Model: Bently Nevada 120M8155-01
Device Class Code: HMI-CTRL (Control Panel Human Interface)
Primary Usage: Local acknowledgment and visualization for vibration protection systems in rotating machinery

Field Case Description

In a steam turbine auxiliary building, operators reported that the 120M8155-01 panel could display machine parameters but did not respond to any touch input. Attempts to change pages or acknowledge alarms were unsuccessful. The symptom appeared gradually—first intermittent touch delay, then full touch failure.

The incident occurred during the rainy season in a facility with high ambient humidity and limited climate control for the instrument cabinet.

Environmental Conditions Relevant to the Failure

Measurements taken at the time showed:

• Ambient temperature: 33–36°C

• Relative humidity: 80–88%

• Cabinet IP rating: IP20, without sealed front cover

• Ventilation: passive only, no dehumidifier present

These conditions are not ideal for display electronics, especially those with resistive or capacitive touch layers.

Engineering Analysis and Mechanism of Failure

Technicians removed the display assembly and found trace evidence of moisture condensation on the lower part of the digitizer flex connector. The mechanism of progressive failure was determined as follows:

1. Moisture Condensation
   Humidity entered through unsealed cabinet openings and condensed on cooler LCD surfaces during night temperature drops.

2. Corrosion of Touch Connector Contacts
   Micro-corrosion developed on the fine-pitch flex connector that links the touch digitizer to the mainboard.

3. Increase in Contact Resistance
   The corrosion showed as increased resistance and intermittent signal dropouts, explaining the initial random latency.

4. Final Loss of Touch Signal
   Eventually, the touch controller no longer detected valid coordinate signals, resulting in complete loss of input.

No software fault or HMI firmware problem was identified.

Corrective Actions Performed On-Site

The service team completed the following steps:

• cleaned the digitizer connector using contact-safe solvent

• dried the panel using controlled heat application

• sealed the cabinet front section with a suitable gasket

• installed a small PTC-controlled cabinet heater to stabilize humidity

• recommended a panel replacement due to long-term corrosion risk

After cleanup, the touch system became functional again, confirming hardware involvement rather than a systemic communication failure.

Recommended Long-Term Engineering Improvements

To prevent recurrence in similar facilities, the following adjustments are recommended:

• maintain cabinet humidity below 65% using dehumidifiers or heaters

• verify that cabinet rating matches environmental exposure (IP rating upgrade if needed)

• avoid installing HMI near steam tracing or moisture sources

• apply conformal coatings or protective films on front panels when moisture risk is known

• include humidity checks as part of scheduled maintenance routines

These measures extend the operational lifespan of HMI hardware in turbine halls, compressor units, and coastal refineries where humidity is a persistent threat.