GB862253A - Improvements relating to electrical testing apparatus - Google Patents

Abstract

862,253. Electric tests. M.L. AVIATION CO. Ltd. Jan. 30, 1958 [Oct. 31, 1956], No. 33283/56. Class 37. Electrical components to be tested are sequentially connected by an automatic switching arrangement in a bridge circuit where each is compared with a corresponding standard and the automatic switching sequence is interrupted in response to out of balance in the bridge. General description of the bridge comparison (Fig. 2).-L1 and L2 constitute two arms of the bridge while the various components under test in a unit 13 are each connected through the fourth level of a switch S4 (set for the test in its third position) and level B1 of a uniselector to one of the pins of a multi-pin connector 12. The other end of each component is connected to the corresponding comparison component in the fourth arm of the bridge which is connected back to the point V by level B2 of the uniselector. The A.C. supply to the bridge is between point G and the junction of the test and comparison components through a series of resistors in box 15 to produce a different sensitivity in the bridge circuit for each element under test. The supply is connected to the appropriate tolerance resistor by actuation of one of relays RL17 to RL66 controlled from the third bank of the uniselector. Unbalance in the bridge is sensed by amplifier ACA the sensitivity of which is adjustable by shunting resistors R101 to R103 selected by switch S6. Indicator lamps IL17 &c. indicate which component is under test. The apparatus also performs flashover and leakage tests. Sequence of operations.-Movement of the main switch to its fourth position initiates removal of a short-circuit connection across the test arm of the bridge which unbalances the bridge. The unbalance is used to initiate the operation of a timing relay which when deenergized has a three second fall-out time. This relay in turn removes the short circuit from the bridge. The first component and the corresponding standard are then connected in the bridge by the uniselector. Unbalance of the bridge is detected by the A.C. amplifier across the bridge diagonal to stop the uniselector by maintaining the timing relay operated and to light an indicating lamp. The main switch may then be moved back to its third position where the uniselector will home or advance to its fifth position when the next component will be tested. If the comparison test is satisfactory a flash-over test is carried out on the same component by applying a two KV. supply between the component and all the others. Flash-over again stops the uniselector which may be made to run on or to home. If the component passes this test a leakage test is applied at a voltage appropriate to the component selected by the uniselector. Leakage is detected by a D.C. amplifier which stops the uniselector and which again can be made to run on or home by operation of the main switch. When all the tests are completed successfully the timing relay drops out and the uniselector advances to the next component. Comparison test of components (Figs. 3 and 4).-When switch S1 is set to the fourth (running position) a supply is connected through contacts of relay RL7 (Fig. 4) and the fifth bank of switch S1 to relay RL5. RL5 energizes completing a circuit through the second bank of switch S1 to energize either RL70 or RL80 depending on the setting of links in a programmer 22 selected by uniselector bank B4. The links are set so that relay RL70 feeds a six volt 50 cycle supply to certain components and RL 80 a 200 volt 4 K.C. supply to the others. Before comparison of the component of the standard can commence, a short-circuit connection between point U and the common connection at 33 through contacts of RL6, RL7 must be removed. The short circuit unbalances the bridge so that amplifier ACA operates RL82. This relay connects the supply through the contacts of either RL70 or RL80 (whichever is operated), and contacts of RL5 and RL6. RL6 in turn operates RL7. RL7 is the relay which times the operation of the uniselector. When RL7 operates it interrupts the supply to RL5 which drops out after a period of 1.5 seconds determined by a parallel CR circuit. Operation of relays RL6 and RL7 removes the short circuit from the component under test and if the component is matched to the standard the output of amplifier ACA will fall and relay R82 will release de-energizing RL6 and RL7. RL7 does not release for three seconds because of a parallel RC circuit. When RL5 releases after the 1.5 seconds referred to, RL70 or RL80 releases removing the supply from the bridge. If the component value is not correct relay RL82 remains operated sufficiently long for RL2, shunted by a large condenser, to operate. This in turn operates RL13 through a supply from the second bank of switch S1. RL13 operates an indicator lamp (on line 43) through contacts of RL82. In addition RL2 completes a circuit through contacts of RL7 and its own contacts to maintain RL5 operated. Thus either RL70 or RL80 remains operated and the supply remains on the bridge. In addition RL7 stays operated and the equipment is locked. Homing of uniselector after fault detection.- When the fault has been located switch S1 can be set either to its third position where the uniselector goes home or to its fifth where it carries on testing. In the third position the second bank of switch S1 connects RL68 to supply and deenergizes RL70 or RL80 to remove the supply from the bridge. RL68 transfers the negative supply to uniselector relay RL7 from contacts 5, 6 to 1, 2 and shunts its timing circuit with a further resistor R15. Since the bridge is deenergized RL82 releases de-energizing in turn RL2 and RL13 interrupting the fault light circuit. RL2 also de-energizes RL5 and RL6. RL6 releases RL7. C4 discharges because of the low shunt resistor R15 now inserted. Release of RL7 passes a supply through the third contact of the fifth bank of S1 to uniselector homing contacts so that the uniselector returns to its zero position. Testing next component after fault detection.- In order to continue testing the next component after a fault has been found on the preceding one during the comparison test switch Sl is moved to its fifth position. Operation is then as described above since the third and fifth contacts of the second level of switch S1 are connected together. When RL7 releases, however, no supply is given to the uniselector homing contacts but to a connection 54 which causes the uniselector to advance one step so that the complete test sequence is re-started. Flash test after satisfactory comparison test (Fig. 5).-Relay RL69 which is shunted by a half second timing circuit is operated by a circuit through contacts of relays RL5 and RL7 which are operated after the completion of the bridge comparison test. RL5 releases after 1.5 seconds extending the supply through contacts of RL69 (which is still operated) a bank of contacts 64 which are individually connected to the contacts of uniselector bank B5 according to whether a flash test on the particular component is required. If the connector is in position parallel relays RL73 and 74 are operated in series with the fourth contact of the second bank of switch S3 to switch the high-voltage supply for the flash test. RL73 connects the 2 K.V. negative supply at 70 through one coil of a double coil relay RL8 to a row of terminals 71 which are commoned together and connected individually to programming links in unit 72 and contacts 13 of relays of RL17 to RL66 to the component under test. Operation of one of these connects the component under test to the positive terminal of the 2 K.V. supply while all the other components for which a link has been inserted in programmer 72 are connected to the negative terminal. Flash-over from the component to any of the others energizes RL18 which can only occur in a flash-over because of the high impedance of the source. Relay RL8 locks on its second winding by a supply from the second bank of switch S 1. RL7 is also locked by a supply brought in by RL8 and RL5 is re-operated to prevent the next test proceeding and a flash-over fault lamp 86 is illuminated. Main switch S1 may now be set to cause the uniselector to home or run on as described above. Insulation or leakage test (Figs. 5 and 6).- If no fault occurs during the flash-over test RL69 is released after 15 seconds operating RL4. RL4 discharges C20, charged when the apparatus was switched through uniselector bank B6 through RL72. Level B6 contains a programmer 94 which comprises a number of links which may be inserted to determine whether or not the leakage test is to be applied to a particular component. If the link is in place C20 is charged. The charging circuit may also be disabled at the fifth position of the second bank of switch S3. The switching on of the apparatus also energizes RL7 to maintain input leads 102, 103 to D.C. amplifier DCA shortcircuited. Operation of RL72 de-energizes RL71 after 0.25 second. RL72 remains operated for 1.25 seconds during which time it connects a voltage appropriate to the component under test from a bank 107 of potential source through uniselector bank B7 the contacts of which are appropriately cross-connected to the sources, bank B1, the component under test in unit 74 the appropriate relay contacts RL 17- RL66 and line k which is isolated from the conmon negative. All the components except the one under test are connected by relay 4 to the D.C. amplifier input so that leakage produces a small positive voltage. As a result tube 112 conducts at a value depending on the setting of tolerance switch 53. The anode winding of relay 81 is energized to bring in a supply to illuminate a leakage test fault lamp. RL81 also gives the supply to a relay RL66 which restores the operating voltage to RL7 which is prevented from releasing at the end of the test period so that operation does not proceed. If the D.C. amplifie