Configuring Y-Axis Scaling and Dynamic Trend Ranges on APL PIDConL Faceplates in PCS 7

In SIMATIC PCS 7 Advanced Process Library (APL), the Y-axis range of the trend display in faceplates such as PIDConL (FB1874) is dynamically governed by the process value scale parameters PV_OpScale.High and PV_OpScale.Low configured in CFC. To customize the trend axis limits for individual instances without modifying system templates, update these scale parameters on the controller block. To permanently hardcode or adjust axis limits at the HMI level, create a project-specific copy of @PG_apl_trendPID.pdl, modify the WinCC Function Trend Control properties via C/VBS scripts, and reference the new picture in the block icon TrendPictureName property.

APL Faceplate Trend Architecture and Dynamic Axis Binding

In SIMATIC PCS 7 APL, operator faceplates provide dedicated trend views to visualize real-time and historical process dynamics. For continuous controllers such as PIDConL (FB1874), the trend window (@PG_apl_trendPID.pdl) is embedded inside the standard faceplate framework.

The embedded WinCC Function Trend Control contains multiple value axes:
* Value Axis 0 (PV / SP Axis): Displays the process value (PV_Out.Value) and the active setpoint (SP.Value).
* Value Axis 1 (MV Axis): Displays the manipulated variable (MV.Value), typically scaled from 0.0% to 100.0%.

By default, the APL faceplate initialization script (APL_OpenFaceplate / apl_trend_init) queries the AS technological block via structured tags. Specifically, it reads the structure PV_OpScale (PV_OpScale.High and PV_OpScale.Low) and dynamically sets the begin and end values of Value Axis 0, ensuring the trend window automatically reflects the physical sensor range (e.g., 0.0 to 250.0 °C).

CFC Parameter Scaling vs WinCC Trend Control Customization

Engineers can adjust the Y-axis scale using two distinct engineering approaches:

Method / ApproachConfiguration LocationScope of ChangeAdvantages and Trade-offsCFC PV_OpScale ConfigurationPIDConL.PV_OpScale in CFCSingle controller instanceStandard PCS 7 workflow; updates faceplate trend, bargraph limits, and alarm limits seamlessly without scripting.Custom Trend Picture Template@PG_apl_trendPID_Custom.pdl in WinCCSelected block icons or plant-wideAllows customized grid lines, non-standard axis divisions, or fixed hardcoded zoom levels, but requires creating and managing custom PDL files.Runtime Script AdjustmentC-Script / VBScript on Trend ButtonPicture-level dynamic adjustmentProvides operator pushbuttons or I/O fields to zoom/scale axes interactively during runtime, but requires script maintenance.

Table 1: Comparison of trend scaling methods in SIMATIC PCS 7 APL.

Configuring Instance-Specific Scaling via PV_OpScale in CFC

The recommended, native PCS 7 method to adjust Y-axis trend limits is configuring the process value scale directly in the Continuous Function Chart:

Open the CFC chart containing the PIDConL block instance in SIMATIC Manager.
Locate the input structure parameter PV_OpScale.
Expand the structure and set the engineering limits:
* PV_OpScale.High: Desired upper Y-axis limit (e.g., 300.0).
* PV_OpScale.Low: Desired lower Y-axis limit (e.g., 0.0).
Execute Chart > Compile > Changes Only and download changes to the S7-400 CPU.
In WinCC Explorer, perform an OS Compile (Changes Only) to synchronize technological structure tags.
When an operator opens the PIDConL faceplate and clicks the Trend icon, Value Axis 0 automatically scales from 0.0 to 300.0.

Creating Project-Specific Trend Templates via TrendPictureName

If a project requires custom axis behavior (such as dedicated buttons to toggle between 0–100 bar and 0–300 bar):

Duplicate Standard Trend Picture:
* In WinCC Graphics Designer, open @PG_apl_trendPID.pdl from GraCS.
* Save a copy with a custom name: @PG_apl_trendPID_Custom.pdl.
Add Dynamic Scripting to Value Axis:
* Add a button or configure the picture open event.
* Use ANSI-C code to reconfigure the value axis range dynamically:
c SetPropWord(lpszPictureName, "_TrendCtrl1_", "ValueAxisIndex", 0); SetPropBOOL(lpszPictureName, "_TrendCtrl1_", "ValueAxisAutoRange", FALSE); SetPropDouble(lpszPictureName, "_TrendCtrl1_", "ValueAxisBeginValue", 0.0); SetPropDouble(lpszPictureName, "_TrendCtrl1_", "ValueAxisEndValue", 300.0);
* Save the modified picture in the project GraCS directory.
Assign to Block Icon:
* Open the plant process picture containing the PIDConL block icon.
* Open the block icon Object Properties and select the Trend property group.
* Change the static attribute TrendPictureName from @PG_apl_trendPID.pdl to @PG_apl_trendPID_Custom.pdl.
* Save the picture. Future faceplate calls from this block icon will load the custom trend template.

Verification

To confirm proper Y-axis scaling:

In WinCC Runtime, locate and click the PIDConL block icon.
In the faceplate header toolbar, click the Trend View button.
Observe the left vertical axis (PV/SP): verify that the bottom label matches PV_OpScale.Low (e.g., 0.0) and the top label matches PV_OpScale.High (e.g., 300.0).
If a custom trend template with dynamic buttons was implemented, click the range adjustment button and confirm that the grid labels update immediately without script errors in WinCC_Sys_01.log.

Limitations and Operational Precautions

Never overwrite standard APL templates (@PG_apl_trendPID.pdl) directly in the installation directory; always create project copies in the OS GraCS folder to avoid being overwritten during library updates.
Ensure that PV_OpScale in CFC matches the physical measurement span of the upstream analog input channel driver (Pcs7AnIn.Scale); mismatches between channel scale and controller scale cause distorted faceplate bar graph readings.
Avoid setting ValueAxisAutoRange = TRUE on closed-loop control faceplates, as continuous autoranging causes confusing visual oscillations for plant operators during steady-state control.

Engineer FAQ

Why does the MV trend line use a different scale than PV?

In @PG_apl_trendPID.pdl, the Manipulated Variable (MV) is assigned to Value Axis 1, which is standardized to 0.0% to 100.0% output, while Value Axis 0 scales to engineering units for PV and SP.

Can operators manually zoom the trend axes in APL faceplates?

Yes. Operators with appropriate authorization can use the trend control toolbar buttons (Magnifying Glass icons) to marquee zoom or pan time and value axes during runtime.

Does modifying PV_OpScale require a CPU stop?

No. Modifying PV_OpScale.High or Low in CFC is a standard online parameter change that can be downloaded in CPU RUN mode without interrupting controller execution.