. A defendant today faces an untested patent with all 16 claims intact — and, correspondingly, has a completely clean slate to file a first IPR (no § 325(d) repetition problem, no § 315(e) estoppel, no adverse FWD findings to argue around). The defensive posture is "open field," not "hardened patent," but also not "dead patent."

I performed independent web verification (Google Patents litigation/PTAB links, PTAB E2E, CourtListener, and general docket aggregators) and found no AIA trial proceeding referencing this patent number or any of its family members. I did not find, and am not reporting, any proceeding I could not confirm.

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Proceedings

None to enumerate. There is no proceeding number to report, and I will not invent one. Per the constraint not to fabricate, this section is intentionally empty.

For completeness, here is what the verification did surface, flagged so it is not misread as activity against the '872 patent:

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Strategic summary

Claim status. All claims of US 10,557,872 — claims 1–16, including independents 1 and 16 — are UNTESTED and uncanceled. Because no IPR/PGR was ever instituted, there is no FWD, no certificate canceling claims, and no narrowed claim set. Whatever scope the patent issued with on 2020-02-11 is the scope in force today. Note for claim-charting purposes that independent claim 1 recites the full four-compensating-coil architecture (compensating coils 11/12 on either end of measuring coil 6; coils 13/14 on either end of measuring coil 7) plus first and second measuring coils on opposite sides (35, 36) of the conductor receptacle, whereas independent claim 16 substitutes a third detection device (23) for the fourth compensating coil — i.e., claim 16 covers the three-detector variant. A defendant should treat these as two distinct infringement theories, not one.

Estoppel landscape. There is no estoppel. § 315(e)(1)/(2) estoppel attaches only to a petitioner that obtains an FWD; no FWD exists. Likewise no § 325(d) "same art previously presented" risk has been crystallized by an earlier petitioner, and no § 315(b) one-year bar has run against any party absent prior service of an infringement complaint. Practically: a first-mover IPR petitioner has the widest possible ground set — all of the prior art that appears in the "Patent Citations (11)" list (US 5,012,218; US 5,057,769; US 5,107,212; US 5,617,019; US 2003/0112000; US 2006/0113987; US 7,164,263; US 2010/0207603; US 2014/0210463; EP 2 589 971 A2; CN 103575968 A) is available, plus anything else — and faces no discretionary-denial history on this patent.

Pattern signals. (a) No serial petitioner — there has never been a first petition. (b) The patent owner is an operating company, not an NPE: Testo SE & Co. KGaA is a German test-and-measurement instrument maker. That matters for PTAB strategy, because the "asserted in parallel litigation → discretionary denial" trend and the PTO's 2025 tightening rules cut against institution more heavily in NPE cases; a challenge here would be against a product-practicing patentee. (c) No defensive aggregator (e.g., Unified Patents) appears anywhere in the '872 chain — Unified's IPR filings are public and none reference this patent. (d) Testo's own PTAB footprint is small and fully accounted for (2 IPRs filed, both denied institution on unrelated Parker patents), which reinforces that the '872 patent has simply never been commercially or litigatively important enough to attract a challenge. That is consistent with the litigation summary's finding that the patent has never been asserted.

Caveat on the "absence is a signal" inference. Absence of IPRs is normally a weak-but-real signal that a patent has not been worth attacking — well-asserted patents do eventually attract petitions. Here the patent is only ~6.5 years old as of 2026-09-29 and, per the litigation summary, has never been asserted in any court. So the absence is explained by non-assertion rather than by proven strength. Do not read it as evidence the claims are valid or as evidence they are weak — it is genuinely neutral.

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Recommended next steps

Because no AIA trial exists, this is a "file first, decide later" situation — not a "find the FWD" situation. Concretely:

1. Confirm the null result before relying on it. My verification used public web indexes and docket aggregators. For a definitive negative, run the exact number 10,557,872 through the USPTO PTAB E2E docket system (https://ptacts.uspto.gov/ptacts/) and a paid docket service (Docket Navigator / Lex Machina covering both PTAB and district court). I could not complete a full PACER/PTAB API pull, so treat this as "no proceeding found in searched sources," not a certified-negative.

2. If you are a defendant served with an infringement complaint citing the '872 patent, calendar the § 315(b) one-year bar from service date immediately — it is the single hard deadline that governs whether an IPR/PGR is available at all. There is no prior proceeding that would independently bar you.

3. Treat claim 1 and claim 16 as separate validity targets. Because the claims' architectures diverge (four compensating coils in claim 1 vs. a third detection device in claim 16), a single-reference § 102 theory will rarely cover both; budget for a § 103 combination, and consider whether a first petition should challenge all 16 claims (the patent is small enough that one petition can do so — no need for the multi-petition structure you sometimes see with 60+ claim patents).

4. Prior-art mining should start with the cited references, then look for the fork-clamp / Rogowski / compensated-coil art. The two references the examiner apparently leaned on hardest to distinguish are US 5,505,769 (Sensorlink AC current sensor) and US 7,164,263 (Fieldmetrics current sensor) — both cited with asterisks as examiner-cited art. The distinguishing feature the specification emphasizes is that only the common (compensated) signal was previously detected, and the invention adds a separate detection of an individual measuring coil for plausibility checking, activation, and range switching (spec ¶¶ re: second detection device 5, third detection device 23, measuring error recognition device 31, activation apparatus 32, measuring range switching device 33). Art that teaches or suggests tapping an individual measuring coil in parallel with a compensated sum is the highest-value search target.

5. If an IPR is filed, the statutory clock is fixed: institution decision within 6 months of the PO's preliminary response, and FWD due within 12 months of institution (35 U.S.C. § 316(a)(11)), extendable for good cause. Note that as of the Director's October 16, 2025 memorandum, institution determinations in new AIA trials are made centrally by the Director rather than by the merits panel, and the USPTO's October 2025 proposed rules would (if finalized) bar IPRs against patents that already survived a validity challenge and require § 102/§ 103 venue-limiting stipulations. Because the '872 patent has no prior validity adjudication, it would not fall within the proposed "already survived" bar — but that is a proposal, not final rule, and should be re-verified as of your filing date.

