General Information
Chapter Eight: Operation in Control Mode
250
If the system is operating far below set point, there will be a large change in pressure between
screen refreshing because the system will be quickly moving towards set point. Within the
one-third second time frame, the deviation could range from -22% (at the beginning of the time
frame), to -4% (at the end of the time frame). In this case, the middle three segments in the
lower half of the deviation indicator light up (refer to Figure 84, page 249).
Another example is when the pressure oscillates above and below set point. Upper and lower
deviation indicator segments light up to indicate over and under pressure readings. In effect, the
deviation indicator provides similar information to that provided by an oscilloscope. If the
oscillation continues, it is possible that reducing the Gain setting may improve system stability.
When the system does stabilize, none of the deviation indicators are lit.
When the Set Point is 0:
If the set point is 0 and the pressure reading is 0, no segments light up.
If the set point is 0 and the pressure is above 0, the uppermost segment lights up.
If the set point is 0 and the pressure is below 0, the lowermost segment lights up.
The Rear Panel Override Indicator
The Valve Position parameters (Open, Auto, Close, Hold, and Manual), and the Active Recipe
parameter can be selected through the front panel keyboard. The Open, Close, Manual, and
Active Recipe parameters can also be selected through the bottom connector on the Control
board (digital control lines). A front panel selection can be overridden by a rear panel digital
input. A small arrow appears to the left of the parameter when a rear panel override occurs.
Refer to Figure 12, page 43, to see where the Control Mode parameters and their associated
override arrows are located.
For example, if the Valve Position parameter
AUTO
is selected with the front panel keypad, the
AUTO
legend is displayed in the front panel window. If the Valve Position parameter
CLOSE
is selected through the rear panel, this selection overrides the front panel keypad selection. The
AUTO
legend continues to be displayed, but the
CLOSE
legend is also displayed.
Additionally, a small arrow is shown to the left of the
CLOSE
legend, to indicate a rear panel
override is in effect.
An Active Recipe override is indicated by displaying a small arrow next to the
AUTO
legend.
For example, if the 146 unit is currently operating with the
AUTO
parameter selected, and the
active recipe is recipe 1, the
AUTO
legend is displayed. If the active recipe is changed to recipe
2 through the rear panel, the
AUTO
legend remains lit, but a small arrow now appears to the
left of it.
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