Intelligent process controllers prevent failure and downtime
May 2004
PLCs, DCSs & Controllers
Frustrating failures that cause unscheduled downtime are often a result of:
* Moisture ingress when processes cool down.
* Processes overheating, stopping - or tons of scrap produced due to sensor failure.
* Elements burning out.
* Stress due to thermal expansion in the start-up phase.
These are often largely due to 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).
Modern, advanced temperature controllers can solve these problems. These intelligent controllers look for faults in the process. If a fault is detected, the controller will work around it in order to reduce downtime.
UniTemp is offering Gefran's new 600, 1200 and 1300 series of single loop PID temperature controllers - which include features that are latest developments in this area. With this series the user can switch between two setpoints by either operating a button on the instrument faceplate, or by operating a remote switch. It is possible to switch the system to standby mode, dropping the temperature down to a warm level above dewpoint. Leaving elements at a reduced temperature above dewpoint during off-periods eliminates failure due to moisture ingress and reduces start-up time. A typical example would be on hotrunner systems for injection moulding, where 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 due to thermal expansion in the start-up phase. These controllers also come with a loop break alarm and a sensor failure alarm. As they switch the elements on, they detect if there is a resulting rise in temperature. If there is a fault (a break in the circuit, sensors not being mounted properly, sensor failure, etc), they activate an alarm. The user can configure the controllers 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 downtime.
Cheaper controllers do not come with these advanced features. Using intelligent controllers will allow processes to run more efficiently and also save on downtime.
For more information contact Neil Coetzer, UniTemp, 011 392 5989.
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