Direction of action of the [Control], 2- or 1-way
You can vary the
[Control]
based on various features.
Function: A 2-way
[Control]
operates in two possible directions (Increase AND decrease
measured value).
Application: In a neutralisation process in an industrial waste water system, acidic or
alkaline waste water is produced alternately. Before the water can be fed into the sew‐
erage system, the pH value should, for example, be set to a value between pH 6.8 and
7.5. A 2-way controller with two metering pumps for metering acid and alkali is used for
this purpose. The pH value can be both decreased or increased to come within the nec‐
essary setpoint range.
Measured value
Setpoint
Control variable
Negative
deviation
Negative
Control variable
Time
Time
Positive
Control variable
Positive
deviation
A1471
Fig. 75: Control type two-way PID. Control characteristic without dead zone
Setting the
[Control]
105
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