Fault monitor for NC machine tool data line - uses constant current transmission and voltage drop threshold detectors

摘要

Data from a controller (2) are transmitted over a line (1) to an opto-coupler (3) forming the input to a numerically controlled machine tool (4). The 0 and 5V data levels from the controller are converted to 5 and 25mA by a constant current generator (6) which drives the line. The voltage drop across the line, due to its resistance (5) plus the opto-coupler, is monitored by two threshold detectors (7,8). One detector (7) gives an output (9) to the controller if the line voltage exceeds 2.5V e.g. if the line becomes open-circuit. The other (8) gives an output (10) if the line voltage falls below 0.5V, e.g. short-circuit. Line faults are thus immediately reported to the controller, which can take action to prevent damage or production of scrap. Series padding resistors (11,12,13) allow the same circuit to be used with lines of different resistance.