Chapter Three: Overview
Instrument Components
31
Bias Adjust Potentiometer
The bias adjust potentiometer establishes a valve position offset. Since each valve requires a
slightly different voltage level to move from the fully closed to slightly open position, the bias
adjust allows the 1249 unit to compensate for the difference.
Use the bas adjust pot to determine the minimum voltage required to move your valve from the
fully closed to the slightly open position. Refer to How To Change the Bias Adjust Setting, page
36, for more information.
Valve Position Indicator LED
The valve position indicator LED illuminates with different colors to indicate the approximate
position of the valve (refer to Table 8). When the valve is fully closed, the color of the LED is
red. When the valve is fully open, the color of the LED is green. When the valve is in
intermediate positions, the color of the LED varies from orange to yellow.
Valve Position Indicator Colors
Color
Valve Position
Red
Fully Closed
Orange to Yellow
Partially Open
Green
Open
Table 8: Valve Position Indicator Colors
Only the valve position commands will definitely result in a red or green color. When the valve
is being driven by a set point, the full red and green colors may not be shown since the actual
voltage required to fully close or open a valve varies with each valve.
For example, if 9 V fully positions the valve (either open or closed) the LED will look orange or
yellow (since 9 V < 10 V), however, the valve is already in the fully open or closed position.