6. If you are the patent owner / a licensee, the takeaway is defensive: your claims are intact and unstained by any adverse PTAB record — an unusual advantage in litigation, and one worth preserving by keeping the patent out of litigation if possible, since a first adverse FWD would be the first chink in the armor.

Sources consulted (all specific opinions/dockets referenced)

• USPTO PTAB E2E — https://ptacts.uspto.gov/ptacts/ (searched; no proceeding for 10,557,872)
• Google Patents, US10557872B2 — https://patents.google.com/patent/US10557872/en (claims, family, citations, legal events)
• CourtListener — https://www.courtlistener.com/ (searched; no '872 appeal or PTAB filing)
• IP Verse / GreyB Testo PTAB tracker — https://ipverse.greyb.com/competitive-analysis/company/testo (source for IPR2023-00685 / IPR2023-00691, institution denied)
• Willkie Farr client alert on the October 16, 2025 Director memorandum and October 15, 2025 proposed rules — https://www.willkie.com/publications/2025/10/ptab-announces-new-institution-policy

Confidence: High that no AIA trial proceeding has been instituted on this patent (corroborated by the ODP structured list plus independent searches). Moderate-high that none has ever been filed; a very recent, sealed, or unindexed petition could in principle have escaped detection, and I flag that rather than paper over it. I have deliberately not attributed any proceeding, FWD, or appeal to this patent.

I'll research the assignment record for US 10557872, starting with the record evidence and targeted searches for the reel/frame and any later transfers.

Let me search for the assignment record details, correspondent, and Testo's corporate history.

Let me try to identify the attorney/agent of record and any Testo AG→Testo SE name-change recording.

Assignment & Ownership Analysis — US 10,557,872

Data-source caveat up front: I could not reach a live Patent Assignment Search / Assignment Center record through the search tool (the queries returned unrelated IP-office gazettes and off-target documents). My timeline below is reconstructed from the Google Patents "Legal Events" tab of the authoritative patent text you supplied, which mirrors the USPTO assignment abstract (reel/frame, conveyance, assignors, assignee, execution and recording dates). The correspondent of record (the attorney/firm who filed the recording) was not retrievable from any source I reached — see the "Repeat correspondent" signal below, which I therefore mark unclear rather than guessing.

Inventors

Pattern check — no unusual signals. All three inventors executed the assignment to TESTO AG (effective 2016-07-22), i.e. the standard inventor→employer assignment taken within weeks of filing (2016-06-29). There is no evidence of inventors departing the assignee, and no second/competing assignment from the inventors to any third party. Inventors remaining with the operating company and assigning to it at filing is the opposite of the "all inventors depart within 12 months → portfolio fire-sale" tell.

Original assignee

Entity on the issued patent: the record lists "Testo SE and Co KGaA" as both the original and current assignee, with the recorded 2016 assignment naming "TESTO AG" as owner (reel 039381/0591). These are the same company across a legal-form change: per Testo's corporate history, the firm converted from Testo AG to Testo SE & Co. KGaA in the summer of 2016 — which brackets the 2016-07-22 assignment execution date almost exactly (see the German/English Wikipedia corporate histories: "Im Sommer 2016 änderte sich die Rechtsform der Firma von Testo AG zu Testo SE & Co. KGaA."). This is a change of legal form, not a transfer to a new owner.

• Primary line of business: Testo is a German manufacturer of portable and stationary measurement instruments (temperature, humidity, flue-gas/emissions analysis, thermal imaging, refrigeration/AC service tools, fine-particle measurement). It describes itself as a "world market leader in portable and stationary measurement solutions," ~3,200–3,900 employees, ~€427–466M revenue, 35–37 subsidiaries (testo.com company page; de.wikipedia "Testo (Unternehmen)").
• Does it ship a product embodying the claims? Testo's product line squarely covers electrical test instruments / clamp meters in the "refrigeration, air-conditioning and environmental technology" and electrical-service portfolio — the natural commercial embodiment of a fork-shaped, coreless, contactless current-measurement clamp. I did not independently retrieve a test/teardown confirming that a specific model (e.g. a Testo current clamp) practices these claims, so treat "ships a practicing product" as highly likely but not item-by-item verified.
• Current status: Operating, privately held (majority owner the Knospe family), NOT acquired, NOT dissolved, NOT in bankruptcy. Leadership transition mid-2025 (Eckhard Kloth as first non-family CEO) confirms an active, ongoing enterprise.

Assignment timeline

• 2016-07-22 (executed) / recorded 2016-08-09 — Reel 039381 / 0591

  • Conveyance: Assignment (Assignment of Assignors' Interest)
  • Assignor: Dirk Gopfert; Nebojsa Nesovic; Jorg Volger (the three inventors)
  • Assignee: TESTO AG, Germany
  • Correspondent: not retrievable from the sources available to me — the Google Patents legal-events entry does not expose the recording correspondent, and the Assignment Center record could not be reached. I am not fabricating a name here.
  • Context: Standard inventor→employer assignment at filing — not an acquisition, fire-sale, securitization, or transfer-to-asserter. This is the only transfer of ownership on record.

• Post-issuance events (no ownership change): 2018-12-07 docketed; 2019-05-13 non-final action; 2019-08-18 response; 2019-09-06 & 2019-10-12 notices of allowance; 2019-11-27 issue-fee verified; 2020-01-22 patent granted; 2023-07-25 maintenance fee paid (4th year, LARGE entity). None of these are assignments.

Finding: The Assignment Center record for this patent, as reflected in the Legal Events, contains one assignment only — the original inventor→employer conveyance. There is no post-issuance assignment, which means the original assignee (Testo, now Testo SE & Co. KGaA) still owns the patent. No record transfers the patent to any LLC, NPE, or defensive aggregator. The AG→SE&Co. KGaA change appears not to have been separately re-recorded as a formal "Change of Name" in the events shown, so the register continues to carry "Testo SE and Co KGaA" as current assignee.

Timeline diagram

timeline
    title Ownership of US 10557872
    2015 : Priority filed in Germany
         : DE 102015008516
    2016 : US application filed
         : Inventors assign to TESTO AG
         : Testo AG becomes Testo SE and Co KGaA
    2020 : Patent issued as US 10557872
    2023 : Fourth-year maintenance fee paid
    2036 : Adjusted expiration

NPE / troll-pattern signals

1. Shell-entity transfer — Not present. The only recorded assignment (Reel 039381/0591) runs into an operating manufacturer (TESTO AG), not out to any "IP/Licensing/Holdings LLC." No single-purpose Delaware/Texas entity appears anywhere in the chain.

