FUME HOOD EXHAUST TERMINAL HAVING AN ELECTRICALLY DRIVEN LINEAR ACTUATOR

A fume hood exhaust terminal for controlling gas flow in an exhaust duct has an electrically driven linear actuator for angularly positioning a damper in the terminal. Drive circuitry employed in the preferred embodiment prevents the possibility of shorting out the actuator motor in the event of an input sign al condition which would attempt to operate the motor in two directions simultaneously. T he circuit also includes a power failure detection circuit which includes the c apability of storing sufficient power to place the damper in a preferred position until p ower is restored to the exhaust terminal.