Patent GB-1394670-A (GB)
Title: Identification of conductors in multi-conductor arrangements
IPC: G01R31/02
Filed: 1971-05-13
Abstract: 1394670 Identifying electrical conductors POST OFFICE 12 May 1972 [13 May 1971] 14646/71 Heading G1U To enable conductor pairs at an unknown end 3, Fig. 1, of a multiconductor cable 1 to be identified, the known end 2 of each pair is connected to a respective resistance - diode network (e.g. R1-R3, D1-2, Figs. 7, 8) arranged to provide either a first (R1) or a second (R2) value of resistance according to the state of conduction of the diodes, no two such networks providing the same pair of resistance values so that each conductor pair is thereby distinctly "marked". A selected unknown pair of the other end of the cable can then be identified by applying first a voltage of one polarity to measure the first resistance value and then a voltage of the opposite polarity to measure the second resistance value. The apparatus described also checks electrical properties of the cable. The marking network Each of 100 conductor pairs at the known end of the cable is allocated a two digit number t u. The digits 0-9 are assigned distinct resistance values from 820# to 20 k#, and the marking network for a given pair t u comprises resistors R1, R2 having values corresponding to the tens and units digits t, u respectively. Diodes D1, D2 in the marking network allow either R1 or R2 to be selected to terminate the pair by applying a voltage of appropriate polarity. Resistor R3 connects the "B" conductor of the pair to a common point C which itself is connected (via a known conductor pair if necessary) to a common point CE at the other end of the cable. Checking continuity and that conductors are a pair An assumed pair of conductors at the unknown end of the cable is connected into one arm SQ of the bridge of Fig. 7 by closing a first key switch KA Figs. 3, 4 (not shown). If there is no fault, the appropriate resistor R2 will constitute the bridge arm SQ, and since R2 must be less than the 33 k# in the arm PS the bridge will be unbalanced in one sense and an indicator lamp lit. If either conductor A, B is discontinuous arm SQ will be opencircuited and if the conductors in fact belong to different pairs arm SQ will include a resistance of at least 36 k# (two x R3), so in either case the bridge will be unbalanced in the opposite sense and the lamp will not be lit. Identifying a pair; checking for crossed conductors or short circuits By closing another key switch (KC) the selected pair is now connected into the bridge Fig. 8 which includes as an adjustable arm ten resistors BR1-10 having the values which correspond to the digits 0-9. Under the control af an astable multivibrator (MV, Fig. 4) relays (AA-LL,) Figs. 4-6 (not shown), are successively triggered to select resistors BR in turn. When the selected BR resistor matches the RL resistor of the pair the bridge balances, and this stops the multi-vibrator, the last relay operated, which will correspond to the tens digit t of the pair, being identified by a lamp. To determine the units digit u a further key switch (KC) is closed to repeat the operation with the battery and bridge unbalance detector reversed in polarity. If the A and B conductors have been crossed, or if there is a short circuit from the A conductor either to earth or to the B conductor, the bridge will effectively have one short-circuited arm. Under these conditions the multi-vibrator will trigger the ten relays AA-KK without reaching balance and will then trigger a final relay LL which will operate a warning lamp. Further short-circuit check To check for short-circuits from the B conductor to earth, closing of another key switch (KB) completes the bridge of Fig. 10, which will be unbalanced by a short circuits in such a sense as to light a lamp. Modification Using the modified marking network of Fig. 12, only a single conductor rather than a pair is selected at the unknown end, the return path to the bridge being provided by a control pair. With A conductors it will be possible to identify both the tens and units digits, but with B conductors only the units digit. To then check that an A and a B conductor are a pair of simple loop continuity test is made with a battery and a lamp.