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An industrial level reading goes unstable with foam, dense dust or condensation because these media conditions attack the measurement physically: foam and dust form a partly reflective layer the sensor cannot cleanly assign to the true surface; condensation and product buildup on an antenna or transducer attenuate or distort the signal; agitation multiplies surfaces; and condensation-driven false echoes compete with the real one. The first safe check is correlation — trend the unstable readings against process state (foam events, filling, agitation, temperature cycles) before touching the instrument. Do not open process equipment or clean antennas on live vessels: vessel access, depressurization and confined-space work follow the site's process-safety procedures.
Foam, dust and condensation are physics problems, not calibration problems. They change what signal returns to the sensor; recalibration cannot restore a signal the medium has absorbed or scrambled.
Correlate before you adjust. An unstable-reading log against foam events, agitation, filling cycles and temperature swings identifies the active mechanism in most cases — with zero process risk.
Each medium condition has a signature. Foam: readings jump between the foam layer and the liquid surface. Dust: gradual signal loss and dropouts on bulk solids. Condensation: drift and echo-profile changes that track temperature cycles. Agitation: fast oscillation while the mixer runs.
Technology matters, and so does geometry. Radar tolerates dust and light foam better than ultrasound in general comparison; both suffer from antenna/transducer contamination and dead-zone geometry — the selection trade-offs are owned by E07 ({{URL_E07}}) and C10 ({{URL_C10}}).
Vessel-structure echoes are a separate fault family. If the instability does not correlate with media but with level positions, that is a geometry/echo problem — owned by the radar-reflection guide ({{URL_T04}}).
