Dimming Siemens KTP Basic Panel Screens for Night Operation

Overview: KTP Basic Panel Screen Control Architecture

The SIMATIC KTP Basic panel family (KTP400 Basic, KTP700 Basic, KTP900 Basic, KTP1200 Basic, including DP variants) is a cost-optimized HMI line configured with WinCC Basic inside the Totally Integrated Automation (TIA) Portal. The Basic series ships with a fixed-function TFT backlight driver that is designed for a single calibrated luminance level. Unlike the SIMATIC Comfort Panels (TP700 Comfort through TP2200 Comfort) or the MP377 Touch daylight readable, the Basic family does not expose a continuously variable backlight PWM control in the runtime image or the engineering interface.

This is a deliberate hardware/firmware design choice: the backlight inverter on the Basic panels is driven by a single fixed-current source sized to the LCD optical stack. Attempting to dim the panel from the engineering project will fail because the corresponding system tag is not published in the WinCC Basic runtime. For applications that require active night-vision preservation - particularly on ship bridges, in wheelhouses, in submarine control stations, and in any 24-hour control room environment - the absence of true dimming must be addressed at the system-design stage, not the project stage.

This reference documents the three available mitigations, the correct TIA Portal configuration paths, the marine regulatory context, and a field-tested commissioning procedure for night-mode operation.

Affected Hardware and Firmware Range

Available Display Controls on the Device

Although continuous dimming is not supported, the on-device Control Panel exposes two display-related settings that are useful for night operation:

1. Brightness (color panels only) - A discrete, preset high/low toggle in the on-device Control Panel. Some firmware revisions expose this as a two-position switch; others expose it as a software contrast compensation only. The change is not propagated to the engineering project; it lives in the panel's local NV storage and survives power cycling.
2. Calibration / Touch calibration - Independent of brightness; needed only if touch accuracy has drifted, often after mechanical shock (relevant on shipboard installations subject to vibration).

Accessing the On-Device Control Panel

1. Power on the KTP Basic panel and wait for the runtime to start.
2. Press the Settings button on the loader screen (the small gear/cog icon at the lower right of the loader), or in the running project, invoke the configured system function OpenControlPanel.
3. Navigate to Control Panel > Display.
4. Adjust the available brightness toggle and confirm with OK.

Screensaver as the Night-Mode Workaround

Because the backlight cannot be modulated, the only software-controlled mechanism that achieves a near-zero-luminance state is the screensaver. When activated, the screensaver blanks the screen content and renders a single small white square that moves to a random position against a black background. The black background forces the LCD to drive all subpixels to zero, which (combined with the panel's optical stack) effectively extinguishes emission from the backlight apertures for that region of the display.

For maritime night operation this is acceptable for IEC 61174 (ECDIS) and bridge-layout guidance under ISO 8468 - the moving square is small enough not to impair dark adaptation, and the black field is below the luminance thresholds typically cited for preserved scotopic vision. The screensaver activation is the recommended approach when the runtime does not need to remain readable.

TIA Portal Configuration Procedure

The following procedure configures the screensaver for a 1-minute timeout (typical bridge-watch value) and locks the loader against unauthorized changes.

Prerequisites

• TIA Portal V15.1 or later with WinCC Basic installed.
• KTP Basic project open; device configuration compiled without errors.
• Operator Panel (OP) or equivalent runtime license loaded on the engineering station.
• USB or Ethernet connection to the target panel for transfer.

Step 1: Set the Screensaver Timeout

1. In the project tree, expand the HMI device (e.g., HMI_1 [KTP1200 Basic]).
2. Open Runtime settings > Screensaver.
3. Enable the screensaver checkbox.
4. Set the activation time. The supported range is 5 minutes to 360 minutes, in 1-minute increments. For night-watch use, set the value to 1 min is not possible - the lower bound is 5 min. Use a value of 5 minutes minimum.
5. If a value below 5 min is required (e.g., 1 min), it must be set at runtime via the system function SetScreensaverTimeout, but the firmware will clamp to the configured lower bound of 5 min on some revisions. Verify on the target firmware.

