Sartorius DCU 3 - pH PID Control Function

Operators Handbook DCU3 – System
6., Main function „Control Loops“
BAEDCU3 - Rev. 4.6 - 0504 6 - 11
6.8 pH - Control Function Operating as PID - Controller
The pH - control function of the DCU system usually works in PID - behavior. The pH - control function
triggers the corrective agent pumps (or dosing valves) in split-range mode via two pulsewidth-
modulated outputs. This allows a simultaneous control of both the acid and base pump (or valves).
 As a special feature the acid and base control signals remain „off“ as long as the deviation
of the actual value lies within the parametrized dead band. This feature prevents unneces-
sary dosage of acid or base.
6.8.1 Operating Display
 For a description of the tags, the physical units or entries, the displayed value or function
and of the required inputs see the table in section 6.3, Controller Operation in General.
6.8.2 Operating Information
 For entering controller parameters in the parametrization menu see the section „Controller
Parametrization in General“ further above.
6.8.3 Special Notes
 The dead band is the percent span of the measuring range; it is symmetrical to the setpoint.
– Example: measuring range: 2 - 12 pH, span: 10 pH, DEADB: 0,1 pH, SETP: 7,0 pH
In this example the controller output is inactive in the range of 6.9 pH to 7.1 pH
 When a gas mixing system is connected, the CO
2
valve is controlled via the negative output
signal of the pH controller (0 ... (-100) %)
 If you select one of the operation modes „auto“, „profile“ or „manual“, the dosing counters
ACID and BASE will automatically be switched over to the „tlize“-mode.