2. Known asserter in the chain — Not present. Neither the assignor (inventors) nor the assignee (Testo AG / Testo SE & Co. KGaA) matches any of the listed NPEs (Acacia, Marathon, IV, IPNav, Wi-LAN, Conversant/Mosaid, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, DGC, Spangenberg entities) or any RPX/Unified high-frequency-plaintiff list I can identify. Testo is a ~€450M privately held product manufacturer.

3. Repeat correspondent across the chain — Unclear / no finding. Because there is only one assignment in the chain and I could not retrieve its recording correspondent, there is nothing to establish (or rule out) recurrence. A single appearance would in any event be a weak signal; the tell here requires recurrence, which I cannot demonstrate either way. Recommend a direct Assignment Center pull on reel 039381/0591 to capture the correspondent.

4. Cascading transfers — Not present. One assignment total; no chained LLC-to-LLC hops in any window, let alone <24 months.

5. Pre-litigation transfer — Not present. There is no infringement suit naming this patent (see prior litigation section: none found), and no assignment within 6 months before any hypothetical suit. The lone assignment predates issuance by ~3.5 years and is the routine filing-time conveyance.

6. Bankruptcy fire-sale — Not present. Testo has not filed Chapter 7/11; it is an expanding, profitable operating company (revenue grew from ~€200M in 2011 to ~€427M+ in 2023; new plants opened 2019–2025). No Kodak/Nortel/Polaroid-type event.

7. Privateering — Not present. No transfer from Testo to a third-party assertion vehicle. (Separately, the Parker-Hannifin v. Testo ED-Pa. case found in the prior section casts Testo as a defendant on unrelated refrigeration-sensor patents US 10,281,183 / US 10,739,051 — the inverse of privateering, and it does not involve the '872 patent.)

8. Defensive aggregator (anti-NPE) — Not present. The chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN; it terminates at the original operating manufacturer.

Verdict

Operating-company assertion — not an NPE. The patent's entire recorded ownership history is a single inventor→employer assignment to TESTO AG (executed 2016-07-22, recorded 2016-08-09, Reel 039381/0591), and the current assignee Testo SE & Co. KGaA is the same company after its 2016 legal-form change — a solvent, privately held, ~€427M-revenue measurement-instrument manufacturer that sells electrical test and climate-measurement products. No post-issuance transfer, no shell entity, no chained LLCs, and no known asserter appear anywhere in the record, and no litigation asserting this patent was found; the chain simply never left the operating company, which still owns it.

Verification link: USPTO Assignment Center — https://assignmentcenter.uspto.gov/ (search patent 10,557,872; the one record to confirm is Reel 039381/0591). Note: I was unable to load this record live, so the single-entry finding rests on the Google Patents Legal Events tab of the authoritative patent text rather than a first-hand Assignment Center query — please confirm the reel/frame and, in particular, the correspondent of record directly before relying on it.

I'll research US 10557872 and its cited prior art references. Let me start with searches on the patent itself and its key citations.

Good data so far. Let me research the remaining cited references.

Prior Art Analysis — US 10,557,872 B2

1. Patent identification confirmed

The number 10557872 resolves unambiguously in the USPTO-mirrored records (Google Patents, Justia) to:

• US 10,557,872 B2 — "Measuring arrangement and method for contactless electric current measurement"
• App. 15/196,520; filed 2016-06-29; priority 2015-06-30 (DE 102015008516.6); granted 2020-02-11
• Assignee: Testo SE and Co KGaA / TESTO AG; inventors Gopfert, Nesovic, Volger

This is the same document analyzed in the earlier sections, so I build on that claim map rather than restating it.

2. Methodology and an important framing caveat

The references below are the "References Cited" list printed on the face of the patent (the examiner's Form 892 citation list), as reproduced in the authoritative text. Two things must be stated up front, because they govern how the § 102 analysis should be read:

1. This patent granted with 16 claims, including the two independent claims 1 and 16. Therefore, by definition, none of these cited references alone anticipated the claims as issued — if any had, the claims would not have been allowed in that form. "Potentially anticipates" below must be read as "is relevant to / could be argued against claim X in an invalidity challenge," not "was found to anticipate."
2. Because the priority date is 2015-06-30 (post-AIA), the governing provision is 35 U.S.C. § 102(a)(1) (patented, described in a printed publication, in public use, etc., before the effective filing date) and § 102(a)(2) (earlier-filed published U.S. applications), not the pre-AIA § 102(a)/(b)/(e) subsections. All cited references published well before 2015, so each qualifies as § 102(a)(1) art at minimum.

Search limitation (honest disclosure): I confirmed the citation list and retrieved substantive full text for several references, but I was unable to complete full-text retrieval for every reference before hitting my search-step limit. Descriptions of US 2003/0112000 A1, US 2006/0113987 A1, US 7,164,263 B2, EP 2 589 971 A2, CN 103575968 A, US 2014/0210463 A1, and WO 2008/145813 A1 are therefore of lower confidence and are flagged as such. Where the German counterpart's specification (DE 102015008516 B4, which I did retrieve) expressly discusses a reference, I use that discussion as strong corroboration.

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3. Reference-by-reference analysis

Tier 1 — Most relevant (closest to the claimed architecture)

(1) US 5,057,769 A — "AC current sensor"

• Assignee: Sensorlink Corporation | Priority: 1989-07-27 | Grant: 1991-10-15
• Description: A sensor with a skeleton board defining a "measuring recess" for the conductor, a main coil with a fixed gap, and a pair of compensating coils. The main coil and compensating coils are electrically connected in series; amplifier means amplify the combined output. Claim 9 recites that the sum of the total area of turns of the compensating coils is approximately equal to the total area of turns the missing main-coil portion would have had across the gap. Claim 27 covers compensating/trimming the relative contribution of main vs. compensating coils.
• Why it is the closest art: The applicant's own German specification expressly identifies US 5,057,769 A as a known arrangement: "a substantially C-shaped measuring coil, at whose ends a compensating coil is arranged in each case" (DE 102015008516 B4, ¶[0006]), and criticizes it because "error states cannot always be unambiguously determined and assigned, e.g. whether or on which side the conductor to be measured lies outside the measuring coils." That is precisely the problem US 10,557,872 addresses via its second/third detection devices.
• Potentially relevant to: Claim 1 (measuring-coil + compensating-coil arrangement with a common detected signal), claim 8 (coils in a common series mesh), claim 9 (corresponding winding directions), claim 3 (amplification members). Its forked/recess structure also speaks to claim 11.
• Confidence: High (full text retrieved).

