Patent GB-1240263-A (GB)
Title: Improvements in or relating to testing insulated conductors
Inventor: ARNOLD ALAN
IPC: G01R31/02
Filed: 1967-07-10
Abstract: 1,240,263. Testing insulation. BRITISH INSULATED CALLENDER'S CABLES Ltd. July 9, 1968 [July 10, 1967], No.31580/67. Heading G1U. In a system for simultaneously detecting and counting pin holes and detecting bare portions in the insulated covering of an enamelled conductor C1 as it is advanced lengthwise, the conductor is passed in contact with or in close proximity to an electrode 7, a source of potential being connected between the conductor and electrode. When a pin hole passes the electrode a detectable current pulse flows while when a bare portion in the covering passes the electrode a detectable fault current distinguishable from that caused by a pin hole flows. These current flows are detected in an arrangement which detects and counts pulses corresponding to pin holes and which detects signals representing the duration of fault current flow through any bare portions. A visual and/or audible indicator is connected to the detector arrangement to show when an unacceptable number of pin holes has occurred during the passage of a predetermined length of conductor and when signals representing an unacceptable length of bare conductor are received in the detector. The arrangement is designed to test up to 20 wires simultaneously, the supply for testing each wire being derived from e.g. an A. C. source 1 rectified at 4. This supply is smoothed in each test channel by a capacitor 8, whose magnitude is not enough to smooth the supply properly if a steady fault current flows, and applied via a high resistor 10 and screened cable 14 to the test electrode 7 across which the wire C1 under test is drawn. Diodes 11 isolate the channels from one another. If a pinhole fault in the wire passes over the test electrode, a pulse appears across resistor 9 which is amplified at 17, to operate a monostable trigger 18, which activates a relay unit 19 to operate a lamp 20 and counter 21. The trigger also supplies an integrator 22, and if the integrated level from this rises above a preset value as detected at 23 a further output is supplied via a relay unit 26 to alarm arrangements (lamp or buzzer) 27 and 28 to warn that an excessive number of faults in a given cable length have occurred. The level detector feeds back a signal to the trigger 18 to hold it on, so that the lamp 20 is permanently illuminated to show which particular channel is faulty. Resetting of the units is achieved by operating the switch 38 in the supply path to the level detector 23 &c from the stablized power pack 30. If a bare portion of wire passes the test electrode, a pulsating voltage appears across the resistor 9 due to the inadequate smoothing of capacitor 8, and this can be monitored by the same circuitry. Alternatively, an additional circuit fed from the amplifier 17 and consisting of an integrator (42) Fig. 2 (not shown) and level detector (43) connected to a bi-stable (44) may be used to respond to the fluctuating signal representing a bare wire portion, so that a further relay unit and alarm (46, 47) may be operated to indicate this particular fault. A further modification Fig.3 (not shown) has the pin hole detecting circuits completely separated from the bare wire detection by using a voltage pulse across a resistor in parallel with the capacitor 8 to operate them. Another system uses A. C. to energize the test electrodes 7 and picks up current pulses due to faults inductively Fig. 4 (not shown). In yet another arrangement Fig. 5 (not shown) fully stabilized D. C. is used, pin hole detection being achieved by using the current impulse to charge a capacitor, the impulse being monitored as before, while bare wire is detected by the change in steady voltage across a resistor due to the flow of fault current.