另外要注意，一些高密度輸入點的模塊對一起接通的輸入點數(shù)有約束，一般一起接通的輸入點不得超越總輸入點的 60 ％； PLC 每個輸出點的驅動才干（ A/ 點）也是有限的，有的 PLC 其每點輸出電流的大小還隨所加負載電壓的不同而異；一般 PLC 的允許輸出電流隨環(huán)境溫度的升高而有所降低一級。在選型時要考慮這些問題。
PLC 的輸出點可分為共點式、分組式和阻隔式幾種接法。阻隔式的各組輸出點之間能夠選用不同的電壓品種和電壓等級，但這種 PLC 均勻每點的價格較高。假如輸出信號之間不需求阻隔，則應挑選前兩種輸出辦法的 PLC 。
First, clear the total i/o points of the control system, and then reserve 15 ~ 20% of the total points required in practice (leaving room for the transformation of the system), and then confirm the number of PLC points required.
In addition, it should be noted that some modules with high-density input points have restrictions on the number of input points connected together. Generally, the input points connected together shall not exceed 60% of the total input points; The driving ability (a/ point) of each output point of PLC is also limited. The output current of some PLCs varies with the applied load voltage; Generally, the allowable output current of PLC decreases by one level with the increase of ambient temperature. These problems should be considered when selecting models.
The output points of PLC can be divided into common point connection, grouping connection and blocking connection. Different voltage varieties and voltage grades can be selected between each group of output points of barrier type, but the price of this kind of PLC is higher. If there is no need to block between the output signals, the PLC of the first two output methods should be selected.
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