(2) US 2010/0207603 A1 — "Ammeter with improved current sensing"

• Inventor: William J. McNulty | Priority: 2009-02-18 | Publication: 2010-08-19
• Description: Again per the patent's own DE counterpart (¶[0007]): a configuration "in which, however, there are not a C-shaped coil but rather a plurality of measuring coils arranged in a C shape and connected to one another. In addition to the compensating coils arranged at the ends of the C shape, a compensating coil is in each case also arranged approximately in the middle of the legs." The DE spec says this improves error-state detection/location but is "quite complicated overall."
• Why it is highly relevant: This is the reference that most closely pre-dates the multiple measuring coils each with assigned compensating coils, i.e., the structural core of independent claim 1 (first and second measuring coils, each with compensating coils at its ends) and the dual-independent-coil idea behind claim 16.
• Potentially relevant to: Claim 1, claim 7 (turn-count relationships between measuring and compensating coils), claim 16. Its "locating which side the fault is on" purpose maps directly onto the measuring-error-recognition concept of claim 13 (though claim 13 adds the specific "common signal less than individual-coil signal" comparison logic).
• Confidence: High for the structural characterization (corroborated by the applicant's own admission in the DE spec); medium for exact claim wording (I did not retrieve the full US text).

(3) US 5,012,218 A — "Device for measuring an electric current using a solenoid with regular pitch in the form of a torus"

• Assignee: Centre National De La Recherche Scientifique | Priority: 1984-02-06 | Grant: 1991-04-30 | Inventors Haug, He, Hahn
• Description: A toric, core-wound solenoid with a gap, plus compensation coils serially connected at the solenoid ends. The stated purpose of the compensation coils is to make the coefficient of mutual induction "constant inside the solenoid and zero outside" — i.e., to cancel the effect of currents outside the sensing region.
• Why relevant: It is the classic "compensation coil to null external fields" reference and is directly on point for the flux-sum-equals-zero for an external conductor feature.
• Potentially relevant to: Claim 12 (mirror symmetry + flux sum = zero for a conductor outside the receptacle), claim 11 (receptacle), and, because it discloses a coreless/regular-pitch solenoid concept, it is background for claim 10 (air coils). Note it uses a core, so it does not by itself disclose the coreless claimed arrangement.
• Confidence: High (full text retrieved).

(4) US 5,617,019 A — "Inductive measuring device for measuring alternating current components superposed to a high direct current"

• Assignee: Liaisons Electroniques-Mecaniques LEM S.A. | Priority: 1995-02-23 | Grant: 1997-04-01
• Description: A magnetic circuit with two air-gaps around the conductor and two substantially identical measuring coils; an adding circuit sums the voltages induced in the two coils, feeding an integrator. Adjustable voltage dividers/capacitors are tuned so that, under an external (parasitic) field, the sum of the two opposite-phase voltages becomes zero — rendering the device "practically entirely immune against parasitic magnetic fields."
• Potentially relevant to: Claim 8 (coils combined in a mesh / voltages physically added before detection), claim 9 (corresponding winding directions), and — as the "sum to zero for external fields" teaching — claim 12. The two-coil addition concept also touches claim 3 (amplification/addressing).
• Confidence: High (full text retrieved).

Tier 2 — Relevant for specific sub-features

(5) EP 2 589 971 A2 — "Proximity electric current sensing device and method"

• Assignee: Industrial Technology Research Institute | Priority: 2011-11-02 | Publication: 2013-05-08
• Description: A proximity/non-contact current-sensing device and method (title-level info only; full text not retrieved).
• Potentially relevant to: Background for the general contactless-measurement concept and possibly claim 11/12 (rigid receptacle geometry). Lower confidence.
• Confidence: Low–medium.

(6) US 5,107,212 A — "Measuring arrangement having axially and radially offset sensor coils for contactless determination of rotation angle"

• Assignee: Robert Bosch GmbH | Priority: 1989-01-20 | Grant: 1992-04-21 | Inventors Dobler, Hachtel
• Description: Not a current sensor — it measures rotation angle using two wire coils on a coil body, offset both axially and radially (by 180°), with a damping "measuring part" whose overlap with the coils changes with rotation, changing the coils' AC resistance. I retrieved the full text and it is squarely an angular-position/eddy-current sensing arrangement.
• Why it appears here: It was almost certainly cited for a structural sub-feature — e.g., the concept of two coils offset/arranged on a common body — not for current-measurement substance.
• Potentially relevant to: At most claim 6 (two measuring coils with substantially identical construction) or the general "two-coil" idea. It is not good § 102 art against claims 1 or 16 because it lacks a compensating-coil arrangement, a common detected signal, or a conductor receptacle.
• Confidence: High (full text retrieved).

(7) US 2003/0112000 A1 — "Current measurement device"

• Inventor: Thomas Sorenson Jr. | Priority: 2000-04-17 | Publication: 2003-06-19
• Description: A current-measurement device (title-level; full text not retrieved).
• Potentially relevant to: General current-measurement background; possibly claims 3/4 (signal handling) or claim 11 (receptacle). Lower confidence — I cannot responsibly assign a specific anticipated claim.
• Confidence: Low.

(8) US 2006/0113987 A1 — "Apparatus for measuring an a.c. current in a cable"

• Assignee: Airbus Deutschland GmbH | Priority: 2003-03-27 | Publication: 2006-06-01
• Description: Apparatus for measuring AC current in a cable (title-level; full text not retrieved). Marked as an examiner citation.
• Potentially relevant to: General contactless/clamp-type AC current measurement; possibly claim 10 (air coils) or claim 11. Lower confidence.
• Confidence: Low.

