S5 AWL Command: SI (Pulse Timer)

SI starts a pulse timer. The timer output is TRUE for the programmed duration. If the start condition (VKE) goes FALSE before the timer expires, the output goes FALSE immediately — the pulse is cut short.

Syntax#

L  KT xxx.y     // Load timer value (xxx = value, y = time base)
SI T n           // Start timer n as pulse

Time Bases#

Example: KT 030.2 = 30 × 1s = 30 seconds

S7 Equivalent#

Important difference: The S5 SI timer is cut short when the input goes FALSE. The IEC TP timer runs for the full duration regardless of the input. For exact SI behavior in S7, use S_PULSE (S7-300/400 compatibility function), not TP.

Code Example#

U   E 0.0          // Start condition
L   KT 050.1       // 50 × 100ms = 5 seconds
SI  T 1             // Start T1 as pulse timer

U   T 1             // Query timer status
=   A 4.0           // Output ON for max 5 seconds

Behavior: When E 0.0 goes TRUE, A 4.0 goes TRUE for 5 seconds. If E 0.0 goes FALSE after 3 seconds, A 4.0 goes FALSE after 3 seconds (not 5).

Timing Diagram#

E 0.0:  ____/‾‾‾‾‾‾‾‾\____
T 1:    ____/‾‾‾‾‾\________    (cut short)
        |---5s max---|

Related Timer Commands#

• SE (Extended Pulse) — Pulse runs full duration regardless of input
• SD (On-Delay) — Output delayed after input
• SS (Retentive On-Delay) — Stored on-delay
• SA (Off-Delay) — Output extended after input goes FALSE

Try our free tools: S5 Timer Calculator → | S5→S7 Address Converter →

Part of the S5 AWL Command Reference. Maintained by PLCcheck.ai.

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