
946 Controller Instruction Manual
pg. 54
b) If Ceiling setting is less than the Start value, the Start will be overridden by
Ceiling.
The range is from 0 to 100% of full scale for a MFC, or from 0 to 100 % for a control
valve. The default setting is 0, and it must be equal or larger than Base parameter
value.
•
End: The End value is the ending set point value for MFC (or the ending position for
valve) during the slow start control process (ramp before PID control)
a) If Base setting is greater the End value, the End will be overridden by
Base.
b) If Ceiling setting is less than the End value, the End will be overridden by
Ceiling.
The range is from 0 to 100% of full scale for a MFC, or from 0 to 100 % for a
control valve. The default setting is 0, and it must be equal or larger than Base
parameter value.
•
CtrlStart: The CtrlStart value is the time period (in seconds) over which the valve
drive signal (thus, the valve position) or the MFC flow drive signal goes from the Start
to the End. See Figure 6-15..
There is no ramping of the MFC drive signal if the CtrlStart is set to zero.
•
Direction: Direction sets the valve control to either Upstream or Downstream. During
Upstream control, higher set point often leads to higher chamber pressure, while it is
opposite during Downstream pressure control process. When a Throttle Valve is
used, the Direction must be set to Downstream. When MFC is used, it is
automatically set to Upstream.
•
GainSchedBand: This is the band for gain scheduling PID control, that is, allows
different proportional gain
K
p
at different error band during pressure control. This is
often used for maintaining stable control around the set point (within the scheduled
PID control zone as shown in Figure 6-16), while ensuring fast approach to the set
point in the normal PID control zone where the control error is large (such as at the
beginning of the control process).
The GainSchedBand is defined as
, the valid range for
GainSchedBand is from 0 to 30%, and default setting is 0.
•
GainSchedCoeff: The SchedGainCoeff is the Gain reduction coefficient for PID
scheduled control. By reducing the proportional gain
K
p
in the scheduled PID control
zone, more stable control near the set point is achieved, avoiding potential large
overshoot during the control. The valid range is from 1 to 200, and the default value
is 1 (no scheduled PID).