VARIABLE OUTPUT DEVICES
Position Indicators
VARIABLE OUTPUT DEVICES
Variable output devices provide an accurate position indication of a valve or
control rod.
EO 1.3
DESCRIBE the following variable output position indicators to
include basic construction and theory of operation.
a.
Potentiometer
b.
Linear variable differential transformers (LVDT)
Potentiometer
Potentiometer valve position indicators (Figure 5) provide an accurate indication of position
throughout the travel of a valve or control rod. The extension is physically attached to a variable
resistor. As the extension moves up or down, the resistance of the attached circuit changes,
changing the amount of current flow in the circuit. The amount of current is proportional to the
valve position.
Figure 5 Potentiometer Valve Position Indicator
Potentiometer valve position indicator failures are normally electrical in nature. An electrical
short or open will cause the indication to fail at one extreme or the other. If an increase or
decrease in the potentiometer resistance occurs, erratic indicated valve position occurs.
IC-05
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