Configuring Decimal Precision on OpAnS Block Icons and APL Faceplates in SIMATIC PCS 7

To increase the number of decimal digits displayed on an Advanced Process Library (APL) OpAnS (Analog Operable Small) block icon and its corresponding faceplate, modifying Scale.Min and Scale.Max in CFC will not work because scale limits define the measurement engineering range, not display precision. To change decimal places on the block icon: in WinCC Graphics Designer, select the OpAnS block icon, open Properties -> Configurations, and modify AnalogValueFormat1 (for PV) or AnalogValueFormat2 (for SP) to '0.000' (3 decimals) or '0.0000' (4 decimals). To change decimal places in the faceplate: open the CFC chart, expand parameter SP_OpScale (or PV_OpScale) on OpAnS, set sub-parameter DEC to 3 or 4, and download changes.

Executive Summary

In continuous manufacturing and dosing operations automated with SIMATIC PCS 7, small technological blocks like OpAnS (FB1915 - Analog Operable Small) are widely deployed to allow operators to input analog setpoints or manual trim adjustments while consuming minimal screen space and controller memory. A frequent engineering question arises when an operator needs to input a high-precision setpoint with three or four decimal places (e.g. 0.125 or 1.5000): engineers often attempt to adjust decimal precision by modifying the Scale.Min and Scale.Max inputs on the block in CFC online mode, only to find that the display remains locked to two decimals. This article explains the technical segregation between scale bounds and display formatting, detailing how to configure format strings on block icons and the DEC attribute on APL faceplates.

Architecture and Fundamental Mechanics

APL Small Block Architecture, Decimal Precision Formatting, and Scale Structure Mechanics:

Why Scale.Min and Scale.Max Do Not Affect Decimal Precision:
The parameters Scale.High / Scale.Low (or Scale.Min / Scale.Max) define the physical engineering range (e.g. 0.0 to 100.0 kg) used to calculate percentage bar graph fills and limit clamping.
These parameters are floating-point real numbers that contain no metadata regarding how many decimal places should be rendered on screen.
Architecture of Decimal Formatting in the APL Faceplate (DEC Parameter):
The APL faceplate standard view queries structured parameters from the controller to configure its numeric input fields:
- SP_OpScale: Structure containing High (REAL), Low (REAL), and DEC (INT - Decimal Places).
- PV_OpScale: Structure containing High (REAL), Low (REAL), and DEC (INT - Decimal Places).
If SP_OpScale.DEC = 2 (default), the WinCC faceplate input dialog restricts operator setpoint typing and visual display to two decimal places (e.g. 12.34).
Setting SP_OpScale.DEC = 3 or 4 in CFC instructs the faceplate C-script (@pg_apls_standard.pdl) to allow entering and displaying 3 or 4 decimal places dynamically.
Architecture of Decimal Formatting on the Block Icon (AnalogValueFormat):
Block icons rendered on process screens do not automatically adapt their character width to DEC to avoid visual overlap with adjacent graphics.
The block icon's numeric display is governed by format attributes under Properties -> Configurations:
- AnalogValueFormat1: Format pattern for the primary process value (PV).
- AnalogValueFormat2: Format pattern for the setpoint value (SP).
Format String Patterns:
- 0.00: Displays exactly 2 decimal places.
- 0.000: Displays exactly 3 decimal places.
- 0.0000: Displays exactly 4 decimal places.
- ###0.000: Displays up to 4 integer digits and 3 mandatory decimal places.

Step-by-Step Implementation Procedure

Configure Faceplate Precision in CFC (Controller Scale Structure):
* In SIMATIC Manager, open the CFC chart containing the OpAnS block.
* Select the block and locate parameter SP_OpScale (for setpoint) and PV_OpScale (for process value).
* Expand the structure by clicking the small + icon.
* Locate sub-parameter DEC.
* Change the value of DEC from 2 to 3 (or 4).
* Execute a delta compile and download of the CFC changes.
Configure Block Icon Precision in WinCC Graphics Designer:
* In WinCC Explorer, open the graphic picture containing the OpAnS block icon.
* Select the OpAnS block icon on the canvas.
* In the Object Properties window, expand the Configurations property group.
* Locate AnalogValueFormat1 (and AnalogValueFormat2).
* Change the format string to 0.000 (for 3 decimals) or 0.0000 (for 4 decimals).
* Save the graphic picture.
Permanent Configuration via Master Typicals (Recommended for Plant Standardization):
* If new block icons will be generated via the Plant Hierarchy wizard:
* Open @PCS7TypicalsAPLV9.pdl (in the OS GraCS directory).
* Locate the @OpAnS block icon template.
* In Configurations, set AnalogValueFormat1 and AnalogValueFormat2 to 0.000.
* Save @PCS7TypicalsAPLV9.pdl and run Plant Hierarchy -> Create/Update Block Icons in SIMATIC Manager.

Verification

Activate WinCC Runtime.
Navigate to the screen with the modified OpAnS block icon; confirm that the block icon displays 3 or 4 decimal digits.
Click the block icon to open the APL faceplate.
Click on the setpoint input field; enter a high-precision value (e.g. 12.345).
Confirm that the faceplate accepts the setpoint without rounding or truncating to two decimals.

Limitations and Operational Precautions

Adding decimal places widens the text string; verify that the text does not exceed the physical bounding box of the block icon, which can cause text clipping. In high-precision floating-point operations, standard IEEE 754 single-precision (REAL) values have 24 bits of mantissa (~7 decimal digits of total precision); entering large numbers with many decimal places can experience minor floating-point representation rounding.

Engineer FAQ

Why did changing Scale Min and Max not increase decimal places?

Because Scale parameters define the engineering range for bar graphs and clamping, while decimal precision is governed by the DEC parameter and format strings.

What parameter controls faceplate decimal precision on OpAnS?

Sub-parameter DEC inside the SP_OpScale or PV_OpScale parameter structure on the CFC block.

Where do I configure decimal places for the OpAnS block icon?

In Graphics Designer, select the block icon and modify AnalogValueFormat1 and AnalogValueFormat2 under Configurations properties.

What format string displays three decimal places in WinCC?

Use 0.000 or ###0.000.

What is the difference between OpAnL and OpAnS?

OpAnL is the full Large operable analog block with alarms and gradient limits; OpAnS is the compact Small version designed for basic setpoint entry with reduced memory footprint.