Function: A 1-way
[Control]
operates in only one of two possible directions (Increase OR
decrease measured value).
Application: This affects, for example, a disinfection process, in which chlorine is added
to water. The incoming water has a chlorine concentration of 0 ppm and is to be adjusted
to 0.5 ppm by the addition of sodium-calcium hypochlorite. The addition of sodium-cal‐
cium hypochlorite increases the measured value.
Valu epHControl variable
Positive deviation
Setpoint
Negative control variable
Time
Time
A1470
Fig. 77: Control type 1-way PID, pH-lowering direction
Setting the
[Control]
107
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