GB711132A - Improvements in or relating to the control of hoists and cranes - Google Patents

Abstract

711,132. Electric control systems. CLAYTON CRANE & HOIST CO., Ltd. June 5, 1951 [June 5, 1950], No. 13942/50. Class 40 (1). [Also in Group XXX] In apparatus for controlling a crane or hoist from a distance by radio, a transmitter under the control of the operator transmits a modulated carrier, the modulations being selected at the receiver by note selector cricuits of the type in which all frequencies except the selected one are attenuated by negative feed back. The transmitter (Fig. 1) is self-contained, miniature components being used throughout and may be carried in a haversack by a hoist operator. The radio-frequency section comprises a regenerative crystal oscillator and frequency multiplier 12, which feeds the grid of a power amplifier 13 in the anode circuit of which is a resonant parallel line feeding the antenna by either a balanced or co-axial low impedance matched feeder. The output of the transmitter is modulated at one of a number of audio frequencies produced by closing one of press buttons 18 to 21 so that one of crystals 17b to 17e produces a low frequency oscillation which beats with an oscillation produced by a further crystal 17a. This beat frequency signal is amplified at 22, and impressed on the radiofrequency signal so that a radio-frequency modulated at a frequency corresponding to the button pressed is transmitted. The receiver (Fig. 2).-The audio frequency modulated signal received at the antenna 26 feeds the radio-frequency amplifier 28 through a balance or co-axial low impedance line. If the receiver operates at or above a frequency of 465 m.c.'s the amplifier 28 mixer 29 and local oscillator employ cavity resonators and disc seal valves though this is not necessary for the second frequency changer 31 and intermediate frequency amplifiers 32, 33 or detector 34. A noise limiter is included before the low frequency amplifier 36, which feeds a number of tuned circuits 37 to 40 (see below) each tuned to the beat frequency produced by one of push buttons 18 to 21 (Fig. 1) and operating one of relays 37 to 40. Each relay effects a different control on the crane e.g. lowering or hoisting and all relays are interlocked so that only one control may be operated at a time. The frequency selection is accomplished by a number of circuits such as are shown in Fig. 3. each of which strongly attenuates all frequencies except the selected one by means of filter circuit 43 and a negative feed back connection.