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Post-installation drift splits into two families: the process really changed (temperature, media, pulsation, trapped pressure), or the measurement chain shifted (installation stress on the process connection, zero shift, supply variation, wiring/grounding faults, analog scaling). The first safe check is comparative, with the system in a known state: compare the reading against a trusted reference at zero and at one working pressure. Stop-work warning: never loosen, remove or re-torque a process connection on a pressurized system, and never open electrical enclosures energized — depressurization, lockout and all electrical work belong to qualified personnel under the site's procedures.
"Drift" is a conclusion, not a symptom. Verify the process first: a reading that moved after installation may be reporting reality (temperature change, trapped pressure, a valve position that differs from commissioning).
Installation stress is a leading post-installation cause. Over-torqued threads, misaligned fittings and pipe strain mechanically preload the sensing element and shift the zero — often appearing immediately after tightening.
Temperature acts twice. Media temperature and ambient swings both move the output; compensation works within the model's stated range, not beyond it.
Zero shift vs. span shift matters. An output wrong by a constant offset at all pressures points to zero/installation/supply causes; an output wrong proportionally points to span, scaling or the sensing element.
Verification beats recalibration. Confirm true zero with a reference before any zero/span adjustment — and treat every adjustment as manual-plus-qualified-personnel work on a depressurized system.
This article covers readings that moved after installation or drift over days to weeks:
Offset drift — wrong by a roughly constant amount across the range;
Proportional error — error grows with pressure;
Slow creep — reading wanders with time or temperature without a process reason;
Step change after installation work — the reading shifted at the moment of mechanical or electrical work.
