Patent GB-890174-A (GB)
Title: Monitor circuit for detecting failures in a data transmission system
IPC: B64D45/00
Filed: 1960-04-11
Abstract: 890,174. Monitoring selsyn systems. BENDIX CORPORATION. April 11, 1960 [April 17, 1959], No. 12858/60. Class 40 (1). [Also in Group XXXVII] In a transmission system including an inductive transmitter with three or more connections to its secondary winding (e.g. a selsyn), failure of the primary winding or the excitation thereof is detected by a pair of rectifiers joined respectively between two of the connections and a common point, and a capacitor-shunted winding, such as a relay coil, joined between the common point and a third connection, which produces a warning effect when the rectified current falls below a certain minimum. A selsyn system in which the receiver rotor is automatically driven into a null position by a servomotor may also include means, as described below, for detecting breaks in the polyphase stator windings of the transmitter and receiver and the lines connecting them, a break in the receiver rotor winding or a fault in the servomotor, amplifier or follow-up mechanism. In Fig. 1, a selsyn transmitter has its rotor winding 12 energized from an A.C. source and its three-phase stator winding 14 connected by leads 36, 37, 38 to the corresponding receiver stator winding 22. Rectifiers 81, 83 are joined to two of the leads via resistors, and the circuit is completed back to the third lead via a relay coil 87 which is shunted by a capacitor 90. If voltage ceases to be induced in the stator winding, the voltage across the capacitor will decay to zero and the relay will be de-energized. The connecting leads between the transmitter and receiver are broken by capacitors 39, 40, 41. Two of these are shunted by resistors, while a D.C. bridge 47 is joined across the third, this bridge being normally balanced. If a break occurs in either stator winding or in a connecting lead, the effective resistance presented to the bridge will rise, so that an output will be obtained which is amplified at 65 and used to energize a relay coil 67. A similar bridge 107 is provided to energize a relay 127 if a break occurs in the receiver rotor winding 28. The voltage induced in this winding is passed to a rectifier 160 and relay coil 156 across which is a capacitor 162. Normally, this voltage is reduced to zero by operation of a servomotor 33, and the time-constant of the rectifier circuit does not allow the relay to operate. Failure of the servomotor or its associated amplifier 31 or follow-up link 35 will prevent the receiver rotor from being turned to its null position and the relay 156 will operate. The various relay contacts and the corresponding contacts of a second similar system are all joined in series with a D.C. source 174 and relay coil 175 so that a fault anywhere in either system will cause relay 175 to be de-energized and light a warning lamp 189. Two selsyn systems of the above type are associated with a vertical gyro in an aircraft attitude indicating system (Fig. 3, not shown) as in Specification 882,795, using the indicator of Specification 796,260. Operation of relay 175 energizes a warning flag of the kind shown in Specification 686,818.