Cascade control

Cascade Control Custom Search In a cascade control system, two or more controllers are cascaded to control one or more process variable. Controllers are said to be "in cascade" when the output OP. When two or more controllers are cascaded, each will have its own measurement input PV.

Cascade control

A Tutorial on Cascade Control | Control Notes

What is Cascade Control? Cascade control is a control algorithm in which the output of one control loop provides the target for another loop, as shown in the diagram below. The ultimate goal of the cascaded loops is to control the end process. Cascade control can provide precise control for certain difficult systems, for example systems in which some lag time exists.

To better understand cascade control, consider the following example in hydraulic motion control: The figure above shows a very large hydraulic cylinder with a 3-stage proportional valve.

The goal is to control the cylinder position. The first two valve stages have internal electronic controls, and all we need to know about them is that the first two stages will produce a velocity on the third stage that is roughly proportional to the Control Output signal received by the valve.

The third stage has no electronic controls. A standard PID control loop can be applied to this system, as shown in Cascade control figure.

However, this results Cascade control poor control. The valve spool responds very quickly compared to the cylinder. Therefore, when the Position Target of the system the desired position of the cylinder changes, the valve spool will immediately move over its full length of travel, while the cylinder has barely begun moving, and when the actual position eventually catches up to the target, the spool will immediately move back the full length, and in that way, the system can begin to oscillate and will result in poor control.

A better method is to apply an additional inner PID loop to the valve in a cascaded configuration, as shown in the figure below. This requires spool position feedback from the third stage of the valve.

Cascade control

The valve will then provide a much more linear flow in relation to the Control Output, which will make the outer position PID much easier to tune and will provide better control. Cascade Control Advantages Allows inner loop to handle non-linear valve and other final control element problems.

Allows operator to directly control inner loop during certain modes of operation such as startup. Allows controller to respond quickly to the faster inner loop. Cascade Control Disadvantages Cost of measurement of the secondary variable assuming it is not measured for other reasons.

Cascade control

Requirements for Cascade Control: Inner loop system dynamics must be significantly faster such as four times faster than the outer loop system dynamics. If the inner loop is not faster than the outer loop, then the cascade will not offer any significant improvement in the system control.

Inner loop must have influence over the outer loop. Inner loop must be measured and controllable. For the inner loop, define a standard Control axis.

For the outer loop, define a Cascading Outer Loop axis. This axis type provides a virtual Control Output, but does not use a physical Control Output. If you have more than two loops, all loops except the inner loop should be Cascading Outer Loop axes.

If the inner loop is position, use the Gear Absolute 25 command. Set the Gear Absolute command parameters as listed below. The Slave Point A and Slave Point B command parameters should be set to the minimum and maximum values that you want the inner loop axis to control to. For example, if the inner loop is a valve spool that you want to allow to travel from 0 to 0.

Set the Endpoint Behavior command parameter to Truncate.Cascade Control is an advanced application of the PID that can improve control of systems that are subject to significant lag.

Since such systems are slow to respond to disturbances their performance can suffer with each upset. Offering professional pest control services to the Seattle, Pacific Northwest regions - with offices in Bothell and Chalan County, call The solution is a cascade of two or more control loops, each with its own input, in series forming a single regulating device.

The product setpoint temperature is set on the master control loop. This is compared to the product temperature, and the master’s PID output is used to set the remote setpoint of the slave. Cascade control is two or more control loops, each with its own input, in series forming a single regulating device.

Read more about cascade control loops & controllers.

What Is Cascade Control?

Cascade control should always be used if you have a process with relatively slow dynamics (like level, temperature, composition, humidity) and a liquid or gas flow, or some other relatively-fast process, has to be manipulated to control the slow process. Cascade Pest Control has skilled, experienced rodent control experts that can remove rats, mice or any rodent infestation in your home or business.

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Fundamentals of cascade control | Control Engineering