Peter Nachtwey
Member
This video shows the things I think about on page 1.
I use Laplace transforms a lot. Laplace transforms allow one to express differential equations as simple lgebra
The pump has a gain with units of flow/% control output. This must be more than the maximum inflow or the level cannot be controlled. The tank itself has a gain which is 1/area. It should make sense that the larger the surface are of the tank the slower the level will change. It is also better to think in terms of the tank gain being 1/surface are because the surface area may change as a function of level.
I show how to compute the formulas for the controller gain and the integrator time constant. It is pretty easy.
The next part is the simulation. A PLC person wouldn't care about this because he is stuck with the system before him. "It is what it is". I hate that. Engineers would need to know how tall to make the tank by doing simulations like I show. At the end I show what happens when the in-flow exceeds the pump capacity. The closed loop time constants need to be fast enough to react to the changes in the in-flow.
At the end I make the time constants too short. 0.05 minutes is 3 seconds and the sample time is 1 second.
https://deltamotion.com/peter/Videos/tank level control outflow.mp4
I use Laplace transforms a lot. Laplace transforms allow one to express differential equations as simple lgebra
The pump has a gain with units of flow/% control output. This must be more than the maximum inflow or the level cannot be controlled. The tank itself has a gain which is 1/area. It should make sense that the larger the surface are of the tank the slower the level will change. It is also better to think in terms of the tank gain being 1/surface are because the surface area may change as a function of level.
I show how to compute the formulas for the controller gain and the integrator time constant. It is pretty easy.
The next part is the simulation. A PLC person wouldn't care about this because he is stuck with the system before him. "It is what it is". I hate that. Engineers would need to know how tall to make the tank by doing simulations like I show. At the end I show what happens when the in-flow exceeds the pump capacity. The closed loop time constants need to be fast enough to react to the changes in the in-flow.
At the end I make the time constants too short. 0.05 minutes is 3 seconds and the sample time is 1 second.
https://deltamotion.com/peter/Videos/tank level control outflow.mp4