Magnetic output amplifiers for digital control

WITH the advent of power-frequency magnetic-amplifier devices for logic systems, a need has developed for power-output magnetic amplifiers to raise the very low output level of logic elements to the moderate power requirements of transducer devices. Logic devices generally replace small control relays in industrial applications, but, instead of being able to control loads of approximately 100 to 1,000 volt-amperes, their output is in the range of 0.1 to 1 volt-ampere. Output amplifiers must supply the power required to operate transducer devices such as pneumatic or hydraulic solenoid valves, large power contactors, small motors, etc. Moreover, the output requirements of magnetic amplifiers so applied are unusual and much more stringent in comparison with more common applications such as servomotor amplifiers or proportional-control-device amplifiers. This difficulty in application is principally the result of current design practice for solenoid-operated devices. These solenoids, intended to operate from a power line directly or through a step-down transformer, impose upon the amplifier definite requirements which are discussed. Because a complete line of transducer devices is available, the best interim solution (and possibly the best long-range solution to the problem posed) is to adapt the amplifier to the load rather than to redesign the transducer to be compatible with the amplifier.