Anamplidyne is an obsoleteelectromechanicalamplifier invented prior toWorld War II byErnst Alexanderson. It consists of anelectric motor driving a DCgenerator. The signal to be amplified is applied to the generator'sfield winding, and its output voltage is an amplified copy of thefield current. The amplidyne was used in industry in high powerservo and control systems, to amplify low power control signals to control powerfulelectric motors, for example. It is now mostly obsolete.
An amplidyne comprises anelectric motor which turns agenerator on the same shaft. Unlike an ordinarymotor–generator, the purpose of an amplidyne is not to generate a steady voltage but to generate a voltage proportional to an input current, toamplify the input in applications where high output power is required. The motor provides the power, turning the generator at a constant speed, and the signal to be amplified is applied to the generator'sfield winding. The higher the current applied to the winding, the stronger themagnetic field and thus the higher the output voltage of the generator. So the output voltage of the generator is an amplified copy of the current waveform applied to the field winding. In a typical generator, the load brushes are positioned perpendicular to the magnetic field flux. To convert a generator to an amplidyne, what would normally be the load brushes are connected together and the output is taken from another set of brushes that are parallel with the field. The perpendicular brushes are now called the 'quadrature' brushes. This simple change can increase the gain by a factor of 10,000 or more.
The amplidyne's frequency response is limited to low frequencies, it cannot even handle audio frequencies, so its use is limited to amplifying low frequency control signals in industrial processes.
Historically, amplidynes were one of the first amplifiers to generate very high power (tens of kilowatts), allowing precisefeedback control of heavy machinery.Vacuum tubes of reasonable size were unable to deliver enough power to control large motors, but vacuum tube circuits driving the input of an amplidyne could be used to boost small signals up to the power needed to drive large motors. Early (World War II era) gun tracking and radar systems used this approach.
Amplidynes are now obsolete technology, replaced by modernpower semiconductor electronic devices such asMOSFETs andIGBTs which can produce output power in the kilowatt range.[1]
The amplidyne was first used in the US Navy in servo systems to control the electric motors rotating naval gun mounts, to aim the gun at a target. The system(diagram right) is afeedback control system in which a feedback signal from a sensor representing the current position of the gun is compared with the control signal which represents the desired position, and the difference is amplified by the amplidyne generator to turn the gun mount motor. The components are:
Chapter 10 of theU.S. Navy manualNaval Ordnance and Gunnery, Volume 1 (1957) explains the operation of the amplidyne:[2]
Specifically, the phase of the control transformer's output (in phase with the synchro power source, or opposite phase)provided the polarity of the error signal. A phase-sensitive demodulator, with the synchro AC power as its reference, created the DC error signal of the required polarity.
Amplidynes were initially used for electric elevators and to pointnaval guns, and antiaircraftartillery radar such asSCR-584 in 1942.[citation needed]Later used to control processes insteelworks.[citation needed]
Used to remotely operate thecontrol rods in early nuclear submarine designs (S3G Triton).[citation needed]
Diesel-electric locomotive control systems. EarlyALCO road-switcher locomotives used this technology.
Alternating current linear induction pump for secondary sodium inEBR-II.[4]