Tech & Tools

Technical information

Control of drug injection in pH neutralizer

<Time division proportional control [NN-2000 / NN-200 type]>
Time-division proportional control is a control method in which when three parameters of the target value, proportional band, _and cycle time are set, the drug injection pump is operated intermittently as the pH approaches the target value, _and completely stops when the target value is reached. Suitable for those that require microinjection in the neutralization range such as pH neutralization. This control is mainly used when pH control is performed with a chemical solution.

● Three parameters of time division proportional control

SP [target value] Control is targeted at this value.
PB [proportional band] Set the band to execute time division proportional control. Time division control is performed when the SP + PB value is entered in the case of alkaline neutralization _and the SP-PB value is entered in the case of acid neutralization.
TI [cycle time] It is the cycle time of time division control. During time division control, pump operation time + pump stop time = cycle TI.

In the above figure, area A is the band for time division proportional control, _and area B is the continuous output band. In region B beyond the proportional band, pump control is not performed _and continuous operation is performed. When the pH value falls within the proportional band of region A, the pump is operated intermittently according to the ratio within the proportional band. For example, if the current value is 25% of PB, the pump will run 25% of the cycle time [TI] _and the remaining 75% will be stopped. The pH value at the end of one TI cycle determines the start / stop time for the next cycle.

<ON-OFF control [NN-1000 / NN-100 type]>
ON-OFF control is a method of continuously operating the pump when the pH value is above [_or below] the set value. ON-OFF control is often used for pH monitoring / alarm, _and is rarely used for pH control.

<PID control [PXR5 type]>
P, I, _and D are English acronyms, respectively.
P stands for Proportion, I stands for Integral, _and D stands for Defferentiation.
PID control determines how to inject in order to quickly reduce the difference between the target pH value _and the current pH value. P is a time-division proportional control function, _and based on this, control is performed by adding differential _and integral elements. I accumulates the deviation due to control within a certain period of time, adds it if the control is insufficient, subtracts it if there is an overshoot, _and D immediately responds to the control amount when the amount of change within a certain period of time is large. The element. These three operations make the best judgment of the current situation _and work to quickly approach the target value. However, it is not optimized for pH neutralization with chemicals, _and we only use it for carbon dioxide neutralization equipment.


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