Position Indicators SYNCHRO EQUIPMENTSYNCHRO EQUIPMENTPosition indicating instrumentation is used in DOE nuclear facilities to provideremote indication of equipment positions including control rods and major valves.EO 1.1 DESCRIBE the synchro position indicators to includethe basic construction and theory of operation.Position indicating instrumentation is used in nuclear facilities to provide remote indication ofcontrol rod position with respect to the fully inserted position, and remote indication of the openor shut condition of important valves. This remote indication is necessary for the monitoring ofvital components located within inaccessible or remote areas. Remote position indication can beused at any DOE facility, not only nuclear facilities, where valve position indication is requiredfor safety.SynchroEquipmentRemote indication or control may be obtained by the use of self-synchronizing motors, calledsynchro equipment. Synchro equipment consists of synchro units which electrically govern orfollow the position of a mechanical indicator or device. An electrical synchro has two distinctadvantages over mechanical indicators: (1) greater accuracy, and (2) simpler routing of remoteindication.There are five basic types of synchros which are designated according to their function. Thebasic types are: transmitters, differential transmitters, receivers, differential receivers, and controltransformers. Figure 1 illustrates schematic diagrams used to show external connections and therelative positions of synchro windings. If the power required to operate a device is higher thanthe power available from a synchro, power amplification is required. Servomechanism is a termwhich refers to a variety of power-amplifiers. These devices are incorporated into synchrosystems for automatic control rod positioning in some reactor facilities.The transmitter, or synchro generator, consists of a rotor with a single winding and a stator withthree windings placed 120 degrees apart. When the mechanical device moves, the mechanicallyattached rotor moves. The rotor induces a voltage in each of the stator windings based on therotor’s angular position. Since the rotor is attached to the mechanical device, the induced voltagerepresents the position of the attached mechanical device. The voltage produced by each of thewindings is utilized to control the receiving synchro position.Rev. 0 Page 1 IC-05
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