Flow sensors with variable speed port to target constant GPH?

[chadowens]

Is it possible to use the flow sensor on a return pump coupled with the variable speed port (i'm running a varios 8 return pump) to set a constant flow rate? I'm running a herbie style drain with manifold and would like to use the apex/fmm to maintain a constant return rate as my media ages. Anyone done this and have some example code if so?

Thanks!

[zombie]

You can do sort of a stepped code to simulate a feedback loop (make sure the sensor goes on the return and not the overflow or bubbles can mess up the reading). Say for example your target flowrate is 1000 gph and you have run the pump to find that approximately 70% will reach said target you could do something like this.

Fallback ON
Set 66
If flow < 1100 Then 68
If flow < 1050 Then 70
If flow < 1000 Then 72
If flow < 950 Then 74
If flow < 900 Then 76

You might be an engineer if...You have no life and can prove it mathematically.

[chadowens]

Appreciate the reply but I don't think this would solve what I'm after unless I'm missing something. I was hoping that if I open up a manifold valve for example which would reduce flow to the return (all else constant) the variable speed port could increase the pump speed to compensate to maintain the same return flow. Equal return flow would therefore occur at different levels depending on what I'm running through the manifold or if media is clogged etc., whereas the above rates would be preset based on current conditions if I follow.

[zombie]

Appreciate the reply but I don't think this would solve what I'm after unless I'm missing something. I was hoping that if I open up a manifold valve for example which would reduce flow to the return (all else constant) the variable speed port could increase the pump speed to compensate to maintain the same return flow. Equal return flow would therefore occur at different levels depending on what I'm running through the manifold or if media is clogged etc., whereas the above rates would be preset based on current conditions if I follow.

That is actually what I show above does. As the flow reduces (as would happen if you opened a manifold) then the pump power increases to compensate. Testing would need to be done to find the right flows and percentages to use for each step by purposely clogging lines, opening or closing manifolds, etc.

One backdraw to this is that the apex is not capable of doing PI or PID type feedback loops so your only option is stepped proportional feedback as I described. Because there cam be no integral or differential terms in the feedback control it cannot hold flow steady exactly where you want it. Flow will still be reduced if you add more head or additional exits and will be increased if something clogs but the effect will be reduced compared to setting the return at a constant power.

You might be an engineer if...You have no life and can prove it mathematically.

[zombie]

Also of note, this will only work if the sensor is placed on the pipe that goes between the return manifold and the tank. If placed on the overflow bubbles will create error in the measurement and if placed before the manifold it won't compensate for changes as you desire.

You might be an engineer if...You have no life and can prove it mathematically.

[chadowens]

Okay, I see what you mean now. I'll give it a shot. And thanks for the info of the location for the sensor. I have it installed in the correct location. Thanks