Position Indicators POSITION INDICATION CIRCUITRYPOSITION INDICATION CIRCUITRYValve position circuitry provides indication and control functions.EO 1.4 Given a diagram of a position indicator, STATE the purpose ofthe following components:a. Detection deviceb. Indicator and control circuitsEO 1.5 STATE the two environmental concerns which canaffect the accuracy and reliability of position indicationequipment.As described above, position detection devices provide a method to determine the position of avalve or control rod. The four types of position indicators discussed were limit switches, reedswitches, potentiometer valve position indicators, and LVDTs (Figure 7). Reed and limitswitches act as ON/OFF indicators to provide open and closed indications and control functions.Reed switches can also be used to provide coarse, incremental position indication.Potentiometer and LVDT position indicators provide accurate indication of valve and rod positionthroughout their travel. In some applications, LVDTs can be used to indicate open and closedpositions when small secondary windings are used at either end of the valve stem stroke.The indicating and control circuitry provides for remote indication of valve or rod position and/orvarious control functions. Position indications vary from simple indications such as a light tometer indications showing exact position.Control functions are usually in the form of interlocks. Pump isolation valves are sometimesinterlocked with the pump. In some applications, these interlocks act to prevent the pump frombeing started with the valves shut. The pump/valve interlocks can also be used to automaticallyturn off the pump if one of its isolation valves go shut or to open a discharge valve at some timeinterval after the pump starts.Valves are sometimes interlocked with each other. In some systems, two valves may beinterlocked to prevent both of the valves from being opened at the same time. This feature isused to prevent undesirable system flowpaths.Control rod interlocks are normally used to prevent outward motion of certain rods unless certainconditions are met. One such interlock does not allow outward motion of control rods until therods used to scram the reactor have been withdrawn to a predetermined height. This and allother rod interlocks ensure that the safety of the reactor remains intact.Rev. 0 Page 11 IC-05
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