A pressure sensor that suddenly reads zero, or drifts between readings for no obvious reason, is rarely an electrical fault — trace it back far enough and the adhesive bond line is usually the actual point of failure.
How Adhesive Mounting Interferes With Pressure Sensing
Industrial and aerospace pressure sensors typically rely on strain gauges, piezoresistive elements, or capacitive diaphragms that convert minute physical deformation into an electrical signal. Adhesive mounting is generally preferred over mechanical fastening because it distributes stress evenly, cuts weight, and provides a hermetic seal — but if the adhesive layer is too thick, too soft, or applied inconsistently, it starts acting as a mechanical filter that dampens the very force the sensor is supposed to measure.
A “zero reading” typically means applied pressure isn’t reaching the sensing element at all. “Inconsistent readings” usually mean the adhesive itself is shifting, expanding, or contracting independently of the sensor — often driven by temperature swings or internal bond-line stress.
Root Causes of a Zero or Dead Reading
- Excessive cushioning — a low-Shore-hardness adhesive can absorb mechanical energy before it reaches the diaphragm, so the sensor reports near-zero pressure because the polymer itself compressed instead of the sensing element.
- Air entrapment — trapped bubbles or voids compress under pressure rather than transmitting it, often producing no signal change until a threshold collapses the void and the reading jumps non-linearly.
- Delamination — if the adhesive doesn’t fully wet either the sensor or the substrate, the sensor can “float” in its housing, usually traced to poor surface prep or a chemical mismatch with the sensor’s coating.
Why Readings Drift Over Time
Inconsistency is often more dangerous than a dead sensor because the data still looks plausible. The main drivers:
CTE mismatch. Every material expands at a different rate with temperature. Because polymers typically expand faster than the metals or ceramics they’re bonded to, a mismatched adhesive creates parasitic strain that the sensor misreads as a pressure change — the same physical pressure can read 10 PSI cold and 15 PSI warm.
Hysteresis and creep. A viscoelastic adhesive that doesn’t fully spring back after pressure is released causes a baseline shift, so the sensor never quite returns to zero during rapid cycling.
Incomplete cure. An under-cured epoxy or UV adhesive keeps cross-linking after installation, especially once it’s exposed to heat from the sensor’s own electronics. As the modulus continues to change, the sensor’s calibration drifts along with it — a slow-motion failure that often isn’t caught until weeks into service.
Best Practices for a Stable Bond Line
- Rigorous surface prep — degrease with an electronics-grade isopropanol or aqueous cleaner, lightly abrade without damaging the diaphragm, and use plasma or corona treatment on low-surface-energy plastics like PTFE or PEEK.
- Match chemistry to the application — epoxies generally offer the lowest CTE and best stability for high-precision sensing but require careful mixing to avoid bubbles; UV-curable adhesives allow cure-on-demand alignment and can be tuned to a specific Shore hardness; cyanoacrylates work for quick fixes but are usually too brittle for long-term pressure duty.
- Control bond line thickness — a thin, uniform bond line minimizes CTE-related drift; glass-bead spacers of a defined micron size help hold that thickness consistent across production runs.
- Degas before application — vacuum degassing removes the microscopic bubbles that would otherwise compress under pressure and disrupt force transmission.
UV-curable adhesives have become the standard for many sensor-mounting lines because they lock a sensor into its calibrated zero position in seconds, avoiding the drift risk of a slow room-temperature cure. The one caveat: if the adhesive is shadowed behind an opaque housing, UV light can’t reach it, leaving uncured liquid inside the assembly. Dual-cure systems (UV plus heat or moisture) solve this by guaranteeing full cure in shadowed zones.
A Practical Troubleshooting Sequence
If a production run is already showing bad readings, work through this checklist: cross-section a failing unit to look for voids near the sensing element; run a thermal cycling test at zero pressure to reveal CTE mismatch; check the adhesive’s technical data sheet for Young’s modulus, since a low modulus signals dampening; and hold off on final calibration for 24–48 hours after cure to account for post-cure shrinkage.
When adhesive doubles as a potting or encapsulation layer, one more variable enters the picture: a poorly chosen potting compound can apply hydrostatic pressure to the sensor as it cures, pre-loading it and creating a permanent output offset. Low-shrinkage formulations avoid this.
Contact Our Team if your line is seeing zero readings or output drift that traces back to the bond rather than the electronics — Incure’s engineers can help match adhesive modulus and cure chemistry to your specific sensor geometry.
The Bond Is Part of the Sensor’s Mechanical Circuit
Precision manufacturing depends on precision chemistry. The adhesive holding a pressure sensor in place isn’t incidental packaging — it’s a functional part of how force reaches the sensing element, and treating it as such is what separates reliable sensor lines from ones fighting recurring field returns. For related guidance on UV-cure versus epoxy trade-offs in fast-turnaround assembly, Email Us with your production volumes and we can help scope the right chemistry.
Visit www.incurelab.com for more information.