The automatic analysis of gas chromatogram could be realized by a controller made up of a time relay and an intermediate relay with simple manufacture and low cost.

In the light of that many problems exist in the intermediate relay c ontrol used in the pressure filter, the programmable controller is used for the control of the pressure filter, the single unit control is transformed into the centralized control, increasing greatly the working reliability of the reverse d evices.

For the problem that power does not match with the equipment that happens during the design,by using the intermediate relays and regulator DC power supply,it is controlled.

In view of bad closing winding by non-full-voltage closing and high voltage node mal-trip,the time relay and middle relay of control circuit are adding in the control circuit within limited situation to avoid the accident.

This paper explains the concept of CPU s time-sharing treatment and output buffers in the application of PLC,doubled output points of PLC by auxiliary relays out of the machine and time-sharing software.

The selection of an auxiliary relay is a key question of reliability to improve control system operation.

This paper basically describes that PROFIBUS-DP and valve-island are used instead of the traditional auxiliary relay,sensor and electromagnetic valve,adopting fieldbus control system replaced the way of distributed connection to control executive component in the Cigarette Making and Plug Assembling Combination.