In a level-to-flow cascade arrangement (LC sending SP to FC), I’m trying to understand what the level controller is actually doing.

Does the LC calculate and send a flowrate setpoint to the flow controller?
For example:

• if level increases slightly → send flow SP = X m³/h
• if level increases further → send flow SP = X + Δ m³/h

Or is the LC simply increasing/decreasing a 4–20 mA signal to the FC, and the FC interprets that somehow?
Basically, how does the cascade interaction physically and functionally work between the LC and FC in a typical DCS/PLC implementation?

 

The level controller adjusts it output relevant to the level, this output is then scaled to a flow setpoint for the flow controller

 

Why is flow cascade control being used at all

 

Why is flow cascade control being used at all

If you need a fast reacting system and your downstream conditions can change, affecting flow rate

 

Tank levels are rarely fast acting, but a reservoir. Fast acting and accurate flow control is common in some processes, but rarely will tank level be used to control the discharge flow.

For example, high pressure boilers are a totally different category, especially where super heaters, steam turbines, condensate recovery, and deaerators are involved.

 

Tank levels are rarely fast acting, but a reservoir. Fast acting and accurate flow control is common in some processes, but rarely will tank level be used to control the discharge flow.

Never say never, the type of process isn’t even mentioned