Prioritize Filter Effluent Flow by Performance

I need to develop logic for controlling the flow through 8 media filters with a Siemens S7. The flow will be divided by the total number of filters that are online. That is the easy part. A PID will monitor the effluent flow from each individual filter and modulate the effluent valve.

Where I am running into trouble is with the development of a "flow trim" based on filter performance. This Trip will be 10-20% of the control loop.

The idea is for filters with higher turbidity to receive less flow and the filters with the lowest will see more flow.

So for example:

(Max allowable flow through any given filter = 1MGD)

Filter 1 Turbidity 0.08 -> Eff Flow 1.00 MGD
Fitler 7 Turbidity 0.10 -> Eff Flow 0.95 MGD
Filter 5 Turbidity 0.15 -> Eff Flow 0.90 MGD
Filter 2 Turbidity 0.20 -> Eff Flow 0.85 MGD
Fitler 4 Turbidity 0.20 -> Eff Flow 0.80 MGD
Filter 3 Turbidity 0.25 -> Eff Flow 0.75 MGD
Fitler 6 Turbidity 0.27 -> Eff Flow 0.65 MGD
Filter 8 Turbidity 0.30 -> Eff Flow 0.60 MGD
......

Let me know if you have any ideas or need me to clarify. Thanks!

What are you filtering out? I assume filters are in parallel? Piping diagram would sure help. What kind of filters - sand or??


Dan Bentler