SWITCHESPosition IndicatorsLimit switch failures are normally mechanical in nature. If the proper indication or controlfunction is not achieved, the limit switch is probably faulty. In this case, local position indicationshould be used to verify equipment position.ReedSwitchesReed switches, illustrated in Figure 4, are more reliable than limit switches, due to theirsimplified construction. The switches are constructed of flexible ferrous strips (reeds) and areplaced near the intended travel of the valve stem or control rod extension.Figure 4 Reed SwitchesWhen using reed switches, the extension used is a permanent magnet. As the magnet approachesthe reed switch, the switch shuts. When the magnet moves away, the reed switch opens. ThisON/OFF indicator is similar to mechanical limit switches. By using a large number of magneticreed switches, incremental position can be measured. This technique is sometimes used inmonitoring a reactor’s control rod position.IC-05 Page 6 Rev. 0
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
