Intelligent process controllers
March 2005
PLCs, DCSs & Controllers
Failure in the production process is often due to burnt out elements, stress as a result of thermal expansion in the startup phase or processes overheating or suddenly stopping.
These are generally caused by sensor failure, sensors not being mounted properly, a break in the circuit, condensation or moisture ingress when elements are turned off or controllers that do not have advanced functions (eg, switching between two predetermined temperatures). Today's more advanced temperature controllers can solve these problems as they look for faults in the production process. If an error is detected, the controller will work around it to reduce downtime. Some good examples of these intelligent temperature controllers are Gefran's new 600, 1200 and 1300 series.
With these controllers it is possible to switch between two setpoints by either operating a button on the instrument faceplate, or by operating a remote switch. Dropping the temperature down to a warm level above dewpoint can be achieved by switching the system onto standby mode.
This is particularly useful during off-periods as it eliminates failure due to moisture ingress and reduces start-up time. For instance: On hotrunner systems for injection moulding, the degrading of plastic (eg, Acetal) can be avoided during stoppage without having to switch elements off completely.
Another benefit is soft start, which causes the output power to increase linearly when the controller is powered up. Soft start allows moisture to escape from the elements before full heating power is applied. This prevents damage to elements due to moisture ingress and reduces the stress caused by thermal expansion in the startup phase.
Gefran's new temperature controllers also come with a loop break alarm and a sensor failure alarm. As the controllers switch the elements on, they detect if there is a resulting rise in temperature. If there is a fault (eg, a break in the circuit, sensors not being mounted properly, sensor failure, etc) an alarm is activated. This series can be configured to default to a predetermined output power if the sensor fails or manually tune the output power to the desired level. This allows completion of a run even if the sensor fails and therefore avoids down time.
For more information contact Neil Coetzer, UniTemp, 011 392 5989, [email protected], www.unitemp.com
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