ATI
Q46H/65 Residual Chlorine Dioxide System
Part 6
– Configuration
42
O&M Manual
Rev-J (11/18)
6.25 Control Menu [CONTROL]
The Control Menu contains all of the output control user settings:
Set PID 0%
If the PID is enabled, this function sets the minimum and maximum
Set PID 100%
controller end points. Unlike the standard 4-20 mA output, the controller
[Iout1=PID]
does not “scale” output values across the endpoints. Rather, the
endpoints determine where the controller would normally force minimum
or maximum output in an attempt to recover the setpoint (even though
the controller can achieve 0% or 100% anywhere within the range.)
If the 0% point is lower than the 100% point, then the controller action
will be “reverse” acting. That is, the output of the controller will increase
if the measured value is less than the setpoint, and the output will
decrease if the measured value is larger than the setpoint. Flipping the
stored values in these points will reverse the action of the controller to
“direct” mode.
The entry value is limited to a value within the range specified in “Set
Range”, and the 0% and the 100% point must be separated by at least
1% of this range Use the LEFT arrow key to select the first digit to be
modified. Then use the UP and LEFT arrow keys to select the desired
numerical value. Press ENTER to store the new value.
PID Setpnt
The measured value which the controller is attempting to maintain by
[Iout1=PID]
adjusting output value. It is the nature of the PID controller that it never
actually gets to the exact value and stops. The controller is continually
making smaller and smaller adjustments as the measured value gets
near the setpoint.
PID Prop
Proportional gain factor. The proportional gain value is a multiplier on
[Iout1=PID]
the controller error (difference between measured value and setpoint
value.) Increasing this value will make the controller more responsive.
PID Int
Integral is the number of “repeats-per-minute” of the action of the
[Iout1=PID]
controller. It is the number of times per minute that the controller acts on
the input error. At a setting of 2.0 rpm, there are two repeats every
minute. If the integral is set to zero, a fixed offset value is added to the
controller (manual reset.) Increasing this value will make the controller
more responsive.
PID Deriv
Derivative is a second order implementation of Integral, used to suppress
[Iout1=PID]
“second-order” effects from process variables. These variables may
include items like pumps or mixers that may have minor impacts on the
measured value. The derivative factor is rarely used in water treatment
process, and therefore, it is best in most cases to leave it at the default
value. Increasing this value will make the controller more responsive.
