1. My question Is concerned about the weight of the enclosure.1mm thik Galvanized Mild Steel sheet is very heavy with respect to others. as 60 % of the instrument area is occupied by the machanism not relavent to the noise, is it really naccesary to keep them inside this Galvanized Steel sheet, or a kind of double enclosure is employed where outer cabinet is made of fibre and only the electronic Circuit is kept in the Prescribed encloser. Is there any harm?

You need to enclose only your electronic circuit inside galvanised steel enclosure. Rest of the things such as motor etc should be outside the enclosure. Since your aim is to shield your control circuit against noise generated by motors etc. As far as weight is concerned for 1mm thick mild steel box having dimensions 6 inches X 6 inches X 4 inches the weight will be approximately 800 grams.

Regards,
Prahlad Purohit