Why Field Controllers and Sensors Fail in Building Management Systems

Why Field Controllers and Sensors Fail in Building Management Systems

Many commercial buildings in Sydney and Melbourne are still operating Building Management Systems (BMS) installed 15–20 years ago. While the system may still appear to function, the field controllers and sensors that make up the system are often approaching the end of their reliable operating life.

Understanding why this equipment fails helps explain why older BMS systems begin to show intermittent and difficult-to-diagnose faults.

Ageing Electronics Inside Field Controllers

At the heart of every field controller and sensor are microchips built from silicon semiconductors. These chips contain millions of microscopic electronic switches called transistors, which are constructed using two types of semiconductor material known as N-type and P-type silicon.

Together, these transistors form the digital logic that allows a controller to:

• Read sensors
• Interpret signals
• Communicate with the network
• Control HVAC equipment

Over many years of operation, these microscopic semiconductor structures begin to degrade due to:

• Continuous electrical stress
• Heat from plant rooms and ceiling spaces
• Power fluctuations and voltage spikes
• Long-term material fatigue within the silicon itself

As these components age, the electrical characteristics inside the chip slowly drift.

The Problem with Digital Signals

Controllers operate by interpreting electrical voltages as digital signals:

• A low voltage represents a “0”
• A higher voltage represents a “1”

When semiconductor devices are new, these voltage thresholds are very stable and clearly defined.

However, as electronic components age, leakage currents and internal drift begin to occur within the silicon. This can cause the signal voltage to sit somewhere between a clear “0” and “1”.

When this happens, the controller can misinterpret the signal, resulting in:

• Intermittent faults
• Random communication failures
• Sensors reporting incorrect values
• Equipment starting or stopping unexpectedly
• Control logic behaving unpredictably

These faults are often extremely difficult to diagnose because the equipment may work normally most of the time, only failing intermittently.

Why Older BMS Systems Become Increasingly Unreliable

When multiple controllers and sensors in a building begin ageing at the same time, the system gradually becomes less stable.

Property managers may start noticing:

• More frequent service callouts
• Intermittent HVAC complaints from tenants
• Sensors drifting out of calibration
• Network communication faults between controllers
• Spare parts becoming harder to obtain

Because many legacy BMS platforms are now obsolete or unsupported, even simple failures can become costly to repair.

The Practical Solution: Planned Modernisation

Rather than waiting for failures to occur, many commercial buildings are now undertaking planned BMS upgrades or staged controller replacement programs.

Modern BMS platforms offer:

• Far more reliable electronics
• Secure remote access and monitoring
• Better energy optimisation
• Easier integration with modern HVAC equipment
• Long-term manufacturer support

A planned upgrade approach allows building owners to reduce risk, control costs, and maintain reliable building operation.

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WR8TECH specialises in diagnosing and modernising obsolete BMS systems across Sydney and Melbourne, helping commercial buildings transition from ageing control platforms to reliable modern systems.