Multizone Control - Thought Leadership with Ian Collins

Ian Collins, Product Manager at West Control Solutions talks about the Cascade Control feature found in the PRO-EC44 controller.

Transcript 

To achieve even temperature throughout a process, more than one temperature controller can be required.

Multiple zones, with a separate sensor and heater in various points of the machine, are each controlled independently, allowing for stability and assured temperature throughout the process.

An example of this is in an a lean furnace, large sheets of glass are required to reach a desired temperature across the complete product, it’s not possible to achieve this with a single controller

Multiple control zones are required to ensure optimum quality across the full surface area of the glass.

When there is a change in setpoint, its generally a requirement to change all control loops similarly in a multizone application

As a manual process this can be time consuming and is a high risk of human error.

Two common methods allow for changing setpoint in a single device by transmitting it to other control loops in the system.

Linear transmission uses an analogue output from the controller for example 4 to 20 milliamps, this is used as a setpoint reference by other controllers.

Analog methods of transmission are prone to error and it can be difficult to achieve accurate results.

Transmission via serial communications is the second option, the main controller is set as a communications master with the setpoint constantly transmitted to other slave devices in the network.

The setpoint is changed, this modification is transmitted to the other slaves devices that will follow.

This method has the benefit that specific setpoint data values are transmitted with no error.

In heat treatment processes, setpoint change may be required over a period of time as part of the hardening process.

If each zone had individual profiling capability it would be complex to sequence all zones to have the same setpoint.

By running a profile in the mater this moving setpoint can be transmitted to all slave devices that will follow, this simplifies the implementation and reduces cost.

Some systems requires deviation from the setpoint transmitted, each controller can have an offset parameter which allows a specific value to be added or subtracted from the transmitted setpoint

To recap, the main benefits of master slave transmission are: accurate transmission of setpoint, there are no errors as found with analogue signals.

Implementation is simplified – where profiling is needed and saves cost.

For more information, please visit our website www.west-cs.com