Differential Capacitive Bias Stability under Non-Uniform Substrate Thermal Fields
Spatial thermal gradients disrupt differential capacitive balance, requiring symmetric substrate layout and strain isolation to preserve bias stability.
Localized Heating Error
Thermal Gradients
Internal power dissipation within a sensing element creates micro-scale temperature imbalances that distort the accuracy of temperature and flow measurements. This self-generated temperature rise introduces a localized heating error that shifts the sensor reading away from the true ambient value. The discrepancy is particularly severe in media with low thermal conductivity.
Dissipation Coefficient
The magnitude of the temperature offset depends on the power supplied to the sensor and the ability of the surrounding medium to carry heat away. High-resistance RTDs driven by excessive excitation currents experience elevated power dissipation that increases the localized heating error. This error is inversely proportional to the thermal dissipation constant of the sensor package, which varies depending on whether the sensor is placed in stagnant air or flowing liquid.
Circuit Design
Pulsed excitation techniques and low-current current sources minimize the energy delivered to the sensor during the measurement cycle. By keeping the duty cycle of the sensor current low, the average power dissipation remains negligible. This design approach prevents the sensor from acting as a heat source and ensures that the physical properties of the medium under test are not altered.
Calibration Correction
Measuring the sensor resistance at two different excitation currents allows the internal temperature rise to be mathematically determined and compensated. This procedure identifies the thermal resistance between the sensing element and the environment. Corrective algorithms subtract this calculated value from the raw sensor reading to recover the true unperturbed temperature.