Board Layout Mitigation Strategies for Thermally Coupled Internal Reference Voltage Drift
Isothermal component placement, substrate trenching, and balanced copper pours mitigate internal reference voltage drift caused by thermal board stress.
Thermal Time Constant Latency
Thermal Lag
Temperature measurements are subject to a delay while heat flows from the surrounding environment to the active sensing element inside the probe housing. This delayed response is characterized by thermal time constant latency, which is the time required for the sensor output to reach sixty-three percent of a step change in temperature. The metric is dependent on both the physical design of the probe and the properties of the fluid being measured.
Convective Heat
Heat transfer from the fluid to the sensor is governed by conduction and convection across the boundary layer. When a sensor is placed in a moving fluid, the higher flow rate reduces the boundary layer thickness and accelerates the heat transfer. This dynamic makes the time constant shorter in moving fluids than in stagnant ones.
The design of the sensor sheath and the use of internal thermal compound determines the speed of the thermal response.
Measurement Error
Rapidly changing temperatures can lead to significant errors if the time constant is too long. In these scenarios, the sensor output lags behind the actual temperature, resulting in an underestimation of the peak values. This lagging behavior can compromise the effectiveness of control loops.
Calibration Standard
Metrologists measure this latency by plunging the sensor from a room-temperature environment into a stirred hot water bath and recording the response curve. This test is repeated at a specified flow rate to ensure consistent results across different batches. If the measured latency exceeds the maximum limit set by the specification sheet, the sensor must be rejected or redesigned.
This standard test ensures that the temperature sensor reacts quickly enough for the intended application.