Asset management systems, for example, are becoming increasingly prevalent in more and more systems.
The reliability of these quiet often extremely highly-advanced systems in technological terms, commences at the base of the automation pyramid with the obvious “simple” signal processing tasks, such as binary position feedbacks. For example, the “open” / “closed” signals from butterfly- and ball valves are extremely common.
If butterfly- or ball valves are operated by automated drives, a standardised drive conform to VDI/VDE 3845 (NAMUR) is generally used. Position feedbacks in a separate modular housing (black box) are usually the most common solutions at the present. It is generally a plastic housing which normally features a very complex mechanical construction. In addition to a large diversity of individual components which logically have an effect on the price, a cost-intensive adjustment of the switching points must usually be made.
The introduction of the ATEX guideline in 2003 has made the issue even more complex, as the different components such as the housing, sensors or microswitches including their associated wiring, must be checked separately for their compliance to the standard or a separate approval must be requestet, not to mention the effort and expense involved if the reliability in terms of the SIL directive IEC 61508 has also to be determined.
It is therefore appreciable that open solutions utilising dual sensors are more frequently the preferred choice. A compact housing, optimised connection and simple mounting features have proven themselves in practice in diverse systems.
TURCK has had dual sensors from different device series to suit the demands of different markets in its product range for many years. The most well-known being the DSC26 housing style for the food industry and the DSU35 series which is used by almost all leading chemical, petrochemical and pharmaceutical companies...
Author:
Sander Makkinga is
Productspecialist Sensors for the Processautomation,
Hans Turck GmbH & Co. KG, Mülheim/Ruhr
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