Chemtrac Systems, Inc.
Page 38
The AUTO or Manual control mode can also be changed from the
Pump Control (1)
menu. When
Pump Control (1)
menu is displayed, move the text cursor on the far left
hand side of the screen (
}
) to
“Pump Ctrl:”
then press
u
key, the control text will blink.
The controller mode can be set by pressing
p
or
q
key, this will toggle between AUTO
and MAN modes. Set the controller to AUTO. When completed the change, press the
t
key then press
p
or
q
key to get to other parameters on that screen. The
Proportional Band, Integral Time, and PID Rate can be changed by following the same
procedures. The
SAVE Function Key
must be pressed save current setting
modifications and brings up the MAIN screen. The
MAIN Function Key
can be used to
discard any new modification made to this screen and brings up the MAIN screen.
To adjust tuning constants (refer to section 3.2):
Follow these three guidelines when establishing correct tuning constants:
1. Change only one control action at a time. Making two or more corrections is
confusing and can cause the controller to get out of control.
2. Never make a large change in a tuning constant. Make a small change and
observe the effect it has on the control action.
3. Allow plenty of time for the process to stabilize before making another change,
making changes in an unstable process can be misleading.
3.9
FLOW CONTROL
Flow control is a feature that allows the Controller to perform coagulant pump control in
the process that is varying their process flow. During large process flow variation, the
PID control alone may not be able to response to the flow changes. The Controller
monitors the process flow and uses it in the flow control calculation. The Controller is
equipped with auxiliary analog input (4-20mA). When the flow control is enabled, the
pump control output is proportionally changed by the amount of process flow changes in
conjunction with the PID loop based on the SCV setpoint. The following are parameters
used in the flow control:
q
Flow Ctrl: The flow control modes are ENABLED or DISABLED. When the flow
control is ENABLED, pump output percent % will increase or decrease
automatically in response to process flow changes and SCV deviation from the
setpoint. When the flow control is DISABLED, the pump output percent will
increase or decrease automatically in response PID Loop control only.
q
SCV Control Band: Percent band around the flow control proportional pump
output, based on the four parameters below, that the PID loop can effect.
q
Flow Min: Minimum process flow in percent set for the produce the minimum
pump control output for the parameter below (Pump Output Min).
q
Pump Output Min: Pump control output for the minimum process flow set above
(Flow Min).
q
Flow Max: Maximum process flow in percent set for the produce the maximum
pump control output for the parameter below (Pump Output Max).
q
Pump Output Max: Pump control output for the maximum process flow set
above (Flow Max).