Answer / himanshu bhardwaj

In CASCADE control output of one system works as the set
point for the next system , this is called cascading and
hence the system is said to be cascade control system.

Answer / abhishek vyas srf limited

Best example of cascade control is level control of a
tank. first taking care of it's actual level( getting
signal from level transmitter) then controlling it's flow.
so only controlling element is flow and level singnal will
work as a setpoint for flow controlling.
There are two controller used one for level whose
controller o/p will work as a set point for flow controller
then final control signal from flow controller will actuate
the control valve. Thus actual level will achived.

Answer / sanjay kumar it-bhu

Cascade Control uses the output of the primary controller
to manipulate the setpoint of the secondary controller as
if it were the final control element.

Reasons for cascade control:

Allow faster secondary controller to handle disturbances in
the secondary loop.
Allow secondary controller to handle non-linear valve and
other final control element problems.
Allow operator to directly control secondary loop during
certain modes of operation (such as startup).
Requirements for cascade control:

Secondary loop process dynamics must be at least four times
as fast as primary loop process dynamics.
Secondary loop must have influence over the primary loop.
Secondary loop must be measured and controllable.
Reasons not to use cascade:

Cost of measurement of secondary variable (assuming it is
not measured for other reasons).
Additional complexity.
Examples of cascade control:


Control of heat exchanger outlet temperature using steam
flow as secondary loop.

Answer / swarndeep signh

Cascade Control system in process instrumentation is
defined as a system whose gain is dependent of other
control controlled variable vice versa.For Example: Four
conveyor running process if the speed of any one drive is
changed other will also vary acording to its defined gain.

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A temperature sensor (RTD) connected via a temperature transmitter is adjusted to give an output of 4ma at 60 deg and 20 ma at 600 deg. This output (4-20ma) from the transmitter is connected to an IGBT-inverter to control a high speed (-12,000 to +12,000 RPM) DC motor. And in the inverter it is programmed as, for 4ma the motor speed will be -3,000 RPM and for 20ma the motor speed will be +10,000 RPM. The question is : If the motor speed is +5,500 (RPM), what will be the temperature? (-sign indicates that the motion is in reverse direction).

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