The Main Sensor Types and What Each One Measures
Selecting sensors requires matching physical transduction principles to measurands while accounting for thermal drift, noise floor, and fab availability.
Thermal Gradient Shift
Temperature Nonuniformity
Discrepancies in the output of a precision instrument occur when heat is distributed unevenly across its internal components. A thermal gradient shift arises when one side of a bridge circuit or a reference diode is warmer than the other. This creates parasitic thermocouple effects at junctions of dissimilar metals.
Even small differences of a fraction of a degree can lead to measurable offset errors.
Heat Source
Internal power dissipation from regulators or microprocessors is a common cause of localized warming. When a thermal gradient shift develops, it often follows a change in the operating state of the device that alters the equilibrium of the circuit. High-power components should be placed far from sensitive analog front-ends.
Enclosures with poor airflow can exacerbate the buildup of heat in specific corners.
Design Countermeasure
Symmetrical board layouts help to ensure that any temperature changes affect all parts of a sensitive circuit equally. Managing thermal gradient shift involves the use of copper planes to spread heat and thermal barriers to isolate critical nodes. Some high-end sensors use active heaters to maintain a constant, albeit higher, internal temperature.
This eliminates the gradients by swamping the environmental fluctuations.
Verification Process
Testing in a climate chamber with controlled ramp rates identifies how the sensor responds to dynamic thermal environments.