How to Configure Parameter DELTA_T on Retentive Timer TONR (FC80) in SIMATIC PCS 7

In SIMATIC PCS 7, the retentive on-delay timer block TONR (FC80 from the TI-S7 Converting Blocks library) requires the sampling time parameter 'DELTA_T' to be configured with the exact cyclic execution period of the Organization Block in which it executes. Parameter DELTA_T represents the incremental time step (of data type TIME) added to the internal accumulator on each execution cycle while input IN is true. In Continuous Function Charts (CFC), if TONR is placed in cyclic interrupt OB35 (100 ms execution frequency), DELTA_T must be assigned 'T#100ms'. In modern PCS 7 APL development, engineers should migrate to the standardized 'TimerP' block, which automates cycle time integration via parameter SAMPLE_T.

Operating Architecture of TONR (FC80) from the TI-S7 Library

The TONR block (FC80) originates from the legacy TI-S7 Converting Blocks library, designed to emulate the retentive on-delay timer instruction of Texas Instruments (TI 505) PLCs within SIMATIC S7-300 and S7-400 controllers:

Functional Behavior:
When input IN is TRUE, the block increments an internal accumulated elapsed time (ET).
When IN transitions to FALSE, ET stops accumulating and holds its current value (retentive freeze).
When IN becomes TRUE again, accumulation resumes from the frozen value.
When ET >= PV (Preset Value), output Q transitions to TRUE.
An explicit pulse on input RESET clears ET to zero and drops Q to FALSE.

The Critical Role of Parameter DELTA_T in Cycle Time Accumulation

Unlike standard IEC timers (SFB4 TON), which query the CPU system clock (TIME_TCK) dynamically:

Mathematical Accumulator: TONR calculates elapsed time by adding a discrete time delta on every block call:
$$\text{ET}{\text{new}} = \text{ET}$$}} + \text{DELTA_T
The Configuration Trap:
If parameter DELTA_T is left disconnected or set to T#0ms, the accumulator will never advance, and output Q will never trip.
If DELTA_T is set to T#1s while the block executes every 100 ms (OB35), the timer will run 10 times faster than real time, expiring in 6 seconds instead of 60 seconds!
Parameter DELTA_T must strictly match the real-world execution interval of the host Organization Block.

Configuring DELTA_T Across Cyclic Organization Blocks (OB30 to OB38)

To correctly configure DELTA_T in CFC:

Identify the Block's Execution Group:
* In CFC, click the run sequence bar at the top of the TONR block.
* Open the Run Sequence Editor to determine which cyclic interrupt OB hosts the chart (e.g., OB35, OB32, OB38).
Assign Matching TIME Literals:
* For OB38 (10 ms cycle): Set DELTA_T := T#10ms.
* For OB35 (100 ms cycle): Set DELTA_T := T#100ms.
* For OB32 (1000 ms cycle): Set DELTA_T := T#1s.
CFC Dynamic Interconnection:
* Alternatively, interconnect DELTA_T to a global time base or system variable to ensure automatic adjustment if the OB scan rate is modified in HW Config.

Migrating Legacy FC80 Logic to PCS 7 Advanced Process Library (APL)

While FC80 remains functional for legacy compatibility, Siemens strongly discourages using TI-S7 converting blocks in modern PCS 7 systems:

Why Migrate Away from FC80?:
FC80 is an FC (Function) requiring external instance storage; it does not support WinCC operator faceplates, OS alarm generation, or APL feature bits.
It does not adhere to APL structured signal types (Struct with .Value and .ST).
The Modern Replacement: TimerP (FB1810):
Part of the official PCS 7 Basis / APL Library.
Automatically binds parameter SAMPLE_T (REAL in seconds) to the OB cycle time during CFC compilation.
Fully integrated with WinCC faceplates and operator control.

Comparison of Timer Blocks in SIMATIC STEP 7 and PCS 7

The table below compares timer block options across SIMATIC S7 and PCS 7 platforms.

Timer BlockLibrary OriginRetentive?Cycle Time ParameterAPL Faceplate SupportRecommended ApplicationTONR (FC80)TI-S7 ConvertingYesDELTA_T (TIME)NoLegacy TI-505 migrationsTimerP (FB1810)PCS 7 Basis / APLConfigurableSAMPLE_T (REAL)YesModern PCS 7 StandardTON (SFB4)Standard IECNoSystem Clock TCKNoBasic S7-400 machine logicS_ODT / S_PULSES7 Standard (S5TIME)NoBCD Time BaseNoDeprecated legacy logicTotalL (FB1906)APL LibraryYesSAMPLE_T (REAL)YesContinuous mass integration

Verification

To confirm that TONR (FC80) timing is accurate:
1. In CFC, insert TONR into OB35 (100 ms).
2. Configure DELTA_T := T#100ms and PV := T#30s.
3. Switch CFC to Test Mode: set input IN = TRUE.
4. Using a precision stopwatch, verify that parameter ET matches real elapsed time at 10 s, 20 s, and 30 s.
5. Set IN = FALSE at 15 seconds: confirm that ET freezes at exactly T#15s.
6. Set IN = TRUE: confirm accumulation resumes seamlessly and sets Q = TRUE upon reaching 30 seconds.
7. Apply a momentary pulse to RESET: confirm ET resets to T#0ms and Q transitions to FALSE.

Limitations and Operational Precautions

Never place TONR (FC80) into OB1 (free-wheeling cyclic task); because OB1 execution time varies dynamically with CPU load, DELTA_T accumulation will suffer severe timing drift.
Ensure that the execution group containing TONR is not disabled or throttled by runtime phase logic unless timer freezing is explicitly desired.
Do not interconnect DELTA_T to an uninitialized memory word, as passing zero or negative values will corrupt the timer calculation.
Always validate final software licensing and system documentation against the applicable Siemens catalog and authorized distributor quotation.

Engineer FAQ

Why did my TONR timer run 10 times too fast?

You likely set DELTA_T to T#1s while the block was executing inside OB35 (100 ms). Because the block was called 10 times per second, it added 1 second on every call, running 10x faster than real time. Change DELTA_T to T#100ms.

Can I enter DELTA_T as a REAL number in seconds?

FC80 requires the IEC TIME data type for DELTA_T (e.g., T#100ms). If you prefer working with REAL seconds, migrate to the APL TimerP block which uses SAMPLE_T : REAL.