Understanding Process Object Counting Rules and Tag Consumption in PCS 7

In SIMATIC PCS 7 (from V7.0 onward), Process Object (PO) licensing is decoupled from raw WinCC tag counts: one Process Object does not equate to a fixed number of tags. An Automation System Runtime Process Object (AS RT PO) is consumed exclusively by each SFC instance or technological block that is operator-controllable (S7_m_c := 'true') and generates alarms via internal ALARM_8P calls (e.g., MotL, VlvL, PIDConL). A single MotL block may create 30 to 50 WinCC tags in the OS database but consumes exactly one AS RT PO. Crucially, raw signal driver blocks (Pcs7AnIn, Pcs7DiIn) and pure logic blocks consume zero AS RT POs.

Decoupling Process Objects from WinCC Tag Counts

In traditional standalone SCADA systems (such as standalone WinCC V7 or TIA Portal WinCC Professional), software licensing is strictly tag-based (e.g., 2048 Tag RT, 64k Tag RT). In that model, every analog input, digital status bit, or internal setpoint decrements available tag count.

In SIMATIC PCS 7, Siemens transitioned to a technological licensing model based on Process Objects (PO). A Process Object represents a complete technological entity (a motor, a modulating valve, a closed-loop controller, or an SFC sequence). Whether a motor block exchanges 15 tags or 60 tags with the operator station, it represents exactly one Process Object. There is no fixed ratio converting POs to tags.

Exact Counting Criteria for AS Runtime Process Objects

According to official Siemens licensing rules, a block instance in the Continuous Function Chart (CFC) consumes an AS RT PO if and only if it satisfies the following criteria:

Operator Control and Monitoring: The block definition contains the system attribute S7_m_c := 'true' on block pins, indicating OS relevance.
System Alarm Generation: The block generates process alarms or messages via integrated system blocks (ALARM_8P, NOTIFY_8P, or ALARM_DQ).
Non-Driver Classification: The block is a technological or algorithmic block and is not part of the low-level signal driver library.
SFC Sequences: Every SFC chart and SFC type instance running in the controller consumes exactly one AS RT PO.

Why Driver Blocks Consume Zero Process Objects

A foundational design principle of PCS 7 is that raw I/O channel drivers do not penalize project licensing:

Signal Channel Drivers (Pcs7AnIn, Pcs7DiIn, Pcs7AnOu, Pcs7DiOu): These blocks read peripheral addresses (PIW, PQW), perform raw wire-break diagnostics, and output IEEE floating-point structures. Because they do not call ALARM_8P directly and belong to the certified driver library, they consume zero AS RT POs.
Mathematical and Interlock Logic: Blocks such as Add04, Mul04, AND, OR, Intlk02, and Intlk08 provide logical interlocking without alarm generation and consume zero AS RT POs.
Custom DB Tags: Variables created in standard user Data Blocks (DBs) for custom communication do not consume AS POs, though if compiled to WinCC without technological block wrappers, they are licensed under standalone tag rules.

Equipment Schedule and Process Object License Packages

The table below details official Siemens AS and OS Process Object runtime expansion licenses.

License / Software PackageMLFB / Order NumberLicense TypeTechnological ScopeSIMATIC PCS 7 AS RT PO (100 PO)6ES7658-2BA00-0YB0Software Runtime LicenseExpands controller runtime capacity by 100 AS POsSIMATIC PCS 7 AS RT PO (500 PO)6ES7658-2BB00-0YB0Software Runtime LicenseExpands controller runtime capacity by 500 AS POsSIMATIC PCS 7 OS RT PO (100 PO)6ES7658-2XA00-0YB0OS Server Runtime LicenseExpands WinCC OS Server capacity by 100 process objectsSIMATIC PCS 7 OS RT PO (1000 PO)6ES7658-2XC00-0YB0OS Server Runtime LicenseExpands WinCC OS Server capacity by 1,000 process objectsCPU 410-5H System Expansion Card (500 PO)6ES7653-2CA00-0XB0Hardware DongleEmbeds 500 PO runtime execution capacity into CPU 410-5H

[!IMPORTANT]
Commercial Accuracy and Procurement Disclaimer: License requirements and MLFB numbers must be verified against authorized > Siemens documentation and official distributor quotations. Configuration tools such as CDT serve as planning aids and do not > establish contractually binding license entitlements.

Step-by-Step Procedure to Audit PO and Tag Consumption

Follow this procedure in SIMATIC Manager to evaluate exact PO consumption and tag counts:

Open Process Object View:
- In SIMATIC Manager, select View -> Process Object View (or press Alt + 3).
- Highlight the multiproject root to inspect all automation systems.
Examine PO Consumption by Block:
- Select the Blocks tab in Process Object View.
- Filter the table by column PO relevant: every row marked Yes consumes exactly one AS RT PO.
- Notice that MotL, VlvL, and PIDConL are marked Yes, while Pcs7AnIn and Intlk04 are marked No.
Check Booked vs Licensed POs:
- In Component View, select the target CPU.
- Select Options -> Charts -> Process Objects -> Display booked process objects.
- Record the 'Booked POs', 'Licensed POs', and 'Available POs'.
Inspect WinCC Tag Counts:
- Open WinCC Explorer on the OS Server.
- Select Tag Management: check the status bar for total tags created across the project.

Verification

Verify licensing compliance through the following checks:
1. In Process Object View, confirm that total 'Booked POs' is less than or equal to 'Licensed POs'.
2. In Automation License Manager on the Engineering Station, verify that AS RT PO license keys show status 'OK' without expiration.
3. Compile CFC charts: confirm that compilation finishes without 'PO limit exceeded' license warnings.
4. On redundant OS servers, verify that identical OS RT PO license quantities are recognized in ALM on both servers.

Limitations and Operational Precautions

Never attempt to calculate PO licensing by dividing total I/O count by an arbitrary factor (such as 3 or 4). In high-density analog installations with complex monitoring, PO consumption can exceed I/O estimates; conversely, in basic digital I/O arrays using channel drivers without monitoring blocks, PO consumption will be nearly zero. Sizing must always be based on the actual count of technological control loops and SFC instances.

Engineer FAQ

Does a user-created DB tag consume a Process Object in PCS 7?

No. Raw DB tags do not call ALARM_8P and are not technological blocks, so they consume 0 AS Process Objects. However, they appear as standard tags in WinCC Tag Management.

How many tags does a MotL block create in WinCC?

Depending on configured feature bits and message options, a standard APL MotL block generates approximately 35 to 45 WinCC tags, but still consumes only 1 AS RT PO and 1 OS RT PO.

What happens if booked POs exceed the licensed PO quantity on CPU 410-5H?

On CPU 410-5H, PO limits are strictly enforced by the physical System Expansion Card (SEC). Exceeding the SEC limit blocks CFC delta downloads entirely until the SEC is upgraded.