S5 AWL Command: SS (Retentive On-Delay)
S5 AWL instruction SS (Retentive On-Delay): Timer continues counting even when input goes FALSE. Output goes TRUE when full duration has elapsed. Must be explicitly reset with R.
S5 AWL Command: SS (Retentive On-Delay)
SS starts a retentive (stored) on-delay timer. Unlike SD, the timer does NOT reset when the input goes FALSE. Once started, it continues counting until the set time has elapsed. The output then goes TRUE and stays TRUE until the timer is explicitly reset with the R instruction.
Syntax
L KT xxx.y
SS T n
S7 Equivalent
| S5 AWL | S7 Function | IEC 61131-3 |
|---|---|---|
| SS | S_ODTS | No direct IEC equivalent |
Warning: SS ≠ TONR. The IEC TONR (accumulating timer) accumulates time across multiple input pulses. SS does not accumulate — it starts once, runs to completion regardless of input, and then latches. These are fundamentally different behaviors.
Timing Diagram
E 0.0: ____/‾‾‾\____/‾\__________
T 4: ________________/‾‾‾‾‾‾‾‾‾ (stays TRUE until R)
|--5s--|
Reset: _________________________/‾\
T 4: ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾\__
Code Example
U E 0.0
L KT 050.1 // 5 seconds
SS T 4
U T 4
= A 4.0 // ON after 5 seconds, stays ON
U E 0.1 // Reset condition
R T 4 // Explicitly reset timer
Key Difference: SD vs. SS
| SD (On-Delay) | SS (Retentive On-Delay) | |
|---|---|---|
| Input goes FALSE before time | Timer resets | Timer continues |
| Output after time elapsed | TRUE (while input is TRUE) | TRUE (latched, until R) |
| Explicit reset needed | No | Yes (R T n) |
Related: SD (On-Delay) — Non-retentive version
Part of the S5 AWL Command Reference. Maintained by PLCcheck.ai.
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