TP Pulse Timer Elapsed Time (ET) in TIA Portal: Configuration

Overview: TP Pulse Timer and the Meaning of Elapsed Time

The TP (Pulse Timer) is an IEC 61131-3 compliant function block that emits a fixed-duration output pulse on the rising edge of its trigger input. The pulse width is governed entirely by the PT (Preset Time) parameter, not by the duration of the trigger signal. In SIMATIC S7-1200 and S7-1500 controllers, TP is one of four IEC timer primitives (TP, TON, TOF, TONR) located under Instructions › Basic Instructions › Timers in the TIA Portal task card.

TP exposes two outputs that are useful to your program:

• Q (BOOL) — pulse state. TRUE while the timer is running, FALSE otherwise.
• ET (TIME) — elapsed time. The current internal counter, beginning at T#0ms on a rising edge of IN and increasing monotonically toward PT.

Elapsed time is the current accumulated time inside the timer. It is not a remaining time, not a status flag, and not a count of completed pulses — it is purely the running total since the last accepted rising edge of IN. Monitoring ET lets a program answer questions such as "how long has the output been high?" or "did the pulse complete?" without polling Q, and it lets an HMI display a real-time progress bar during a pulse.

TP Function Block Pinout

The internal TIME data type in S7-1200/1500 is a signed 32-bit double integer representing milliseconds. The valid range is T#-24d_20h_31m_23s_648ms to T#24d_20h_31m_23s_647ms. Because ET is non-negative during a pulse, only the positive half of the range is ever observed in practice.

Timing Diagram (IN, Q, ET)

Elapse Time Behavior Step-by-Step

1. Idle state. IN is FALSE. Q is FALSE. ET is T#0ms.
2. Rising edge on IN. The TP block captures the edge, sets Q to TRUE, and starts the internal counter at T#0ms.
3. Active pulse. Each OB1 cycle (or the configured time base for legacy blocks), ET increments by the elapsed interval. Q remains TRUE.
4. Re-trigger attempt. Additional rising edges on IN while Q is TRUE are ignored. ET is not reset; the pulse runs to completion.
5. Pulse end. When ET reaches PT, Q falls to FALSE. ET holds at the value of PT until the next rising edge of IN.
6. Next cycle. A new rising edge on IN resets ET to T#0ms and restarts the cycle.

Declaring a TP Instance and Tagging ET in TIA Portal

To read ET you must have a TP instance. There are two options, both supported on S7-1200 and S7-1500.

Option A — Single-Instance DB (recommended for TIA Portal V13+)

1. Drag TP from the task card into a code block (OB, FB, or FC). TIA Portal auto-generates an instance DB named IEC_Timer_0_DB (or your custom name).
2. Open the instance DB. The DB contains the standard IEC TP interface plus internal members STIME, STATE, and a tag named ET of type TIME.
3. To make ET visible on the HMI or in a watch table, expose it as a multi-instance or assign it to a global tag:
   "MyPulse_ET" := "TP_DB".ET;

Option B — Multi-instance inside a parent FB

1. Create an FB (e.g., FB_PulseMonitor) and declare a multi-instance section:

VAR
  PulseTimer : TP;       // multi-instance
  Elapsed    : TIME;
END_VAR

2. Call the TP in the FB body and copy ET to a static tag:
PulseTimer(IN := bTrigger, PT := tPreset);
Elapsed := PulseTimer.ET;

3. Make Elapsed accessible by adding the FB to the watch table, or by reading it in a higher-level block.

Data Type Mapping for ET

Programming Examples

LAD (Ladder) — TP with ET mirrored to a global tag

Network 1:
  |    TP_DB            |
  |   IN := "StartBtn"|
  |   PT := T#2.5s      |
  |   Q  => "PulseOut"|
  |   ET => "PulseElapsed"|
  |---------------------|

The ET => "PulseElapsed" assignment moves the running ET value into the global tag PulseElapsed of type TIME. PulseElapsed is selectable in the PLC tag table and will appear in the watch table and on HMI screens.

FBD (Function Block Diagram)

The FBD representation is identical in pinout. Use the same ET => Tag connector syntax. ET is on the lower output pin of the TP block.