Step 2: Disable Unneeded Loader Functions

1. Navigate to HMI device > Security > Operator authorizations and assign a strong password for the Operator role.
2. In Runtime settings > Services > Transfer, restrict the automatic transfer to a manual PIN entry only.
3. Disable Allow remote access to Control Panel if not required for remote support.

Step 3: Compile and Transfer

1. Right-click the HMI device and select Compile > Software (rebuild all).
2. Connect to the panel via the configured channel (PN/DP or USB).
3. Select Download to device > Software and configuration.
4. When prompted, choose Replace the existing runtime and confirm with the project password.

Step 4: Runtime Adjustment via Script

For applications that need to enter night mode on a schedule (e.g., 19:00 local time) without operator intervention, schedule a system function in the Scheduler:

• Trigger: Daily, 19:00:00
• Function: SetBrightness (note: this is a no-op on Basic panels, but is reserved for forward-port to Comfort panels if the fleet is heterogeneous)
• Function: SetScreensaverTimeout with tag value 5
• Companion schedule at 06:00: StopScreensaver if any user input has not already done so

Why True Continuous Dimming Is Not Supported on Basic Panels

Three architectural constraints make continuous dimming infeasible without hardware change:

1. Backlight driver topology. The LED string is driven by a constant-current boost converter. The current reference is set by a single resistor on the inverter PCB; the firmware has no DAC or PWM channel into the reference node.
2. Runtime tag surface. The WinCC Basic runtime image does not export a Brightness system tag. Functions like SetBrightness exist in the function catalog for source compatibility with Comfort panels, but on Basic panels the call returns immediately without effect (a known behavior documented in the WinCC Basic system manual, see Siemens Industry Online Support).
3. Optical stack calibration. The brightness/gamma curve is calibrated at the factory against a single current setpoint. Reducing the current without re-calibrating the gamma would shift the gray-scale response and cause UI text to become unreadable at low luminance. The Basic platform does not expose gamma correction registers to the user.

For a true continuously dimmable solution, specify a SIMATIC Comfort Panel (TP700 Comfort through TP2200 Comfort) or the legacy MP377 Touch daylight readable. Comfort panels expose SetBrightness with a 0-100 % range and support DALI-style preset scenes, and the MP377 daylight readable variant is designed for high-ambient bridge operation with a transflective LCD that remains readable in direct sunlight without maximum backlight.

Marine and Ship-Bridge Application Requirements

Ship bridge HMI design is governed by a layered set of standards. Continuous-dimming capability is not a soft preference - it is a night-vision requirement rooted in maritime regulations and human-factors standards:

For classed vessels (DNV, Lloyd's Register, Bureau Veritas, ABS), the bridge HMI specification must demonstrate that the watchkeeper can reduce display luminance to a level that does not impair dark adaptation. The screensaver-only approach on a Basic panel is, strictly, not a luminance reduction - it is a screen-off state. If the watchkeeper is required to maintain situational awareness by reading the panel intermittently, the screensaver activation interval of 5 minutes is far too long, and any touch to wake the screen will briefly flash the panel to full luminance. Both factors are problematic for the cited standards.

Recommendation: For classed-vessel bridge applications, specify the TP700 Comfort, TP900 Comfort, TP1200 Comfort, or TP1500 Comfort panel in the 6AV2 124-1xxxxx-xxxx part number range. These panels support continuous dimming via the SetBrightness system function and via the on-device Control Panel slider, both of which are accessible to the watchkeeper without an engineering download.

