Automatic control systems

Claim 1

APPARATUS FOR CONTROLLING THE OPERATING OF A STEAM TURBINE DURING START-UP AND IN ACCORDANCE WITH A DESIRED PROGRAM OF INCREASING TURBINE SHAFT SPEED, COMPRISING: AN ACTUAL SPEED SIGNAL GENERATOR SENSING ACTUAL TURBINE SHAFT SPEED AND DERIVING A FIRST VARIABLE SIGNAL REPRESENTATIVE THEREOF, A PROGRAM SPEED SIGNAL GENERATOR AND FIRST DRIVE MEANS THEREFOR, SAID PROGRAM SPEED SIGNAL GENERATOR DERIVING A SECOND VARIABLE SIGNAL THAT NORMALLY INCREASES PROGRESSIVELY DURING TURBINE START-UP AND IS REPRESENTATIVE OF THE DESIRED PROGRAM SPEED AT EACH TIME INSTANT, COMPARATOR MEANS RECEIVING SAID FIRST AND SECOND SIGNALS AS INPUTS AND DERIVING AN ERROR SIGNAL REPRESENTATIVE OF THE INSTANTENEOUS DIFFERENCE BETWEEN ACTUAL SPEED AND PROGRAM SPEED, A SECOND DRIVE MEANS COUPLED TO SAID PROGRAM SPEED SIGNAL GENERATOR WHICH SECOND DRIVE MEANS IS ORDINARILY INACTIVE, AND SERVO MEANS RESPONSIVE TO SAID ERROR SIGNAL AND APPLYING A DRIVING SIGNAL TO SAID SECOND DRIVE MEANS WHENEVER SAID ERROR SIGNAL EXCEEDS A PREDETERMINED LIMIT VALUE, SAID SECOND DRIVE MEANS IMPARTING DRIVE TO SAID PROGRAM SPEED SIGNAL GENERATOR IN OPPOSITE SENSE TO SAID FIRST DRIVE MEANS.