DEV-1067: decode an open circuit on gen-2 GSR range 3 as open

[marknolan]

DEV-1067

Problem

SensorADC raises range-3 codes below GSR_UNCAL_LIMIT_RANGE3_SR68 to that limit before calibration, so that an open circuit reads as open. The limit was 1134, which is below the 0.4986 V this decode divides by for the gen-2 front end (code 1134.3 at 1.8 V). So 1134, and every code clamped up to it, decodes to a negative resistance. The nudge turns that into 8 kΩ in auto-range — 125 µS, the highest conductance there is — and 680 kΩ on fixed range 3. An SR68-9 with its electrodes open (DEV-793 dataset B6) reads range-3 codes peaking at 1126–1136.

Fix

The limit is now 1138, the first code above 0.5 V at 1.8 V. That clears this decode's 0.4986 V and the Java driver's 0.5 V alike, and it is the value the Java driver and C# API get in the PRs below. CHANGELOG.md has an entry under [Unreleased].

Tests

The existing clamp test asserted only that a clamped sample decoded like one at the limit. It passed at 1134 because both sides came out at the 8 kΩ floor. It now uses 1138, and two tests are added:

• codes 1134–1138 on range 3 must read ≥ 4.7 MΩ on an SR61-5 and an SR68-9, in auto-range and on fixed range 3
• the limit must be the first code above 0.5 V

Limit	Result
1134	4 tests fail
1138	the suite passes (1892)

typecheck, lint and prettier are clean.

Release

No version bump here. The consoles pick this up at the next vendoring bump or release.

Not changed here

In auto-range the nudge also caps resistance at 4.7 MΩ, so an open circuit now reads 0.213 µS. That is still above the 0.03 µS threshold, so connectivity still says 'Connected'. Java and C# only floor at 8 kΩ in auto-range (ASM-2156). This needs its own change, and the CHANGELOG entry says so.

Sibling PRs (same constant, same ticket)

• Java driver: DEV-1067: decode an open circuit on gen-2 GSR range 3 as open Shimmer-Java-Android-API#305
• C# API: DEV-1067: decode an open circuit on SR68 GSR range 3 as open Shimmer-C-API#205
• ASM_BaseStation, two copies of the C# class: ShimmerResearch/ASM_BaseStation#460

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