Position Indicators
POSITION INDICATION CIRCUITRY
POSITION INDICATION CIRCUITRY
Valve position circuitry provides indication and control functions.
EO 1.4
Given a diagram of a position indicator, STATE the purpose of
the following components:
a.
Detection device
b.
Indicator and control circuits
EO 1.5
STATE the two environmental concerns which can
affect the accuracy and reliability of position indication
equipment.
As described above, position detection devices provide a method to determine the position of a
valve or control rod. The four types of position indicators discussed were limit switches, reed
switches, potentiometer valve position indicators, and LVDTs (Figure 7). Reed and limit
switches 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 position
throughout their travel. In some applications, LVDTs can be used to indicate open and closed
positions 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/or
various control functions. Position indications vary from simple indications such as a light to
meter indications showing exact position.
Control functions are usually in the form of interlocks. Pump isolation valves are sometimes
interlocked with the pump. In some applications, these interlocks act to prevent the pump from
being started with the valves shut. The pump/valve interlocks can also be used to automatically
turn off the pump if one of its isolation valves go shut or to open a discharge valve at some time
interval after the pump starts.
Valves are sometimes interlocked with each other. In some systems, two valves may be
interlocked to prevent both of the valves from being opened at the same time. This feature is
used to prevent undesirable system flowpaths.
Control rod interlocks are normally used to prevent outward motion of certain rods unless certain
conditions are met. One such interlock does not allow outward motion of control rods until the
rods used to scram the reactor have been withdrawn to a predetermined height. This and all
other rod interlocks ensure that the safety of the reactor remains intact.
Rev. 0
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IC-05
