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<< Click to Display Table of Contents >> Cascade Control |
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The Strategy Controller can be used to trim the set point of one controller based on the output of another. This is used in many applications where the desired measurement is 'thermally remote' from the heat source. Examples include:
| • | Controlling from the internal (part) sensor of a furnace |
| • | Using 'Deep/Shallow' thermocouples on an extruder barrel |
In this example the output of the 'Master' controller is used to adjust the set point of the 'Slave' controller. (If the master is a programmer type controller then 'Master.Working SP' should be added to the 'SpecView.SP Trim' instead of the 'Slave.SP')
The example below shows the use of a SpecView User Variable to give more flexibility in tuning:
| 1. | Define two SpecView Number (with decimals) User Variables, called 'Cascade Gain' and 'SP Trim' |
| 2. | Add a value based event: Value to watch = Master.Output; Test to Perform = Changed |
| 3. | Add an action Parameters: Math Function: COPY FROM Master.Output MULTIPLY SpecView.Cascade Gain COPY TO SpecView.SP Trim |
| 4. | Add a second math function action: COPY FROM Slave.Setpoint ADD Strategy Controller.SP Trim COPY TO Slave.Setpoint |
The Strategy Controller boxes for this example are shown below:
Event:
Action 1:
Action 2:
