Patent GB-782017-A (GB)
Title: An improved apparatus for testing electrical circuits
IPC: G01R31/28
Filed: 1954-02-26
Abstract: 782,017. Electric tests. WALTON, J. H. D. Feb. 2S, 1955 [Feb. 26, 1954], No. 5736/54. Class 37. Electrical apparatus for testing a plurality of electrical circuits in a continuous operation, of the kind comprising test result indicating means and a moving selector element operatively associated with a plurality of contacts connected to the circuits under test, has means for applying an over-riding pass or acceptance signal to the indicating means during such periods when the selector element is moving from one group of contacts to another and may not be making good and simultaneous contact with one group only of the contacts. The selector element comprises a number of radially spaced wipers 2-7 acting on a corresponding number of concentric rows of studs 2-7, Fig. 1, the wipers 2-6 moving between radial rows may be broad enough to contact two arcuately adjacent studs, whereas the wiper 7 completely leaves one stud 7 before engaging the next. If a pass signal is given the wipers move on, but a reject signal stops the motor driving the wipers. Continuity test.-The circuit under test, Fig. 1, is connected as shown to studs 4, 5. In order to ensure that test result is given only when the wipers 4, 5, indicated by arrow heads, are making good contact with the studs 4, 5, a relay A operating switch A1 is provided with a winding A(b) which holds the relay to give an over-riding pass signal when the wipers are making partial contact with studs 4, 5 so that such a partial contact cannot give a reject signal. When the narrow wiper 7 makes contact with stud 7 the broad wipers 4, 5 are making good contact with the studs 4, 5, the winding A(b) is shorted to cancel the over-riding pass signal, and the test is made through winding A(a). Resistance and Capacitance Test.-A bridge detector circuit, Fig. 2, is provided consisting of a double valve V1 and a polarized relay B which is actuated by the difference between anode currents, the relative potentials of the grids of V1 determining whether a pass or reject signal is given through B1. The unkown circuit resistance Rx and a standard high or low resistance such as Rt are connected as shown to form a bridge with resistances 8, 9 when the wipers contact the studs 3, 4, 6 and 7. The energizing of relay E by wiper 7 breaks switch E and causes the relay winding B(b) to be de-energized, thus removing the over-riding pass signal. The supply S3 is reversed for a low resistance test. If Rt is replaced by a short-circuit, e.g. for continuity, then a resistance 12 is provided in the supply S3. The apparatus of Fig. 2 may also be used for capacitance testing if Rx is replaced by capacitance or a parallel combination of resistance and capacitance and provided the test period exceeds the time constant period. The supply S3 is taken through a normally broken contact pair of the relay E. Insulation Test.-A bridge detector, Fig. 3 (not shown), similar to that of Fig. 2, is used and a high voltage supply is provided. Control Circuit.-The control circuit, Fig. 4, comprises a pass circuit through supply S7, line X, test finished lamp 18 which does not light when in this circuit, a non-polarized winding D(a) and a biased start switch 17 to earth. The reject signal passes through lamp 19 to earth and shorts out D(a), thus shorting the armature of motor 21 as shown and stopping the motor. To start the motor again the switch 17 is manually operated to excite D(a) and move switch D1. The motor then runs until B returns to the pass position which occurs when the wiper 7 leaves its stud. The motor then stops again and is finally restarted upon release of the biased switch 17 which restores normal running conditions. Upon completion of the test sequence the wiper 7 reaches a stud 7 which is connected to a point y as shown, thus shorting D(a) and lighting lamp 18. Dummy Tests.-Known impedances connected to the studs may be provided. If a reject impedance is used then a correct response would cause the motor to stop, and failure of the apparatus to respond would only be indicated momentarily. These disadvantages may be avoided by the use of a winding D(b) which is energized through relay E in an opposite sense to D(a). If an incorrect pass signal is given then D(a) and D(b) will cancel out and stop the motor causing reject dummy lamp 20 to light, but if a correct reject. signal is given then D(a) is deenergized and the winding D (b) causes the motor to continue running.