Error Squared Controller (Ph Applications); Contacts Output Controller - ABB AW400 Series Instruction Manual

5.2.2.4

Error Squared Controller (pH Applications)

When the instrument detects that pH sensor has been selected for the controller, it enables a special PID
algorithm with an "Error Squared" function. The error squared function is applied only within a band defined in
the "BAND" parameter of the controller's configuration menu. When the error is outside this band, the effective
error is a linear response (see Fig. 13).
If "BAND" parameter is set to "0", then the controller operates like a standard PID controller
5.2.2.5

Contacts Output Controller

This controller, also known as Proportional Speed Floating Controller, is particularly suitable for operation with
an electrically motorised control valve, or dosing pump, and it actuates the final control element through
output contacts closure rather than 4–20 analog signal. The controller performs process control through the
velocity algorithm, a term that describes a control action in which the direction and rate of motion of the final
control element is proportional to the deviation of the controlled variable from the set point.
In the control with contacts the PID algorithm is not active. and the output is calculated in function of the Gain
parameter. The Gain parameter is functionally similar to the Proportional Action; explaining with an example,
considering constant the difference between set-point and process variable, contact will be closed longer if
Gain parameter is low , while it will be closed shorter time if Gain parameter is high.
% output duty cycle
Gain is defined as:
Time cycle parameter represents the duty cycle of the contact output. Its action is similar to the Integral Action
(TR) , in fact it represents time (expressed in seconds) of a cycle of control. Considering the difference
constant, if it is set to a high value the control action will be slow, while if it is set to a low value the control
action will be faster.
Dead Zone parameter represents the range around set-point where control action has no effect. So, when the
difference between process variable and set-point is lower than this value contacts are kept open.
The contacts used by the controller to drive the final element are assigned as per the following table:
Decrease
Table 8 - Contacts Output Controller assignment
40
Fig. 13 - Error versus control band
% input deviation
PID 1
CCO 3 CCO 4
Increase
PID 2 (optional)
CCO 5 CCO 6
Decrease Increase