robotics//sensor//operating envelope

The region of conditions in which a device is meant to work and in which its behaviour is known: temperature, supply voltage, vibration, speed, humidity, signal level, every variable that changes how it responds. A sensor's datasheet figures, and any calibration done on it, are true inside that region and silent outside it.

The region of conditions in which a device is meant to work and in which its behaviour is known: temperature, supply voltage, vibration, speed, humidity, signal level, every variable that changes how it responds. A sensor's datasheet figures, and any calibration done on it, are true inside that region and silent outside it.

The practical consequence is coverage. A characterization is only as wide as the conditions it spanned: a GPS measured under open sky says nothing about a narrow street, a gyroscope characterized at room temperature says nothing about its bias in a hot engine bay. Recording across the envelope, at its corners and not only at its centre, is what makes the numbers usable in service (noise characterization).

Outside the envelope the error model is unknown, not merely larger. A saturated sensor does not become noisier; it sticks at its maximum and stops telling anything, and no variance describes that.

Inside the envelope the noise may still change with the conditions. A sensor whose variance grows with temperature is characterized as a function of temperature, and a filter can then be handed a different noise level at each step (measurement noise).

Knowing where the envelope ends is part of the design. A filter can check the conditions it is running in against the ones its sensors were characterized for, and distrust a reading taken outside them.