A Variable-Radio-Frequency-Follower System

This paper deals with a new follow-up or servo system for amplification of mechanical forces and remote positioning. The system described makes use of variable radio frequencies representative of the respective positions of system leader and follower. Two parallel-resonant circuits are provided, one of which is the frequency-determining circuit of an oscillator, while the other is the balance-frequency-determining circuit of a balanced-frequency discriminator. One of the circuits can be tuned by the leader, while the other is tuned by the follower; or, one of the circuits can be tuned by both leader and follower. System balance is reached when both circuits are tuned to the same frequency. Of the possible variety of system modifications, four significant types are described with their particular applications. The system provides for low-frequency keying of the radio-frequency signal before application to the frequency discriminator, in order to obtain a low-frequency-discriminator output signal of one phase or opposite phase, depending upon the direction of system unbalance. For system balance no discriminator output signal is produced. The low-frequency signal is used to control a two-phase induction motor driving the follower. System design considerations and performance data are given. Wide-band frequency-discriminator tuning is discussed with respect to constant system sensitivity. Experimental and production models are described.