Modification of cascade control
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A cascade control of temperature and flow rate, with a temperature main loop and a flow rate secondary loop. I don’t want to add another flow meter now; instead, I’d like to change this cascade control to one based on the opening degree of a temperature-control valve, using the valve’s opening degree as the secondary loop. Is that possible?
You can just change it to a temperature control loop; it’s enough to configure it in the DCS.
It shouldn’t be possible. I’ve never seen anyone do this. The usual approach is to keep only flow control in automatic mode, or to disengage the cascade control and switch to manual control of the control valve in order to adjust the flow rate; the flow rate is then changed intermittently based on temperature changes.
A control system with one parameter is a simple control system; it simply feeds the temperature control signal directly to the actuator for adjustment....
If you don’t want cascading, just go with a single-stage circuit directly
By modifying the configuration, it can be turned into a control system with master-serie switching.
Adding a valve position for a secondary circuit doesn’t serve any practical purpose; in fact, it may even degrade the control performance. Generally, the valve position is only displayed on the control panel, and most control valves don’t require their position to be sent back to the control system. A single-loop temperature control is sufficient.
Direct single-loop temperature control valve available