(9) US 7,164,263 B2 — "Current sensor"

• Assignee: Fieldmetrics, Inc. | Priority: 2004-01-16 | Grant: 2007-01-16
• Description: A current sensor (title-level; full text not retrieved). Marked as an examiner citation.
• Potentially relevant to: Current-sensor structural background; possibly claims 5/6 (identical coil parameters). Lower confidence.
• Confidence: Low.

(10) US 2014/0210463 A1 — "Current sensor and printed circuit board for this sensor"

• Assignee: Commissariat à l'énergie atomique et aux énergies alternatives (CEA) | Priority: 2011-09-07 | Publication: 2014-07-31
• Description: A current sensor realized on a PCB (title-level; full text not retrieved). Marked as an examiner citation.
• Potentially relevant to: Coil/PCB integration and possibly claim 10 (air coils / coreless) and claim 12 (symmetric winding layout). Lower confidence.
• Confidence: Low.

(11) CN 103575968 A — "Non-contact direct current detection device"

• Assignee: Xi'an University of Arts and Science (西安文理学院) | Priority: 2013-10-15 | Publication: 2014-02-12
• Description: Non-contact DC detection device (title-level; full text not retrieved). Chinese-language art.
• Potentially relevant to: General non-contact current detection / claim 11. Lower confidence.
• Confidence: Low.

Non-patent citation

(12) WO 2008/145813 A1 — Verho, Jarmo; Magnasense Oy — "Device and coil arrangement for measuring magnetic particles and corresponding method"

• Publication: 2008-12-04 | Priority: 2007-05-25 | Class G01N27/72
• Description: A coil arrangement for measuring magnetic particles (not electric current). It appears in the record as a Non-Patent Citation, listed with the family of "Family Cites Families."
• Potentially relevant to: At most the coil-arrangement geometry generally. It is not material § 102 art for the current-measurement claims. Its inclusion appears to be a formal/USPTOIDS item rather than substantive current-measurement prior art.
• Confidence: Medium (title/classification confirmed; full text not retrieved).

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4. Consolidated relevance map

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5. Overall assessment

• Closest single reference: US 5,057,769 A (Sensorlink). It discloses the fundamental "measuring coil + pair of compensating coils, series-connected, common output, recess for the conductor" architecture, and it is the very reference the applicant's own German specification singles out as the starting point. However, it lacks the second (and third) detection device that separately taps the individual measuring coil(s) — which is the actual point of novelty recited in independent claims 1 and 16. So US 5,057,769 A is strong art against the coil arrangement limitations but does not, by itself, anticipate claims 1 or 16.
• Second most relevant: US 2010/0207603 A1 (McNulty) — the closest art for the plural measuring coils each with compensating coils structure underlying claim 1 and claim 16.
• Best art for the "cancel external fields" limitation (claims 12): US 5,012,218 A and US 5,617,019 A.
• Likely-not-substantive citations: US 5,107,212 A (rotation-angle sensor, not current) and WO 2008/145813 A1 (magnetic-particle measurement) were cited for coil-arrangement/formal reasons, not for current-measurement substance.

Bottom line: The strongest potential § 102 arguments run against the dependent structural claims (notably 8, 9, 12 and the coil-turn relationships in 5/6/7), where the cited references are individually on point. For independent claims 1 and 16, no single cited reference appears to disclose the dual-detection feature (separately and simultaneously detecting the individual measuring-coil signal alongside the common compensated signal), so a validity challenge would more plausibly proceed under § 103 by combining, e.g., US 5,057,769 A or US 2010/0207603 A (coil/compensation architecture) with a signal-processing/plausibility-check reference — rather than on § 102 anticipation.

Confidence: high for the Tier-1 references (full text retrieved and, in two cases, corroborated by the applicant's own DE specification); low for the Tier-2 references whose full texts I could not retrieve — those descriptions are title-level only and should be verified against the actual documents (e.g., via USPTO PatentCenter or Espacenet) before being relied upon in any validity opinion.

I'll ground this analysis in the actual cited references before building the § 103 combinations. Let me pull details on the key prior-art documents.

Good — the Sensorlink and CNRS references are highly material. Let me pull the remaining cited references.

Obviousness Analysis — US 10,557,872 B2 under 35 U.S.C. § 103

This section assumes and builds on the Patent Summary, Litigation Summary, and PTAB Analysis already generated. It does not repeat the bibliographic table or claim-overview already given. Where those sections flagged textual inconsistencies (the claim-1 numeral mismatch at "second compensating coil (12)"; the claim-4 "digital signal processing device (19, 20)" numeral mislabel), that flagging still stands and I do not re-argue it here.

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1. Analytical framework and level of ordinary skill

Governing standard. Obviousness asks whether the claimed subject matter as a whole would have been obvious to a person having ordinary skill in the art (POSITA) at the effective filing date — here 30 June 2015 (DE 10 2015 008 516.6). The Graham v. John Deere factors apply: scope/content of the prior art, differences between the prior art and the claims, the level of ordinary skill, and objective evidence of non-obviousness. Under KSR Int'l v. Teleflex, a claim is obvious not only when the prior art expressly teaches the combination, but also when it would have been "the predictable use of prior art elements according to their established functions," or a "simple substitution of one known element for another," or an "obvious to try" variation on a finite number of identified, predictable solutions.

POSITA profile. A person having ordinary skill here would hold a bachelor's degree in electrical engineering (or equivalent) with roughly 2–4 years of experience designing inductive/coil-based current sensors, including Rogowski coils, current transformers, and compensated air-coil clamps, and would be familiar with the source–load field structure of a conductor, the concept of Gauss/line-integral sensing, common-mode rejection of external magnetic fields, and routine signal-conditioning (amplification, filtering, FFT, auto-ranging). Coil geometry, winding density, turns ratios, and orthogonal/angular placement of auxiliary (compensating) coils are all within ordinary design skill.

Critical admission in the specification. The '872 specification itself states: "Coil arrangements which deviate herefrom and which have compensating coils for compensating interference fields are also known. In these arrangements, a common signal induced in the measuring coil and in an assigned compensating coil is detected and evaluated." This is an applicant admission that the entire "measuring coil + compensating coil → common signal" architecture — the heart of claim 1's first detection device 4 — was already known. Under In re Constant / ACS Hospital Systems v. Montefiore, such admissions are treated as prior art and limit what the applicant can claim as new. The patent's own framing of the inventive contribution is narrow: "a signal of at least one measuring coil of the measuring coil arrangement is detectable by a second detection device" (Summary). The § 103 question therefore collapses to whether separately tapping an individual measuring coil, in parallel with the compensated common signal, would have been obvious.

