Introduction

According to IEC 61131-3, a parallel branch must always be terminated with a parallel merge. The number of parallel branches must not coincide with the number of parallel merges however.

Greater Amount of Merges

String with 1 Parallel Branch and 2 Parallel Merges:

If...

Then

If transition condition a is true,

then a sequence runs to S_19_2, S_19_3 and S_19_4.

If steps S_19_2, S_19_3 and S_19_4 are activated,

then the strings run independently of one another.

If transition condition b is true,

then a sequence runs to S_19_5.

If steps S_19_2 and S_19_5 are active and transition condition c, is true,

then the parallel string is departed.

Greater Amount of Branches

String with 2 Parallel Branches and 1 Parallel Merge:

If...

Then

If transition condition a is true,

then a sequence runs to S_19_2 and S_19_3.

If steps S_19_2 and S_19_3 are activated,

then the strings run independently of one another.

If transition condition b is true,

then a sequence runs to S_19_4 and S_19_5.

If steps S_19_4 and S_19_5 are activated,

then the strings run independently of one another.

If steps S_19_2, S_19_4 and S_19_5 are active and transition condition c is true,

then the parallel string is departed.

Nested Parallel Strings

Nested Parallel Strings:

If...

Then

If transition condition a is true,

then a sequence runs to S_8_10 and S_8_11.

If transition condition b is true,

then a sequence runs to S_8_12 and S_8_13.

If transition condition c is true,

then a sequence runs to S_8_14, S_8_15 and S_8_16.

If steps S_8_13 and S_8_14 are active and transition condition d, is true,

then a sequence runs to S_8_17.

If steps S_8_12 and S_8_17 are active and transition condition e, is true,

then a sequence runs to S_8_18.

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