Evaluating Temperature Coefficient Wander in Thin Film Platinum Resistance Elements
Evaluating temperature coefficient wander in thin film platinum RTDs requires tracking substrate strain, glass passivation diffusion, and multi-point calibration.
Glass Encapsulation
Protective Barrier
Hermetic sealing of electronic components provides a high-integrity barrier against moisture and atmospheric contaminants that cause drift or failure. This isolation method, often achieved through glass encapsulation, is critical for temperature sensors operating in harsh environments. It protects the sensitive active element from oxidation and chemical attack.
Sealing Mechanism
Thermal bonding of a glass sleeve around the sensor leads creates a high-density joint that prevents gas leakage. During glass encapsulation, the glass is heated to its softening point and then cooled slowly to form a solid bead. This process must be controlled to prevent micro-cracks from forming at the metal-to-glass interface.
Metrological Stability
Calibration drift in thermistors is minimized when the active oxide material is isolated from the surrounding atmosphere. The glass encapsulation ensures that the resistance-temperature characteristics remain stable over thousands of hours of continuous operation. This stability is essential for sensors deployed in industrial process control and laboratory instrumentation where frequent recalibration is impractical.
Without this hermetic barrier, atmospheric humidity would penetrate the sensor body and cause a gradual shift in the nominal resistance.
Mechanical Constraint
Mismatch between the thermal expansion coefficients of the glass and the internal platinum wire can introduce mechanical stress. These stresses, if unresolved, alter the electrical resistance of the sensor via the piezoresistive effect. Matching the coefficients ensures that the encapsulation does not introduce parasitic resistance shifts during thermal cycling.