Abstract :
Experience of electronic servos in industry since 1932, and under arduous military conditions since 1939, indicates that correctly engineered equipments will give at least ten years´ service under heavy industrial conditions, with maintenance confined to occasional valve replacements and routine attention to auxiliary contacts. Failures of the latest high-quality components will be statistically insignificant up to fifteen years´ life. Transient and steady-state errors of linear continuous-control servos can readily be predicted, and the use of electronic amplifiers permits very close approach to the known fundamental limits. Non-linearity seldom improves accuracy in the normal range, but is necessary for good recovery from disturbances exceeding this range, and can readily be introduced at the required signal level in electronic amplifiers. Electronic position-control servos, highly developed for military applications, appear essential to future nuclear-power plants and are immediately applicable to the mechanical handling problems of heavy industry. Electronic voltage regulators of the thyratron type have been used since 1935 for controlling the voltage of generators, not only for special testing installations requiring voltage regulation to within ?0.1%, but also for controlling the voltage of large alternators in power stations. Electronic speed regulators are used for controlling the speeds of d.c. motors, the method of control being by variation of shunt field-current, armature voltage, or a combination of both. Motors of 4000 h.p. are being controlled by acting on the shunt field of the generator supplying armature power to the motor. Speed control of a.c. commutator motors of the Schrage type is achieved by the automatic operation of the brushgear-shifting motor. These points are illustrated by description of typical industrial applications of position control servos and automatic regulators for current, voltage and speed.
