How to Configure Engineering Units and Find Unit Codes (RPM / U/min) in PCS 7 APL

How to Configure Engineering Units and Find Unit Codes (RPM / U/min) in PCS 7 APL

In SIMATIC PCS 7 Advanced Process Library (APL), engineering units are configured by assigning standardized integer codes to the block parameter PV_Unit (or Unit) on analog monitoring and driver blocks. The standard code for revolutions per minute is 1085, which displays as rpm on WinCC faceplates and block icons in compliance with international standard IEC 61158-2 / PROFIBUS PA Profile 3.02. Because U/min is the German localized translation of revolutions per minute rather than a separate international unit code, the standard APL displays rpm. If a project strictly requires the German label U/min, engineers must configure a user-defined unit entry in the STEP 7 project's Global Declarations unit table or customize the WinCC faceplate unit text list.

Table of Contents

• Engineering Unit Standards in PCS 7 APL (IEC 61158-2)
• Finding and Assigning the Revolutions Per Minute (RPM) Unit Code
• Display Differences: English 'rpm' vs. German 'U/min'
• Method: Configuring Custom and Localized Engineering Units
• Verification
• Limitations and Operational Precautions
• Engineer FAQ
• Technical References
• Related Articles
• Related Tags

Engineering Unit Standards in PCS 7 APL (IEC 61158-2)

In modern DCS engineering, hardcoding unit strings into individual blocks consumes unnecessary controller memory and causes translation mismatches across multi-language operator stations. SIMATIC PCS 7 resolves this by utilizing standardized integer enumeration:
- Standard Reference: APL engineering units adhere strictly to IEC 61158-2 / PA Profile 3.02 / NAMUR NE 53.
- Data Exchange: The AS controller stores only an integer code (e.g., 1085, 1001, 1342) in the block instance DB.
- Dynamic Faceplate Translation: When the WinCC OS compiles, the OS compiler transfers the integer code. The APL faceplate engine queries internal text libraries to display the corresponding text string based on the active runtime language.

Finding and Assigning the Revolutions Per Minute (RPM) Unit Code

The integer code mapping for rotational speed and frequency units is defined in the standard PCS 7 APL documentation:

To assign revolutions per minute in CFC:
1. Open the target CFC chart containing an analog block (such as MonAnL or MotSpdCL).
2. Locate the parameter PV_Unit (or channel driver PV_InUnit).
3. Set the parameter value to 1085.
4. Compile the CFC chart and execute an OS Compile.

Display Differences: English 'rpm' vs. German 'U/min'

Engineers operating German-language facilities frequently question why code 1085 renders as rpm instead of U/min:
* Under IEC 61158-2, the standardized scientific abbreviation for rotational speed is rpm.
* Siemens APL standard text lists map code 1085 to rpm across all installed WinCC runtime languages to preserve international consistency and prevent layout truncation on dense operator faceplates.
* Code 1085 represents both physical concepts identically; rpm and U/min represent the exact same 1:1 mathematical magnitude.

Method: Configuring Custom and Localized Engineering Units

If technical specifications or plant standards mandate the literal display string U/min, configure a customized engineering unit in SIMATIC Manager:

Step 1: Open Global Declarations in SIMATIC Manager

1. In SIMATIC Manager, navigate to your multiproject or project tree.
2. Open the Shared Declarations (or Global Declarations) folder.
3. Double-click the Units catalog to open the table editor.

Step 2: Define a Custom Unit Entry

1. Scroll down to the user-definable range (codes 1999 and above, or unused indices).
2. Insert a new row:
   - Value / Code: Assign an available integer (e.g., 1998 or custom index).
   - Display String (Default): Enter U/min.
   - Display String (German): Enter U/min.
   - Display String (English): Enter rpm (or U/min if forced globally).
3. Save and close the Global Declarations editor.

Step 3: Assign the Custom Unit in CFC

1. Open the CFC chart and navigate to the target block.
2. In the parameter table for PV_Unit, select the newly defined unit U/min from the drop-down menu, or manually type the custom integer code.
3. Save the CFC chart.

Step 4: Compile and Synchronize WinCC OS

1. Right-click the OS project in SIMATIC Manager and select Compile.
2. Ensure that Tags and messages and Picture Tree are selected.
3. Upon completion, start or refresh WinCC Runtime.
4. Open the block icon and faceplate: the unit displays U/min adjacent to the process value.

Verification

To confirm that the unit is correctly displayed across the system:
- In CFC online mode, hover over PV_Unit on the block face: confirm the parameter reads 1085 (or your custom integer code).
- In WinCC Runtime, open the faceplate for the motor or analog value: confirm that the unit string appears clearly next to the live numerical value without truncation or character corruption.
- Open the WinCC Alarm Logging list during a simulated limit violation: verify that the alarm message text includes the correct engineering unit string in the process data column.

Limitations and Operational Precautions

• Do Not Overwrite Standard IEC Codes: Avoid changing the text of established standard codes (such as changing 1001 from °C to something else) in central libraries, as this corrupts unit reporting across all existing blocks.
• OS Compile Requirement: Modifying unit texts in Global Declarations requires a complete OS compilation to update the WinCC runtime text database.
• Third-Party Fieldbus Modules: Field devices communicating over PROFIBUS PA or Foundation Fieldbus send unit codes directly via device descriptors. Ensure the fieldbus transmitter's internal PA profile parameter matches the code expected by the PCS 7 channel driver.

Engineer FAQ

Where can I find the complete list of all APL engineering unit codes?

The complete list is published in the SIMATIC PCS 7 Advanced Process Library (APL) manual in the section titled "Selecting a unit of measure" or in the STEP 7 Online Help under "Engineering Units".

Can I enter the unit as a text string directly on the block input?

No. APL blocks evaluate unit parameters as 16-bit signed integers (INT). Text strings cannot be wired to PV_Unit. The translation to text occurs exclusively at the WinCC HMI layer.

What happens if I set PV_Unit to 0?

Setting PV_Unit = 0 configures the parameter as unassigned or dimensionless. The WinCC faceplate will display the numerical value without any trailing unit label.

Will changing PV_Unit require an AS STOP?

No. Modifying PV_Unit in CFC is a standard parameter value adjustment. It can be downloaded to the AS controller in RUN mode via a normal change download.

Technical References

• Siemens Industry Online Support: SIMATIC Process Control System PCS 7 Advanced Process Library (APL) Manual.
• International Electrotechnical Commission: IEC 61158-2 Industrial Communication Networks - Fieldbus Specifications.
• PROFIBUS PA Profile for Process Control Devices, Version 3.02.
• SIOS Entry 109742323: PCS 7 Compendium Part A - Engineering Guidelines.

Related Articles

• How to Pack and Unpack Double Words (DWORD) in SIMATIC PCS 7 CFC
• How to Create and Name Custom Block Icons in SIMATIC PCS 7 OS
• How to Resolve SCL String Length Limits When Mapping Large STRUCTs to PCS 7 OS

Related Tags

• APL
• PCS 7
• Engineering Units
• IEC 61158-2
• WinCC Faceplates
• Motor Control
• Industrial Automation