SCL (Structured Control Language)

// Pulse generator with elapsed-time feedback
IF "StartBtn" AND NOT "StartBtn_Old" THEN
    "TP_DB".IN := TRUE;            // start on rising edge
ELSE
    "TP_DB".IN := FALSE;
END_IF;

"TP_DB".PT := T#2s500ms;          // 2.5 second pulse

"PulseOut"       := "TP_DB".Q;
"PulseElapsedMs" := TIME_TO_DINT("TP_DB".ET);  // convert to ms for HMI bar

"StartBtn_Old" := "StartBtn";

Notes on the SCL pattern:

• TIME_TO_DINT strips the sign and returns milliseconds as a 32-bit signed integer. This is the conventional format for HMI progress bars (range 0 to 2 147 483 647).
• You can also use DINT_TO_REAL and divide by 1000.0 to get seconds as a floating-point value for trending.
• If you are using a multi-instance TP inside an FB, the syntax is identical — just use the instance name (e.g., PulseTimer.ET) instead of the DB name.

Version Differences and Time Base

The S7-1200 system manual and S7-1500 system manual, both available from the Siemens Industry Online Support portal, are the authoritative source for the IEC TP block signature and behavior. Always confirm the block type pulled into your project (right-click → "Block Properties" → "Information" tab) against the system manual of the firmware version installed on your CPU.

Monitoring ET in Watch Tables, Web Server, and HMI

Watch Table / Online & Diagnostics

1. Open Watch and force tables from the project tree.
2. Add the TP instance DB ("TP_DB") and either expand it or add the explicit path "TP_DB".ET.
3. Go online and toggle the trigger. The ET column will count from T#0ms to PT, then hold at PT until the next trigger edge.

S7-1500 Web Server

1. Enable the Web server in the CPU properties (TIA V13+) and create a user with read access.
2. Add TP_DB to the variable list of the standard Web page, or create a custom Web page that polls TP_DB.ET.
3. Access from a browser at https://<CPU-IP>. ET displays in Time format.

HMI / WinCC (Comfort Panel, Unified, WinCC Professional)

1. In the HMI tag table, add a tag PulseElapsed with PLC connection to TP_DB, member ET, data type TIME.
2. For a numeric display, set the format pattern to 999 d 23:59:59.999.
3. For a progress bar, convert ET to DINT ms (TIME_TO_DINT(TP_DB.ET)) and divide by 1000 in a script or use the bar's percentage property with max set to PT (in ms).

Edge Detection: When ET Resets and When It Does Not

Common Pitfalls and Field-Proven Caveats

• Confusing ET with a remaining-time output. ET is elapsed. To get remaining time, compute PT - ET in your application code.
• Reading ET from the wrong block family. The legacy S7-300/400 TP uses S5TIME encoding (BCD), not TIME. Reading its ET as a TIME will return garbage on the S7-1500 IEC TP block.
• Polling ET in a slow OB. If the OB1 cycle time is 50 ms, ET updates in 50 ms steps even though the firmware internal resolution is finer. For sub-cycle resolution, use a time-driven OB (e.g., OB35 at 1 ms on S7-1500).
• Using TP where TONR is correct. TP ignores re-triggers. If you need an accumulating timer (e.g., total run-time of a motor), use the retentive on-delay timer (TONR) instead.
• Displaying negative TIME on HMI. HMI controls configured for "Signed" TIME will show a negative bar if the value falls below zero (e.g., a corrupted instance). Configure the field as unsigned or clamp the value at zero in the PLC.
• Forgetting to call TP in the cyclic OB. A TP FB inside an FC that is only called conditionally will not accumulate time. Place the call in OB1 or in a cyclic interrupt OB that is always triggered.

Troubleshooting Matrix

Verification Procedure After Configuration

1. Compile and download the project to the CPU. Perform a warm restart if the instance was changed.
2. Go online and add TP_DB to a watch table.
3. Force IN briefly to TRUE (or pulse the physical input). Verify Q goes TRUE.
4. Observe ET counting from T#0ms to PT in the watch table.
5. Confirm Q falls exactly when ET reaches PT (within one OB1 cycle).
6. Toggle IN repeatedly while Q is TRUE. Confirm ET does not reset and Q does not extend.
7. Read the same tag from the HMI or web server to verify end-to-end visibility.

Related Siemens Documentation

• SIMATIC S7-1200 Programmable Controller System Manual — authoritative reference for the IEC TP block on S7-1200.
• SIMATIC S7-1500 Programmable Controller System Manual — authoritative reference for the IEC TP block on S7-1500.
• SIMATIC S7-1200/1500 Programming Guideline (TIA Portal) — best-practice patterns for timer usage.
• Siemens Industry Online Support — firmware release notes and KB articles indexed by CPU order number.