what is diffrence between cascade & three element system.

Answer Posted / senthil.doosan

cascade control - it is a combination of two controllers in
which one act as a master and other as a slave.i.e the
output of one controller is fed as a setpoint to other
controller.
we use this cascade control in three element system(drum
level control)
three element-level,feed water flow and steam flow.
theory:
single element:here the feedback of the drum level is given
to feedwater flow controller to control the level in the
tank.the output of this controller controls the 30% valve
three element:the output of this controller will be summed
with the mass steam flow(combination of density and volume
flow rate) and given to the other controller(input is
feedwater flow) as a setpoint.the output of this controller
controls the 100% valve.

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