Based on principle of reverse osmosis and used microcomputer 89C52 as controller

an automatic detection instrument of sludge density index（SDI） of water pollution is designed.The instrument can realize automatic detection of the SDI of water pollution

warning of over-index and showing results.Besides these

by using the function of serial communication of 89C52

the RS485 bus circuit is designed to achieve data remote transmission.At the same time technological process of automatic detection is introduced

which is belong to this instrument.The results show that the system can reduce error from artificial detection but also improve reliability.