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2. Key claim limitations and their constructions

Claim 16 substitutes a third detection device (23) for the second pair of "bookend" compensating coils (L3) — i.e., claim 16 = L1, L2, L4, L5, L6 plus a third detection device reading coil 7 alone.

The only genuinely differentiating limitations across both independent claims are L5 (tapping coil 6 alone) and, for claim 16, its third detection device counterpart (tapping coil 7 alone).

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3. The cited prior art and what each reference actually discloses

The record's prior-art citations (11 references) plus the Verho/Magnasense non-patent citation supply the universe. I have verified the disclosures of the most material references against their full texts; for the remainder I flag limited confidence in §8.

3.1 US 5,057,769 A — Sensorlink, "AC current sensor" (1991-10-15) — the primary reference

(Google Patents)

• C-shaped main coil (14) with a fixed gap, defining a measuring recess (30) into which the conductor is placed ("AC current carrying conductor is located within the skeleton board's measuring recess 30 while the measurement is made").
• A pair of compensating coils (16, 18) mounted on coil blocks at the two ends (42, 44) of the main coil — i.e., a compensation coil at each end of the measuring coil.
• Series connection of main coil and compensating coils ("said main coil and said compensating coils are electrically connected in series with each other" — claims 8, 10–17).
• Amplifier means producing "an output measuring voltage which is a function of said AC current," with gain varying inversely with frequency (claim 18).
• Balancing means for "selectively adjusting the amount said voltages in said main coil and in said compensating coils are amplified… with respect to each other, to enable said amplifier means to compensate for undesirable differences in said main coil and in said compensating coils" (claim 27).
• Turns/area relationship: "the sum of the total area of turns of said compensating coil wires is at least generally equal to the total area of turns of said main coil wire said main coil missing portion would have had" (claim 9).

Relevance: US 5,057,769 discloses L2/L3 (compensation coils at both ends of a measuring coil), L4 (common series output), the amplifier, the fork/recess geometry (L6, in part), and the turns-balance relationship of dependent claim 7. The patentee's own admission quoted in §1 almost certainly describes this class of device.

3.2 US 5,012,218 A — CNRS (1991-04-30) — end-mounted compensating coils

(Google Patents)

• Toric solenoid interrupted by a gap; "a first compensation coil serially connected to said first end of the solenoid, said first coil overlying the first end of the solenoid" (claim 1) and, optionally, "a second compensation coil serially connected to said second end" (claim 2).
• Explicitly states the purpose: "thanks to the provision of the or each compensation coil, the coefficient of mutual induction … follows a law of variation … very close to the ideal law according to which this coefficient of mutual induction has a constant value inside the solenoid and a zero value outside the solenoid."
• The reference expressly notes the gap creates a detrimental non-zero external coupling ("for currents normally outside the solenoid 1, there is a non-zero coefficient M1, which is detrimental, as currents remote from the gap are thus measured") and cures it with the end compensation coils.
• States the device "may be used as clip forming intensity sensor and remaining permanently open."

Relevance: Directly supplies L2/L3 (compensation coils serially at both ends of a measuring coil) and the functional rationale the '872 relies on — driving external-field coupling to zero (claim 12's "sum of the magnetic flux … equals zero"). US 5,012,218 also teaches toward, not away from, the invention.

3.3 US 5,617,019 A — LEM (1997-04-01) — two measuring coils on opposite sides; summed; individual taps

(Google Patents)

• Magnetic circuit "substantially symmetrical with respect to at least one cross-sectional plane" having "two air-gaps of same dimensions formed on either side of said plane of symmetry."
• "Two substantially identical measuring coils (7, 8)" arranged inside the two air-gaps — i.e., on mutually opposite sides of the conductor (L6) — connected in series "such that the voltages induced … add up" (adding means).
• Crucially, "Each coil is connected in parallel with a respective voltage divider 12, 13 and 14, 15" — so the individual coil voltage across each coil is separately accessible, and one divider is adjustable "so that in the presence of an outer alternating magnetic field, the voltages of opposite phases … can be adjusted so that the sum thereof becomes zero."
• Includes an integrating circuit (10), an op-amp (21), and a band-pass filter (11).

Relevance: This is the second pillar. It supplies L1 (two measuring coils), L6 (opposite sides of the conductor), the summing function of L4, and — importantly for the inventive delta — it establishes that the individual coil signals are already separately available and are already used to null external fields. It also supplies the signal-chain limitations (filtering/integration) relevant to dependent claim 4.

3.4 EP 2 589 971 A2 — ITRI (2013-05-08) — multiple sensing units + comparison for position/installation error

(Google Patents; INPI record)

• Main body with a hole (111) for a conducting wire, and first/second/third sensing units (140, 150, 160) "adjacent to a first/second/third side of the conducting wire" — sensing the magnetic flux on multiple sides.
• A processing unit with comparing units (610, 620) that receive and compare the individual flux signals to determine the wire's position/installation and then compute current.
• Explicit problem statement: "existing proximity electric current sensors mostly have a problem of big measurement error caused by installation position."

Relevance: Supplies the concept that the '872 uses its second/third detection devices for — determining whether the conductor is properly seated / where it is, by comparing individual coil outputs. This is the closest art to dependent claim 13 (measuring-error recognition) and to claim 16's dual-tap architecture.

3.5 US 7,164,263 B2 — Fieldmetrics (2007-01-16) — two sensor modalities/one head; range coverage

(Google Patents; OSTI record)

• Clamp-on current sensor using a plurality of magnetic field sensors around the conductor, "substantially immune to … conductor position, nearby current carrying conductors."
• Its prior-art review expressly discusses Karrer et al., US 6,366,076 — "the use of a Rogowski coil together with a magnetic field point sensor such as a Hall sensor to create a current sensor with a wide bandwidth capability… the point sensor is used to measure DC and low frequency currents, while the Rogowski coil provides sensitive measurements of high frequency currents."

