In ordertoimprove thereliability of power automation device,accordingto actual working environ ment,a series of contrasting experiments for reasonable selection of small size intermediate relay have been done.

Through the analysis and comparison of field data obtained from actual measurement,the interference source properties of important relay protection\'s out-tripping relay and switching input optical couple that generating mal-operation are analytically demonstrated.

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.