Configuring Decimal Axis Values on LOGO! Web Editor Trend View

Overview

The LOGO! Web Editor (LWE) is a browser-based visualization tool introduced with LOGO! 8.2 firmware (FS03) that lets operators view the LOGO! 8 logic module data log through the integrated web server. A documented limitation in early LWE revisions is that the Trend view vertical (Y) axis renders only integer tick values regardless of the underlying process variable magnitude. Operators who trend analog process values such as temperature (°C), pressure (bar), or flow (L/min) cannot force decimal increments on the chart axis from within the browser interface. This article documents the affected firmware versions, the underlying VM data model, and four engineering workarounds that recover true decimal scaling without modifying the firmware.

Trend View and Data Logging Architecture

The Trend view is the chart component of the LOGO! data log subsystem. Three elements interact when a chart is rendered:

1. Variable memory (VM) in the LOGO! base module, holding 16-bit signed integers.
2. Data Log profile in the LOGO! Soft Comfort project, which selects VM addresses to sample at a configured rate and writes the values to the SD card.
3. LOGO! Web Editor running inside the LOGO! web server, which reads the on-board CSV log and renders the trend chart in the browser.

The data path is therefore strictly numeric on the LOGO! side and visualization-only in the browser. No fractional scaling is applied at the rendering layer in LWE V1.0.x.

Problem Description

When a data log is opened in the LOGO! Web Editor Trend view, the vertical axis of the chart is labeled with whole-number tick values such as 0, 200, 400, 600, 800, 1000. The user cannot select or enter decimal axis increments (e.g., 0.0, 2.5, 5.0, 7.5, 10.0) even when the logged variable represents a fractional engineering unit. There is no axis-format dialog or right-click context menu on the chart that exposes decimal precision.

Root Cause Analysis

LOGO! 8 stores every analog value in VM as a signed 16-bit integer. The mapping between raw VM integer and engineering unit is defined per analog input by the Gain and Offset parameters of the input block (or, for the Analog Amplifier / Math function blocks, by the gain and offset inputs on the block itself). The chart engine reads the integer directly from the CSV log file and does not consult any per-variable scale metadata when rendering axis labels.

Axis tick generation in LOGO! Web Editor V1.0.x is performed client-side from the integer extremes of the logged data. No Format Axis dialog is exposed in the DOM, comparable to the Format Axis task pane found in desktop charting tools such as the Microsoft Office chart axis controls. The chart rendering branch implements integer mode as the only available number format, which is the source of the limitation.

Affected Versions

The decimal-axis behavior was reported against LOGO! 0BA8 standard FS04 modules running LOGO! Soft Comfort V8.3 projects. Siemens has not published a public defect number for the LWE V1.0.x axis-formatting limitation. Always confirm the latest behavior against the Siemens Industry Online Support portal for the installed firmware revision.

Prerequisites

1. LOGO! 0BA8 base module with FS03 firmware or higher (typical part numbers: 6ED1052-1CC08-0BA1 for the LOGO! 8 with Ethernet, or 6ED1052-1HB08-0BA1 for the LOGO! 8 without Ethernet).
2. LOGO! Soft Comfort V8.3 (or current) installed on the engineering workstation.
3. SD card installed in the LOGO! if persistent data logging is required (recommended for production systems).
4. Web server access enabled in the LOGO! Soft Comfort project (Tools > Ethernet Connections > Web Server Access = On).
5. Network reachability from the engineering workstation to the LOGO! IP address on TCP/80 (HTTP) or TCP/443 (HTTPS if activated).
6. Browser: Chrome, Edge, or Firefox at a current LTS line. Internet Explorer 11 is no longer certified by Siemens for LWE V2.

Workaround 1 - Apply a Decimal-Scaled VM Variable (Analog Amplifier)

Create an explicit scaled variable for the Trend view and log that variable rather than the raw analog input. This shifts the decimal point from the chart layer to the application layer where the engineer controls the resolution.

1. Insert an Analog Amplifier block (Function Blocks panel > Analog > Analog Amplifier, B1).
2. Wire the source analog input (e.g., AI1) to the amplifier input.
3. Set Gain = 10 for one decimal place (e.g., logged integer 235 represents 23.5 °C).
4. Set Gain = 100 for two decimal places (e.g., logged integer 1234 represents 12.34 bar).
5. Set Offset = 0 if the input is already zero-based, otherwise enter the required offset in raw integer units.
6. Assign the amplifier output to a named variable (e.g., Temp_Scaled_x10).
7. In the data log configuration, log the scaled variable only.
8. Document the scale factor on the operator HMI screen next to the trend so the displayed value is interpreted correctly (divide by 10 or 100 in the operator's mind).

Workaround 2 - Use the Math Instruction Block for Arbitrary Scaling

When the input scaling does not match a simple decimal factor (for example, a 4 - 20 mA input representing 0 - 5000 RPM, requiring a 0.3058 multiplier), use the Math function block to compute the engineering-unit integer directly.

1. Insert a Math block (Function Blocks panel > Analog > Math, B2).
2. Configure equation: Result = (Gain * Input) + Offset where Gain and Offset are constants.
3. Use rational or floating-point form: for 4 - 20 mA mapped to 0 - 5000 RPM, enter Gain = 312.5, Offset = -1250 (subtract the 4 mA zero).
4. Route the Math output to a VM variable named for the engineering unit (e.g., RPM_Display).
5. Log the engineering-unit variable in the data log profile.

The Math block maintains integer precision up to ±32,767. Above that range the LOGO! clamps the result to the integer limit. For wider dynamic range, use two cascaded Math blocks or an external controller.

