Phoenix Contact 2701027 NLC-050-024D-06I-04QTP-00A nanoLine Base Unit 24ßV/DC / PNP 2701027 数据表

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2701027

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4-4

PHOENIX CONTACT

2373_en_B

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Add statements to the expression using logical operators (see Figure 4-2). The result

of the expression is either TRUE or FALSE, enabling or disabling the flow chart

respectively.

Figure 4-2

The “Enable Block” dialog box showing an expression

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The AND and OR “Operator” in the dialog box permits addition of a second Boolean

condition to the expression. AND has greater precedence than OR (in other words AND

expressions are evaluated before OR expressions, and then they are evaluated from

top-down). nanoLC supports one or two Boolean conditions in an Enable block.

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nanoLC evaluates the Enable block every scan, at the time when the flow chart

executes (based on the position of the flow chart in the flow chart list—see “Changing

Execution Order” on page 3-15. The flow chart only runs if its expression is true at the

start of the scan.

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On the first scan or whenever the Enable block expression transitions from FALSE to

TRUE, flow chart execution starts at the Enable block output. Otherwise, execution

starts where it left off the previous scan.

Table 4-1 defines all possible Enable block combinations. This table shows valid data item

types and the conditions that appear in the “Condition” drop-down list. For example, it is

possible to test to see if an Input is “ON” or “OFF”.

Table 4-1

Valid Enable Block Expression

X=valid

Data Item Type

OFF

Input

Output

Flag