Automation of a bypass

I am trying to implement in my model a condition that could let me to automate an specific bypass of a % of the influent flow to the primary decanter depending on the value of the DQO/NTK relationship. For example, two orders that I want to create are that when DQO\NTK= 6, then the 0% of the influent flow bypasses the primary decanter, but when DQO\NTK= 8, then the 25% of the influent flow bypasses the primary decanter.

As a first step, I am able to create the new variable "DQO\NTK in the influent" with the calculator tool, but I am not sure about what other blocks I should use in order to create this kind of automation that I would like to implement. I do not see a direct application to this aim with the typical blocks of control like "timers" and "PI", etc....

Thanks for your help and time.

[quote author=Héctor Rey link=topic=2997.msg6715#msg6715 date=1457772891]
I am able to create the new variable "DQO\NTK in the influent" with the calculator tool[/quote]

You will not be able to use your [b]calculator variable[/b] in a model - you will need to use a controller to regulate the opening of the valve.

You would not be able to make use of the same variable added to the [b]fractionation model[/b] either ("V" block).

The only way I see is that you add your variable (DQO / NTK) to a [b]sensor model[/b] (you could use the MultiSensor and just add a new output interface variable).
Then you will:
[list]
[li]insert the sensor block upstream of the valve[/li]
[li]insert a controller (most likely a new model too) that takes the DQO/NTK sensor output from the sensor; the output signal will be linked to the f_Out2 of the valve[/li]
[/list]

As a general remark, make sure that the state of the valve changes "gradually" - i.e. avoid "hard switches" where the 1st derivative is discontinuous.
If this should be the case, consider inserting a [b]response-time model[/b] (2nd order is sufficient) between the controller and the valve.