Workaround 3 - Export CSV and Chart Externally

The LOGO! data log is written to /log/<projectname>.csv on the SD card. The same file is exposed through the LOGO! Web Server under Data Log > Download. Once downloaded, the CSV can be opened in any charting tool that supports decimal axis labels.

Default CSV format produced by LOGO! Soft Comfort data log:

Import procedure for Microsoft Excel:

1. Open Excel, select Data > From Text/CSV.
2. Choose the LOGO! CSV file. Excel auto-detects the semicolon or comma delimiter based on locale.
3. Click Transform Data if decimal separator conversion is required (period vs. comma).
4. Insert a chart (Insert > Charts > Line with Markers).
5. Right-click the value (Y) axis, choose Format Axis, and under Number set the desired decimal places. The Microsoft Office Format Axis dialog exposes the decimal-place field directly.

LibreOffice Calc, Matplotlib (Python), and Grafana (with the CSV data source plugin) provide equivalent decimal axis formatting and are recommended alternatives for production dashboards.

Workaround 4 - Use the Web Server Status Page

The legacy Web Server status page (HTML frames variant) renders each VM value as raw integer text. For simple decimal display without a chart, navigate to http://<logo-ip>/status in the browser. The values appear as integers because the underlying data is integer, but the surrounding HTML can be polled and styled by an external dashboard (Node-RED, Grafana, custom SCADA) to present decimals via downstream formatting.

Data Log Configuration Procedure

1. In LOGO! Soft Comfort, open the project and select Tools > Data Log Profile.
2. Click Add Variable and select VM addresses or symbolic names. For analog channels, use the Analog Amplifier or Math block output (Workarounds 1 and 2).
3. Configure the sample rate. Valid range: 1 second minimum to 86400 seconds (24 hours) maximum. Typical rates: 1 s for fast processes (pressure, flow), 60 s for trending (temperature, level).
4. Enable Append to existing log if continuous logging without overwriting on power-cycle is required.
5. Save the project and download to the LOGO! via Ethernet (Tool > PC > LOGO! Transfer).
6. On the LOGO! Web Server home page (http://<logo-ip>), authenticate if a password is configured, then open the Trend link.
7. Select the logged variable(s) from the dropdown. The Trend view renders with integer axis labels.
8. Apply Workaround 1, 2, 3, or 4 as required for the application context.

Firmware Update Procedure

If a firmware update is preferred over a workaround, confirm compatibility with the installed LOGO! Soft Comfort version before proceeding.

1. Identify the LOGO! module part number from the front label (typical formats: 6ED1052-1CC08-0BA1, 6ED1052-1MD08-0BA2).
2. Visit the Siemens Industry Online Support portal and search for the LOGO! part number.
3. Download the latest firmware updater (Siemens provides a self-extracting firmware update tool compatible with Windows 10 / 11).
4. Place the LOGO! in STOP mode (LOGO! front-panel ESC + OK, or via the LOGO! Soft Comfort online connection).
5. Connect the Ethernet cable directly to the PC, run the firmware updater, enter the LOGO! IP address, and follow the wizard.
6. Verify the new FS state in the LOGO! on-board menu: Setup > Diagnostics > Firmware (visible on the LOGO! base module display).
7. Reload the user program from the .lsc backup.

Verification Checklist

After applying a workaround or firmware update, verify with the following checks.

1. Open the LOGO! Web Editor Trend view and confirm the vertical axis labels render correctly (integers in raw mode, scaled integers after Workaround 1 or 2).
2. For Workaround 1: inject a known analog value (e.g., 5.0 V on AI1 with Gain = 100) and confirm the logged VM value is 500.
3. For Workaround 2: confirm the Math block output matches the expected engineering-unit integer under steady-state input.
4. For Workaround 3: export the CSV and confirm the timestamp column and value columns are present and correctly populated, then verify the chart in Excel displays decimal axis labels.
5. For Workaround 4: navigate to /status and confirm the VM register shows the expected scaled integer.
6. Cycle power to the LOGO! and confirm the data log resumes without corruption.
7. Run a 24-hour soak test at the configured sample rate and verify the CSV file size is within SD card capacity.

Troubleshooting Matrix

Browser and Network Considerations

• HTTPS: Starting with LOGO! 8.3 FS04, HTTPS can be enabled on the LOGO! web server. Confirm the certificate trust in the browser before opening the Trend view, otherwise the chart assets may fail to load silently.
• Concurrent users: The LOGO! web server accepts up to 8 concurrent HTTP connections. Exceeding this returns HTTP 503 and the Trend view will not render. Use a polling SCADA gateway for production-grade concurrent access.
• CORS: Direct cross-origin AJAX requests to the LOGO! web server are not supported. Use a server-side proxy for external dashboards consuming the CSV or status endpoints.
• Time zone: The data log timestamp is the LOGO! on-board RTC time. Configure the LOGO! clock (Setup > Date/Time) or enable SNTP time sync in the project to keep trend timestamps accurate.

Performance and Storage Notes

When sampling at 1 s with multiple variables, the LOGO! web server response time for the Trend view may exceed 2 s. Increase the sample interval to 5 s or 10 s for slow-changing processes to maintain a responsive chart without overwhelming the on-board web server.

Related Siemens Documentation

• LOGO! 8 System Manual (entry ID 109751156 on Siemens Industry Online Support)
• LOGO! Soft Comfort V8.3 Online Help (bundled with the software installation)
• LOGO! Web Editor V2.0 Release Notes (entry on Siemens Industry Online Support)
• LOGO! 0BA8 Firmware Update Tool Quick Start Guide