A servo system uses FEEDBACK for precise control of some physical characteristic (pressure, temperature, position).

The basic idea behind a servo system is that we TEST whatever it is we are trying to control, and we use the result of our test to fine tune our control even better.

A COMPARATOR is used to compare what is actually happening with what we want to happen, and the output of the comparator is used to push the system in the direction necessary to achieve our goal.

The temperature control system on a refridgeration unit is an example, we set the DESIRED temperature and the thermostat reads the ACTUAL temperature, turning on and off the unit as required to maintain the actual temperature as close as possible to the desired temperature.

A MECHANICAL servo system uses a motor to provide physical movement, transducers are used to feedback positional information which is COMPARED with our positioning COMMANDS and the motor is slowed and stopped exactly as required.

HUNTING can be a problem in servo system design, it is caused by system inertia or "reaction time".... hunting causes the system to OSCILLATE around the desired pressure, temperature or position.

HUNTING is caused by the difference in the time it takes to issue a command and monitor its effect on the system being controlled. What happens is that the system overshoots the point at which it should stop changing and then has to be brought back... only to overshoot in the other direction because we cant find out its actual value in time to stop it

The elimination of hunting will always be an open area for research as we seek to make a better (i.e. more accurate) servo system.... but in many practical applications, where extreme accuracy is not required, hunting is not a problem.

© copyright 2002 Stephen E. Mendes, Barbados.

EL31P Homepage