Fume hood exhaust terminal having an electrically driven linear actuator

A fume hood exhaust terminal (10) for controlling gas flow in an exhaust duct (12) has an electrically driven linear actuator (40) for angularly positioning a damper (20) in the terminal. Drive circuitry (90) employed in the preferred embodiment prevents the possibility of shorting out the actuator motor (76) in the event of an input signal condition which would attempt to operate the motor in two directions simultaneously. The circuit also includes a power failure detection circuit which includes the capability of storing sufficient power to place the damper (20) in a preferred position until power is restored to the exhaust terminal (10).