GB1022414A - Electrical systems - Google Patents

Abstract

1,022,414. Advancing mine roof supports. COAL INDUSTRY (PATENTS) Ltd. Jan. 1, 1963 [Jan. 4, 1962], No. 432/62. Heading F1P. In an electrical system, Figs. 1 and 2 (not shown), for an hydraulic mine roof support system wherein electrical signals can be received from and/or transmitted to a plurality of roof supports arranged to be operated in a predetermined sequence through signalling conductors, the contacts of a relay A in each circuit associated with a particular support is arranged on receipt of a signal to connect the signalling conductors to the electrohydaulic valves of the appropriate roof support, each circuit being such that when its relay is actuated a voltage pulse is developed thereby and is passed along a linking line c to the circuit associated with the next roof support in the sequence whereby the relay A associated therewith is actuated. By appropriate switching at a control station potentials are applied to the signalling conductors which cause the electrohydraulic valves to operate and hence the associated roof support. The valves may be arranged as described in Specification 967,164. The system consists of a chain of identical operating circuits S1, S2 . . . (Fig. 2) connected by an earth line b, a D.C. power supply line a, and the linking line c to each other and to a control station CS. In operation the D.C. supply is fed to one end of the line a and a positive voltage pulse is applied to the opposite end of the linking line c so that the end circuit (S, in Fig. 2) is operated, a bridge formation of diodes B prevents operation of other circuits. The relay A in the operated circuit is therefore actuated. A very short negative pulse is then generated by a stepping pulse generating circuit SPG having a mechanical make-and-break stepping contact MSC such as a telephone dial, manual, button or relay contact and used to initiate the pulse. The negative pulse is applied to the line a whereby a transistor TI in the operated circuit is caused to conduct thereby de-energizing the relay A therein and producing a positive pulse which is passed to the next operating circuit through the linking line c to cause the relay A in the circuit S2 to be energized. Further short negative pulses operate successive circuits in sequence and a series of relay contacts A1 in the line a are each operated by their corresponding relay A to ensure that preceding circuits in the sequence are not operated. A switch DS in the control station CS allows circuits to be operated in sequence in the reverse direction.