Hi Eric -

Gaetan may want to incorporate hsyteresis and a dead zone in his application - especially if he is using a noisy (or poor resolution) input device.

As to definitions, I differentiate between hysteresis and dead zone.

As I view it, dead zone is stationary over the entire range of interest. Dead zone acts to create a range of no response, which can be helpful when using an input device having poor repeatability to command a position, temperature or whatever physical parameter is to be controlled. It's useful if the input device has an output drift which stays within a known range to prevent the downstream signal processing chain from responding to the drift.

Hysteresis on the other hand has a dead zone that moves with a physical parameter once the physical parameter has overcome a dead zone. On a change of direction, no change in hysteresis output occurs until the hysteresis range is overcome. An example of hysteresis is the backlash found in some gear trains and mechanical linkages.

Comparators as used to charaterize an analog signal into logic high and logic low have a parameter called hysteresis, but I've no problem with that terminology because I've learned the context and history of the terms.

My view on dead zone vs hystersis in motion control (motion as alluded to by Gaetan), have been shaped by a couple dozen or so years doing analysis, design & implmentation of various types of control systems (navigation, terminal guidance, flight, position, speed, temperature, fluid, magnetic, locomotive engine/generator/alternator/traction).

Cheers,

Bruce