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.
Annealing Stabilization
Thermal Conditioning
Thermal treatment represents a fundamental step in the manufacture of high-precision platinum resistance thermometers to ensure long-term stability. This protective process, known as annealing stabilization, relieves the mechanical stresses introduced during the winding of the sensor coil. Relieving these internal stresses prevents drift.
Structural Evolution
Sub-microscopic grain growth and dislocation density reductions occur when the sensor undergoes controlled heating below the melting point of the metal. During annealing stabilization, the crystalline structure of the platinum relaxes into a lower energy state. This stops subsequent resistance shifts.
Metrological Security
Primary laboratories verify the success of the process by measuring the electrical resistance at the triple point of water both before and after the thermal exposure. If the change in resistance corresponds to an equivalent temperature shift of less than one millikelvin, the annealing stabilization is deemed complete. A larger shift indicates that further heat treatment is necessary to secure the sensor calibration, as unresolved internal stresses would continue to cause measurement drift during routine laboratory operations.
This verification cycle is repeated until the sensor reaches a state of equilibrium.
Boundary Condition
Upper limits for the process temperature are determined by the purity of the platinum wire and the transition temperature of the support material. If the thermal exposure exceeds these limits, contamination from the ceramic mandrel can occur, which compromises the purity of the platinum. Such contamination degrades the temperature coefficient of the sensor permanently.