Encapsulation Integrity
Protective housing and coating materials applied to foil strain gauges insulate sensitive resistive elements from mechanical damage and environmental degradation. Maintaining strain gauge packaging stability prevents baseline zero drift caused by physical package deformation. Hermetic sealing protects sensing grids.
Moisture Ingress
Moisture absorption within polymer carrier films and protective overcoats alters the dielectric constant and mechanical stiffness of the gauge package. Hygroscopic swelling generates internal stress fields that transfer directly into the piezoresistive grid, inducing false strain signals independent of applied mechanical loads. Water vapor penetration degrades insulation resistance between the gauge grid and the underlying metallic substrate, creating electrical leakage paths that shift bridge balance points.
Polyimide and glass-filled epoxy matrix materials offer low moisture absorption rates, minimizing signal drift in humid operating environments. Environmental seals prevent fluid intrusion under continuous outdoor exposure.
Substrate Creep
Polymeric adhesive layers bonding the gauge carrier to the load cell structural element exhibit viscoelastic relaxation under sustained mechanical strain. Viscoelastic creep reduces force transfer efficiency from the carrier film and underlying metallic substrate to the foil grid over extended time intervals. Differential thermal expansion between the carrier film, adhesive bonding layer and metal substrate introduces thermal hysteresis during temperature cycling.
Selecting low-creep thermosetting adhesives stabilizes signal response under long-term deadweight loading.
Qualification Testing
Accelerated environmental testing subjects packaged strain gauges to combined temperature and humidity aging cycles within environmental test chambers. Insulation resistance checks verify that package resistance exceeds gigaohm thresholds throughout long-term thermal exposure. Test certificates document zero stability and span drift limits under simulated field operating conditions.
