Radiation density gauge control of sludge transfer operations in sewage works

Claim 1

APPARATUS FOR CONTROLLING THE REMOVAL OF SLUDGE FROM A SETTLING TANK SO AS TO WITHDRAW THEREFROM ONLY SLUDGE HAVING A DESIRED SOLIDS CONTENT, WHICH COMPRISES SLUDGE WITHDRAWAL MEANS IN CONNECTION WITH SAID SETTLING TANK FOR PROVIDING A FLOW OF SLUDGE FROM SAID TANK, MEANS FOR DIRECTING A BEAM OF PENETRATIVE RADIATION SELECTED FROM THE GROUP CONSISTING OF GAMMA RAYS, X RAYS, BETA RAYS AND NEUTRONS ACROSS THE PATH OF SAID FLOW, MEANS FOR QUANTITATIVELY DETECTING A PORTION OF SAID RADIATION WHICH HAS BEEN MODIFIED BY INTERACTION WITH THE MASS OF SAID FLOW TO PROVIDE AN INDICATION OF THE DENSITY OF SAID FLOW, MEANS FOR INITIATING OPERATION OF SAID SLUDGE WITHDRAWAL MEANS TO START SAID FLOW, MEANS FOR MAINTAINING SAID OPERATION FOR AN INTERVAL NOT LESS THAN THE TIME REQUIRED FOR SAID FLOW OF SLUDGE TO TRAVEL THE DISTANCE FROM SAID SETTLING TANK TO SAID DETECTING MEANS REGARDLESS OF SAID DENSITY INDICATION, MEANS RESPONSIVE TO SAID DENSITY INDICATION FOR TERMINATING SAID OPERATION AFTER THE LAPSE OF SAID INTERVAL WHEN SAID DENSITY INDICATION HAS BEEN REDUCED TO A SELECTED VALUE, AND ALARM SIGNAL MEANS ACTIVATED BY FAILURE OF SAID DENSITY INDICATION RESPONSIVE MEANS TO TERMINATE SAID OPERATION WITHIN A PRE-DETERMINED PERIOD OF TIME AFTER SAID LAPSE OF SAID INTERVAL.