Relevance: Establishes that deriving two independent measurement variables from one sensing head, for different measurement regimes, was known, which undergirds the motivation for the '872's second detection device (used, per the spec, for range switching and plausibility). Supplies the motivation for dependent claim 15 (range switching).

3.6 The remaining cited/considered art

• US 5,107,212 A (Bosch) — "sensor coils axially and radially offset," used for contactless position/angle determination. Relevant to dependent claim 2's angular offset (45°–135°) and to the general practice of placing auxiliary coils at a non-parallel orientation. I did not retrieve full text; treat with the caution in §8.
• US 2006/0113987 A1 (Airbus) — "apparatus for measuring an A.C. current in a cable." Full text not retrieved.
• US 2010/0207603 A1 (McNulty) — "ammeter with improved current sensing." Full text not retrieved.
• US 2014/0210463 A1 (CEA) — "current sensor and printed circuit board for this sensor" (coil-based). Full text not retrieved.
• CN 103575968 A — "non-contact direct current detection device." Full text not retrieved.
• US 2003/0112000 A1 (Sorenson) — "current measurement device." Full text not retrieved.
• WO 2008/145813 A1 (Verho, Magnasense Oy) — coil arrangement for measuring magnetic particles; listed in the record as a non-patent citation only. Adjacent field, limited relevance.
• US 5,617,019's family — EP 0 392 439 A1 / CH 679 527 A5 (LEM) disclose a Hall-cell-plus-measuring-winding device in which "un circuit de sécurité, agencé pour détecter le dépassement d'au moins un seuil de la tension de mesure … et pour fournir un signal de défaut lors d'un tel dépassement" — i.e., a threshold-exceeding defect/threshold signal. This is relevant to dependent claims 14 and 15, but is a family member, not the reference itself, so I attribute it as LEM-family art rather than to US 5,617,019 proper.

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4. Independent claim 1 — obviousness

Primary combination: US 5,057,769 (Sensorlink) + US 5,617,019 (LEM), optionally further in view of US 5,012,218 (CNRS).

4.1 Element-by-element mapping

Conclusion for claim 1: every limitation is disclosed in the combination, and the only element not explicitly presented as an independent measurement channel (L5) is nonetheless structurally present in US 5,617,019 as separately accessible coil voltages.

4.2 Motivation to combine (KSR rationales)

1. Same field, same problem. All three references are coil-based, non-invasive AC current sensors addressing the same problem the '872 states — rejection of magnetic fields external to the conductor being measured (US 5,057,769 compensates imbalance; US 5,012,218 explicitly drives external mutual inductance "to zero"; US 5,617,019 nulls "parasitic outer magnetic fields"). A POSITA optimizing an open/fork clamp sensor for external-field immunity would consult exactly this art.

2. Simple substitution / predictable use of known elements (KSR). US 5,057,769 already places a compensating coil at each end of a measuring coil; US 5,617,019 already places two identical measuring coils symmetrically about a conductor. Combining them — a symmetric pair of compensated measuring coils — is the predictable use of each element according to its established function. Duplicating US 5,057,769's comp-coil pair for a second, mirrored measuring coil requires no new principle.

3. Improvement of a known technique at the time of filing. US 5,012,218 expressly recognizes that the gap in a toroidal/open sensor produces a detrimental non-zero external coupling and cures it with end compensation coils; the '872's four-comp-coil arrangement is a straightforward extension of that cure to a two-coil (two-gap) head.

4. The patentee's own admission. The specification concedes that "a common signal induced in the measuring coil and in an assigned compensating coil is detected and evaluated" is known. That admission removes L2–L4 from the novelty calculus and leaves L5 as the sole point of departure.

5. Two-variable sensing was known to be desirable. US 7,164,263's discussion of the Karrer Rogowski+Hall combination shows that using one sensor head to produce two independent measurement variables (for different ranges/regimes) was an established technique with a known benefit. That supplies motivation for the second detection device, and the spec's own stated benefits (plausibility check, activation, range switching) are the ordinary, predictable uses of a second signal.

4.3 Alternative / secondary combinations for claim 1

• US 5,057,769 + US 5,012,218 + US 5,617,019 — the strongest three-reference combination; adds the "both ends" bookend compensation explicitly and the filter/integrator signal chain.
• US 5,057,769 + US 5,617,019 + EP 2 589 971 A2 — substitutes ITRI's per-side sensing units (each with its own signal path and a comparing unit) for the L5 tap, giving an even cleaner teaching of "separate detection device per coil."
• US 5,617,019 + US 5,012,218 + EP 2 589 971 A2 — uses LEM as the base structure (twin coils on opposite sides of a conductor) and CNRS/ITRI for the compensating-coil and separate-detection features.

Argument the patentee will make (and why it likely fails): The patentee will argue that none of the cited art evaluates an uncompensated single-coil signal as an independent measurement variable — in US 5,617,019 the individual coil taps exist only to null the sum. Under KSR, this is an argument that the prior art used a known structure for a different-but-related purpose; it does not defeat obviousness where the new use is a predictable one. The Federal Circuit's KSR "predictable use of prior art elements according to their established functions" rationale squarely applies: the established function of the individual coil signal is to represent the local field at that coil; using it as a separate measurement channel (to sense position, detect mis-seating, or cover a high-current range) is that function, unchanged.

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5. Independent claim 16 — obviousness

Claim 16 replaces the third and fourth compensating coils of claim 1 with a third detection device (23) that separately detects the signal of the second measuring coil (7).

Combination: US 5,057,769 + US 5,617,019 + EP 2 589 971 A2.

• L1/L6 (twin coils on opposite sides): US 5,617,019 (coils 7, 8 in the two air gaps either side of the conductor).
• L2 (comp. coil at one end of each measuring coil): US 5,057,769 (pair of comp. coils at the coil ends) and US 5,012,218 (comp. coil serially at the first end).
• L4 (common signal of measuring + comp. coils): US 5,617,019's adding means; US 5,057,769's series output.
• L5 + third detection device (separate reading of coil 6 and coil 7): EP 2 589 971 A2 — independent sensing units (140/150/160 or 462/464/466/468), each sensing a different side of the conductor, each with its own path to a processing unit that compares the individual fluxes. This is the most direct teaching of a pair of separate coil-detection channels. US 5,617,019's per-coil voltage dividers provide independent corroboration.

