在作出體系操控計劃的決議計劃之前，要詳細(xì)了解被控目標(biāo)的操控要求，然后決議是否選用 PLC 進(jìn)行操控。
在操控體系邏輯聯(lián)系較雜亂（需求大量中心繼電器、時刻繼電器、計數(shù)器等）、工藝流程和產(chǎn)品改型較頻頻、需求進(jìn)行數(shù)據(jù)處理和信息管理（有數(shù)據(jù)運算、模擬量的操控、 PID 調(diào)理等）、體系要求有較高的牢靠性和安穩(wěn)性、預(yù)備實現(xiàn)工廠主動化聯(lián)網(wǎng)等狀況下，運用 PLC 操控是很必要的。
目前，國內(nèi)外眾多的生產(chǎn)廠家供給了多種系列功用各異的 PLC 產(chǎn)品，運用戶眼花繚亂、無所適從。所以全面權(quán)衡利弊、合理地挑選機(jī)型才干達(dá)到經(jīng)濟(jì)實用的意圖。一般挑選機(jī)型要以滿意體系功用需求為主旨，不要盲目貪大求全，以免構(gòu)成投資和設(shè)備資源的糟蹋。機(jī)型的挑選可從以下幾個方面來考慮。

Before making the decision plan of the system control plan, it is necessary to understand the control requirements of the controlled target in detail, and then decide whether to use PLC for control.
Under the condition that the logic connection of the control system is messy (requiring a large number of central relays, time relays, counters, etc.), the process flow and product modification are frequent, data processing and information management are required (including data operation, analog quantity control, PID conditioning, etc.), the system requires high reliability and stability, and the factory is ready to realize active networking, it is necessary to use PLC control.
At present, many manufacturers at home and abroad provide a variety of PLC products with different functions, which makes users dazzled and at a loss. Therefore, only by comprehensively weighing the advantages and disadvantages and reasonably selecting models can we achieve the purpose of economy and practicality. Generally, the selection of models should be based on satisfying the functional needs of the system, and do not blindly seek perfection, so as to avoid the waste of investment and equipment resources. The selection of models can be considered from the following aspects.