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.
Platinum Thin Film
Sensor Deposition
Precision resistance elements are fabricated by applying a micro-scale layer of precious metal onto an insulating ceramic base. Utilizing a platinum thin film allows manufacturers to produce small, highly responsive temperature sensors at a lower cost than wire-wound alternatives. This layer is structured using photolithography to create a serpentine resistance path.
The resulting sensor responds quickly to rapid temperature variations due to its low thermal mass.
Substrate Interaction
The mechanical bond between the metal layer and the ceramic substrate must withstand repeated thermal cycles. Differences in thermal expansion can induce mechanical strain on the film, which alters its electrical resistance. Adhesion layers are applied to prevent the film from lifting off the substrate.
Calibration Behavior
The electrical behavior of the deposited layer differs slightly from bulk platinum due to structural grain boundaries. This difference reduces the temperature coefficient of resistance of the element. Sensors must be individually calibrated to account for this reduced sensitivity.
Performance Standard
Industrial specifications define the permissible deviation from the standard temperature-resistance curve. The sensor must maintain its stability and resistance value after prolonged exposure to its maximum operating temperature. These tests ensure that the thin-film element remains reliable in demanding field conditions.