1、應遵守梯形圖語言中的語法規(guī)定 2、設置中間單元在梯形圖中，若多個線圈都受某一觸點串并聯(lián)電路的控制，為簡化電路，在梯形圖中可設置用該電路控制的輔助繼電器，類似于繼中的中間繼電器。3、分離交織在一起的電路設計梯形圖時以線圈為單位，分別考慮繼電器電路圖中每個線圈受到那些觸點和電路的控制，然后畫出相應的等效梯形圖電路。4常閉觸點提供的輸入信號的處理設計輸入電路時，應盡量采用常開觸點，如果只能用常閉觸點，梯形圖中對應觸點的常開/常閉類型應與繼電器電路相反。5、時間繼電器的瞬動觸點的處理對于有瞬動觸點的時間繼電器，可以在梯形圖中對應的定時器的線圈兩端并聯(lián)輔助繼電器，后者的觸點相當于時間繼電器的瞬動觸點。6、斷電延時的時間電器的處理用通電后延時的定時器來實現(xiàn)斷電延時功能。7、外部聯(lián)鎖電路的設計在梯形圖中設置對應的輸出繼電器的線圈串聯(lián)的常閉觸點組成的軟件互鎖外，還應在PLC外部設置硬件互鎖電路。熱繼電器過載信號的處理1)自動復位型熱繼電器，其觸點提供的過載信號必須通過輸入電路提供給PLC，用梯形圖實現(xiàn)過載保護;2)手動復位型熱繼電器，常閉觸點可以在PLC的輸出電路中與控制電機的交流接觸器的線圈串聯(lián)。9、盡量減少PLC的輸入信號和輸出信號10、注意PLC輸出模塊的驅動能力能否滿足外部負載的要求。PLC一般只能驅動額定電壓在AC220V以下的負載線圈電壓為380V的，應將線圈換成220V的，或者在PLC如果系統(tǒng)原來的交流接觸器的外部設置中間繼電器。
1. Observe the syntax in ladder diagram language. 2. Set the intermediate unit. In the ladder diagram, if multiple coils are controlled by a series parallel circuit of a contact, in order to simplify the circuit, an auxiliary relay controlled by this circuit can be set in the ladder diagram, which is similar to the intermediate relay in the relay. 3. Separate the intertwined circuit design ladder diagram, take the coil as the unit, respectively consider the control of each coil in the relay circuit diagram by those contacts and circuits, and then draw the corresponding equivalent ladder diagram circuit. 4 processing of input signals provided by normally closed contacts when designing input circuits, normally open contacts should be used as much as possible. If only normally closed contacts can be used, the normally open / normally closed type of the corresponding contacts in the ladder diagram should be opposite to the relay circuit. 5. Processing of instantaneous contact of time relay for time relay with instantaneous contact, the auxiliary relay can be paralleled at both ends of the coil of the corresponding timer in the ladder diagram, and the contact of the latter is equivalent to the instantaneous contact of time relay. 6. The time of power-off delay the processing of electrical appliances uses the timer of power-on delay to realize the function of power-off delay. 7. For the design of external interlocking circuit, in addition to the software interlocking composed of normally closed contacts connected in series with the coil of the corresponding output relay in the ladder diagram, the hardware interlocking circuit should also be set outside the PLC. Processing of overload signal of thermal relay 1) for automatic reset thermal relay, the overload signal provided by its contact must be provided to PLC through input circuit, and the overload protection is realized by ladder diagram; 2) The normally closed contact of the manual reset thermal relay can be connected in series with the coil of the AC contactor controlling the motor in the output circuit of the PLC. 9. Minimize the input and output signals of PLC. 10. Pay attention to whether the driving capacity of PLC output module can meet the requirements of external loads. Generally, PLC can only drive loads with rated voltage below AC220V. If the coil voltage is 380V, the coil should be replaced with 220V, or an intermediate relay should be set outside the original AC contactor of the PLC system.