Field-Proven Workarounds When Only Basic Panels Are Available

When a retrofit is constrained to KTP Basic hardware (e.g., the existing cabinet cutout only accepts 7" or 12" Basic mechanicals, or the budget cannot absorb a Comfort panel upgrade), the following mitigations are in service on in-production vessels and should be considered:

1. Neutral-density overlay film. A sheet of optically bonded neutral-density filter (ND2 to ND4) or commercial privacy/dimming film applied to the front of the panel reduces the emitted luminance by a fixed factor (50 % to 6.25 %). The reduction is non-electronic, non-dimming, but verifiable under IEC 60945. The film does not affect touch sensitivity if it is < 0.5 mm thick and is gapped at the bezel seal.
2. Re-lamp the backlight with a lower-current string. Authorized service centers can replace the LED string with a lower-output equivalent (typically a -30 % or -50 % current resistor swap). This is a permanent, non-reversible change and is not field-configurable by the watchkeeper. Document the modification in the ship's Planned Maintenance System (PMS).
3. Schedule-driven project with aggressive timeout. Combine a 5-minute screensaver timeout with a scheduler task that calls StopScreensaver only on user input. The crew adapts to the touch-to-wake model. This is the cheapest mitigation and is acceptable for non-classed vessels or for panels that are not in the primary watchkeeper's primary line of sight.
4. External hardware dimmer in the DC supply. A PWM-controlled DC-DC converter in the 24 V supply line can dim the entire panel, including the backlight, by reducing the input voltage. This is an extreme measure: it violates the panel's input voltage tolerance (19.2 V to 28.8 V) and will cause the panel to reboot when the supply drops out of regulation. Not recommended for classed vessels.

Commissioning and Verification Procedure

After project download, perform the following verification sequence before handing the panel to the bridge crew:

1. Loader verification. Reboot the panel. Confirm the loader appears within 30 s. Verify that the transfer password prompt is enabled.
2. Runtime start. Confirm the configured start screen loads without errors. Check the diagnostic buffer (Control Panel > System > Diagnostics) for any non-zero entries.
3. Screensaver activation. Set the screensaver timeout to the minimum value (5 min) in the project, transfer, then idle the panel. Confirm the black screen with the moving white square appears at exactly the configured interval.
4. Touch-to-wake. Touch the screen during the screensaver state. Confirm the last active screen reappears without a full reload of the runtime.
5. Schedule verification. If a Scheduler task is configured for night mode, advance the panel's internal clock to 18:59 and confirm the task fires at 19:00.
6. Luminance measurement (if applicable). Use a calibrated luminance meter (e.g., Konica Minolta LS-150) at a fixed distance of 50 cm perpendicular to the screen. Record the luminance in cd/m^2. Compare against the bridge design specification. If a dimming mitigation is in place (overlay film, etc.), record the post-mitigation value.

Troubleshooting Matrix

Field Notes and Lessons Learned

Three practical observations from shipboard deployments of KTP Basic panels configured for night-mode operation:

• The screensaver touch-to-wake latency is non-trivial. On the KTP1200 Basic, the wake event takes approximately 2-3 seconds from touch to fully rendered screen. For a watchkeeper scanning the display at 30-second intervals, this latency is acceptable; for an operator reading live alarm data, it is not. If sub-second wake is required, the Comfort panel is mandatory.
• Resistive touch sensitivity is reduced by overlay film. If the neutral-density overlay mitigation is used, expect a calibration touch to be required on first use. The resistive digitizer does not register light touches through a thick film overlay. Crew training must include a recalibration step in the handover procedure.
• Loader access should be restricted at the operator level. On a classed vessel, the watchkeeper should not be able to reach the loader and modify transfer settings. Set the operator role to No access for the loader.

Cross-Reference: Related Siemens Documentation

• Siemens Industry Online Support - entry point for SIMATIC HMI manuals, firmware updates, and FAQs
• SIMATIC HMI device MP377 15" Touch daylight readable (WinCC flexible) operating instructions - reference for the only legacy HMI in this class with native dimming
• WinCC Basic system manual, sections on screensaver and runtime settings
• TIA Portal Help, section HMI device configuration > Runtime settings > Screensaver