Patent GB-1433048-A (GB)
Title: Electromagnetic wave minimum interval detection means and system using it
IPC: G01S13/931
Filed: 1973-06-28
Abstract: 1433048 Radar INTERNATIONAL STANDARD ELECTRIC CORP 28 June 1973 [29 June 1972] 30758/73 Heading H4D An electromagnetic wave minimum interval detection means for use with a plurality of mobile apparatuses, such as travelling cranes P1 to P5, Fig. 1, comprises a main transmitreceive arrangement I1 on one apparatus (P2) and a co-operating subsidiary arrangement R1 on another apparatus (P1). Other co-operating pairs of main/subsidiary arrangements shown in Fig. 1 are (I1, R2), (I3, R3). (I4, R4), which are installed respectively on the apparatuses (P2, P3), (P4, P3), (P4, P5). Each transmit-receive arrangement comprises an aerial, coupling means, a pulse transmitter with triggering means, a unit for receiving signals from the associated arrangement, checking their identity and measuring their amplitude, and for monitoring the operation of the arrangements, and alarm circuits controlled by the said unit. In a first embodiment, a main arrangement comprises an aerial 1, Fig. 2, which is coupled via a circulator or 3dB coupler 2 to a transmitter 3 and to a detection circuit 6. A generator 5 supplies pulses, at a repetition frequency adjusted to a predetermined value, to a monostable circuit 4, which repeats said pulses with a length adjusted to a predetermined characteristic value. The detection circuit 6 supplies three channels through an amplifier 38, the first directly and the second and third through a low-pass filter 29, Each channel comprises a respective threshold circuit 37, 9, 8, the first passing only high-level signals due to leakage from the coupler 2 during transmission, the second passing signals received by the aerial 1 which exceed a predetermined value corresponding to a critical minimum distance between the apparatuses in which the main and subsidiary arrangements are installed, and the third passing said received signals when they exceed a predetermined value corresponding to the maximum possible distance between the apparatuses. The circuits 9, 8 provide respective first inputs to AND gates 11, 10, said gates being inhibited during transmission on account of deactivation of their second inputs, which are connected via an inverter 39 to the output of the circuit 4. Output from the circuit 37 is applied to a retriggerable monostable circuit 7 which provides an output at level 1 to the first input of an AND gate 12 so long as there is a regular succession of transmitted pulses. A second input to the gate 12 is provided by the gate 10 between transmitted pulses when received pulses are above the threshold of the circuit 8. An AND gate 40 has one input from the gate 12 and another from an authorization circuit 41, which has an input from the monostable circuit 4, and which supplies pulses corresponding in durations and positions with the pulses received from the associated subsidiary arrangement. Thus, if both arrangements are operating correctly the gate 40 provides a succession of pulses which maintain a retriggerable monostable circuit 13 so that it provides a signal at level 1 to the first input of an AND gate 15. The gate 11 normally supplies a signal at level 0 to a retriggerable monostable circuit 14, which thus supplies a signal at level 1 to the second input of the gate 15, the output signal from which controls a supply source 16 to energize a relay 17 and break the circuit of an alarm 18, Should, however, the gate 11 give an output signal at level 1, by reason of it receiving output from the threshold circuit 9, the monostable circuit 14 is regularly retriggered to supply a signal at level 0 to the gate 15. Consequently, with no output from the said gate the relay 17 is de-energized, and the alarm 18 is operated. The alarm is similarly operated should there be no output from the monostable circuit 13. The circuit of the subsidiary arrangement is somewhat similar to that of the main arrangement. The pulse generator 5 is replaced by a main arrangement identification and triggering pulse generation circuit (19), Fig. 3 (not shown), which receives input from the AND gate 10 and which provides output both to the monostable circuit 4 and, through a monostable circuit (20), to the inverter 39. The gates 12, 40 and the circuits 13, 41 are omitted, the output side of the monostable circuit 7 being connected directly to the first input of the gate 15. The circuit (19) is shown in detail in Fig. 4 in which a represents the input from the gate 10, 21, 22 are monostable circuits having pulse lengths which are respectively shorter and longer by the same small amounts than those of the pulses transmitted by the associated main arrangement, 23 is a reset circuit operating with an adjustable delay after the pulse from the circuit 22, and 24, 25 are D-type flip-flops with outputs 1 connected to respective inputs of a NAND circuit 27. The outputs 0 of the monostable circuits 21, 22 are connected to respective clock inputs of the flip-flops 24, 25, whose D inputs are connected to the input a, an inverter 26 being inserted in the case of the flipflop 25. If pulses are received which have the predetermined length the NAND circuit 27 provides triggering pulses for a monostable circuit 28, which has an adjustable pulse duration, and which triggers the transmission monostable circuit 4. In another embodiment all arrangements, main and subsidiary, are operated at the same repetition frequency. The arrangements used comprise the same circuit components in both cases, internal switching being provided for operation according to whether a main or a subsidiary arrangement is required (Fig. 7, not shown). A pulse generator in each arrangement derives pulses from the electric power mains waveforms (Fig. 8, not shown).