Direct Acting (Acid) - ABB AnalyzeIT AX460 User Manual

Single input ph/redox (orp) analyzer

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1.1.2 Direct Acting (Acid) Single PID Control – Fig. 1.3

Direct acting control is used when the process pH is greater than the required output pH. Normally, acid is added to the sample to

decrease the pH value.

100%

Control

Output

0pH

1.2 Dual (Bi-directional) PI Controller – Figs 1.4 and 1.5

The dual (bi-directional) PI controller is a a dual-feedback control system using P + I control with two local set points.

High Set Point

Process Variable

Low Set Point

Process Variable

Fig. 1.3 Direct Acting (Acid) Single PID Control

PI Control Loop

Fig. 1.4 Dual (Bi-directional) PI Controller

7pH

Manual Output

PI Output

1 INTRODUCTION...

Direct

Acting

14pH

Output 1

Output 2

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