GB1291833A - Weighing device - Google Patents

Abstract

1291833 Weighing CONVEYANCER Ltd 2 Jan 1970 [31 Oct 1968] 51711/68 Heading G1N [Also in Division G4] A weighing device on a forklift truck includes a strain gauge 45 responsive to fluid-pressure in an hydraulic jack supporting the forks or other load bearing members of the truck and reed switches 1, 2 actuable by a permanent magnet 4 on the carriage 3 of the truck to control a weighing sequence. In use the jack is operated to bring the arrows 6 into alignment, then the "Weigh" button 9 is pressed to close contacts 16, 17 which are electromagnetically latched by coil 18 and "lower" lamp 27 is illuminated. The jack is operated to lower the carriage to bring arrows 7 into alignment when switch 2 closes to light "stop" lamp 28. Transistor VT3 is turned on after a predetermined delay (R8C3) to energize the coil of relay RL2 which turns off VT2, after a short interval during which capacitor C2 discharges, and removes the D.C. supply from an inverter 32. During the charging time of C3 the inverter supplies A. C. to a bridge network 44, 45, 46, 54, 55, 56, 117. Unbalance voltages are developed across the rheostat 56 and fed to a phase sensitive amplifier 53 which drives the wiper of a rheostat 59 to balance the bridge and position the disc 13 of the indicator 12. However if the carriage is lowered too slowly, C2 discharges fully so that VT2 turns off, the holding circuit for switches 16 and 17 is broken and the weighing sequence has to be re-initiated by closure of switch 1. The measuring arm includes a series rheostat 44 coupled to a zeroadjust 11, a rheostat 46 for off-setting the weight of the load lifting member and a fixed resistor 117 selectable to provide a no-load simulation. A fixed resistor 92 may be switched into the bridge instead of the measuring arm to provide a 75% full scale reading on the disc 13, during a sequence actuated by "check" button 10. When the relay RL2 is energized the servomotor 95 is turned off and the disc 13 comes to rest, simultaneously the "Read" lamp 61 is lit. The disc is connected to a digital encoder (see Division G4).