Ingress path and electrical contact exposure

Draw the real wetted boundary through the sensor

Harsh-media review begins by colouring every surface that liquid, vapor, condensate or particles can reach. Include the passive track, moving opening, terminal faces, lead interfaces, housing seams, vents and cavities. Then draw the dry boundary protecting wiring or electronics. A label such as sealed does not reveal the path. Capillary gaps can follow conductors, pressure cycling can move liquid across a joint, and a vent can exchange contaminated air. The circuit consequence depends on which nodes a path connects, not only on whether moisture appears somewhere inside.

Represent ingress as competing paths and reservoirs

Model each seam, terminal transition and moving aperture as a path with driving pressure, capillary behavior, diffusion or drainage as applicable. Cavities can store liquid and release it after the external surface looks dry. Orientation may make one terminal the low point. Do not force all mechanisms into one linear leakage coefficient. A simple relation Q = deltaP/Rpath can screen pressure-driven flow, but it does not describe capillary entry or multiphase transport. Use it to compare geometry only within stated assumptions.

Place each media path on the electrical schematic

A wet route from wiper to return changes output differently from a route between two terminals or from a conductor to housing. Add candidate leakage resistances at the physical nodes they may bridge. Include receiver input and source impedance. As an illustration, 5 V across 1 megohm supports 5 microamps; whether that is consequential depends on the circuit and detection margin. Avoid converting this into a universal insulation requirement. Guarded measurements can separate some surface paths, but the guard geometry and fixture blank must be recorded.

Treat the sliding contact as a moving boundary

A wiper opening must permit motion and may also admit media or residue. Contact force, surface films, particles and drainage change as the mechanism moves or dwells. Evaluate the first movement after exposure separately from steady sweeping, because it may clear or redistribute material. Preserve position-resolved noise and dropouts rather than one total resistance. If the card is intentionally wetted, keep electronics and terminal sealing questions separate from passive material compatibility.

Use exposure stages that preserve when a fault begins

Inspect and measure dry baseline, controlled exposure, energized or de-energized dwell as approved, immediate post-exposure state and defined recovery. Record temperature, pressure, orientation and media revision. Run unexposed controls and fixture blanks. Where pressure reversal or thermal cycling is relevant, stage it separately so a static soak is not credited with testing every ingress mechanism. Safety and media handling belong to the qualified system or laboratory owner; this page defines the information path rather than a universal procedure.

Use timing and nodes to locate the ingress route

Leakage present only while wet suggests an active liquid bridge. A persistent change after bulk drying may indicate trapped media, residue or interface damage. Intermittency confined to motion points toward the contact opening. Terminal-to-terminal change with a stable passive track focuses the sealing transition. A control fixture that moves at the same time invalidates specimen attribution. Preserve sectioning until after electrical mapping, then choose cut planes from the suspected route.

Specify seals, vents, drainage and electrical nodes together

The section drawing should name media side, protected side, sealing materials, compression or bond geometry, terminal stack, vent path, drain orientation and moving clearances. Link these features to signal, supply, return and housing nodes. State which surfaces are allowed to be wetted and which require protection. If a generated application image is used later, it cannot prove this construction; release depends on drawings and reviewed evidence. Changes to media, seal, terminal, housing, vent, cleaning or pressure cycle trigger renewed path analysis.

Provide composition, path and circuit information

Send the media composition or controlled designation, temperature and pressure history, immersion or splash route, orientation, cleaning and recovery rules. Include the sensor section, terminal and seal drawings, wetted materials, circuit impedances, raw leakage or output records and required system response. Separate material-compatibility ownership from seal integrity and diagnostic action. The component review can address printed-card and terminal interfaces under supplied conditions, but complete enclosure rating, chemical qualification and safety acceptance remain outside an unsupported supplier claim.

A media review also needs a realistic exposure sequence. Continuous immersion, splash followed by drying, pressure pulsing and a warm contaminated soak can produce different transport paths even when the same fluid is used. Specify whether electrical bias is present during exposure, since an energized interface may respond differently from an unpowered coupon. After exposure, measure promptly and again after a controlled recovery interval; a reversible surface film and permanent material change should not be combined into one endpoint. Disassembly photographs can locate ingress, but they should be interpreted beside seal compression, vent condition and terminal orientation. If a cleaning step precedes measurement, document it explicitly so the procedure does not remove the very residue or moisture that the test is intended to reveal.

Material compatibility and sealing integrity must also remain separate decisions. An unchanged coupon does not prove that a terminal path stays dry, while a dry cavity does not establish that every exposed ink, glass or metal tolerates the fluid. Use appropriate witnesses for each question and retain the media lot or composition identifier. If mixed fluids, detergents or ageing products are credible, define them as new exposure states rather than assuming the neat fluid represents all service chemistry. Any conclusion should name the tested construction, exposure sequence, bias state and recovery rule.