When should the plastic casing and when should the metal casing be used?

ANSWER:

The enclosure material choice is based on the application and environment that the positioner will be used in. The standard enclosure for the PS2 valve positioner is a reinforced polycarbonate material, trade name Macrolon. This plastic material has both excellent chemical resistance and due to its light weight excellent resistance to vibration. If the Polycarbonate material is not suitable, or a metal enclosure is specified, there are three options. Two Aluminum enclosures are available-- the standard (rectangular) form factor for single acting applications (model: 6DR5 *11-0*), and a flameproof EExd enclosure available in single or double acting versions. A feature of these enclsoures is the low copper content of the Aluminum used, which improves the corrosion protection.  A stainless steel enclosure is also available for severe corrosion environments (model: 6DR5 **2-0*).