Motivation. EP 2 589 971 A2 states the very problem claim 16's third detection device solves — measurement error from conductor installation position — and solves it by comparing the outputs of independent sensing units. A POSITA seeking to distinguish the side on which an external conductor sits, or to verify that the conductor is correctly seated in the receptacle (the '872's stated purpose), would be led directly to ITRI's multi-unit/compare architecture and would combine it with the compensated coil head of US 5,057,769 / US 5,617,019. The result — read each measuring coil separately, and still read the compensated sum — is a predictable combination of known elements with known functions.

Note on the two-claim divergence. Because claim 1 and claim 16 differ in architecture (four-comp-coil "bookend" vs. third detection device), a single rejection theory need not cover both; two distinct § 103 rejections are appropriate. Cross-family check: the Chinese counterpart's granted claim 1 (as published in CN 10 664 5864 B) omits the third/fourth compensating coils and recites the first/second compensating coils only — consistent with the U.S. claim 16 branch — while the U.S. claim 1 folds in the four-comp-coil architecture.

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6. Dependent claims 2–15 (all depend from claim 1)

Overall: claims 3, 8, 9, and 12 read on the cited art almost element-for-element; claims 2 and 13 are the most defensible. The strongest dependent-claim non-obviousness argument is likely claim 2 (the 45°–135° angular orientation), because the cited art's auxiliary coils are predominantly in-line/overlying — but even there, the range is broad and the specification concedes the effect "can be achieved in an ever improved manner, the more the angle approaches 90°," i.e., a monotonic tuning parameter, which is the classic In re Boesch/Aller result-effective-variable scenario.

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7. Anticipation overlap (§ 102) worth flagging

Independent claim 1 as a whole is not anticipated by any single cited reference (none discloses four compensating coils across two measuring coils plus a second detection device). However, several dependent claims are arguably anticipated rather than merely obvious:

• Claim 8 (common series mesh) — US 5,057,769 claims 8/10–17 verbatim.
• Claim 3 (amplification member) — US 5,057,769 claim 18.
• Claim 12 (mirror symmetry / net-zero external flux) — US 5,617,019, whose stated design goal is exactly that the summed coil voltage carry "no components due to the outer field."

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8. Counter-considerations and objective evidence

1. Family prosecution history cuts both ways. The listed non-patent citations show a Chinese Office Action dated 2019-07-31 in CN 201610824343.9, and the CN examiner's "对比文件" list includes EP 2 589 971 A2, US 5,057,769 A, US 5,617,019 A, US 2003/0112000 A1, US 2010/0207603 A1, CN 103575968 A — i.e., the same references that form my combinations were considered, and the CN application still granted (CN 10 664 5864 B, 2020-10-16). The patentee will (and should) argue that examiners who considered this exact art still allowed the family. Rebuttal: (a) a foreign examiner's allowance is not binding on a U.S. § 103 analysis; (b) the CN claim set differs materially from the U.S. claims (see §5 note); (c) the CN Office Action of July 2019 apparently did not result in substantive narrowing of the granted CN claim 1, suggesting the cited art was distinguished on scope, not on the merits of the inventive delta. Without the full text of the 2019 Office Action and the applicant's response, I cannot say which limitations the CN examiner relied on — and I will not speculate.

2. No objective indicia on this record. There is no evidence of commercial success tied to the claimed feature, no copying, no unexpected results, no industry praise, and no long-felt-but-unmet need in the material provided. Significantly, the Litigation Summary found the patent has never been asserted, and the PTAB Analysis found no AIA trial ever filed — so there is no adverse validity adjudication to weigh and no nexus evidence from litigation. This means the § 103 analysis proceeds on the prior art alone, with no Graham factor-four counterweight.

3. No teaching away. The closest references teach toward the invention. US 5,012,218 identifies the open-gap external-coupling problem and cures it with end compensation coils; US 5,057,769's balancing means and US 5,617,019's adjustable dividers are express invitations to use the individual coil signals to reject external fields. I found no reference that criticizes or discourages separate detection of an individual measuring coil.

4. A colorable non-obviousness story exists but is narrow. The patentee can argue that the cited art uniformly evaluates only the compensated sum, so a POSITA would not have thought to add a standalone, uncompensated measurement channel — and that the spec's three uses (plausibility check, auto-activation, range switching) are non-obvious applications. That is the best argument available. It is weakened by (i) the applicant's own admission that common-signal evaluation was known, and (ii) US 7,164,263, which shows that producing two independent measurement variables from a single clamp-type head was a recognized technique with a recognized benefit.

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9. Bottom line

The single most vulnerable feature of the patent is that its own specification concedes the compensated "common signal" architecture was known, leaving only the second (separate) detection device as the asserted point of novelty — and the art shows that individual coil signals were already separately available (US 5,617,019) and that independent multi-side detection with comparison was already used to solve the installation-position problem (EP 2 589 971 A2).

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10. Confidence and limitations (explicit)

• High confidence in the disclosures of US 5,057,769, US 5,012,218, US 5,617,019, EP 2 589 971 A2, and US 7,164,263 — verified against full text/claim text retrieved during this analysis, with URLs above.
• Low confidence / unverified for US 5,107,212 A, US 2006/0113987 A1, US 2010/0207603 A1, US 2014/0210463 A1, CN 103575968 A, US 2003/0112000 A1, and WO 2008/145813 A1 — I could not retrieve their full texts before exhausting my search budget. My categorization of them is based on title/class and should be verified before any of them is relied upon in a rejection, particularly for claim 2 (which leans on US 5,107,212).
• Attribution caution: the "signal de défaut" threshold teaching in §3.6/claim 14 belongs to the LEM family (EP 0 392 439 A1 / CH 679 527 A5), not to US 5,617,019 itself. Do not attribute it to US 5,617,019 without checking that reference's own disclosure.
• I could not obtain the text of the 2019-07-31 Chinese Office Action or the applicant's response; any inference about what the CN examiner actually objected to is speculative, and I have not drawn one.
• This is a technical § 103 assessment from the face of the record, not a legal opinion on validity; a formal invalidity opinion would require full document discovery, claim-construction analysis under Phillips, and confirmation of the priority-date prior art.